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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) 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
             7 Leaf bases cordate to rounded.
               8 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
               8 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.
                 9 Styles 2; inflorescence a dense axillary cyme (almost a head); fruit a multiple of achenes; plant lacking stinging hairs; [exotic plant of weedy situations]
                 9 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.
                   10 Ovary inferior or half-inferior.
                     11 Leaf base cordate; calyx 3-lobed, fused into a bilaterally symmetrical, curved brown or yellowish tube; fruit a capsule
                     11 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.
                       12 Leaves subsessile or very short petiolate, elliptic or narrowly elliptic, broadest near the middle; [native]
                       12 Leaves distinctly petiolate, rhombic, widest near the base; [rarely naturalized exotics].
                          13 Inflorescence of a single axillary flower
                          13 Inflorescence terminal, spikelike
                   10 Ovary superior.
                            14 Inflorescence a leaf-opposed (sometimes apparently terminal) spike or raceme; flowers visually white from white petaloid sepals, white bracts, or white stamens.
                              15 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].
                                16 Sepals 4; carpels 1; fruit subglobose berries or apically lobed achenes
                                16 Sepals 5; carpels 6-12, distinct; fruit an oblate berry
                              15 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].
                                  17 Fruit a 1-seeded drupe; stamens 2; plants terrestrial or epiphytic
                                  17 Fruit a capsule or schizocarp with 3-4 mericarps; stamens 3 or 6-8; plants terrestrial
                            14 Inflorescence not leaf-opposed, either simpler (single axillary or glomerules of flowers) or more complexly branched (axillary or terminal panicles or complex cymes); flowers white, reddish, scarious, or greenish.
                                    18 Stipules tubular, sheathing (= ocreae); flowers subtended by tubular, sheathing bracteoles (= ocreolae); nodes usually prominently swollen; perianth usually of 5-6 white to pink tepals
                                    18 Stipules not tubular or sheathing; flowers not subtended by ocreolae; nodes not swollen; perianth absent or of 3-5 sepals.
                                       19 Inflorescence an terminal involucrate cluster; flowers bisexual; stamens 9
                                       19 Inflorescence axillary, or a terminal panicle or raceme that is not involucrate; stamens 3-6.
                                         20 Ovary 3-locular; styles 3, each bifid; fruit a capsule, with 6 seeds
                                         20 Ovary 1-locular; styles 1-3, not bifid; fruit a utricle or achene (1-seeded).
                                           21 Styles 1, stigma 1; flowers unisexual
                                           21 Styles 1-3, if style 1, then stigmas 3; flowers bisexual or unisexual.
                                             22 Tepals acute, scarious
                                             22 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).
                                               23 Ovary inferior or half-inferior.
                                                 24 Petals connate.
                                                    25 Inflorescence leaf-opposed, a dense, cylindrical spike
                                                    25 Inflorescence various, either a terminal head, or axillary and solitary, or variously axillary or terminal and more diffuse.
                                                      26 Leaves toothed; flowers blue to white
                                                      26 Leaves entire; flowers white
                                                 24 Petals distinct.
                                                        27 Petals 5; stamens 5; inflorescence a head; fruit a schizocarp of 2 mericarps
                                                        27 Petals 4 7; stamens 6 or more; inflorescence various, not a head; fruit a capsule.
                                                          28 Petals 4-7; stamens 1× or 2× as many as the petals, 4-7, 8, 10, 12, or14; leaves herbaceous in texture
                                                          28 Petals 5 (or sometimes doubled in horticultural forms); stamens 6-40 (or more); leaves fleshy in texture
                                               23 Ovary superior.
                                                            29 Corolla bilaterally symmetrical, petals connate (except distinct in VIOLACEAE); fruit a capsule or legume (except a 1-seeded indehiscent spinose pod in Krameria in KRAMERIACEAE).
                                                              30 Petals distinct, 5; carpels 3; fruit a 3-loculed capsule
                                                              30 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).
                                                                 31 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.
                                                                   32 Stamens fused, monadelphous or diadelphous.
                                                                     33 Stamens 10, monadelphous or diadelphous; fruit a legume
                                                                     33 Stamens 6-8, monadelphous; fruit a capsule
                                                                   32 Stamens distinct.
                                                                       34 Carpel 1; fruit a legume
                                                                       34 Carpels 3-6; fruit a capsule
                                                                 31 Stamens 4-5, less than the number (5) of the petals; fruit a 2-5-carpellate capsule.
                                                                         35 Pistil 5-carpellate; capsule 5-locular, explosively dehiscent; inflorescence axillary, small clusters of flowers
                                                                         35 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).
