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| | 2. Plant in hand pistillate |
| |
| | 3. Outermost sepal > others, tip acute, spine-like; bracts >> inner sepals |
| 2 A. palmeri |
| | 3' Outermost sepal slightly > others, obtuse to notched, short-pointed; bracts slightly > inner sepals |
| |
| | 4. Bract midrib keeled; styles generally 3; inflorescence axis and bracts glabrous |
| 2 A. arenicola |
| | 4' Bract midrib moderately thickened, not keeled; styles generally 2; inflorescence axis and bracts sparsely gland-stalked |
| 2 A. watsonii |
| | 2' Plant in hand staminate |
| |
| | 5. Outer sepal spine-tipped, > others; bracts = or > sepals |
| 2 A. palmeri |
| | 5' Outer sepal short-pointed, slightly > others; bracts < or = sepals |
| |
| | 6. Bracts < sepals; inflorescence axis and bracts glabrous |
| 2 A. arenicola |
| | 6' Bracts generally = or > sepals; inflorescence axis and bracts generally sparsely gland-stalked |
| 2 A. watsonii |
| | 1' Monoecious (staminate flowers sometimes only near inflorescence tip) |
| |
| | 7. Most nodes with 2 rigid spines |
| A. spinosus |
| |
| | 8. Fruit indehiscent, generally inflated, thick-walled; plant prostrate |
| A. deflexus |
| | 8' Fruit circumscissile, thin-walled; plant prostrate to erect |
| |
| | 9. Inflorescence clusters axillary, throughout plant, not clearly terminal |
| |
| | 10. Stems ascending to erect, plant spheric; pistillate sepals 3, 0.7–2.2 mm |
| A. albus |
| | 10' Stems prostrate; pistillate sepals (1)3–5, 1–3.5 mm |
| |
| | 11. Seed 1.2–1.7 mm diam; pistillate sepals 4–5, outer green along midrib, 1.5–3.5 mm |
| A. blitoides |
| | 11' Seed 0.8–1.1 mm diam; pistillate sepals 1–3, white and scabrous throughout |
| A. californicus |
| | 9' Inflorescence clearly terminal (sometimes also axillary) |
| |
| | 12. Axillary clusters scattered generally to plant base |
| |
| | 13. Pistillate bracts < sepals; pistillate sepals widely fan-shaped, < or = 2.5 mm wide, margin with small, finger-like projections |
| A. fimbriatus |
| | 13' Pistillate bracts generally > sepals; pistillate sepals ± spoon-shaped, 0.7–1.5 mm wide, irregularly toothed |
| A. torreyi |
| | 12' Axillary clusters 0 in lower 1/2 of plant |
| |
| | 14. Inner pistillate sepals spoon-like to obovate, tip obtuse to notched, generally irregularly toothed |
| |
| | 15. Pistillate sepals = fruit, ± obovate, 1.8–2.2 mm; pistillate bracts ± = sepals, midrib projecting; inflorescence a long, thick, recurved, terminal spike, sometimes subtended by shorter, lateral spikes |
| A. caudatus |
| | 15' Pistillate sepals > fruit, spoon-like, 2.5–3 mm; pistillate bracts 1.5 × sepals, midrib thick; inflorescence many stiff, crowded lateral spikes, terminal not very long |
| A. retroflexus |
| | 14' Inner pistillate sepals narrow, sometimes spoon-like, tips acute to short-pointed |
| |
| | 16. Pistillate bracts < sepals and fruit; inflorescence many lateral, slender, ascending, cylindric spikes |
| A. cruentus |
| | 16' Pistillate bracts > sepals and fruit; inflorescence various |
| |
| | 17. Pistillate bracts generally 2–3.5 mm; staminate sepals and stamens 3–5; inflorescence many short, crowded, lateral spikes |
| A. hybridus |
| | 17' Pistillate bracts 4.5–8 mm; staminate sepals and stamens 3–4; inflorescence generally 1 long, terminal spike and few lateral spikes |
| A. powellii
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