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Key P1: herbaceous dicots with alternate, simple, and unlobed leaves on the stem

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1 Inflorescence an involucrate head subtended by phyllaries, the heads solitary or many and variously arrayed in secondary inflorescences, the ovary inferior, the corolla connate and tubular at least basally, the calyx absent, the stamens 5, the fruit a cypsela
1 Inflorescence, flower, and fruit structure various, but not with the combination of features as above (sometimes the flowers in a head, e.g. Eryngium in APIACEAE, but then with other features differing, such as stamens 4, or green calyx present, or fruit a schizocarp of mericarps, etc.).
  2 Perianth uniseriate (represented only by undifferentiated tepals or sepals; look at the front and back of the flowers for two layers) or completely absent; flowers usually unisexual, less commonly bisexual).
    3 Inflorescence a cyathium, consisting of a single pistillate flower (reduced to a single 3-carpellate pistil) and 2 or more staminate flowers (each reduced to 1 stamen), borne in a cup-like involucre, the involucre bearing pointed or rounded glands, these sometimes brightly colored and petaloid, mimicking an individual flower (the cyathia then secondarily arranged in terminal cymes, or solitary and axillary, etc.); fresh plants with milky juice; fruit a 3-lobed, 3-locular capsule
    3 Inflorescence not a cyathium (and staminate or bisexual flowers with > 1 stamen; fresh plants lacking milky juice (except Stillingia in EUPHORBIACEAE); fruit various, not as above.
      4 Leaf margins toothed in some manner (serrate, dentate, crenate, etc.)
        5 Leaf teeth rounded to subacute, resembling shallow lobes, irregular, few (mostly < 6 per leaf side).
          6 Fruit a single-seeded achene or utricle; [plants of various disturbed or saline, usually sunny habitats]
          6 Fruit a 3-lobed, circumscissilely dehiscent capsule; [plants native of rich moist shaded forests or exotics in suburban woodlands]
        5 Leaf teeth sharp to crenate, not lobe-like, regular, many (mostly > 10 per leaf side).
             7 Leaf bases cuneate (or strongly oblique in Begonia, with one leaf base usually being cuneate, the other variously rounded or cordate).
               8 Flowers typically with 2 or 4 (-5) showy, white-colored tepals; leaves sometimes variegated; fruit unequally or subequally 3-winged capsules; [ornamental waifs or uncommon non-natives]
               8 Flowers cyathia, not merely bearing showy tepals; leaf not variegated but sometimes bearing darkened red or black splotches; fruit capsules, but these not conspicuously winged; [natives and non-natives, usually not ornamental]
             7 Leaf bases cordate to rounded.
                 9 Styles 3; fruit a 3-lobed, 3-carpellate capsule (1 carpel sometimes aborting); inflorescence either a terminal or leaf opposed raceme, or a dense axillary condensed cyme with conspicuous toothed bracts subtending the flowers
                 9 Styles 1 or 2; fruit either an achene or a multiple of achenes; inflorescence either an axillary dense cyme (almost a head), or an axillary spike with glomerules, or a terminal or axillary panicle.
                   10 Styles 2; inflorescence a dense axillary cyme (almost a head); fruit a multiple of achenes; plant lacking stinging hairs; [exotic plant of weedy situations]
                   10 Style 1; inflorescence an axillary spikes with glomerules, or a terminal or axillary panicle; plant either with stinging hairs or not; [plant a rare exotic (Boehmeria nivea) or a native of moist forests (Boehmeria cylindrica, Laportea)]
      4 Leaf margins entire.
                     11 Ovary inferior (flowers epigynous, the ovary sitting below the perianth and androecium) or half-inferior (perigynous, the ovary sitting level with the remaining floral parts).
                       12 Leaf base cordate; calyx 3-lobed, fused into a bilaterally symmetrical, curved brown or yellowish tube; fruit a capsule
                       12 Leaf base cuneate, rounded, or truncate; calyx of 3-4-5 distinct sepals, radially symmetrical, white or yellow; fruit a dry, nutlike drupe or an achene.
                          13 Leaves subsessile or very short petiolate, elliptic or narrowly elliptic, broadest near the middle; [native]
                          13 Leaves distinctly petiolate, rhombic, widest near the base; [rarely naturalized exotics].
                            14 Inflorescence of a single axillary flower
                            14 Inflorescence terminal, spikelike
                     11 Ovary superior (flowers hypogynous, the ovary sitting above the perianth and androecium).
                              15 Inflorescence a leaf-opposed spike or raceme, the inflorescence arising opposite of stem leaves (except Saururus, whose spikelike racemes are leaf-opposed and/or terminal); flowers visually white from white petaloid sepals, white bracts, or white stamens.
                                16 Sepals present, 4 or 5; petaloid, white; carpels 1 to many (-12); stamens 4 to many (-25); fruit a berry or an apically 2-lobed achene (as in Petiveria); leaf bases cuneate or rounded (but not cordate); [Eudicots].
                                  17 Sepals 4; carpels 1; fruit subglobose berries or apically lobed achenes
                                  17 Sepals 5; carpels 5-12, distinct; fruit an oblate berry
                                16 Sepals absent; carpels 3-4; stamens 2-6 (-8); fruit a capsule, a 1-seeded drupe, or a schizocarp of 3-4 mericarps; leaf bases cordate or subcordate; [Basal Angiosperms].
                                    18 Fruit a 1-seeded drupe; stamens 2; plants terrestrial or epiphytic
                                    18 Fruit a capsule or schizocarp with 3-4 mericarps; stamens 3 or 6-8; plants terrestrial
                              15 Inflorescence not leaf opposed, instead arising with stem leaves (axillary) or terminal, the inflorescence not spikes nor racemes, instead either simpler (single axillary or glomerules of flowers) or more complexly branched (terminal or axilary panicles or terminal complex cymes); flowers white, reddish, scarious, or greenish.
