| | 1. Plant generally aquatic, stem generally submersed or floating (sometimes stranded); petals white, white and yellow, or yellow |
| |
| | 2. Most leaves floating or emergent, simple, entire |
| R. hydrocharoides |
| | 2' Most or all leaves submersed, generally 2–6-dissected (if floating or emergent, leaves, if any, sometimes simple, 3-lobed) |
| |
| | 3. Floating or emergent leaves generally 0 or like submersed, 3–6-dissected, segments thread-like, entire |
| R. aquatilis |
| | 4. Petiole below generally flat, wide, above generally thread-like; leaf generally = or < internode; pedicel ± straight in fruit; fruits 10–30 |
| R. aquatilis var. capillaceus |
| | 4' Petiole generally flat, wide ± throughout; leaf generally << internode; pedicel recurved in fruit; fruits 10–50 |
| R. aquatilis var. subrigidus |
| | 3' Floating or emergent leaves generally 0 or unlike submersed, ± 3-lobed to 1-ternate, lobes or leaflets linear to obovate, entire to lobed |
| |
| | 5. Petals yellow throughout; sepals 4.5–8 mm; fruit body sides smooth or slightly papillate on sides |
| R. flabellaris |
| | 5' Petals white, bases yellow or not; sepals 1.5–5 mm; fruit body cross-ridged |
| |
| | 6. Receptacle in fruit hairy; fruits 15–many, bodies 1–2 mm; submersed leaves 3–6-dissected; perennial herb |
| R. aquatilis var. hispidulus |
| | 6' Receptacle in fruit glabrous; fruits 2–6, bodies 2–3 mm; submersed leaves generally 2–3-dissected; annual |
| R. lobbii |
| | 1' Plant generally terrestrial (if aquatic stem generally emergent); petals generally yellow (sometimes white or reddish throughout) |
| |
| | 7. Basal leaf entire to crenate or lobed << 1/2 way to midrib or blade base |
| |
| | 8. Stem erect to generally prostrate or reclining, often rooting at lower nodes, stolon-like or from stolons |
| |
| | 9. Basal leaf blade linear to lanceolate, base generally tapered |
| R. flammula |
| | 9' Basal leaf blade elliptic to reniform, base generally rounded or lobed |
| |
| | 10. Leaf generally crenate; fruit cluster cylindric, body striate to ridged on sides; major roots slender, not narrowed to stem |
| R. cymbalaria var. saximontanus |
| | 10' Leaf ± entire; fruit cluster spheric, body smooth to striate on sides; major roots thick, narrowed to stem |
| R. gormanii |
| | 8' Stem decumbent to generally erect, not rooting at nodes, not stolon-like, not from stolons |
| |
| | 11. Petals 1–3, 1–3 mm, ± = sepals; fruit body 0.9–1.5 mm |
| |
| | 12. Sepals 3; upper cauline leaf lanceolate to ovate; fruit body smooth to finely net-like |
| R. bonariensis var. trisepalus |
| | 12' Sepals 5; upper cauline leaf linear to oblong; fruit body rough to minutely papillate |
| R. pusillus |
| | 11' Petals 5–many, 3–15 mm, generally > sepals; fruit body 1–2.5 mm |
| |
| | 13. Sepals 1–3.5 mm, ± spreading; petals 3–6.5 mm; cauline leaf blade ovate to cordate, entire to barely toothed |
| R. populago |
| | 13' Sepals 3–7 mm, ± reflexed; petals 5–15 mm; cauline leaf blade linear to lanceolate, entire or deeply 2–3-lobed |
| |
| | 14. Upper cauline leaf linear to narrowly lanceolate, entire; stems generally 3–5 from base, generally branched from base |
| R. alismifolius |
| | 15. Basal leaf blade 2–4 cm, generally ovate |
| var. alismellus |
| | 15' Basal leaf blade 4–12 cm, lanceolate to oblong |
| var. alismifolius |
| | 14' Upper cauline leaf 0 or oblong to ovate, entire or generally deeply 2–3-lobed; stems generally 1 from base, sometimes few-branched above |
| R. glaberrimus |
| | 16. Basal leaf elliptic to obovate; upper cauline leaf 0 or with terminal lobe generally > lateral |
| var. ellipticus |
| | 16' Basal leaf ovate to round; upper cauline leaf 0 or with lobes generally ± equal |
| var. glaberrimus |
| | 7' Basal leaf generally lobed > 1/2 way to midrib or blade base to dissected or compound |
| |
| | 17. Leaf blades generally glabrous, petiole hairs very sparse or generally 0 |
| |
| | 18. Petals white, red-tinged or not; fruit body 8–15 mm, very compressed, sides 6–10 mm wide, margin wing-like; plant scapose |
| R. andersonii |
| | 18' Petals yellow; fruit body < 7 mm, compressed to plump, sides < 4 mm wide, margin ± thick, not wing-like (but back sometimes keeled); plant scapose or generally not |
| |
| | 19. Fruit body 2–7 mm, beak 2–4 mm, cluster spheric |
| |
| | 20. Basal leaf toothed to deeply 3-lobed; fruit body sides spiny, back very keeled; annual, biennial |
