1. Raquis de los racimos sin setas largas; espiguillas de 2-2,8(3) mm de longitud, múticas, dispuestas en 4 filas; cariopsis blanquecina ............................... 4. E. colona – Raquis de los racimos con setas largas, ± abundantes; espiguillas de (2,8)3-5,5(6) mm de longitud, todas o en parte ± aristadas, dispuestas irregularmente; cariopsis amarillenta, pardusca o pardo-rojiza .............. 2 2. Vainas de las hojas basales con tonos purpúreo-violáceos; espiguillas (2,8)3-3,6(3,8) mm; cariopsis 1,4-2,2 × 1,3-1,8 mm, de ovoide a anchamente elipsoidal ......... 1. E. crus-galli – Vainas de las hojas basales de color verde, a menudo sin tonos purpúreo-violáceos; espiguillas (3,6)3,8-5,5(6) mm; cariopsis 2,2-3 × 1,9-2,5 mm, de elipsoidal a subesferoidal .. ...................... 3 3. Inflorescencia de ordinario muy inclinada, nutante en la madurez; espiguillas ancha- mente elíptico-ovoides, de ordinario con tonos purpúreos evidentes, al menos en las aristas; gluma inferior de 1/3-1/2 de la longitud de la espiguilla; embrión c. 3/4 de la longitud de la cariopsis ........................................... 2. E. oryzoides – Inflorescencia erecta o levemente inclinada en la madurez; espiguillas estrechamente elíptico-ovoides, verdosas, de ordinario sin tonos purpúreos evidentes; gluma inferior de 1/2-4/5 de la longitud de la espiguilla; embrión de c. 4/5 a subigual que la longitud de la cariopsis .............................................................................. 3. E. oryzicola

Fig. 21.–Aspecto general de la espiguilla, vista desde la gluma inferior: a) Echinochloa crus-galli [var. crus-galli]; b) E. oryzoides; c) E. oryzicola; d) E. colona.

Owing to nomenclatural and taxonomic uncertainties, the key is considered provisional; for a different recent interpretation, see Martínez-Azorín and Crespo (2021).

1 Fertile floret not disarticulating at maturity. Spikelets unawned. Fertile floret and caryopsis markedly humped. Inflorescence compact, usually contracted and with the axis often hardly visible, sometimes with spreading branches (Fig. 1) 2 1' Fertile floret disarticulating at maturity. Spikelets awned or not. Fertile floret and caryopsis not markedly humped. Inflorescence not strongly contracted when fully developed, with the axis showing through (but compare with clearly different E. muricata var. wiegandii when in doubt) 3 2 Spikelets dark brownish or purplish at maturity (Fig. 2), ca. 3–4 mm long. Caryopsis brownish E. esculenta 2' Spikelets pale (yellowish or greenish) at maturity (Fig. 1), ca. 3–3.5 mm long. Caryopsis whitish E. frumentacea 3 Spikelets < 3 mm long and lower glume ca. 1/2 length of the spikelet, which is always unawned. Axis of the inflorescence branches (almost) without bristles (except at the base). Inflorescence without secondary branches (Fig. 3). Leaves narrow, usually not exceeding 6 mm. Caryopsis whitish E. colona 3' Spikelets usually ≥ 3 mm long, awned or not. (If spikelet < 3 mm, then lower glume only ca. 1/3 length of the spikelet.) Axis of the inflorescence branches with bristles. Inflorescence often with secondary branches. Leaves usually wider. Caryopsis usually darker, yellowish or brownish 4 4 Spikelets ≥ 4 mm long and at least some spikelets with lower glume up to 2/3 length of the spikelet (Fig. 4D). Mature inflorescence more or less erect (Fig. 5). Spikelets unawned or with an awn up to 20 mm long. Caryopsis 2–2.4 mm long. Embryo at least 0.75 to over 0.9 length of the caryopsis. (An obligate weed of rice.) E. oryzicola 4' Spikelets ≥ 4 mm long and lower glume not longer than 1/2 length of the spikelet. Mature inflorescence drooping (Fig. 6). Spikelets usually awned, with an awn up to 50 mm long. Caryopsis 2.2–2.8 mm long. Embryo 0.65–0.75(–0.85) length of the caryopsis. (An obligate weed of rice.) E. crus-galli var. oryzoides 4" Spikelets ≤ 4 mm long and lower glume usually clearly less than 1/2 length of the spikelet. (If spikelets > 4 mm, see 6, E. muricata var. muricata. Solely a rare casual?) 5 5 Lemma of the fertile floret with a membranous tip that is clearly differentiated from the coriaceous body of the lemma (Fig. 7A); the membranous tip demarcated from the coriaceous body by a line of minute hairs (the latter, however, not or hardly visible with a hand lens). Palea of the fertile floret with a blunt, soft, frayed looking, usually strongly recurved tip (Fig. 7B). Spikelets unawned or awned; awn length extremely variable (up to 40 mm long or more). The leaf subtending the distal inflorescence with the demarcation between blade and sheath more or less semicircular or forming a slightly elongated upside-down U; blade usually patent from the base. (A complex taxon with several difficult-to-distinguish intergrading forms that are not keyed out here; see comments below.) E. crus-galli ...

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