1. Plant fully aquatic, submersed, floating in water, or stranded on mud
2. Plant generally free-floating, at or just below water surface, plant body 0.4–10 mm; leaves and stems not differentiated; roots 0–few, unbranched — stamens emerging from tiny lateral, membrane-covered pouch or from minute cavity on top of plant body ..... ARACEAE {G2,8,13,15}
2' Plant rooted in bottom sediments or free-floating, >> 10 mm; leaves and stems clearly differentiated; roots often branched
3. Lvs alternate
4. Fls in dense, spheric heads, these solitary or in axillary or terminal clusters, not enclosed in leaf sheaths; freshwater habitats ..... TYPHACEAE (Sparganium) {G2,8,13}
4' Fls in axillary spikes, these generally enclosed and concealed in sheaths of subtending leaves; marine habitats ..... ZOSTERACEAE {G2,8,13}
3' Lvs opposite or whorled
5. Lf blades entire, toothed, or shallowly lobed ..... HYDROCHARITACEAE {G2,8,16}
5' Lf blades [at least those of submersed leaves] divided into linear or thread-like lobes
6. Blades of leaves repeatedly forked ..... CERATOPHYLLACEAE {G2,8,14,15}
6' Blades of leaves pinnately divided ..... HALORAGACEAE {G2,8,14,20}
1' Plant terrestrial or parasitic on stem of woody host plant, or if growing in wet habitat, rooted in place and emerging well above water surface
7. Plant parasitic on stem of woody host plant
8. 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 {G8}
8' 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 {G7,8,9,11,12,14}
7' Plant free-living
9. Lvs opposite or whorled, not all basal
10. Sts or leaves thick and fleshy; inflorescence a terminal spike
11. Lvs ± cylindric or 3-angled in ×-section; petal-like perianth parts 4 ..... BATACEAE {G8,15,24}
11' Lvs fleshy, scale-like; petal-like perianth parts 0 ..... CHENOPODIACEAE (2) {G7,8,9,11,15}
10' Sts and leaves of normal texture, not thick and fleshy; inflorescences various
12. Lvs palmately compound or simple and deeply lobed ..... CANNABACEAE {G8,15}
12' Lvs simple, entire or toothed
13. Lvs whorled ..... RUBIACEAE (Galium) {G7,8,9,12}
13' Lvs opposite
14. Lvs sessile or nearly so, entire ..... CARYOPHYLLACEAE {G8,15,24}
14' Lvs conspicuously petioled, toothed
15. Stamens 8–15(20); stinging hairs 0 ..... EUPHORBIACEAE (Mercurialis) {G8}
15' Stamens 4; stinging hairs present or 0 ..... URTICACEAE {G8,15}
9' Lvs alternate or all basal
16. Lvs stiff and sword-like, 5–15 dm; inflorescence a large panicle; perianth parts 6 ..... RUSCACEAE (Nolina) {G7,8,9,16}
16' Lvs not sword-like, often smaller; inflorescences various; perianth parts often other than 6
17. Lf blades linear or narrowly lanceolate, simple and entire, veins parallel; leaf bases sheathing
18. Infl a panicle or raceme of showy flowers; perianth parts all petal-like, white to ± yellow, each with a glistening, ± green-yellow gland in proximal half ..... MELANTHIACEAE (Toxicoscordion)
18' Infl a cluster of spikelets (sometimes panicle- or raceme-like); perianth parts 0 or minute scales
19. St triangular, nodes not swollen; leaf blades channeled ..... CYPERACEAE (Carex)
19' St round; nodes generally swollen and knot-like; leaf blades generally flat ..... POACEAE {G2,5,8,13}
17' Lf blades variously shaped, sometimes toothed, lobed, or compound, veins mostly pinnate or palmate; leaf bases generally not sheathing
