| | 1. Dioecious (rarely some flowers bisexual); stem erect, slender, generally < 4 dm; perianth ± red in flower, tubercles 0 in fruit (subg. Acetosa) |
| |
| | 2. Leaves generally sagittate to hastate; stem single from slender rhizome; inner perianth lobes ± = fruit faces |
| R. acetosella |
| | 2' Leaves linear to lanceolate; stems clustered on taproot; inner perianth lobes >> fruit faces |
| R. paucifolius |
| | 1' Flowers generally bisexual; stem decumbent to erect, generally stout, generally > 7 dm; perianth generally green in flower, tubercles various or 0 in fruit (subg. Rumex) |
| |
| | 3. Leaves cauline; main stem prostrate to ± erect, generally with smaller branches at most nodes, branches often producing flowers after main stem; native (sect. Axillares) |
| |
| | 4. Inner perianth lobes > 12 mm; Modoc Plateau |
| R. venosus |
| | 4' Inner perianth lobes < 6 mm; widespread |
| R. salicifolius |
| | 5. Tubercles 0 or inconspicuous; inner perianth lobes triangular, with short, triangular teeth near base |
| var. denticulatus |
| | 5' Tubercles 1 or 3 per flower, ± obvious; inner perianth lobes lanceolate to round, teeth generally 0 |
| |
| | 6. 1 tubercle obvious, width > 1/3 width of inner perianth lobe |
| |
| | 7. Inflorescence dense; leaf ± thick, some oblong to elliptic; coastal |
| var. crassus |
| | 7' Inflorescence ± open; leaf thin, linear to lanceolate; coastal or in mtns |
| var. salicifolius |
| | 6' 3 tubercles obvious, ± equal, width < or > 1/3 width of inner-perianth lobe |
| |
| | 8. Tubercles ovate to nearly round, > 1/3 width of inner perianth lobe |
| var. transitorius |
| | 8' Tubercles lanceolate, generally << 1/3 width of inner perianth lobe |
| |
| | 9. Some leaves oblong to elliptic; Great Basin Floristic Province — shores, ± salty lake beds |
| var. lacustris |
| | 9' Leaves linear to lanceolate; especially Sierra Nevada |
| var. triangulivalvis |
| | 3' Leaves basal and cauline (basal rosette often withered when fruit mature); stem ± erect, generally unbranched below inflorescence; native or alien (sect. Rumex) |
| |
| | 10. Tubercles 0 or inconspicuous — margin of inner perianth lobe entire |
| |
| | 11. Leaf blade fleshy, base tapered; inner perianth lobe 8–15 mm |
| R. hymenosepalus |
| | 11' Leaf blade ± leathery, base truncate to cordate; inner perianth lobe 4–10 mm |
| R. occidentalis |
| | 10' Tubercles 1 or 3 per flower, obvious |
| |
| | 12. Margin of inner perianth lobe entire |
| |
| | 13. Inner perianth lobe 2–3 mm, tubercle 1/3 width of lobe or wider; inflorescence open, interrupted |
| |
| | 14. Perennial; tubercle ± 1/2 width of perianth lobe; widespread, alien |
| R. conglomeratus |
| | 14' Annual; tubercle ± 1/3 width of perianth lobe; generally Desert, native |
| 2 R. violascens |
| | 13' Inner perianth lobe 5–6 mm, tubercle << 1/3 width of lobe; inflorescence dense, continuous |
| |
| | 15. Tubercle ovate to round; abundant |
| R. crispus |
| | 15' Tubercle ± lanceolate; uncommon |
| R. orbiculatus |
| | 12' Margin of inner perianth lobe with 0.5–4 mm teeth |
| |
| | 16. Annual (sometimes biennial) |
| |
| | 17. Inner perianth lobe 4–5 mm, teeth ± 1.5 mm; inflorescence interrupted throughout; alien — uncommon |
| R. dentatus |
| | 17' Inner perianth lobe 2–3.5 mm, teeth 0.5–4 mm; inflorescence dense, not interrupted near tip; native |
| |
| | 18. Widest inner perianth lobe narrowly ovate, teeth 2–4 mm, fine; inflorescence dense, leafy; widespread |
| R. maritimus |
| | 18' Widest inner perianth lobes widely ovate or ± equilaterally triangular, teeth < 1 mm, or obscure; inflorescence ± open, nearly leafless; especially Desert |
| 2 R. violascens |
| |
| | 19. Largest leaf 20–75 cm, blade lance-ovate, ± cordate; inner perianth lobe narrowly ovate-triangular |
| R. obtusifolius |
| | 19' Largest leaf < 20 cm (if larger, blade narrowly lanceolate, tapered); inner perianth lobe widely ovate-triangular to round-cordate |
| |
| | 20. Inflorescence branches spreading; teeth of inner perianth lobe slender to base, longest ± 1.5 mm |
| R. pulcher |
| | 20' Inflorescence branches ascending; teeth of inner perianth lobe coarse, wider at base, longest 0.5–1 mm |
| |
| | 21. Inner perianth lobe > 5 mm, round-cordate, longest teeth ± 0.5 mm, each much wider at base |
| R. kerneri |
| | 21' Inner perianth lobe < 5 mm, ± triangular-cordate, longest teeth ± 1 mm, each somewhat wider at base |
| R. stenophyllus
|