                                       19 Stipules tubular, sheathing (= ocreae); flowers subtended by tubular, sheathing bracteoles (= ocreolae); nodes usually prominently swollen; perianth usually of 5-6 white to pink tepals
                                       19 Stipules not tubular or sheathing; flowers not subtended by ocreolae; nodes not swollen; perianth absent or of 3-5 sepals.
                                         20 Inflorescence a terminal involucrate cluster; flowers bisexual; stamens 9
                                         20 Inflorescence axillary, or a terminal panicle or raceme that is not involucrate; stamens 3-6.
                                           21 Ovary 3-locular; styles 3, each bifid; fruit a capsule, with 6 seeds
                                           21 Ovary 1-locular; styles 1-3, not bifid; fruit a utricle or achene (1-seeded).
                                             22 Sepals petaloid, pink and relatively conspicuous (although the sepals ca. 1-3 mm in length); plants prostrate to somewhat ascending annuals; leaves opposite or nearly whorled; achenes muricate
                                             22 Sepals not petaloid, inconspicuous, green or greyish in color; plants prostrate or erect, annual or perennial; leaves alternate OR either alternate or opposite (Amaranthaceae); achenes variously textured (smooth or textured, sometimes reticulate or verrucose, but rarely muricate).
                                               23 Styles 1, stigma 1; flowers unisexual
                                               23 Styles 1-3, if style 1, then stigmas 3; flowers bisexual or unisexual.
                                                 24 Tepals acute, scarious
                                                 24 Tepals usually blunt, herbaceous
  2 Perianth biseriate (represented by differentiated whorls of sepals and petals, the sepals usually green or drab in color, the petals often brightly colored); flowers nearly always bisexual (there are exceptions).
                                                    25 Ovary inferior (epigynous) or half-inferior (perigynous).
                                                      26 Petals connate (at least basally, often the lower half of corolla).
                                                        27 Inflorescence a leaf-opposed, dense, cylindrical spike
                                                        27 Inflorescence not a dense, leaf-opposed spike, instead a terminal head or variously axillary or terminal (the flowers solitary or not, but not in a dense spike).
                                                          28 Flowers yellow; stamens numerous (15+), monomorphic or heteromorphic (inner and outer of differing length), conspicuously exerted from the flowers, often surpassing the ovary; leaves basally lobed or unlobed (often a mix in M. floridana and M. oligosperma)
                                                          28 Flowers blue or white; stamens fewer (usually < 10), monomorphic, if exerted, the ovary usually still apparent; leaves unlobed.
                                                            29 Leaves toothed; flowers blue to white
                                                            29 Leaves entire; flowers white
                                                      26 Petals distinct.
                                                              30 Petals 5; stamens 5; inflorescence a head; fruit a schizocarp of 2 mericarps
                                                              30 Petals 4 7; stamens 6 or more; inflorescence various, not a head; fruit a capsule.
                                                                 31 Petals 4-7; stamens 1× or 2× as many as the petals, 4-7, 8, 10, 12, or14; leaves herbaceous in texture
                                                                 31 Petals 5 (or sometimes doubled in horticultural forms); stamens 6-40 (or more); leaves fleshy in texture
                                                    25 Ovary superior (hypogynous).
                                                                   32 Corolla bilaterally symmetrical (zygomorphic), petals connate, at least basally (except distinct in VIOLACEAE); fruit a capsule or legume (the capsule conspicuously spiny in Krameria).
                                                                     33 Petals distinct, 5; carpels 3; fruit a 3-loculed capsule
                                                                     33 Petals connate (at least basally), 4, 5, 6, 7, or 8; carpels 1, 2, 4, 5, or 6 (rarely 3 in Reseda in RESEDACEAE); fruit a legume or 1-, 2-, or 5-loculed capsule (except a 1-seeded indehiscent pod in Krameria in KRAMERIACEAE).
                                                                       34 Stamens 6-10 (-25), more than the number (4 or 5) of petals and the number (4 or 5) of the sepals; fruit a legume or a 1-6-carpellate capsule.
                                                                         35 Stamens fused, monadelphous or diadelphous.
                                                                           36 Stamens 10, monadelphous or diadelphous; fruit a legume
                                                                           36 Stamens 6-8, monadelphous; fruit a capsule
                                                                         35 Stamens distinct.
                                                                              37 Carpel 1; fruit a legume
                                                                              37 Carpels 3-6; fruit a capsule
                                                                       34 Stamens 4-5, less than or the same as the number (5) of the petals; fruit a 2-5-carpellate capsule.
                                                                                38 Pistil 5-carpellate; capsule 5-locular, explosively dehiscent; inflorescence of axillary, small clusters of flowers
                                                                                38 Pistil 2-carpellate; capsule 2 locular, opening gradually or not at all; inflorescence a terminal spike, raceme or panicle (or solitary, axillary flowers in Chaenorrhinum in PLANTAGINACEAE and Krameria in KRAMERIACEAE).
                                                                                  39 Fruit 1-seeded, indehiscent; sepals petaloid, red-purple; petals dimorphic, the upper 3 long-clawed, the lower 2 small, thickened, and glandlike; fruit a spiny pod
                                                                                  39 Fruit > 2-seeded, dehiscent; sepals sepaloid, green; petals not dimorphic.
                                                                                    40 Stamens 5; corolla not spurred; capsule septicidal; pubescence of the stem and leaves either gland-tipped or dendritically branched
                                                                                    40 Stamens 4; corolla with a distinct spur or sac at the base between the the 2 lower calyx lobes (except not spurred in Digitalis and Schwalbea); capsule loculicidal (only at the summit in Antirrhinum and Chaenorrhinum, and septicidal in Schwalbea); pubescence of the stem and leaves neither gland-tipped (except in Antirrhinum and Chaenorrhinum) nor dendritically branched.