                                                                           36 Fruit 1-seeded, indehiscent; sepals petaloid, red-purple; petals dimorphic, the upper 3 long-clawed, the lower 2 small, thickened, and glandlike
                                                                           36 Fruit > 2-seeded, dehiscent; sepals sepaloid, green; petals not dimorphic.
                                                                              37 Stamens 5; corolla not spurred; capsule septicidal; pubescence of the stem and leaves either gland-tipped or dendritically branched
                                                                              37 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.
                                                                                38 Capsule septicidal; corolla not spurred
                                                                                38 Capsule loculicidal; corolla spurred (except Digitalis)
                                                            29 Corolla radially symmetrical, petals connate or distinct; fruit various (including a capsule).
                                                                                  39 Petals distinct; stamens 5-many.
                                                                                    40 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.
                                                                                      41 Pistils 5 (-7); inflorescence a compound terminal cyme.
                                                                                        42 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]
                                                                                        42 Fruit a 5 (-7) locular capsule; leaves membranaceous in texture; leaves serrate, with > 20 points per leaf; [plants of wet habitats]
                                                                                      41 Pistils many; inflorescence of solitary flowers, or diffuse.
                                                                                           43 Leaves cuneate at the base; flowers in a diffuse inflorescence
                                                                                           43 Leaves cordate at the base; flowers solitary, on long pedicels
                                                                                    40 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.
                                                                                             44 Petals 4; sepals 4; stamens 6; fruit a silique/silicle
                                                                                             44 Petals 5 (rarely 4 or 6); sepals 5 (rarely 4 or 6); stamens 5 (or multiples of 5), 6, or 12; fruit a capsule or a ring of mericarps.
                                                                                               45 Stamens many, connate into a staminal tube; carpels 5-many; fruit a capsule or ring of mericarps; leaves usually serrate
                                                                                               45 Stamens 5-many, distinct; carpels 2-5; fruit a capsule; leaves entire (serrate in Croton in EUPHORBIACEAE).
                                                                                                 46 Flowers unisexual; leaf vestiture of peltate scales and/or stellate hairs
                                                                                                 46 Flowers bisexual; leaf vestiture simple or stellate.
                                                                                                   47 Flowers 6-merous (the petals and sepals 6, the stamens 6 or 12); corolla pink or purplish (rarely white); fruit a septicidal capsule
                                                                                                   47 Flowers 5-merous (the petals and sepals 5, stamens 5 or various multiples of 5); corolla yellow, reddish, or blue; fruit a loculicidal or septicidal capsule.
                                                                                                     48 Stamens 5; corolla yellow or blue; capsule either 10-locular and septicidal or 1-locular (with 3 carpels) and loculicidal.
                                                                                                        49 Capsule 10-locular (with 5 carpels) and septicidal
                                                                                                        49 Capsule 1-locular (with 3 carpels) and loculicidal
                                                                                                     48 Stamens (5-) 10, 15, 20, 30 (-many); corolla white, pink, yellow, or reddish; capsule 3-, 5- (-10)-locular, loculicidal.
                                                                                                          50 Stamens (5-) 10, 15, 20, 30 (-many); corolla yellow or reddish; capsule 3 (-10)-locular, loculicidal
                                                                                                          50 Stamens 10; corolla white or pink; capsule 5-locular
                                                                                  39 Petals fused; stamens (4-) 5 (-7).
                                                                                                            51 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
                                                                                                            51 Pistil 1 (of 2 or 3 fused carpels); fruit a capsule; plant lacking milky juice; leaves entire or serrate; inflorescence various (but not an umbel).
