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Key to Euphorbiaceae

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1 Plant a twining vine (herbaceous or woody at base) to 5 m long; stem with stinging hairs; [subfamily Acalyphoideae]
1 Plant not twining; instead a tree, shrub, or herb (or weakly twining in some Tragia, but then less than 1 m long); stem either armed with stinging hairs, or not armed.
..2 Shrub or tree (woody).
....3 Leaves entire.
......4 Hairs of vegetative parts of the plant (especially the leaf undersurface) present and either 2-branched, stellate, or modified into lepidote scales (use 10× or more magnification); [subfamily Crotonoideae].
......4 Hairs of vegetative parts of the plant (especially the leaf undersurface) absent or unbranched (simple) (use 10× or more magnification).
........5 Flowers enclosed in a cyathium; plant with copious white latex; [subfamily Euphorbioideae]
........5 Flowers not enclosed in a cyathium; plant either with or without white latex (the sap clear to whitish or absent).
..........6 Leaf blades 1-1.5× as long as wide; [alien trees].
............ 7 Petioles 9-19 cm long; [subfamily Crotonoideae]
............ 7 Petioles 2-6 cm long; [subfamily Acalyphoideae]
..........6 Leaf blades 1.5-5× as long as wide; native or alien shrubs or, rarely, small trees.
............ ..8 Sepals absent; latex watery; leaf margins obscurely gland-toothed; [subtropical hardwood hammocks of far southern FL]; [subfamily Euphorbioideae]
............ ..8 Sepals present; latex absent or watery; leaf margins entire; [various habitats and collectively widespread].
............ ....9 Latex colorless to whitish, watery; capsules ovoid or ellipsoidal; [FL peninsula and s. TX]; [subfamily Crotonoideae]
............ ....9 Latex absent; capsules subglobose; [collectively widespread in our region].
............ ......10 Leaves palmately veined at base; inflorescence bracts not subtended by glands; [s. TX and southwards]; [subfamily Acalyphoideae]
............ ......10 Leaves pinnately veined; inflorescence bracts with 2 subtending glands; [widespread from NC to FL west to AR and e. TX]; [subfamily Euphorbioideae]
....3 Leaves crenate, serrate, and/or palmately lobed.
............ ........11 Plants hairy with 2-branched hairs (malpighiaceous trichomes); [subfamily Acalyphoideae]
............ ........11 Plants either glabrous or hairy with simple or stellate trichomes.
............ ..........12 Leaves palmately lobed, margins entire or serrate.
............ ............ 13 Petals absent; inflorescence a panicle; leaf lobe margins serrate; [subfamily Acalyphoideae]
............ ............ 13 Petals present; inflorescence a cyme or dichasium; leaf lobe margins entire or serrate; [subfamily Crotonoideae].
............ ............ ..14 Shrub or tree; inflorescence a fascicle or cyme; capsule ellipsoidal
............ ............ ..14 Tree; inflorescence a dichasium; capsule subglobose
............ ..........12 Leaves unlobed, margins crenate (obscurely crenate in Hippomane and Adelia) or serrate.
............ ............ ....15 Leaves 8-20× as long as wide (lanceolate to linear); petiole with 0 or 2 glands at summit.
............ ............ ......16 Petiole with 2 glands at summit; [alien, on ballast in Pensacola, FL]
............ ............ ......16 Petiole lacking 2 glands at summit; [native, widespread in our area]
............ ............ ....15 Leaves 1-3× as long as wide (elliptic, ovate, or obovate); petiole with 0 or 1 gland at summit.
............ ............ ........17 Lower leaf surface densely stellate-pubescent; leaf strongly toothed; [TX]; [subfamily Acalyphoideae]
............ ............ ........17 Lower leaf surface glabrous; leaf entire, obscurely crenate, or serrulate.
