1. Perianth 0 or of 1 whorl, generally called sepals even when petal-like
2. Hypanthium present ..... ROSACEAE (4) {G15,20,21,22,23}
2' Hypanthium 0
3. Trees; leaves palmately lobed ..... PLATANACEAE {G7,9,12}
3' Herbs or woody vines; leaves various
4. Plant terrestrial or if aquatic with emergent leaves ..... RANUNCULACEAE (2)
4' Plant aquatic with submersed or floating leaves
5. Perianth parts 1–4
6. Perianth part 1, white, petal-like, enlarging and turning green in age; stamens 6–18; fruit follicle, 4-seeded ..... APONOGETONACEAE {G2}
6' Perianth parts 4, green or ± brown, sepal-like; stamens 4; fruit achene-like drupe, 1-seeded ..... POTAMOGETONACEAE {G2,13}
5' Perianth ± 0
7. Fls bisexual, borne along axis of initially short-peduncled spike, peduncle elongating in fruit; stamens 2; pistils (2)4(8); ovary stalk in fruit 12–35 mm; fruit ± ovoid, smooth, beak 0.5–1 mm ..... RUPPIACEAE {G2,8,13}
7' Fls unisexual, staminate and pistillate together in sessile, 2-flowered axillary cluster; stamen 1; pistils (1)4–5(9); ovary stalk in fruit 0.1–1.5 mm; fruit abaxially curved, minutely roughened, beak 0.7–2 mm ..... ZANNICHELLIACEAE {G2,8,13}
1' Perianth of 2 or more whorls or spirals, the outer generally called sepals, the inner generally called petals
8. Lvs and often stems thick and fleshy; pistils generally as many as petals or sepals — stamens 1–2 × as many ..... CRASSULACEAE {G19}
8' Lvs and stems not very thick and fleshy; number of pistils same as or different from number of sepals or petals
9. Perianth parts in 3s
10. Lvs compound
11. Tree with unbranched trunk; leaves 4–7 m, leaflets many ..... ARECACEAE (Phoenix) {G7,9}
11' Annual; leaves <= 6 cm, leaflets 3–5 — carpels actually united by common style ..... LIMNANTHACEAE (Floerkea) {G16}
10' Lvs simple
12. Fls solitary — sepals and petals all similar, ± white or ± red-purple; leaves floating and peltate or some or all submersed and dissected ..... CABOMBACEAE
12' Fls several–many in raceme- to panicle-like inflorescence
13. Sepals green, petals white (pink) ..... ALISMATACEAE {G2}
13' Sepals and petals the same color, ± white to green or ± red
14. Infl bractless — carpels actually ± fused, separating in fruit ..... JUNCAGINACEAE {G2,13,16}
14' Infl bracted
15. Ovules many per carpel; fruits erect — carpels actually proximally fused [may appear ± free] ..... MELANTHIACEAE {G16}
15' Ovules 1–3 per carpel; fruits spreading ..... SCHEUCHZERIACEAE {G2}
9' Perianth parts generally in 4s or 5s or indefinite in number
16. Stamens > 2 × as many as petal-like perianth segments or > 15
17. Plants obviously woody; shrubs or trees
18. Crushed leaves strongly aromatic; leaves opposite ..... CALYCANTHACEAE
18' Crushed leaves not aromatic; leaves alternate
19. Fls solitary; seeds with arils ..... CROSSOSOMATACEAE (2)
19' Fls clustered; seeds without arils ..... ROSACEAE (4) {G15,20,21,22,23}
17' Plants herbaceous or slightly woody at base
20. Hypanthium present ..... ROSACEAE (4) {G15,20,21,22,23}
20' Hypanthium 0
21. Sepals enlarging and persisting around fruit; stamens maturing from flower center toward edge ..... PAEONIACEAE
21' Sepals deciduous as flower opens or withering as fruit matures; stamens maturing from flower edge toward center
22. Sepals 2–3(4), falling as flower opens, not petal-like; carpels actually weakly fused in flower, ± separating in age ..... PAPAVERACEAE (Platystemon)
22' Sepals 4–many, present in open flowers, sometimes petal-like; carpels generally wholly free ..... RANUNCULACEAE (2)
16' Stamens 2 × as many as petals or fewer
23. Petals fused, at least at base
24. Plant erect, prostrate, or twining; flowers generally conspicuous, not concealed by leaves; ovules many per ovary; milky latex generally present — carpels proximally free but actually united by common stigma ..... APOCYNACEAE {G19}
24' Plant prostrate, mat-forming; flowers minute, subsessile, axillary, generally concealed by leaves; ovules 1–2 per ovary; milky latex 0 ..... CONVOLVULACEAE (Dichondra) {G19}
23' Petals free but sometimes attached to a disk-like to tubular hypanthium
25. Hypanthium well developed
26. Lvs simple, basal or cauline; stipules often 0; veins generally palmate; ovules generally several–many per carpel — carpels slightly fused proximally but free most of their length ..... SAXIFRAGACEAE (2) {G20,21,24}
26' Lvs simple or compound, generally cauline; stipules generally present; veins often pinnate; ovules generally 1–2 per carpel
27. Shrub ..... CROSSOSOMATACEAE (Glossopetalon spinescens var. aridum)
27' Herb ..... ROSACEAE (4) {G15,20,21,22,23}
25' Hypanthium 0 or inconspicuous
28. Plant herbaceous
29. Annual; ovule 1 per ovary; leaves pinnately divided or compound — carpels actually united by common style ..... LIMNANTHACEAE (Limnanthes) {G20}
29' Perennial; ovules several–many per ovary; leaves simple and entire or variously toothed to palmately lobed or compound ..... SAXIFRAGACEAE (2) {G20,21,24}
28' Plant woody
30. Lvs pinnately compound ..... SIMAROUBACEAE (Ailanthus) {G7,9,20}
30' Lvs simple, entire, sometimes scale-like
31. Fls solitary in leaf axils; fruit a cluster of follicles; leaves elliptic, persistent or drought-deciduous ..... CROSSOSOMATACEAE (2)
31' Fls in dense panicles; fruit cluster of ± dry drupes; leaves scale-like to narrowly oblong, early-deciduous — shrub with thorny green stems ..... SIMAROUBACEAE (Castela) {G7,9,23}