                                                                                                              52 Ovary slightly to deeply 2-4-lobed; fruit a schizocarp of 4 mericarps or a drupe.
                                                                                                                53 Ovary deeply 4-parted; style gynobasic; fruit a schizocarp of 4 mericarps
                                                                                                                53 Ovary slightly 2-4-lobed, or not at all lobed; style terminal or reduced to a sessile terminal stigma; fruit a schizocarp of 4 mericarps, or a drupe
                                                                                                              52 Ovary not lobed; fruit a capsule or berry.
                                                                                                                  54 Leaves scale-like, 1-4.5 mm long, appressed to the stem; petals 4; stamens 4
                                                                                                                  54 Leaves larger (or only 2-8 mm long in Pyxidanthera in DIAPENSIACEAE, but then spreading); petals 5-7; stamens 5-7.
                                                                                                                     55 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.
                                                                                                                       56 Leaves 0.2-0.8 cm long and acicular
                                                                                                                       56 Leaves 2-10 cm long and broadly ovate or elliptic
                                                                                                                     55 Plant an herb, erect or sprawling; leaves > 1.5 cm long.
                                                                                                                         57 Leaves cordate at the base; plant a twining vine
                                                                                                                         57 Leaves cuneate to rounded at the base; plant an erect, sprawling, or reclining herb (twining in Solanum dulcamara in SOLANACEAE).
                                                                                                                           58 Inflorescences (solitary or of several flowers) terminal on the stem.
                                                                                                                             59 Corolla lobes longer than the fused corolla cup, blue, pink, or white; styles 2; herbage lacking stipitate glands; fresh plants not aromatic.
                                                                                                                               60 Flowers in axillary cymes; capsule subglobose; leaves 2-12 cm long
                                                                                                                               60 Flowers solitary or paired in the leaf axils; capsule cylindrical; leaves 0.5-8 cm long
                                                                                                                             59 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
                                                                                                                           58 Inflorescences (of solitary or several flowers) axillary or lateral on the stem.
                                                                                                                                  61 Flowers sessile or very-short pedicelled, solitary in the leaf axils.
                                                                                                                                    62 Stamens alternate with the corolla lobes; flower ca. 10 mm in diameter
                                                                                                                                    62 Stamens opposite the corolla lobes; flower ca. 1 mm in diameter
                                                                                                                                  61 Flowers either solitary and obviously pedicelled, or several in an axillary or lateral inflorescence.
                                                                                                                                      63 Corolla lobes longer than the fused corolla cup, blue
                                                                                                                                      63 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).
                                                                                                                                        64 Fruit a capsule, 4-seeded
                                                                                                                                        64 Fruit a berry or capsule, many-seeded

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.).
  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; 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; 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); leaves lanceolate, elliptic, ovate, or broadly ovate; stamens 3 or 5
      4 Perianth in 2 whorls (sepals and petals both present).
               8 Petals distinct; inflorescence diffuse.
                 9 Leaves distinctly 3-veined from the base, the 3 veins converging again at the leaf apex
               8 Petals connate into a tube (at least basally); inflorescence often a head or dense terminal cyme (also axillary, or solitary on long peduncles).
                   10 Petals 5; stamens 3, 4, or 5
                     11 Creeping subshrub; flowers paired at tip of an upright peduncle
                     11 Upright herb; flowers in axils or terminal corymbs
                       12 Flowers in terminal corymbs; fruit dry
                       12 Flowers axillary; fruit fleshy
                   10 Petals 4 (or 6 or 8 in Richardia in RUBIACEAE); stamens 4, 6, or 8.
                          13 Inflorescence a head, subtended by 4 large bright white bracts
                          13 Inflorescence a head or more diffuse (see below), sometimes subtended by green bracts.
                            14 Leaves serrate; corolla bilaterally symmetrical (especially the flowers near the outer edge of the head); inflorescence a head
                            14 Leaves entire; corolla radially symmetrical; inflorescence a head or more diffuse (see below).
                              15 Petals acute; flowers in terminal panicles, cymes, or panicles, or axillary; plant habit various, not simultaneously with all the characters below
                              15 Petals broadly rounded; flowers axillary, solitary; plant a diffusely branched herb with linear leaves
    3 Ovary superior.
                                16 Perianth of a single whorl (petals absent) or missing entirely (petals and sepals both absent). {key lead number needs adjusting}
                                  17 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
                                  17 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.
                                    18 Flowers 1 (or 2) in leaf axils; leaves entire.
                                       19 Flowers unisexual; sepals 0; flowers (staminate) with 1 stamen
                                       19 Flowers bisexual; sepals 4; flowers with 2, 4, or 6 stamens.
                                         20 Leaves of an opposite pair markedly different in size
                                         20 Leaves of an opposite pair essentially the same size
                                    18 Flowers many, in axillary spikes, cymes, or glomerules, or in terminal spikes, heads, cymes, or panicles; leaves entire or serrate.