                                                                                      41 Capsule septicidal; corolla not spurred
                                                                                      41 Capsule loculicidal; corolla spurred (except Digitalis)
                                                                   32 Corolla radially symmetrical (actinomorphic), petals connate or distinct; fruit various (including capsules).
                                                                                        42 Plants herbaceous vines, fleshy and mucilaginous, the leaves variously orbicular, ovate, cordate or sometimes elliptic; fruit utricles (small sacs surrounding an achene), partly to completely enclosed in the persistent, dry to somewhat fleshy perianth; sepals 2
                                                                                        42 Plants not herbaceous vines, the leaves variously shaped; fruit various, but never utricles; sepals 4 or more.
                                                                                           43 Petals distinct (flowers apopetalous); stamens 5-many (4 or 5 in Capraria).
                                                                                             44 Pistils 4-10 (each 1-carpellate) in a ring, these sometimes fused basally, each with its own style/stigma; fruit either an aggregate of achenes or follicles or a 5 (-7) locular capsule.
                                                                                               45 Pistils 5 (-7); inflorescence a compound terminal cyme.
                                                                                                 46 Fruit an aggregate of follicles; leaves fleshy in texture; inflorescence; leaves entire of sparsely and coarsely serrate, with < 12 points per leaf; [plants primarily of dry habitats]
                                                                                                 46 Fruit a 5 (-7) locular capsule; leaves membranaceous in texture; leaves serrate, with > 20 points per leaf; [plants of wet habitats]
                                                                                               45 Pistils many; inflorescence of solitary flowers, or diffuse.
                                                                                                   47 Leaves cuneate at the base; flowers in a diffuse inflorescence
                                                                                                   47 Leaves cordate at the base; flowers solitary, on long pedicels
                                                                                             44 Pistil 1, with 1-to many carpels (in many MALVACEAE, the carpels loosely united in a ring [of more than 5] around the single style/stigma); fruit either a 1-, 2-, 3-, 5-, 6-, or 10-locular capsule, or a silique/silicle, or a ring of mericarps.
                                                                                                     48 Petals 4; sepals 4; stamens 6; fruit a silique/silicle
                                                                                                     48 Petals 5 (rarely 4 or 6); sepals 5 (rarely 4 or 6); stamens 4, 5 (or multiples of 5), 6, or 12; fruit a capsule or a ring of mericarps.
                                                                                                        49 Stamens many, connate into a staminal tube; carpels 5-many; fruit a capsule or ring of mericarps; leaves usually serrate or crenate
                                                                                                        49 Stamens (4-) 5-many, distinct (not forming a staminal tube); carpels 2-5; fruit a capsule; leaves entire (serrate in Croton in EUPHORBIACEAE, distally serrate in Capraria in SCROPHULARIACEAE).
                                                                                                          50 Flowers unisexual; leaf vestiture of peltate scales and/or stellate hairs
                                                                                                          50 Flowers bisexual; leaf vestiture (if present) simple or stellate.
                                                                                                            51 Flowers 6-merous (the petals and sepals 6, the stamens 6 or 12); corolla pink or purplish (rarely white); fruit a septicidal capsule
                                                                                                            51 Flowers 5-merous (the petals and sepals 5, stamens 5 or various multiples of 5); corolla white, yellow, reddish (including pinkish), or blue; fruit a loculicidal or septicidal capsule.
                                                                                                              52 Stamens 5 ; corolla yellow or blue; capsule either 10-locular and septicidal (Linum) or 1-locular (with 3 carpels) and loculicidal.
                                                                                                                53 Capsule 10-locular (with 5 carpels) and septicidal (splitting at the septa, opening at the top)
                                                                                                                53 Capsule 1-locular (with 3 carpels) and loculicidal (splitting along outer edges, not only at the top)
                                                                                                              52 Stamens (4-) 10, 15, 20, 30 (-many); corolla white, pink, yellow, or reddish; capsule 2-, 3-, 5- (-10)-locular, loculicidal.
                                                                                                                  54 Leaf margins distally serrate, the surfaces punctate-glandular and also with internal oil-secreting cavities; corolla white (the inside sometimes with scattered purple spots); [s. FL and s. TX only in our flora area]
                                                                                                                  54 Leaf margins entire, serrate, or crenate, lacking punctate-glands and internal oil-secreting cavities; corolla white, pink, yellow, or reddish; [collectively widespread, including s. FL and s. TX].
                                                                                                                     55 Stamens (5-) 10, 15, 20, 30 (-many); corolla yellow or reddish; filaments not densely villous basally, the anthers the anthers not conspicuously tubular and lacking apical pores; capsule 3 (-10)-locular, loculicidal
                                                                                                                     55 Stamens 10; corolla white or pink; filament bases dilated basally and densely villous, the anthers tubular with conspicuous apical pore dehiscence; capsule 5-locular
                                                                                           43 Petals fused (flowers sympetalous, this includes salverform and tubular flowers); stamens (4-) 5 (-7).
                                                                                                                       56 Plants herbaceous vines, fleshy and mucilaginous, the leaves variously orbicular, ovate, cordate or sometimes elliptic; fruit utricles (small sacs surrounding an achene), partly to completely enclosed in the persistent, dry to somewhat fleshy perianth; sepals 2
                                                                                                                       56 Plants not with the above combination of characters, if herbaceous vines then fruit not utricles and sepals 4 or more.