| 2 R. muricatus |
| | 20' Basal leaf generally 1-ternate; fruit body sides smooth, back slightly keeled; perennial herb |
| R. orthorhynchus var. bloomeri |
| | 19' Fruit body 1–2 mm, beak < 1 mm, cluster ovoid to subcylindric |
| |
| | 21. Annual; sepals 2–3 mm; petals 2–5 mm; flowers many, axillary, terminal; stem hollow below |
| R. sceleratus |
| | 21' Perennial; sepals 3.5–7 mm; petals 5–12 mm; flowers few, terminal; stem solid |
| R. eschscholtzii |
| | 22. Basal leaf with 3–5(7) lobes > 1/2 way to blade base, middle lobe with 1 tooth or lobe or generally entire, tips obtuse to rounded |
| var. oxynotus |
| | 22' Basal leaf with 3 lobes > 1/2 way to blade base, middle lobe with 3 teeth or lobes, tips acute |
| var. suksdorfii |
| | 17' Leaf blades generally soft-hairy to tomentose, petiole hairs generally > sparse |
| |
| | 23. Plant scapose; leaf 2–3-dissected, segments linear, ± entire; fruit body < beak, finely tomentose or glabrous, with 2 lateral bulges |
| R. testiculatus |
| | 23' Plant not scapose; leaf entire, toothed, or deeply lobed to 1-compound, lobes or leaflets oblong to round, ± entire to deeply lobed or cut; fruit body generally > beak, sometimes puberulent but not tomentose, lenticular to ovoid, without bulges |
| |
| | 24. Fruit body sides papillate or spiny, puberulent or glabrous; annual, biennial |
| |
| | 25. Sepals ± 1–2 mm; petals 1–2 mm or 0; fruit body 1–3 mm, sides papillate, hairs curved |
| |
| | 26. Petals generally fewer than 5; basal leaf deeply 3–5-lobed to 1-ternate, lobes or leaflets oblanceolate to wedge-shaped, toothed to lobed; upper cauline leaf 3-lobed to 1-ternate |
| R. hebecarpus |
| | 26' Petals generally 5; basal leaf coarsely toothed to deeply 3-lobed, lobes ± semicircular, toothed; upper cauline leaf entire to deeply 3-lobed |
| R. parviflorus |
| | 25' Sepals 3.5–7 mm; petals 5–8 mm; fruit body 4–7 mm, sides spiny, hairs 0 |
| |
| | 27. Basal leaf ± ovate to wedge-shaped; upper cauline leaf lobes linear to lanceolate or narrow-oblanceolate; fruits 4–10; fruit keel generally few-spined |
| R. arvensis |
| | 27' Basal leaf cordate to reniform; upper cauline leaf lobes wide-oblanceolate; fruits generally 10–20; fruit keel not spiny |
| 2 R. muricatus |
| | 24' Fruit body sides ± smooth, not papillate (except sometimes in R. sardous), generally glabrous; perennial herb (annual, biennial in R. sardous) |
| |
| | 28. Stem prostrate to ascending, rooting at lower nodes, stolon-like or not |
| R. repens |
| | 28' Stem ± prostrate to erect, not rooting at nodes, not stolon-like |
| |
| | 29. Petals 2–8 mm, = or 1–2.5 mm > sepals |
| |
| | 30. Basal leaf ovate to deltate, generally 1-ternate, leaflets stalked; sepals 3–6 mm; petals 4–8 mm; fruit beak ± straight or slightly curved |
| R. macounii |
| | 30' Basal leaf generally cordate, deeply 3-lobed; sepals 1.5–3 mm; petals 2–5.5 mm; fruit beak curved |
| R. uncinatus |
| | 29' Petals 4–19 mm, generally 3+ mm > sepals |
| |
| | 31. Caudex bulb-like; sepals generally spreading, hairs 0-sparse — North Coast (waif) |
| R. bulbosus |
| | 31' Caudex 0 or not bulb-like; sepals generally puberulent to hairy, generally reflexed (except in R. acris) |
| |
| | 32. Receptacle, especially in fruit, puberulent to hairy |
| |
| | 33. Petals 7–22, blade generally oblong to obovate, length generally 2 × width |
| 2 R. californicus |
| | 33' Petals 5–8, blade generally widely obovate to round, length generally < 2 × width |
| |
| | 34. Basal leaf cordate to generally ovate, leaflets generally 5; fruit body 2–4 mm, beak 2–4 mm, ± straight |
| R. orthorhynchus var. orthorhynchus |
| | 34' Basal leaf ovate to generally cordate, leaflets generally 3; fruit body 2–3 mm, beak < 0.5 mm, ± straight to curved |
| R. sardous |
| | 32' Receptacle, especially in fruit, generally glabrous |
| |
| | 35. Basal leaf pentagon-shaped, deeply lobed; sepals spreading |
| R. acris |
| | 35' Basal leaf ovate to cordate or round, deeply lobed to compound; sepals generally reflexed |
| |
| | 36. Fruit body 3.5–5.5 mm, sides 3–4.5 mm wide |
| R. canus |
| | 36' Fruit body 2–4 mm, sides 1.5–3.5 mm wide |
| |
| | 37. Petals generally 7–22; fruit beak generally 0.5–1 mm, generally curved |
| 2 R. californicus |
| | 37' Petals generally 5–6; fruit beak generally 1.5–2.5 mm, curved or ± straight |
| R. occidentalis
|