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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].
                              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].
                                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 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.
                                             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).
  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).
                                                        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.
                                                                 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
                                                                   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 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.
                                                                                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).
                                                                                    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.
                                                                                        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
                                                                                             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.
                                                                                                 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]
                                                                                             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.
                                                                                                        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).
                                                                                                                  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]
                                                                                                                                  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]

Key P2: herbaceous dicots with alternate, simple, and palmately 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, but then with other features differing, such as stamens 4, or green calyx present, or fruit a schizocarp of mericarps, etc.).
  2 Plant a vine, climbing by tendrils or twining.
      4 Leaf margins entire; flowers bisexual; plants hermaphroditic; petals connate, large and showy
      4 Leaf margins serrate; flowers unisexual; plants dioecious; petals absent
    3 Vine climbing by tendrils.
        5 Ovary superior; petals distinct; flowers bisexual
  2 Plant an herb, sometimes sprawling, reclining (e.g. Cymbalaria in PLANTAGINACEAE, Aconitum in RANUNCULACEAE), but lacking climbing adaptations such as tendrils or twining stems.
          6 Ovary inferior; inflorescence an umbel (or flowers solitary or in dichasia in Mentzelia); fruit a schizocarp of 2 mericarps or a capsule (Mentzelia).
             7 Flowers solitary or in dichasia; fruit capsules dehiscing via apical valves
          6 Ovary superior; inflorescence various, not an umbel; fruit various, a capsule, an aggregate of achenes or follicles, or a ring of (>2) mericarps.
                 9 Perianth uniseriate, the corolla absent (the calyx petaloid and white in Cnidoscolus); flowers unisexual; plants either with stinging hairs or not
                 9 Perianth biseriate (uniseriate in Aphanes in ROSACEAE and in Trautvetteria in RANUNCULACEAE); flowers bisexual; plants lacking stinging hairs.
                   10 Pistils many (or 2-3 in Aphanes in ROSACEAE), each with 1 carpel, arranged spirally or in a ring (if in a ring, of 2-5); fruit an aggregate of achenes, follicles, or utricles.
                     11 Perianth bilaterally symmetrical, either hooded or spurred; fruit an aggregate of follicles
                     11 Perianth radially symmetrical, not hooded or spurred; fruit an aggregate of utricles or achenes (plumose achenes in Geum)
                       12 Stamens showy, bright white, dilated towards the tip; pistils ca. 15; fruit an aggregate of utricles
                       12 Stamens not showy, white, or dilated towards the tip; pistils many (> 25); fruit an aggregate of achenes.
                          13 Flowers with a prominent hypanthium; achenes with an elongate, plumose beak
                   10 Pistil 1, with 1-to many carpels (in many MALVACEAE, the carpels loosely united in a ring of more than 5 around the style); fruit a capsule, an achene, a follicle, or a ring of 3 or 5-many 1-seeded mericarps.
                              15 Corolla bilaterally symmetrical, the petals connate (except distinct in Delphinium in RANUNCULACEAE); fruit a capsule, a follicle, or a schizocarp of 3 1-seeded mericarps.
                                16 Corolla not spurred; fruit an elongate (10-20 cm) capsule with 2 curved beaks
                              15 Corolla radially symmetrical, the petals distinct (fused and tubular in Ipomoea); fruit a capsule or a schizocarp consisting of a ring of 5-many 1-seeded mericarps.
                                         20 Stamens many, connate into a stamen tube; carpels 5-many, completely or only loosely fused; fruit a capsule or a schizocarp of 5-many mericarps borne in a ring; calyx often subtended by an epicalyx (an additional calyx-like, green, foliaceous whorl of bracts)
                                         20 Stamens 5 or 10, distinct; carpels 2 or 5, fused; fruit a capsule or a schizocarp of 5 1-seeded mericarps.