                                                                                                                         57 Pistils 2, united only by the style and stigma; fruit a schizocarp of 2 follicles (often single by abortion); plant with milky juice when fresh; leaves entire; inflorescence an umbel
                                                                                                                         57 Pistil 1 (of 2 or 3 fused carpels); fruit a capsule, drupe, or a schizocarp splitting into 4 nutlets; plant lacking milky juice; leaves entire or serrate; inflorescence various (but not an umbel).
                                                                                                                           58 Ovary slightly to deeply 2-4-lobed (entire or shallowly lobed in Tiquilia and HELIOTROPIACEAE); fruit a schizocarp of 4 mericarps or a drupe; [BORAGINALES].
                                                                                                                             59 Ovary deeply 4-parted; style gynobasic or terminal.
                                                                                                                               60 Style gynobasic (originating from the base of the ovary's lobes); ovary slightly to deeply lobed; fruit a schizocarp of 4 mericarps
                                                                                                                               60 Style terminal (originating from the apex of the ovary), twice-cleft into 4 branches, each of which then terminates in a stigma; ovary slightly lobed; fruit a drupe with a glutinous mesocarp (or if lacking, a nut)
                                                                                                                             59 Ovary slightly 2-4-lobed, or not at all lobed; style terminal or reduced to a sessile terminal stigma.
                                                                                                                                  61 Plants usually strongly gray or white-colored and villous, growing in short, suffrutescent mounds or mats; leaves densely pubescent (hairs densely appressed adaxially, tomentose abaxially); inflorescence of solitary flowers or extra-axillary, never scirpioid; corolla lavender or whitish-lavender, the lobes 1.8-3.0 (-4.5) mm long, broadly rounded; [s. TX, westward; primarily of the Trans-Pecos region]
                                                                                                                                  61 Plants variously glabrous or pubescent (sometimes villous), usually herbaceous, occasionally suffrutescent and mound or mat-forming; inflorescence variously elongate or racemose, often scirpioid (curved or coiled on one side of the inflorescence axis; e.g., Heliotropium), occasionally solitary (e.g., Euploca, in part; although in this case the leaves of the shrubby Euploca are significantly narrower); corolla variously colored (including lavender); [plants collectively widespread, including TX]
                                                                                                                           58 Ovary not lobed; fruit a capsule or berry.
                                                                                                                                    62 Leaves scale-like, 1-4.5 mm long, appressed to the stem; petals 4; stamens 4
                                                                                                                                    62 Leaves larger (or only 2-8 mm long in Pyxidanthera in DIAPENSIACEAE, but then spreading); petals 5-7; stamens 5-7.
                                                                                                                                      63 Plant a creeping subshrub (keyed here as a failsafe); leaves either 0.2-0.8 cm long and acicular, or 2-10 cm long and broadly ovate or elliptic.
                                                                                                                                        64 Leaves 0.2-0.8 cm long and acicular
                                                                                                                                        64 Leaves 2-10 cm long and broadly ovate or elliptic
                                                                                                                                      63 Plant an herb, erect or sprawling; leaves > 1.5 cm long.
                                                                                                                                          65 Leaves cordate at the base; plant a twining vine
                                                                                                                                          65 Leaves cuneate to rounded at the base; plant an erect, sprawling, or reclining herb (twining in Solanum dulcamara in SOLANACEAE).
                                                                                                                                            66 Inflorescences (solitary or of several flowers) terminal on the stem.
                                                                                                                                               67 Calyces tubular, conspicuously 5-ribbed and bearing numerous stalked, capitate-glands
                                                                                                                                               67 Calyces not as above, flowers typically campanulate (not salverform), if tubular then not also 5-ribbed and capitate-glandular.
                                                                                                                                                 68 Corolla lobes longer than the fused corolla cup, blue, pink, or white; styles 2; herbage lacking stipitate glands; fresh plants not aromatic.
                                                                                                                                                   69 Flowers in axillary cymes; capsule subglobose; leaves 2-12 cm long
                                                                                                                                                   69 Flowers solitary or paired in the leaf axils; capsule cylindrical; leaves 0.5-8 cm long
                                                                                                                                                 68 Corolla lobes very short, much shorter than the corolla cup or tube, sometimes barely perceptible and represented only by teeth on the edge of the corolla limb, white or pink; style 1; herbage often with stipitate glands; fresh plants often rankly aromatic
                                                                                                                                            66 Inflorescences (of solitary or several flowers) axillary or lateral on the stem.
                                                                                                                                                     70 Flowers sessile or very-short pedicelled, solitary in the leaf axils.
                                                                                                                                                       71 Stamens alternate with the corolla lobes; flower ca. 10 mm in diameter
                                                                                                                                                       71 Stamens opposite the corolla lobes; flower ca. 1 mm in diameter
                                                                                                                                                     70 Flowers either solitary and obviously pedicelled, or several in an axillary or lateral inflorescence.
                                                                                                                                                         72 Calyces tubular, conspicuously 5-ribbed and bearing numerous stalked, capitate-glands
                                                                                                                                                         72 Calyces not as above, flowers typically campanulate (not salverform), if tubular then not also 5-ribbed and capitate-glandular.
                                                                                                                                                            73 Corolla lobes longer than the fused corolla cup, blue
                                                                                                                                                            73 Corolla lobes very short, much shorter than the corolla cup or tube, sometimes barely perceptible and represented only by teeth on the edge of the corolla limb, white, yellow, pink, various other colors (rarely including blue).
                                                                                                                                                              74 Fruit a capsule, 4-seeded
                                                                                                                                                              74 Fruit a berry or capsule, many-seeded

Key P3: herbaceous dicots with alternate, simple, and pinnately lobed leaves on the stem

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1 Inflorescence an involucrate head subtended by phyllaries, the heads solitary or many and variously arrayed in secondary inflorescences, the ovary inferior, the corolla connate and tubular at least basally, the calyx absent, the stamens 5, the fruit a cypsela
1 Inflorescence, flower, and fruit structure various, but not with the combination of features as above (sometimes the flowers in a head, e.g. Eryngium in APIACEAE, or the fruit a cypsela in Cevallia in LOASACEAE, but then with other features differing, such as stamens 4, or green calyx present, or fruit a schizocarp of mericarps, etc.).
