| # The grass genera of the world |

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

### Setariopsis Scribner ex Millsp.

From Setaria (another grass genus, q.v.) and the Greek opsis (appearance), denoting likeness.

Habit, vegetative morphology. Annual, or perennial; rhizomatous, or decumbent. Culms 15–50 cm high; herbaceous; branched above. Culm nodes glabrous. Culm internodes solid. Leaves not basally aggregated. Leaf blades broad to narrow; flat; without cross venation; persistent. Ligule a fringed membrane. Contra-ligule absent.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite and sterile (the clusters with undeveloped spikelets at the base).

Inflorescence. Inflorescence a false spike, with spikelets on contracted axes, or of spicate main branches (the basal ‘clusters’ being quite elongated in S. auriculata); contracted. Inflorescence axes not ending in spikelets (produced into long bristles beyond the spikelets). Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets subtended by solitary ‘bristles’ (these longer than the spikelets). The ‘bristles’ persisting on the axis. Spikelets not secund; not two-ranked; pedicellate. Pedicel apices discoid.

Female-fertile spikelets. Spikelets 2–3 mm long (gibbous); compressed dorsiventrally; falling with the glumes; with conventional internode spacings. The upper floret not stipitate. Rachilla terminated by a female-fertile floret. Hairy callus absent. Callus absent.

Glumes two; very unequal; (the upper) about equalling the spikelets; (the upper) long relative to the adjacent lemmas; hairless; glabrous; pointed (G2), or not pointed (G1 blunt); awnless; non-carinate; very dissimilar (the G1 small, broad and cordate, the G2 large, very broad, saccate, auriculate and becoming indurated). Lower glume 7–9 nerved. Upper glume distinctly saccate (and auriculate); 11–19 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. The proximal incomplete florets 1; paleate; sterile (seemingly). The proximal lemmas broad, lyrate with two swellings at the base; awnless; 7–11 nerved; decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas (cartilaginous, harder along the margins); becoming indurated.

Female-fertile florets 1. Lemmas not saccate; decidedly firmer than the glumes; rugose; becoming indurated; entire; pointed (and apiculate); awnless (though apiculate); hairless; glabrous; non-carinate; having the margins inrolled against the palea; with a clear germination flap; 5 nerved. Palea present; relatively long; entire; awnless, without apical setae; textured like the lemma; indurated; 2-nerved; 2-keeled. Palea keels wingless. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Anthers about 0.5 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles free to their bases. Stigmas 2.

Fruit, embryo and seedling. Fruit free from both lemma and palea; small; compressed dorsiventrally. Hilum short.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals much narrower); of similar wall thickness costally and intercostally (thin walled). Mid-intercostal long-cells rectangular; having markedly sinuous walls (irregularly so). Microhairs present; panicoid-type; (45–)48–51(–54) microns long; 5.1–5.4–6 microns wide at the septum. Microhair total length/width at septum 8.3–10. Microhair apical cells (30–)33–34.5(–39) microns long. Microhair apical cell/total length ratio 0.67–0.73. Stomata common; 21–24 microns long. Subsidiaries medium to high dome-shaped, or triangular (occasionally). Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common (in places); not paired (solitary); not silicified. Costal short-cells conspicuously in long rows. Costal silica bodies ‘panicoid-type’; dumb-bell shaped and nodular; not sharp-pointed.

Transverse section of leaf blade, physiology. C4; XyMS–. PCR sheath outlines even. Leaf blade adaxially flat. Midrib conspicuous; having a conventional arc of bundles (the large median bundle flanked on either side by two smaller ones); with colourless mesophyll adaxially. Bulliforms not present in discrete, regular adaxial groups (the epidermis largely bulliform, and complicated by cushion hair bases). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present (with the primaries only); forming ‘figures’. Sclerenchyma all associated with vascular bundles.

Cytology. Chromosome base number, x = 9. 2n = 19. 2 ploid.

Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Cenchrinae. 2 species.

Distribution, phytogeography, ecology. Mexico.

Species of open habitats. Weedy places.

References, etc. Leaf anatomical: studied by us - S. auriculata Scribn.

Special comments. Description based mainly on S. auriculata.

Illustrations. • Setariopsis auriculata: Swallen, Grasses of Guatemala (1955). • Setariopsis auriculata: Sanchez-Ken, Flora del Valle Tehuacán-Cuicatlan (2011).

We advise against extracting comparative information from the descriptions. This is much more easily achieved using the DELTA data files or the interactive key, which allows access to the character list, illustrations, full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, distributions of character states within any set of taxa, geographical distribution, and classifications. See also Guidelines for using data taken from Web publications.

Cite this publication as: ‘Watson, L., Macfarlane, T.D., and Dallwitz, M.J. 1992 onwards. The grass genera of the world: descriptions, illustrations, identification, and information retrieval; including synonyms, morphology, anatomy, physiology, phytochemistry, cytology, classification, pathogens, world and local distribution, and references. Version: 15th June 2025. delta-intkey.com’.

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