1. Lvs opposite or whorled
2. Plant aquatic, weak-stemmed; submersed, floating, or stranded on mud
3. Lvs opposite; ovary lobed or unlobed; seeds 4–many
4. Ovary unlobed, many-seeded ..... LYTHRACEAE (Lythrum portula)
4' Ovary 2- or 4-lobed, 4-seeded ..... PLANTAGINACEAE (Callitriche) {G2,8}
3' Lvs whorled; ovary unlobed; seed 1
5. Lvs dissected into narrow lobes ..... CERATOPHYLLACEAE {G2,6,8,14}
5' Lvs entire ..... PLANTAGINACEAE (Hippuris) {G2,14}
2' Plant terrestrial, sometimes in damp soil, or in areas flooded at high tide
6. Ovary chambers 2 or more (doubtful cases should be keyed both ways)
7. Fls unisexual
8. Style 0, stigma sessile; leaves ± cylindric or 3-angled in ×-section, fleshy; milky latex 0; plants of coastal salt-marshes ..... BATACEAE {G6,8,24}
8' Styles or stigmas 2–3, free; leaves thin; milky latex present or 0; plants of various habitats but not salt marsh ..... EUPHORBIACEAE (3) {G7,9}
7' Fls bisexual
9. Lvs opposite, equal; fruit circumscissile — 1/2-inferior ovary may appear superior ..... AIZOACEAE (Sesuvium)
9' Lvs whorled, often unequal; fruit loculicidal ..... MOLLUGINACEAE
6' Ovary chamber 1
10. Ovules 2–many; fruit a capsule
11. Perianth parts 6(8) — sepals actually present in bud, but early-deciduous, 0 in open flower ..... PAPAVERACEAE (2) {G20,22,24}
11' Perianth parts (4)5
12. Sepals free; flowers generally in cymes ..... CARYOPHYLLACEAE (2) {G6,8,24}
12' Sepals fused; flowers solitary in leaf axils
13. Lvs of a pair unequal; stipules present; fruit circumscissile ..... AIZOACEAE {G14,17,21}
13' Lvs of a pair equal; stipules 0; fruit 5-valved ..... MYRSINACEAE (Glaux)
10' Ovule 1; fruit an achene, 1-seeded capsule, or utricle
14. Style 1, undivided or stigma 1, sessile
15. Sepals petal-like, fused into a tube; leaves entire or slightly lobed, stinging hairs 0 ..... NYCTAGINACEAE {G5,14,17,19}
15' Sepals green, small, inconspicuous; leaves toothed or entire, sometimes with stinging hairs
16. Herbage densely covered with branched hairs ..... AMARANTHACEAE (Tidestromia) (2)
16' Herbage glabrous or ± hairy, hairs not branched (stinging hairs present in Hesperocnide, Urtica) ..... URTICACEAE (2) {G6,8}
14' Styles or style branches 2 or more
17. Lvs palmately compound or deeply lobed ..... CANNABACEAE {G6,8}
17' Lvs simple, entire or toothed
18. Fr a 3-angled achene; perianth parts 6 [actually in 2 whorls of 3, but this may not be evident in open flowers] ..... POLYGONACEAE (3) {G2,6,8,16,19}
18' Fr not 3-angled; perianth parts <= 5
19. Lvs with stipules
20. Lvs petioled, fleshy; fruit a circumscissile capsule ..... AIZOACEAE (Trianthema)
20' Lvs sessile, not fleshy; fruit 1-seeded, indehiscent ..... CARYOPHYLLACEAE (2) {G6,8,24}
19' Lvs without stipules
21. Lvs reduced to fleshy scales; inflorescence a fleshy spike ..... CHENOPODIACEAE (3) {G6,7,8,9,11}
21' Lvs linear to ovate; inflorescences various or flowers solitary
22. Sepals erect, linear, fused below and hardened around ovary; stamens fused to calyx; slender annual, generally <= 15 cm; leaves narrowly linear, <= 15 mm ..... CARYOPHYLLACEAE (Scleranthus) {G14}
22' Sepals erect or spreading, free, not hardened around ovary (sepals generally 0 in pistillate flowers of Atriplex, which has a pair of ± hardened bractlets around fruit); stamens free from calyx; plants often larger, annual or perennial herb; leaves various
23. Bracts subtending flowers dry, scarious; plants neither fleshy nor with powdery or beaded surface; habitats generally not saline ..... AMARANTHACEAE (2)
23' Bracts subtending flowers leaf-like or fleshy; plants often fleshy or with powdery or beaded surface; habitats often ± saline
24. Sepals pink or white, papery; plant from rhizome ..... AMARANTHACEAE (Nitrophila)
24' Sepals green or ± red-tinged, herbaceous; rhizome 0 ..... CHENOPODIACEAE (3) {G6,7,8,9,11}
1' Lvs alternate or all basal
25. Plant aquatic, raft-like, floating on water surface or stranded on shoreline — leaves in rosettes, wedge-shaped, sessile, velvety; flowers enclosed by small, sheathing bracts ..... ARACEAE ([Pistia]) {G2}