  2 Perianth uniseriate, with only undifferentiated tepals; flowers many and small, greenish or brownish, inconspicuous individually; inflorescence of glomerules that are usually further aggregated into racemes or panicles; fruit an achene or utricle
  2 Perianth biseriate, both sepals and petals present and differentiated (except uniseriate and of 2 white to cream-colored sepals 5-10 mm long in Macleaya in PAPAVERACEAE); flowers larger, usually with the petals prominently colored; inflorescence various, but not as above; fruit a capsule, silique/silicle, or a schizocarp of 2 mericarps.
    3 Corolla bilaterally symmetrical and the petals connate into a tube (or the corolla 2-lipped but the corolla lobes twisted so as to make the flower asymmetrical); stamens 4; fruit a 2-locular and loculicidal capsule opening by 2 valves
    3 Corolla radially symmetrical and either connate into a tube or distinct (except Reseda in RESEDACEAE, with bilateral symmetry but separate petals); stamens 5 or more; fruit a silique/silicle, a schizocarp of 4 mericarps, or a 1-, 3-, or 4-locular capsule (2-locular in Ipomoea in CONVOLVULACEAE and Glaucium in PAPAVERACEAE), opening variously.
      4 Ovary inferior; fruit either a schizocarp of 2 mericarps (Eryngium), a 4-loculicidal (Oenothera) or apically dehiscent (Mentzelia) capsule with a persistent perianth (Mentzelia), or a cypsela (Cevallia).
        5 Flowers 4-merous, in a diffuse inflorescence; fruit a 4-locular capsule
        5 Flowers 5-merous (sometimes superficially 10+ in Mentzelia, the numerous "petals" actually a combination of 5+ petaloid stamen filaments and 5 petals).
          6 Flowers aggregated into a head; fruit a schizocarp of 2 mericarps
          6 Flowers solitary or in dichasia (Mentzelia) or if headlike, then plants with abundant trichomes, flowers yellow and fruit a cypsela with a persistent perianth (Cevallia); [LOASACEAE]
             7 Stamens 5; fruits indehiscent (a cypsela with a persistent perianth), bearing one seed each; plants with four trichome types (knobbed, retrorse, dendritic, and stinging), these sometimes but not always all present on the same plant.
             7 Stamens numerous (8-50+), often strongly exerted; petals 5 (sometimes superficially appearing to have ca. 10+ due to the presence of 5+ petaloid stamen filaments and 5 petals), fruits dehiscent (capsules with apical dehiscence); plants with two types of trichomes (antrorse/smooth or retrorse)
      4 Ovary superior; fruit either a silique/silicle, or a 1-, 2-, or 3-locular capsule, or a berry.
               8 Sepals and petals of different numbers, the sepals 2-3, the petals 0, 4, or 6; stamens many
               8 Sepals and petals the same number, 4-8 each; stamens 5 or 6 (10-25 in Reseda in RESEDACEAE).
                 9 Corolla bilaterally symmetrical; stamens 10-25
                 9 Corolla radially symmetrical; stamens 5 or 6.
                   10 Petals 4, distinct; stamens 6; fruit a silique/silicle
                   10 Petals 5, connate into a tube; stamens 5; fruit either a capsule or a berry.
                     11 Plant a twining vine.
                       12 Corolla with a long tube, much longer than the lobes, scarlet, white, pink, or blue; leaves shallowly to deeply pinnately parted into 3-many lobes
                       12 Corolla with a short tube, the lobes longer than the tube, purplish; leaves with a single large terminal l lobe, and 2 small basal lobes (these almost separate as leaflets)
                     11 Plant an erect or sprawling herb.
                          13 Fruit a capsule, 1-locular; corolla white, pink, lavender, or blue, the tube short (< 4 mm long), the lobes flaring, the corolla < 15 mm long or wide
                          13 Fruit either a capsule, 2- or-3 locular, or a berry; corolla scarlet, blue, white, yellow, greenish-yellow, or purple, the tube long (>10 mm long) and cylindrical, the corolla > 10 mm long or wide.
                            14 Stigmas 3; fruit a capsule with 3 valves; leaf lobes 0.5-5 mm wide, often themselves lobed, the sinuses very deep, often nearly to the leaf midvein
                            14 Stigmas 2; fruit either a capsule with 2 valves or a berry; leaf lobes > 5 mm wide, not lobed themselves, the sinuses shallow, often < 1/2 way to the midvein

Key S1: herbaceous dicots with opposite, simple, and unlobed leaves on the stem

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1 Inflorescence an involucrate head subtended by phyllaries, the heads solitary or many and variously arrayed in secondary inflorescences, the ovary inferior, the corolla connate and tubular at least basally, the calyx absent, the stamens 5, the fruit a cypsela
1 Inflorescence, flower, and fruit structure various, but not with the combination of features as above (sometimes the flowers in a head, e.g. Pycnanthemum in LAMIACEAE, but then with other features differing, such as stamens 4, or green calyx present, or fruit a schizocarp of mericarps, etc.; Carpobrotus is superficially asteroid, but heads are composed of numerous petaloid staminodia, and receptacles lack cypselae;).
  2 Leaves scale-like, stems fleshy; flowers embedded in the fleshy stem, no perianth present; [saline environments (coastal or rarely inland)].
  2 Leaves small to large; stems not fleshy (although sometimes plants generally succulent as in Sesuvium); flowers sessile or on pedicels; [collectively of many habitats, saline and not].
