1. Plant fully aquatic, submersed, floating in water, or stranded on mud
2. Plant generally free-floating at or just below water surface, raft-like, the plant body 0.4–10 mm; leaves and stems not differentiated; roots 0–few, unbranched — pistil located in tiny lateral, membrane-covered pouch or in minute cavity on top of plant body ..... ARACEAE {G2,6,13,15}
2' Plant rooted in bottom sediments or free-floating, generally >> 15 mm; leaves and stems clearly differentiated; roots often branched
3. Lvs alternate
4. Frs borne in umbel-like clusters — flowers actually bisexual but stamens easily overlooked and ephemeral ..... RUPPIACEAE {G2,10,13}
4' Frs or flowers borne in spikes or heads
5. Fls in dense, spheric heads, these solitary or in axillary or terminal clusters, not enclosed in leaf sheaths; freshwater habitats ..... TYPHACEAE (Sparganium) {G2,6,13}
5' Fls in axillary spikes, these generally enclosed and concealed in sheaths of subtending leaves; marine habitats ..... ZOSTERACEAE {G2,6,13}
3' Lvs opposite or whorled or all basal
6. Lvs all basal; flowers solitary in leaf-axils; style very elongated, generally 6–20 cm ..... JUNCAGINACEAE (Triglochin scilloides) (2) {G13}
6' Lvs cauline; flowers axillary or variously clustered; styles generally << 6 cm (except in some Hydrocharitaceae)
7. Lf blades [at least those of submersed leaves] divided into linear or thread-like lobes
8. Blades of leaves repeatedly forked ..... CERATOPHYLLACEAE {G2,6,14,15}
8' Blades of leaves pinnately forked ..... HALORAGACEAE {G2,6,14,20}
7' Lf blades entire, toothed, or shallowly lobed
9. Petals and sepals both 3(4), evident; perianth and stigmas borne at water surface at end of long, tubular hypanthium; ovary inferior, sessile in leaf axil ..... HYDROCHARITACEAE {G2,6,16}
9' Petals and sepals both 0; stigmas submersed, borne at end of short styles; ovary or ovaries superior, sessile or short-stalked in leaf axil
10. Pistils 2–10, simple, each with a cup-like stigma; leaves entire ..... ZANNICHELLIACEAE {G2,10,13}
10' Pistil 1, compound, bearing 2–4 slender stigmas
11. Lvs subentire to finely or coarsely toothed; ovary chamber 1, ovule 1; fruit achene-like ..... HYDROCHARITACEAE (Najas) {G2,13}
11' Lvs entire; ovary chambers 4, ovules 4; fruit splitting into 4 nutlets ..... PLANTAGINACEAE (Callitriche) {G2,15}
1' Plant terrestrial or parasitic on stem of woody host, or if growing in wet habitat, rooted in place and emerging well above water surface
12. Plants parasitic on stems of woody host plants
13. Fls of parasite borne directly on stems of host; remainder of parasite internal within tissues of host; stems and leaves not differentiated; on Psorothamnus ..... APODANTHACEAE {G6}
13' Fls borne on leafy branches of parasite; shoots of parasite external; leaves differentiated, though sometimes reduced to scales; on various woody hosts [not Psorothamnus] ..... VISCACEAE {G6,7,9,11,12,14}
12' Plants free-living
14. St fleshy, bearing spiny tubercles; leaves 0 ..... CACTACEAE (Mammillaria dioica)
14' St generally not fleshy, without spiny tubercles; leaves generally present
15. Lvs opposite or whorled, not all basal
16. Sts or leaves thick and fleshy; inflorescence a terminal spike
17. Lvs ± cylindric or 3-angled in ×-section; stigma 1, head-like, 2-lobed; ovary chambers 4; ovaries joining into a fleshy multiple fruit; perianth 0 ..... BATACEAE {G6,15,24}
17' Lvs fleshy, scale-like; stigmas 2, linear; ovary chamber 1; ovaries maturing as utricles, sometimes surrounded by fleshy bracts and perianth elements ..... CHENOPODIACEAE (2) {G6,7,9,11,15}
16' Sts and leaves of normal texture, not thick and fleshy; inflorescence various
18. Lvs compound or deeply lobed, or also some simple
19. Compound leaves palmate ..... CANNABACEAE {G6,15}
19' Compound or deeply lobed leaves pinnate ..... VALERIANACEAE (Valeriana occidentalis)
18' Lvs simple, entire or toothed
20. Lvs whorled; ovary inferior ..... RUBIACEAE (Galium) {G6,7,9,12}
20' Lvs opposite; ovary superior
21. Lvs sessile or nearly so, entire; petals free ..... CARYOPHYLLACEAE {G6,15,24}
21' Lvs conspicuously petioled, toothed; petals fused or 0
22. Corolla showy, bilateral ..... LAMIACEAE {G18,19}
22' Corolla 0
23. Styles 2, ovary 2-chambered; stinging hairs 0 ..... EUPHORBIACEAE (Mercurialis) {G6}