25' Plant terrestrial or rooted in shallow water
26. Infl a ± fleshy spike enclosed by a large, basally sheathing, often petal-like bract; petiole stout ..... ARACEAE {G2,6,8,13}
26' Infl various but not a fleshy spike subtended by a sheathing bract; leaves sessile or ± slender-petioled
27. Lvs with stipules, generally well developed
28. Style 1, unbranched, or stigma sessile
29. Ovule 1; fruit an achene ..... ROSACEAE {G10,20,21,22,23}
29' Ovules several to many; fruit a capsule — late season cleistogamous flowers formed in most Viola species ..... VIOLACEAE {G5,20,24}
28' Styles or stigmas 2 or more
30. Lvs palmately compound ..... CANNABACEAE (Cannabis) {G6,8}
30' Lvs simple, entire to lobed
31. Plant a vine, stems twining
32. Lvs toothed, at least the proximal also palmately lobed ..... CANNABACEAE (Humulus) {G6,8}
32' Lvs entire ..... POLYGONACEAE (Fallopia)
31' Plant prostrate to erect, stems not twining
33. Stipules fused into a membranous sheath [ocrea] around stem, the sheath sometimes torn or shredded as branches develop ..... POLYGONACEAE (3) {G2,6,8,16,19}
33' Stipules free, not fused around stem, not torn or shredded as branches develop
34. Annual; stems prostrate; stinging hairs 0; flowers bisexual ..... CARYOPHYLLACEAE (Herniaria)
34' Perennial; stems spreading to erect; stinging hairs present; flowers unisexual ..... EUPHORBIACEAE (Tragia) {G6}
27' Lvs without stipules, sometimes reduced to scale-like bracts
35. Infl flower-like with a cup-like involucre bearing 1–4(5) nectary glands that sometimes have flattened, white to ± pink, petal-like, marginal appendages — stamens [actually staminate flowers] each with a jointed stalk [composed of a filament and a pedicel], pistillate flower 1, generally exserted from involucre, ovary 3-lobed ..... EUPHORBIACEAE (3) {G7,9}
35' Infl not flower-like or with a cup-like, nectary-gland-bearing involucre
36. Perianth parts 4 or 6, ± petal-like
37. Perianth parts 4 or 6, free; stigmas 1–many, generally sessile; fruit a capsule — sepals actually present in bud, but early-deciduous, 0 in open flower ..... PAPAVERACEAE (2) {G20,22,24}
37' Perianth parts 6, proximally fused; stigmas 3, at tips of slender styles; fruit a 3-angled achene ..... POLYGONACEAE (3) {G2,6,8,16,19}
36' Perianth parts <= 5, sometimes 0, generally not petal-like
38. Lvs all basal, palmately compound; leaflets 3; perianth 0 ..... BERBERIDACEAE (Achlys)
38' Lvs cauline, simple; perianth generally present
39. Ovule 1; inflorescences various
40. Herbage ± densely covered with branched hairs
41. Fls bisexual; hairs soft, irregularly branched, branches all short; fruit indehiscent — leaf arrangement variable, often difficult to interpret ..... AMARANTHACEAE (Tidestromia) (2)
41' Fls unisexual; hairs harshly stellate, central branches often long, spreading, bristle-like; fruit dehiscent ..... EUPHORBIACEAE (Croton setigerus)
40' Herbage glabrous or ± hairy, hairs not branched
42. Stigma 1 ..... URTICACEAE (2) {G6,8}
42' Stigmas 2–4
43. Bracts subtending flowers scarious-margined or dry and scarious throughout ..... AMARANTHACEAE (2)
43' Bracts subtending flowers not scarious or scarious-margined ..... CHENOPODIACEAE (3) {G6,7,8,9,11}
39' Ovules 2–many; inflorescence generally a raceme (spike, axillary cluster)
44. Fls unisexual ..... EUPHORBIACEAE (3) {G7,9}
44' Fls bisexual
45. Plant red- and white-striped, non-photosynthetic, green pigment 0 ..... ERICACEAE (Allotropa)
45' Plant green and photosynthetic
46. Sepals 4 ..... BRASSICACEAE {G2,20,24}
46' Sepals 5
47. Sts ± erect, <= 3(7) m; leaf 6–36 cm; flowers many in spike or raceme; fruit a berry, chambers 5–12; perianth radial ..... PHYTOLACCACEAE
47' Sts ± decumbent, 0.5–3.5 dm; leaf <= 6 cm; flowers 1–few in raceme; fruit a capsule; chambers 2; perianth bilateral — some flowers often ± cleistogamous ..... POLYGALACEAE {G18,22,23,24}