    3 Ovary inferior or partially inferior.
      4 Perianth of a single whorl (petals absent) (note that in Mirabilis in NYCTAGINACEAE the petaloid calyx is subtended by a 5-lobed fused set of involucral bracts).
        5 Leaves herbaceous, suborbicular, about as long as wide or wider than long; calyx 3- or 4-merous; stamens 4, 8, or 12.
          6 Plant ascending, with a single node (2 leaves); leaves > 6 cm long and wide; calyx 3-merous, brown to yellowish; stamens 12
          6 Plant creeping, with many nodes; leaves 3-15 mm long and wide; calyx 4-merous, yellow to greenish; stamens 4 or 8
        5 Leaves fleshy, linear, lanceolate, to broadly ovate, at least slightly longer than broad; calyx 5-merous; stamens 3, 5, or 10.
             7 Flowers axillary, sessile or nearly so, solitary or a few; petaloid sepals widely spreading, separate, usually with a subapical abaxial appendage; leaves linear to oblanceolate; stamens 5 or 30-50
             7 Flowers in terminal cymose panicles; petaloid sepals connate into a narrow tube (reminiscent of the corolla of Ipomoea), lacking subapical abaxial appendages; leaves lanceolate, elliptic, ovate, or broadly ovate; stamens 3 or 5
      4 Perianth in 2 whorls (sepals and petals both present).
               8 Plants succulent, mat-forming subshrubs; flowering heads showy and consisting of numerous petaloid staminodia; [waif, FL]
               8 Plants not as above.
                 9 Petals distinct; inflorescence diffuse.
                   10 Leaves distinctly 3-veined from the base, the 3 veins converging again at the leaf apex
                   10 Leaves with prominently pinnate venation
                 9 Petals connate into a tube (at least basally); inflorescence often a head or dense terminal cyme (also axillary, or solitary on long peduncles).
                     11 Petals 5; stamens 3, 4, or 5
                       12 Creeping subshrub; flowers paired at tip of an upright peduncle
                       12 Upright herb; flowers in axils or terminal corymbs
                          13 Flowers in terminal corymbs; fruit dry
                          13 Flowers axillary; fruit fleshy
                     11 Petals 4 (or 6 or 8 in Richardia in RUBIACEAE); stamens 4, 6, or 8.
                            14 Inflorescence a head, subtended by 4 large bright white bracts
                            14 Inflorescence a head or more diffuse (see below), sometimes subtended by green bracts.
                              15 Leaves serrate; corolla bilaterally symmetrical (especially the flowers near the outer edge of the head); inflorescence a head
                              15 Leaves entire; corolla radially symmetrical; inflorescence a head or more diffuse (see below).
                                16 Petals acute; flowers in terminal panicles, cymes, or panicles, or axillary; plant habit various, not simultaneously with all the characters below
                                16 Petals broadly rounded; flowers axillary, solitary; plant a diffusely branched herb with linear leaves
    3 Ovary superior.
                                  17 Perianth of a single whorl (petals absent) or missing entirely (petals and sepals both absent).
                                    18 Inflorescence a cyathium, consisting of a single pistillate flower (reduced to a single 3-carpellate pistil) and 2 or more staminate flowers (each reduced to 1 stamen), borne in a cup-like involucre, the involucre bearing pointed or rounded glands, these sometimes brightly colored and petaloid, mimicking an individual flower (the cyathia then secondarily arranged in terminal cymes, or solitary and axillary, etc.); fresh plants with milky juice; fruit a 3-lobed, 3-locular capsule
                                    18 Inflorescence not a cyathium (and staminate or bisexual flowers with > 1 stamen, except Callitriche in PLANTAGINACEAE); fresh plants lacking milky juice; fruit various, not as above.
                                       19 Flowers 1 (or 2) in leaf axils; leaves entire.
                                         20 Flowers unisexual; sepals 0; flowers (staminate) with 1 stamen
                                         20 Flowers bisexual; sepals 4; flowers with 2, 4, or 6 stamens.
                                           21 Leaves of an opposite pair markedly different in size
                                           21 Leaves of an opposite pair essentially the same size
                                       19 Flowers many, in axillary spikes, cymes, or glomerules, or in terminal spikes, heads, cymes, or panicles; leaves entire or serrate.
                                             22 Fruit a 2-locular capsule
                                             22 Fruit single-seeded, an achene or utricle.
                                               23 Leaves serrate, regularly and sharply so; plants with stinging hairs (or not)
                                               23 Leaves entire, or with a few very obscure crenations (Iresine) or basally disposed rounded lobe-like teeth (Atriplex); plants without stinging hairs.
                                                 24 Leaves of a pair slightly to strongly different in size
                                                 24 Leaves of a pair the same size.
                                                    25 Styles 1-2 (-3); leaves 2-30 mm long, 0.5-8 mm wide, linear or narrowly elliptic
                                                    25 Style 1; leaves generally either longer than 30 mm, or wider than 8 mm (if linear and smaller than those dimensions, then fleshy).
                                                      26 Tepals scarious; inflorescence of heads, spikes, or panicles
                                                      26 Tepals herbaceous; inflorescence of glomerules, these axillary or arrayed in spikes or panicles
                                  17 Perianth in 2 whorls (sepals and petals both present).
                                                        27 Gynoecium of 4-many pistils, each 1-carpellate.
                                                          28 Pistils 4-5, in a single whorl; stamens 4, 5, 8, or 10; fruit an aggregate of follicles
                                                          28 Pistils many, spiral; stamens many; fruit an aggregate of plumose achenes
                                                        27 Gynoecium either of 1 pistil (with 1 or more carpels), or of 2 pistils, united only by the style and stigma (APOCYNACEAE).
