Statements about leaves refer to well-developed foliage leaves, not necessarily the smaller, often less toothed bracts in the inflorescences. Statements about seeds, especially measurements, refer to fully mature ones. This is a difficult genus in need of more collecting. Sufficient material with mature fruit is not available to establish accurately the distribution and abundance of some of the species in the Chenopodium album group.
1. Leaves linear to linear-lanceolate, less than 4 (–5) mm wide, (1–) 3-nerved, entire.
1. Leaves usually broad, toothed or with irregular margin (if entire, then blades pinnate- or triple-nerved and not linear).
2. Leaves ± densely farinose on underside.
3. Perianth not farinose; blades of principal leaves mostly 1–2.5 (–3) cm long, with margins sinuate and toothed at ± regular intervals; pericarp free from seed; some fruits vertical.
3. Perianth farinose; blades of principal leaves often longer, or entire to irregularly toothed, or both; pericarp closely adherent to seed; all fruits horizontal.
4. Principal leaves with blades broadly ovate to broadly triangular, less than 1.5 times as long as broad, entire; plant with fetid odor (like rotten fish) when bruised.
4. Principal leaves ovate and irregularly toothed to lanceolate and entire; plant not fetid.
5. Pericarp and seed coat not honeycomb-patterned, ±smooth or inconspicuously radially patterned; seeds 1–1.6 mm broad.
C. album (in part)
5. Pericarp with regular honeycomb pattern of raised cell outlines (and seeds 1.7–2 mm broad) or seed coat with conspicuous pits forming a honeycomb pattern.
2. Leaves not farinose (except sometimes when very young).
6. Fruit all or almost all vertical; tepals 3 or erose-toothed.
7. Tepals usually 5, erose-toothed; styles conspicuous, stout, becoming 1 (–1.2) mm long; inflorescence not becoming fleshy; leaves triangular-hastate, not toothed.
7. Tepals usually 3, entire; styles less than 0.5 mm long; inflorescence in some species becoming fleshy; leaves various.
8. Leaf blades triangular-hastate and usually also coarsely dentate; inflorescences (often 1–2 cm across when fully developed) becoming bright red, fleshy and berry-like by coalescence of the perianths in each head.
8. Leaf blades broadly elliptic to rounded, ovate, or obovate, entire to sinuate; inflorescences (small dry heads less than 6 mm across) not becoming red and fleshy.
6. Fruit all or almost all horizontal; tepals 5, entire.
9. Largest leaf blades (2–) 4–13 (–15) cm long, truncate to subcordate at base when well developed, with 1–3 large acute teeth separated by broadly rounded sinuses on each side; seed 1.6–1.8 mm broad.
9. Largest leaf blades often shorter, narrowly to broadly cuneate at base, with teeth more numerous, obscure, or none; seed 1–1.5 (–1.7) mm broad.
10. Tepals scarcely if at all keeled and very slightly if at all farinose; mature fruit 1–1.5 mm broad, largely exposed (tepals too short to cover it).
11. Flowers separate, in an open inflorescence of many spikes, the rachis ± visible between each flower; leaves entire.
11. Flowers aggregated in many-flowered glomerules; at least the lower leaves usually toothed (except sometimes in C. standleyanum).
12. Fruit ca. 1.3–1.5 mm broad; pericarp easily separable; lower leaf blades acute at base.
12. Fruit ca. 1–1.2 mm broad; pericarp slightly adherent to seed; lower leaf blades truncate at base.
10. Tepals slightly to strongly keeled, moderately to densely farinose; fruit 1.2–1.6 mm broad, completely covered by perianth (or sometimes slightly exposed in C. murale).
13. Styles very short (up to 0.2 mm) and stout; margin of seed ± sharply angled; principal leaf blades less than 1.5 times as long as broad, coarsely toothed.
13. Styles when intact usually longer, slender; margin of seed usually rounded; principal leaf blades usually at least 1.5 times as long as broad, entire (and lanceolate) to variously toothed.
C. album (in part)