                                           21 Fruit a 2-locular capsule
                                           21 Fruit single-seeded, an achene or utricle.
                                             22 Leaves serrate, regularly and sharply so; plants with stinging hairs (or not)
                                             22 Leaves entire, or with a few very obscure crenations (Iresine) or basally disposed rounded lobe-like teeth (Atriplex); plants without stinging hairs.
                                               23 Leaves of a pair slightly to strongly different in size
                                               23 Leaves of a pair the same size.
                                                 24 Styles 1-2 (-3); leaves 2-30 mm long, 0.5-8 mm wide, linear or narrowly elliptic
                                                 24 Style 1; leaves generally either longer than 30 mm, or wider than 8 mm (if linear and smaller than those dimensions, then fleshy).
                                                    25 Tepals scarious; inflorescence of heads, spikes, or panicles
                                                    25 Tepals herbaceous; inflorescence of glomerules, these axillary or arrayed in spikes or panicles
                                16 Perianth in 2 whorls (sepals and petals both present).
                                                      26 Gynoecium of 4-many pistils, each 1-carpellate.
                                                        27 Pistils 4-5, in a single whorl; stamens 4, 5, 8, or 10; fruit an aggregate of follicles
                                                        27 Pistils many, spiral; stamens many; fruit an aggregate of plumose achenes
                                                      26 Gynoecium either of 1 pistil (with 1 or more carpels), or of 2 pistils, united only by the style and stigma (APOCYNACEAE).
                                                          28 Petals not at all connate, not even at their bases.
                                                            29 Leaves with pellucid punctate glands (most easily visible with transmitted light); stamens often fascicled into 3, 4, or 5 fascicles; petals yellow or pinkish
                                                            29 Leaves lacking pellucid punctate glands; stamens not fascicled; petals variously colored.
                                                              30 Sepals 2; stamens opposite the petals
                                                              30 Sepals 3-7; stamens opposite the sepals.
                                                                 31 Petals 3; sepals 5, dimorphic, the 2 outer sepals narrower than the 3 inner and concave sepals; stamens (3-) 5-15 (-25)
                                                                 31 Petals 4-7; sepals 4-7, normally monomorphic; stamens 4, 5, 6, 8, 10, or 12 (or sometimes rarely 2 or 3).
                                                                   32 Capsule 2-5 (-6) locular; style 1; perianth 4-7-merous; stamens 4, 6, 8, 10, or 12
                                                                   32 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).
                                                                     33 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)
                                                                     33 Capsule 10-locular (each of the 5 carpels divided at maturity), septicidal; sepals distinct or nearly so; styles 5, perianth 5-merous; stamens 5
                                                          28 Petals connate at least for a short distance at their bases.
                                                                       34 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.
                                                                         35 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
                                                                         35 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.
                                                                           36 Ovary and capsule 3-5-carpellate; capsule 3- or 1-locular.
                                                                              37 Sepals 2
                                                                              37 Sepals 5.
                                                                                38 Inflorescence a terminal cyme; corolla salverform, with an elongated and very narrow tube, pink or white; capsule 3-locular
                                                                                38 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
                                                                           36 Ovary and capsule 2-carpellate; fruit either a 2-locular capsule or of 2 or 4 1-seeded nutlets derived from 2 carpels.
                                                                                  39 Stamens 4-12, the same number as the corolla lobes; corolla (and the flower as a whole) strictly radially symmetrical.
                                                                                    40 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
                                                                                    40 Capsule loculicidal and also deeply 2-lobed; corolla white, pink, or scarlet with a yellow interior; inflorescence of cymosely arranged spikes
                                                                                  39 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).
                                                                                      41 Leaves entire; corolla tube flaring for all of its length
                                                                                        42 Fruit a schizocarp of 4 1-seeded nutlets; inflorescence terminal, of cymes; corolla ca. 5 mm long; leaves prominently 3-veined
                                                                                        42 Fruit a capsule; inflorescence axillary, of cymes or clusters (often reduced to a solitary flower); corolla > 12 mm long; leaves with single primary vein
                                                                                      41 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.