23' Style 0 or 1, ovary 1-chambered; stinging hairs present or 0 ..... URTICACEAE {G6,15}
15' Lvs alternate or all basal
24. Lvs stiff and sword-like, 0.5–1.5 m; inflorescence a large panicle; perianth parts 6 ..... RUSCACEAE (Nolina) {G6,7,9,16}
24' Lvs not sword-like, often smaller; inflorescences various; perianth parts mostly other than 6
25. Blades of leaves linear or narrowly lanceolate, simple and entire; veins parallel; leaf bases sheathing stem
26. Lvs all basal; flowers solitary in leaf axils; styles very elongated, generally 6–20 cm ..... JUNCAGINACEAE (Triglochin scilloides) (2) {G13}
26' Lvs basal and cauline or all cauline; flowers in spikes or spikelets, these generally in 2° clusters; styles generally << 5 cm
27. St triangular; nodes not swollen; leaf blades channeled ..... CYPERACEAE {G2,13}
27' St round; nodes generally swollen and knot-like; leaf blades generally flat ..... POACEAE {G2,5,6,13}
25' Blades of leaves variously shaped, sometimes toothed, lobed, or compound; veins mostly pinnate or palmate; leaf bases often not sheathing stems — flowers not in spikelets
28. Ochreae present, persistent or not; nodes generally ± swollen ..... POLYGONACEAE {G2,6,15,16,19}
28' Ochreae 0; nodes generally not swollen
29. Lvs all basal
30. Lvs compound, leaflets 3; perianth parts in 5s; stolons present ..... ROSACEAE (Fragaria) {G6}
30' Lvs simple, entire; perianth parts in 3s or 4s; stolons 0
31. Perianth parts in 4s; fruit a circumscissile capsule ..... PLANTAGINACEAE (Plantago) {G5,18,19}
31' Perianth parts in 3s; fruit 1–many achenes
32. Perianth clearly differentiated into sepals and petals; pistils many; plant ± emergent aquatic, annual or perennial herb ..... ALISMATACEAE (Sagittaria) {G6}
32' Perianth whorls not strongly differentiated, outer and inner similar; pistil 1; plant terrestrial matted per ..... POLYGONACEAE (Eriogonum) {G6,12}
29' At least some leaves cauline
33. Plants vines
34. Tendrils 0; perianth not at all corolla-like; ovary superior ..... CANNABACEAE (Humulus) {G6,15}
34' Tendrils present; perianth corolla-like
35. Ovary inferior ..... CUCURBITACEAE {G6,14,17,21}
35' Ovary superior ..... SMILACACEAE {G6,7,9,16}
33' Plants prostrate to erect herbs
36. Pistils 2–22, simple; fruit a cluster of achenes or follicles
37. Lvs simple, fleshy ..... CRASSULACEAE (Rhodiola) {G6}
37' Lvs compound, leaflets thin
38. Lflets coarsely crenate or shallowly lobed; sepals generally 4; petals 0; inflorescence an open panicle ..... RANUNCULACEAE (Thalictrum) {G6}
38' Lflets 2-serrate; sepals 5; petals 5; inflorescence a panicle of dense spikes ..... ROSACEAE (Aruncus) {G6}
36' Pistil 1, simple or compound; fruit achene, utricle, capsule, or splitting into 2–13 mericarps
39. Fls in umbels or heads
40. Infl a simple or compound umbel ..... APIACEAE {G2,6,14,20,21}
40' Infl of 1 or more heads
41. Head maturing as bur enclosing 1–5 fruits ..... ASTERACEAE (2) {G6,7,9,12,14,17}
41' Head not maturing as bur
42. Corolla 0; head without involucre; ovary superior ..... CHENOPODIACEAE (2) {G6,7,9,11,15}
42' Corolla tubular; head subtended by an involucre; ovary inferior ..... ASTERACEAE (2) {G6,7,9,12,14,17}
39' Fls solitary or in axillary clusters or in racemes or panicles
43. Style branches 5–19; fruit splitting into 5–19 wedge-shaped mericarps at maturity ..... MALVACEAE {G19,20,22}
43' Style unbranched or branches 2 or 3 (dissected into linear lobes in Croton); fruit unsegmented or splitting into 2–3 segments
44. Lvs palmately compound, leaflets serrate ..... CANNABACEAE (Cannabis) {G6,15}
44' Lvs entire or toothed
45. Lvs densely stellate-scaly or -hairy; ovary chambers generally 3; fruit a capsule ..... EUPHORBIACEAE (Croton) {G6,12}
45' Lvs not stellate-hairy; ovary chamber 1; fruit an achene or utricle
46. Bractlets subtending flower 3, winged, abaxially bearing hooked hairs; stigma 1, sessile, hair-tufted; sepals 4, fused ..... URTICACEAE (Soleirolia) {G6}
46' Bractlets subtending flower 1–2, without hooked hairs; stigmas 2, linear; sepals 0 or 3–5, free
47. Fl enclosed between a pair of bractlets; sepals generally 0; leaves generally bearing bead-like, sessile hairs or powdery scales ..... CHENOPODIACEAE (Atriplex) {G6,12}
47' Fl not enclosed by a pair of bractlets; sepals 3–5; leaves glabrous or glaucous ..... AMARANTHACEAE (Amaranthus) {G6}