............ ............ ..........18 Leaf blades obovate, 2-3× as long as wide, with a rounded apex; petiole < 0.2 cm long; fruit a capsule, 1.0-1.3 cm in diameter; [TX]; [subfamily Acalyphoideae]
............ ............ ..........18 Leaf blades ovate, 1-2× as long as wide, with an acute apex; petiole 1-6 cm long; fruit a drupe, 1.5-2.5 cm in diameter; [FL]; [subfamily Euphorbioideae]
..2 Herb.
............ ............ ............ 19 Leaves palmately deeply divided into 3-many lobes.
............ ............ ............ ..20 Plants with a prominent, round woody shallow subterranean caudex to 13.5 cm in diameter; [subfamily Crotonoideae]
............ ............ ............ ..20 Plants lacking a prominent subterranean caudex.
............ ............ ............ ....21 Leaves peltate; plant glabrous; stamens 100-1000; [subfamily Acalyphoideae]
............ ............ ............ ....21 Leaves cordate to truncate or rounded at base; plant glabrous, stellate, or with conspicuous stinging trichomes; stamens 8-15; [subfamily Crotonoideae].
............ ............ ............ ......22 Plant with stinging trichomes; stamens connate
............ ............ ............ ......22 Plant lacking stinging trichomes; stamens separate.
............ ............ ............ ........23 Latex white; pubescence absent or of non-stellate hairs
............ ............ ............ 19 Leaves generally not lobed, entire or serrate (rarely pinnately lobed in Euphorbia).
............ ............ ............ ..........24 Plants hairy with stellate hairs and/or scales; [subfamily Crotonoideae]
............ ............ ............ ..........24 Plants glabrous or hairy with simple or 2-branched hairs.
............ ............ ............ ............ 25 Plants hairy with 2-branched hairs (malpighiaceous trichomes); [subfamily Acalyphoideae]
............ ............ ............ ............ 25 Plants glabrous or hairy with simple hairs.
............ ............ ............ ............ ..26 Flowers enclosed in a cyathium; plant with copious white latex; [subfamily Euphorbioideae]
............ ............ ............ ............ ..26 Flowers not enclosed in a cyathium; plant with or without white latex.
............ ............ ............ ............ ....27 Flowers in terminal spikes; stout perennial with several to many stems arising from a subterranean crown [subfamily Euphorbioideae]
............ ............ ............ ............ ....27 Flowers strictly axillary or both axillary and terminal, in small clusters, racemes, or spikes; finer perennial or annual, not typically with > 1 stem arising from a subterranean crown; [subfamily Acalyphoideae]
............ ............ ............ ............ ......28 Leaves alternate; carpels 3 (sometimes fewer by abortion).
............ ............ ............ ............ ........29 Pistillate flowers subtended by a conspicuous leafy bract
............ ............ ............ ............ ........29 Pistillate flowers lacking a leafy bract.
............ ............ ............ ............ ..........30 Plant lacking stinging trichomes; styles deeply multifid; [wetland habitats]
............ ............ ............ ............ ..........30 Plant with stinging trichomes; styles undivided; [upland habitats]

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 aliens 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; [alien 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 alien (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 aliens].
............ ............ 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.
..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.
............ ............ ............ ............ 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.
............ ............ ............ ............ ....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
............ ............ ............ ............ ........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.
............ ............ ............ ............ ............ ....33 Stamens 10, monadelphous or diadelphous; fruit a legume
............ ............ ............ ............ ............ 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.
............ ............ ............ ............ ........29 Corolla radially symmetrical, petals connate or distinct; fruit various (including a capsule).
............ ............ ............ ............ ............ ............ ......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.
............ ............ ............ ............ ............ ............ ..........42 Fruit an aggregate of follicles; leaves fleshy in texture; inflorescence; leaves entire of sparesly 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.
............ ............ ............ ............ ............ ............ ......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 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
............ ............ ............ ............ ............ ............ ............ ........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.
