1. Plant parasite on stem of woody host
2. Fls of parasite emerging directly from stem of host, parasite otherwise growing within tissues of host; leaves 0; on Psorothamnus ..... APODANTHACEAE
2' Fls of parasite borne in inflorescences on branches of parasite; leaves scale-like or with expanded blades; on various woody hosts [not Psorothamnus] ..... VISCACEAE {G6,7,8,9,11,12}
1' Plant free-living and rooted in ground or root-parasite
3. Lf blade 1–2+ m, covered with prickles — perianth actually of 2 whorls but petals very small, easily overlooked ..... GUNNERACEAE {G16}
3' Lf blade << 1 m, not prickly
4. Lvs [at least proximal] whorled, all cauline
5. Plant terrestrial ..... RUBIACEAE (2) {G17}
5' Plant ± aquatic
6. Lvs entire ..... PLANTAGINACEAE (Hippuris) {G2,15}
6' Lvs toothed to deeply divided
7. Lvs repeatedly forked ..... CERATOPHYLLACEAE {G2,6,8,15}
7' Lvs [at least submersed] pinnately divided ..... HALORAGACEAE {G2,6,8,20}
4' Lvs alternate or opposite (or sometimes some or all basal)
8. Infl bracts large, petal-like; perianth 0 — inflorescence a flower-like spike ..... SAURURACEAE
8' Infl bracts not at all petal-like; perianth present
9. Perianth parts free or nearly so
10. Lvs glabrous, round-peltate or -reniform; plant aquatic with stolons or rhizomes floating in shallow water or rooted in wet soil ..... ARALIACEAE (Hydrocotyle) {G2,21}
10' Lvs glabrous or hairy, leaf shape various; plant terrestrial if leaves round-reniform
11. Infl a simple or compound umbel ..... APIACEAE {G2,6,8,20,21}
11' Infl various or flowers solitary
12. Plant aquatic, floating, stranded on mud, or rooted in bottom sediments
13. Sepals, stamens 5; pedicel 1–4(8) mm; leaves alternate (sometimes ± opposite or whorled), blade linear ..... CAMPANULACEAE (Howellia)
13' Sepals, stamens 4; pedicel 0–0.5 mm; leaves opposite, blade narrowly elliptic to ± ovate ..... ONAGRACEAE (Ludwigia palustris)
12' Plant terrestrial or sometimes growing in damp soil
14. Lvs all basal ..... SAXIFRAGACEAE (Heuchera cylindrica)
14' Lvs cauline, at least in part
15. Fr an achene; sepals 3–5; leaves alternate, ± entire, petiole ± = blade ..... CHENOPODIACEAE (Beta)
15' Fr a capsule or ± nut-like [hard, indehiscent, 3–9-seeded with 2–5-horns]; sepals 3–9; leaves alternate or opposite, entire to pinnately lobed, petiole often < blade
16. Perennial; stems erect; leaves generally unequally pinnately lobed; styles long, forked ..... DATISCACEAE {G6}
16' Annual; stems prostrate to erect; leaves entire or toothed; styles short, not forked
17. Styles 2–9; leaves ± fleshy, often ± papillate ..... AIZOACEAE {G15,17,21}
17' Style 1; leaves not fleshy, not papillate ..... CAMPANULACEAE {G2,5,17}
9' Perianth parts fused
18. Infl of involucred heads or umbels
19. Ovary truly inferior; anthers fused around style or, if free, the flowers unisexual; stigma lobes 2 ..... ASTERACEAE {G6,7,8,9,12,17}
19' Ovary actually superior, but appearing inferior [tightly enclosed by perianth base]; anthers free; stigma unlobed ..... NYCTAGINACEAE (2) {G5,15,17,19}
18' Infl not of involucred heads or umbels, flowers solitary or variously clustered
20. Fls large, solitary, red to maroon or brown; perianth lobes 3 — leaves cordate to reniform, long-petioled ..... ARISTOLOCHIACEAE (Asarum)
20' Fls generally ± small, generally clustered, not red to maroon or brown; perianth lobes (3)4–5(7)
21. Lvs alternate
22. Tendrils 0; leaves entire; flowers bisexual ..... COMANDRACEAE
22' Tendrils present; leaves palmately lobed; flowers unisexual ..... CUCURBITACEAE {G6,8,17,21}
21' Lvs opposite
23. Fls bilateral ..... VALERIANACEAE {G17}
23' Fls ± radial
24. Perianth lobes 5; ovary actually superior [tightly enwrapped by hardened or winged calyx base]; leaves of a pair equal or unequal
25. Calyx green, not at all corolla-like, very inconspicuous; sepals erect, free or nearly so above the level of the ovary, thickened and linear, erect; leaves narrowly linear, needle-like, generally 1–2 cm or shorter, generally those of a pair equal ..... CARYOPHYLLACEAE (Scleranthus) {G15}
25' Calyx corolla-like in color and texture, often very showy; sepals fused well above level of ovary, calyx lobes wide and thin, ± spreading; leaves linear to ovate, often > 2 cm, those of a pair often unequal ..... NYCTAGINACEAE (2) {G5,15,17,19}
24' Perianth lobes 3–4; ovary truly inferior; leaves of a pair equal
26. Stamens 3–4; leaves entire or teeth minute, prickle-like ..... RUBIACEAE (2) {G17}
26' Stamens 8; leaves with rounded teeth ..... SAXIFRAGACEAE (Chrysosplenium)