                                                                                           43 Fruit a 2-locular capsule; stamens inserted near the base of the corolla tube
                                                                                           43 Fruit a schizocarp of 4 mericarps; stamens inserted near or above the middle of the corolla tube
                                                                       34 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.
                                                                                             44 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).
                                                                                               45 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
                                                                                               45 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
                                                                                             44 Carpels 2, unlobed; fruit a capsule (or an achene in Phryma).
                                                                                                 46 Stamens 2.
                                                                                                   47 Corolla 4 lobed, almost radially symmetrical; corolla scarious, white, or bluish
                                                                                                   47 Corolla 4-5-lobed, either strongly bilabiate or salverform (Pseuderanthemum in ACANTHACEAE); white, blue, or yellow.
                                                                                                     48 Inflorescence an axillary cluster or spike
                                                                                                     48 Inflorescence of solitary (rarely 2) axillary flower. {add [Hypoestes] ACANTHACEAE}
                                                                                                        49 Sepals 4
                                                                                                        49 Sepals 5, distinct or nearly so.
                                                                                                          50 Corolla barely bilaterally symmetrical, the lobes about as long as the tube; outer sepals ovate, much wider than the inner sepals
                                                                                                          50 Corolla distinctly bilabiate, the lobes shorter than the tube; sepals of nearly the same width.
                                                                                                            51 Sterile stamens (the lower pair) consisting of slender filaments
                                                                                                            51 Sterile stamens minute or completely absent
                                                                                                 46 Stamens 4.
                                                                                                              52 Corolla 4 lobed, nearly radially symmetrical; corolla scarious
                                                                                                              52 Corolla 5-lobed, distinctly bilabiate or in some nearly radially symmetrical; corolla colored.
                                                                                                                53 Flowers in terminal racemes, panicles, or spikes, the inflorescence not interspersed with large, leaf-like bracts.
                                                                                                                  54 Sepals separate to the base or nearly so, not forming a tube
                                                                                                                  54 Sepals connate for at least 0.3× their length to form a tube (this cup-like and flaring in Scrophularia in SCROPHULARIACEAE).
                                                                                                                     55 Inflorescence a diffuse panicle; corolla 5-11 mm long, reddish-brown (sometimes with some yellow); fruit a septicidal capsule
                                                                                                                     55 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).
                                                                                                                       56 Corolla 10-50 mm long, pink, blue, purple, or yellow; fruit a loculicidal capsule
                                                                                                                       56 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
                                                                                                                53 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].
                                                                                                                         57 Sepals separate to the base or nearly so, not forming a tube.
                                                                                                                           58 Corolla distinctly bilabiate
                                                                                                                           58 Corolla not bilabiate, only slightly bilaterally symmetrical.
                                                                                                                             59 Leaves serrate, 2.0-4.5 cm long; plant usually blackening on drying
                                                                                                                             59 Leaves entire, either mostly larger or smaller [see below]; plant not blackening on drying
                                                                                                                               60 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]
                                                                                                                               60 Leaves 3-30 cm long, narrowly elliptic to lanceolate, > 2× as long as wide; plants erect or the stems sprawling; [plants mostly of uplands]
                                                                                                                         57 Sepals connate for at least 0.3× their length to form a tube.
                                                                                                                                  61 Corolla yellow, orange, or red.
                                                                                                                                    62 Calyx lobes longer than the tube, or as long as the tube, corolla 25-50 mm long; plants usually blackening on drying
                                                                                                                                    62 Calyx lobes shorter than the tube; corolla 14-22 mm long; plants not blackening on drying.
                                                                                                                                      63 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]
                                                                                                                                      63 Corolla yellow, not narrowly cylindrical, the lower lip arched; plants not blackening on drying; [rare, in seepage wetlands]
                                                                                                                                  61 Corolla white, pale blue, lavender, or pink (sometimes with some yellow).
                                                                                                                                        64 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
                                                                                                                                        64 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.
                                                                                                                                          65 Upper lip of the corolla hooded, enfolding the anthers
                                                                                                                                          65 Upper lip of the corolla not hooded and enclosing the anthers; plants not blackening on drying.
                                                                                                                                            66 Corolla blue; lower lip of the corolla arched upwards into the throat; plants perennial from rhizomes or crowns, 3-13 dm tall
                                                                                                                                            66 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
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