20. Ochreae present, persistent or not; nodes generally swollen ..... POLYGONACEAE {G2,8,15,16,19}
20' Ochreae 0; nodes generally not swollen
21. Lvs all basal
22. Lvs compound, leaflets 3; perianth parts in 5s; stolons present ..... ROSACEAE (Fragaria) {G8}
22' Lvs simple, entire; perianth parts in 3s; stolons 0
23. Perianth clearly differentiated into sepals and petals; plant ± emergent aquatic, annual or perennial herb ..... ALISMATACEAE (Sagittaria) {G8}
23' Perianth whorls not strongly differentiated, outer and inner similar; plant terrestrial, matted per ..... POLYGONACEAE (Eriogonum) {G8,12}
21' At least some leaves cauline
24. Plants vines
25. Tendrils 0; perianth parts not at all petal-like; stamens free ..... CANNABACEAE (Humulus) {G8,15}
25' Tendrils present; perianth parts petal-like
26. Perianth parts fused, at least at base; stamens fused, number difficult to determine ..... CUCURBITACEAE {G8,14,17,21}
26' Perianth parts free; stamens 6, free ..... SMILACACEAE {G7,8,9,16}
24' Plants prostrate to erect herbs
27. Fls in heads or umbels
28. Infl a simple or compound umbel ..... APIACEAE (2) {G2,8,14,20,21}
28' Infl of 1 or more heads
29. Heads without involucres ..... CHENOPODIACEAE (2) {G7,8,9,11,15}
29' Heads each subtended by an involucre
30. Stamens free; petals free ..... APIACEAE (2) {G2,8,14,20,21}
30' Stamens fused by their anthers; petals fused or 0 ..... ASTERACEAE {G7,8,9,12,14,17}
27' Fls in axillary clusters, racemes, or panicles
31. Lvs deeply lobed or compound
32. Lvs palmately compound, the leaflets serrate ..... CANNABACEAE (Cannabis) {G8,15}
32' Lvs pinnately dissected or compound, the lobes or leaflets entire to coarsely toothed
33. Lvs simple or 1-pinnate; anthers subsessile, 3–6 mm — sepals 4–9, inflorescence a leafy raceme or panicle ..... DATISCACEAE {G14}
33' Lvs 2–4-pinnate; anthers exserted on slender filaments
34. Lflets coarsely crenate or shallowly lobed; sepals 4–5; petals 0; anthers linear, 1.5–5 mm; inflorescence an open panicle ..... RANUNCULACEAE (Thalictrum) {G8}
34' Lflets 2-serrate; sepals 5; petals 5; anthers oval, < 1 mm; inflorescence a panicle of dense spikes ..... ROSACEAE (Aruncus) {G8}
31' Lvs entire or toothed
35. Blades of leaves with several main veins; perianth parts >= 6 mm ..... MELANTHIACEAE (Veratrum) {G16}
35' Blades of leaves with 1–3 main veins; perianth parts generally <= 5 mm
36. Herbage armed with stinging, nettle-like hairs ..... EUPHORBIACEAE (Tragia) {G15}
36' Herbage glabrous or with non-stinging hairs
37. Lvs covered with stellate scales or hairs ..... EUPHORBIACEAE (Croton) {G8,12}
37' Lvs without stellate scales or hairs
38. Lvs generally bearing bead-like, sessile hairs or powdery scales ..... CHENOPODIACEAE (Atriplex) {G8,12}
38' Lvs glabrous or glaucous
39. Lvs fleshy; sepals, petals each 4(5) ..... CRASSULACEAE (Rhodiola) {G8}
39' Lvs thin or fleshy; sepals 2–6, petals 0
40. Milky latex present; leaf blade base generally with 2 glands ..... EUPHORBIACEAE (Stillingia)
40' Milky latex 0; leaf blade base without glands
41. Lf ± round, blade with translucent dots; plant mat-forming ..... URTICACEAE (Soleirolia) {G8}
41' Lf linear to (ob)ovate, blade without translucent dots; plant mat-forming to erect ..... AMARANTHACEAE (Amaranthus) {G8}