                                                            29 Petals not at all connate, not even at their bases.
                                                              30 Leaves with pellucid punctate glands (most easily visible with transmitted light); stamens often fascicled into 3, 4, or 5 fascicles; petals yellow or pinkish
                                                              30 Leaves lacking pellucid punctate glands; stamens not fascicled; petals variously colored.
                                                                 31 Sepals 2; stamens opposite the petals
                                                                 31 Sepals 3-7; stamens opposite the sepals.
                                                                   32 Petals 3; sepals 5, dimorphic, the 2 outer sepals narrower than the 3 inner and concave sepals; stamens (3-) 5-15 (-25)
                                                                   32 Petals 4-7; sepals 4-7, normally monomorphic; stamens 4, 5, 6, 8, 10, or 12 (or sometimes rarely 2 or 3).
                                                                     33 Capsule 2-5 (-6) locular; style 1; perianth 4-7-merous; stamens 4, 6, 8, 10, or 12
                                                                     33 Capsule either 1-locular of 10-locular; styles 2-5; perianth 4-5-merous; stamens 4, 5, 8, or 10 (or rarely 2 or 3).
                                                                       34 Capsule 1-locular, dehiscent apically by teeth or valves; sepals connate into a tube or separate; styles 2-5; perianth 4-5-merous; stamens 4, 5, 8, or 10 (or rarely 2 or 3)
                                                                       34 Capsule 10-locular (each of the 5 carpels divided at maturity), septicidal; sepals distinct or nearly so; styles 5, perianth 5-merous; stamens 5
                                                            29 Petals connate at least for a short distance at their bases.
                                                                         35 Corolla radially symmetrical (or so slightly bilaterally symmetrical as to be mistakable as radially symmetrical); stamens as many as the corolla lobes (or 1 less in Ruellia in ACANTHACEAE, Buchnera in OROBANCHACEAE, Trichostema in LAMIACEAE, and Verbena in VERBENACEAE); carpels 2 or 3.
                                                                           36 Pistils 2, united only by the style and stigma; fruit a schizocarp of 2 1-carpellate follicles (often single by abortion); plant with milky juice when fresh (except Catharanthus); leaves entire
                                                                           36 Pistil 1 (of 2-5 fused carpels); fruit either a 2-5-carpellate capsule or of 2 or 4 1-seeded nutlets derived from 2 carpels; plant lacking milky juice; leaves entire or serrate.
                                                                              37 Ovary and capsule 3-5-carpellate; capsule 3- or 1-locular.
                                                                                38 Sepals 2
                                                                                38 Sepals 5.
                                                                                  39 Inflorescence a terminal cyme; corolla salverform, with an elongated and very narrow tube, pink or white; capsule 3-locular
                                                                                  39 Inflorescence various but not cymose, of terminal or axillary racemes or panicles, or of solitary axillary flowers; corolla connate only at the base, the petals appearing nearly separate (not salverform); capsule 1-locular
                                                                              37 Ovary and capsule 2-carpellate; fruit either a 2-locular capsule or of 2 or 4 1-seeded nutlets derived from 2 carpels.
                                                                                    40 Stamens 4-12, the same number as the corolla lobes; corolla (and the flower as a whole) strictly radially symmetrical.
                                                                                      41 Capsule septicidal; corolla white, pink, blue, yellowish white, or greenish white; inflorescence either a terminal or axillary cyme, or a terminal panicle or raceme, or a terminal or axillary cyme reduced to 1 or a few flowers
                                                                                      41 Capsule loculicidal and also deeply 2-lobed; corolla white, pink, or scarlet with a yellow interior; inflorescence of cymosely arranged spikes
                                                                                    40 Stamens either 4, 1 fewer than the 5 corolla lobes, or 2 (with 2 staminodes); corolla usually slightly bilaterally symmetrical (the flower as a whole made bilaterally symmetrical by the 2 or 4 stamens).
                                                                                        42 Leaves entire; corolla tube flaring for all of its length
                                                                                           43 Fruit a schizocarp of 4 1-seeded nutlets; inflorescence terminal, of cymes; corolla ca. 5 mm long; leaves prominently 3-veined
                                                                                           43 Fruit a capsule; inflorescence axillary, of cymes or clusters (often reduced to a solitary flower); corolla > 12 mm long; leaves with single primary vein
                                                                                        42 Leaves serrate; corolla salverform, the tube narrow and nearly the same diameter for most of its length; inflorescence a terminal spike, raceme, raceme of racemes, or head.
                                                                                             44 Fruit a 2-locular capsule; stamens inserted near the base of the corolla tube
                                                                                             44 Fruit a schizocarp of 4 mericarps; stamens inserted near or above the middle of the corolla tube
                                                                         35 Corolla bilaterally symmetrical (or the corolla 2-lipped but the corolla lobes twisted so as to make the flower asymmetrical); fertile stamens fewer than the corolla lobes (except Plantago in PLANTAGINACEAE, which is equal, with 4 each; a few genera have a 5th, sterile, stamen which is obviously different in form than the 4 fertile stamens) (note that many corollas are bilabiate and the number of corolla lobes, 4 or 5, may be difficult to interpret); carpels 2.
                                                                                               45 Carpels 2, each carpel slightly to deeply lobed, separating at maturity into 4 half-carpellate units (not separating in Phyla in VERBENACEAE); fruit a schizocarp of 4 mericarps (or 2 nutlets in Phyla in VERBENACEAE).