............ ............ ............ ............ ............ ............ ............ ..........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
............ ............ ............ ............ ............ ............ ............ ............ ....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 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
............ ............ ............ ............ ............ ............ ............ ............ ..........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.
............ ............ ............ ............ ............ ............ ............ ............ ............ ....57 Leaves cuneate to rounded at the base; plant an erect, sprawling, or reclining herb (twining in Solanum dulcamara in SOLANACEAE).
............ ............ ............ ............ ............ ............ ............ ............ ............ ........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 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
............ ............ ............ ............ ............ ............ ............ ............ ............ ............ 61 Flowers either solitary and obviously pedicelled, or several in an axillary or lateral inflorescence.
............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ....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).

Key Q: herbaceous dicots with whorled leaves on the stem {add [Platycodon] CAMPANULACEAE}

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1 Cauline leaves palmately compound.
..2 Cauline leaves essentially sessile, and also palmately cleft to the base, and further lacerately divided into linear or oblanceolate segments
..2 Cauline leaves petiolate, with 3-5, sessile or petiolulate, ovate, elliptic, or obovate leaflets (these serrate and sometimes with additional lobes).
....3 Inflorescence a spherical umbel of many flowers; fruit a drupe with 2-3 seeds; stem leaves 3-5
......4 Leaflets 3 (-5), sessile or subsessile, the petiolules 0-3 mm long; larger leaflets 4-8 cm long, 0.5-2.5 cm wide, averaging about 2.5× as long as wide, the apex obtuse to acute; fruit yellow-green when ripe, longitudinally winged and ribbed in ×-section; petals white (rarely tinged with pink); inflorescence nodding in bud; underground storage organ a spherical tuber
......4 Leaflets (3-) 5, petiolulate, the petiolules (7-) 10-25 mm long; larger leaflets 6-15 cm long, 3.5-7 cm wide, averaging about 1.8× as long as wide, the apex acuminate; fruit bright red when ripe, smoothly elliptical in ×-section; petals light green; inflorescence erect in bud; underground storage organ an +/- elongate root, this vertical or horizontal, and sometimes branched
....3 Inflorescence of single terminal flowers on the 1-several branches; fruit an aggregate of achenes; stem leaves 3
1 Cauline leaves simple.
........5 Inflorescence an involucrate head subtended by phyllaries, heads solitary or many, variously arrayed in secondary inflorescences; fruit a cypsela
........5 Inflorescence various, but not as above; fruit various, not as above (sometimes the flowers tightly grouped, but then with other features differing, such as stamens 4, or green calyx present, or fruit a schizocarp of mericarps, etc.).
..........6 Fruit a 3-lobed, 3-locular capsule; 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
..........6 Fruit various, not as above; inflorescence not a cyathium (and staminate or bisexual flowers almost always with > 1 stamen); fresh plants lacking milky juice.
............ 7 Leaves succulent, the terminal whorls closely juxtaposed; pistils 4-5; fruit an aggregate of follicles
............ 7 Leaves herbaceous, thin in texture, whorls separated; pistil 1, of 2-5 fused carpels; fruit a capsule, achene, or drupe.
............ ..8 Larger whorled leaves on a plant < 10 mm wide [some taxa keyed here and under the second lead].
............ ....9 Inflorescence a cymule, either axillary, or axillary and terminal; ovary inferior.
............ ......10 Leaves markedly variable in shape or size in each whorl; fruit a capsule; petals 5
............ ......10 Leaves similar in size and shape in each whorl; fruit dry or fleshy, indehiscent; petals (3-) 4
............ ....9 Inflorescence a terminal raceme, panicle, spike, cyme, corymb, or umbel; ovary superior.
............ ........11 Corolla bilaterally symmetrical, the petals connate; carpels 2; stamens 4, 6, or 8.
............ ..........12 Stamens 4; corolla blue or almost white
............ ..........12 Stamens 6 or 8; corolla pink or yellow
............ ........11 Corolla radially symmetrical, the petals separate; carpels 2, 3, or 5; stamens 5, 10, or many.
