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 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