                                                                                                 46 Inflorescence a thyrse, verticillaster, or terminal cyme, the flowers borne in cymose lateral branches; corolla strongly bilaterally symmetrical (rarely nearly radially symmetrical); stems square in ×-section (or sometimes rounded, especially on older growth); fresh plants often (but not always) aromatic
                                                                                                 46 Inflorescence of spikes, racemes, or heads, the flowers or fruits single at nodes; corolla often nearly radially symmetrical; stems rounded in X-section (rarely square); fresh plants usually not aromatic
                                                                                               45 Carpels 2, unlobed; fruit a capsule (or an achene in Phryma).
                                                                                                   47 Stamens 2.
                                                                                                     48 Corolla 4 lobed, almost radially symmetrical; corolla scarious, white, or bluish
                                                                                                     48 Corolla 4-5-lobed, either strongly bilabiate or salverform (Pseuderanthemum in ACANTHACEAE); white, blue, or yellow.
                                                                                                        49 Inflorescence an axillary cluster or spike
                                                                                                        49 Inflorescence of solitary (rarely 2) axillary flower. {add [Hypoestes] ACANTHACEAE}
                                                                                                          50 Sepals 4
                                                                                                          50 Sepals 5, distinct or nearly so.
                                                                                                            51 Corolla barely bilaterally symmetrical, the lobes about as long as the tube; outer sepals ovate, much wider than the inner sepals
                                                                                                            51 Corolla distinctly bilabiate, the lobes shorter than the tube; sepals of nearly the same width.
                                                                                                              52 Sterile stamens (the lower pair) consisting of slender filaments
                                                                                                              52 Sterile stamens minute or completely absent
                                                                                                   47 Stamens 4.
                                                                                                                53 Corolla 4 lobed, nearly radially symmetrical; corolla scarious
                                                                                                                53 Corolla 5-lobed, distinctly bilabiate or in some nearly radially symmetrical; corolla colored.
                                                                                                                  54 Flowers in terminal racemes, panicles, or spikes, the inflorescence not interspersed with large, leaf-like bracts.
                                                                                                                     55 Sepals separate to the base or nearly so, not forming a tube
                                                                                                                     55 Sepals connate for at least 0.3× their length to form a tube (this cup-like and flaring in Scrophularia in SCROPHULARIACEAE).
                                                                                                                       56 Inflorescence a diffuse panicle; corolla 5-11 mm long, reddish-brown (sometimes with some yellow); fruit a septicidal capsule
                                                                                                                       56 Inflorescence of 1 or more terminal (and sometimes upper axillary) spikes or racemes; corolla 10-50 mm long (6-8 mm long in Phryma in PHRYMACEAE), white, pink, blue, purple, or yellow; fruit either a loculicidal capsule (OROBANCHACEAE) or a single seeded achene (Phryma in PHRYMACEAE).
                                                                                                                         57 Corolla 10-50 mm long, pink, blue, purple, or yellow; fruit a loculicidal capsule
                                                                                                                         57 Corolla 6-8 mm long, white to pale pink; fruit a 1-seeded achene contained in the accrescent calyx, this “lopping down” against the inflorescence axis
                                                                                                                  54 Flowers axillary and solitary, borne in the axils of normally-sized leaves or somewhat reduced but still large and leaf-like bracts [some taxa keyed here and below].
                                                                                                                           58 Sepals separate to the base or nearly so, not forming a tube.
                                                                                                                             59 Corolla distinctly bilabiate
                                                                                                                             59 Corolla not bilabiate, only slightly bilaterally symmetrical.
                                                                                                                               60 Leaves serrate, 2.0-4.5 cm long; plant usually blackening on drying
                                                                                                                               60 Leaves entire, either mostly larger or smaller [see below]; plant not blackening on drying
                                                                                                                                  61 Leaves 0.6-2.8 cm long, round, obovate, or broadly elliptic, < 1.8× as long as wide; plants creeping, ascending to 3 dm tall; [plants of wet places]
                                                                                                                                  61 Leaves 3-30 cm long, narrowly elliptic to lanceolate, > 2× as long as wide; plants erect or the stems sprawling; [plants mostly of uplands]
                                                                                                                           58 Sepals connate for at least 0.3× their length to form a tube.
                                                                                                                                    62 Corolla yellow, orange, or red.
                                                                                                                                      63 Calyx lobes longer than the tube, or as long as the tube, corolla 25-50 mm long; plants usually blackening on drying
                                                                                                                                      63 Calyx lobes shorter than the tube; corolla 14-22 mm long; plants not blackening on drying.
                                                                                                                                        64 Corolla red or orange, with a very narrow, cylindrical tube, the lobes then flaring into a limb about 1 cm across; plants blackening on drying; [rare exotic, in crop fields, a noxious hemiparasitic weed under quarantine]
                                                                                                                                        64 Corolla yellow, not narrowly cylindrical, the lower lip arched; plants not blackening on drying; [rare, in seepage wetlands]
                                                                                                                                    62 Corolla white, pale blue, lavender, or pink (sometimes with some yellow).
                                                                                                                                          65 Corolla pink (sometimes almost white), often lined with yellow inside; leaves narrowly linear, often filiform (except lanceolate in A. auriculata); plants usually blackening on drying (some species do not); corolla not strongly bilabiate
                                                                                                                                          65 Corolla white, blue, or combinations of blue and white (sometimes with some yellow markings); leaves broader, mostly lanceolate; plants not blackening on drying; corolla strongly bilabiate.
                                                                                                                                            66 Upper lip of the corolla hooded, enfolding the anthers
                                                                                                                                            66 Upper lip of the corolla not hooded and enclosing the anthers; plants not blackening on drying.
                                                                                                                                               67 Corolla blue; lower lip of the corolla arched upwards into the throat; plants perennial from rhizomes or crowns, 3-13 dm tall
                                                                                                                                               67 Corolla bicolored, the upper lip white or very pale blue, the lower lip bright blue; lower lip of the corolla folded downward into a pouch enfolding the anthers; plants annuals, 0.5-4 dm tall