............ ............ 13 Inflorescence an axillary umbel; leaves narrowly linear and more than 10× as long as wide, > 20 mm long and < 2 mm wide; whorls of 3-6 leaves
............ ............ 13 Inflorescence a terminal cyme, raceme, panicle, or umbel; leaves as above, or broader in shape, narrower, or shorter; whorls of 3-16 leaves.
............ ............ ..14 Inflorescence a terminal cyme or umbel; corolla white; carpels 5.
............ ............ ....15 Leaves narrowly linear, 12-16 in each whorl; stamens 5
............ ............ ....15 Leaves ovate or obovate, 3 (-4) in each whorl
............ ............ ..14 Inflorescence a terminal raceme or panicle; corolla reddish, maroon, or yellow.
............ ............ ......16 Corolla reddish or maroon
............ ..8 Larger whorled leaves on a plant > 10 mm wide.
............ ............ ........17 Inflorescence a spike; perianth absent; fruit a drupe
............ ............ ........17 Inflorescence various, but not a spike; perianth present; fruit various, but not a drupe.
............ ............ ..........18 Inflorescence of terminal involucrate clusters; perianth of 6 tepals; fruit an achene; stamens 9; [plants of very dry habitats]
............ ............ ..........18 Inflorescence various, but not as above; perianth of 2 whorls (the calyx often obsolete in Galium in RUBIACEAE), 3-, 4-, 5-, 6-, or 7-merous; stamens 2-7; [plants of dry-mesic to very wet habitats].
............ ............ ............ 19 Fruit dry or fleshy, indehiscent; petals (3-) 4; ovary inferior
............ ............ ............ 19 Fruit a capsule or follicle, dehiscent; petals 4-7; ovary superior.
............ ............ ............ ..20 Inflorescence an umbel; fresh plants with milky juice
............ ............ ............ ..20 Inflorescence not an umbel; fresh plants with clear juice.
............ ............ ............ ....21 Corolla pink-purple, 6-merous, the petals separate and borne on the edge of a hypanthium; stamens 8, 10, or 12; [plants of wetlands]
............ ............ ............ ....21 Corolla white, yellow, or greenish, 4-, 5-, or 7-merous, the petals fused at least basally into a tube (falling as a unit), not on a hypanthium; stamens 2, 4, 5, or 7; [plants of mesic habitats].
............ ............ ............ ......22 Stamens 4, 5, or 7; corolla radially symmetrical.
............ ............ ............ ........23 Petals yellowish-white, with prominent green streaks; biennial or monocarpic plant, 10-30 dm tall when fertile; leaves 15-35 cm long
............ ............ ............ ........23 Petals white or yellow; perennial plants, 1-15 dm tall; leaves 1-15 cm long.
............ ............ ............ ..........24 Leaves punctate; stem without swollen nodes
............ ............ ............ ..........24 Leaves not punctate; stem with swollen nodes

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
............ ....9 Leaves with prominently pinnate venation
............ ..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.
............ ............ ..........18 Flowers many, in axillary spikes, cymes, or glomerules, or in terminal spikes, heads, cymes, or panicles; leaves entire or serrate.
............ ............ ............ ....21 Fruit single-seeded, an achene or utricle; {YYYY}.
............ ............ ............ ......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.
............ ............ ............ ............ ............ 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.
............ ............ ............ ............ ............ ............ ..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
............ ............ ............ ............ ............ ............ ............ ........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 of solitary (rarely 2) axillary flower. {add [Hypoestes] ACANTHACEAE}
............ ............ ............ ............ ............ ............ ............ ............ ..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.
............ ............ ............ ............ ............ ............ ............ ............ ......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 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 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].
............ ............ ............ ............ ............ ............ ............ ............ ............ ........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]
............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ..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 alien, 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]
............ ............ ............ ............ ............ ............ ............ ............ ............ ............ ......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 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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