| # The grass genera of the world |

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

### Opizia J. & C. Presl

~ Bouteloua sensu lato

Including Casiostega Galeotti

Habit, vegetative morphology. Perennial; stoloniferous (sward forming). Culms 10 cm high; herbaceous. Culm internodes solid. Leaves not basally aggregated; non-auriculate; without auricular setae. Leaf blades linear to linear-lanceolate (acuminate); narrow; 1–2 mm wide; flat, or folded; without abaxial multicellular glands; without cross venation. Ligule a fringed membrane (hairy on the back, with a short fringe); not truncate (rounded); 0.5–1 mm long. Contra-ligule absent.

Reproductive organization. Plants dioecious; without hermaphrodite florets. The spikelets all alike in sexuality (on the same plant); female-only, or male-only. Plants outbreeding.

Inflorescence. Inflorescence of spicate main branches (male plants with short panicles of 2–3 spike-like racemes, each raceme pulvinate at the base, reflexing and deciduous; with minute bristles associated with raceme bases), or a single raceme (female inflorescences solitary, spikelike). Inflorescence with axes ending in spikelets (female racemes), or axes not ending in spikelets (male racemes, which terminate in a short bristle). Inflorescence espatheate; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes disarticulating (males), or persistent (females); males falling entire. Spikelets subtended by solitary ‘bristles’ (each female raceme having short bristles near the tip, with a spikelet beyond). The ‘bristles’ persisting on the axis. Spikelets solitary; secund (in male racemes), or not secund (female racemes); very shortly pedicellate. Pedicel apices slightly cupuliform.

Female-sterile spikelets. Male spikelets 3–4 mm long, shortly pedicellate, secund, awnless; glumes, lemma and palea thinly membranous; glumes 1-nerved, lemma 3-nerved, palea 2-nerved; two fleshy lodicules; no prolonged rachilla, no rudimentary floret. Rachilla of male spikelets terminated by a male floret. The male spikelets with glumes; without proximal incomplete florets; 1 floreted. Male florets 1.

Female-fertile spikelets. Spikelets 3–4 mm long; adaxial; compressed laterally to not noticeably compressed; falling with the glumes; with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; hairy; the rachilla extension with incomplete florets. Hairy callus present. Callus blunt.

Glumes two; very unequal (G1 about a third the length of G2); (the upper) long relative to the adjacent lemmas; dorsiventral to the rachis; hairy (all over the back); awnless; non-carinate; dorsally hairy, hyaline, the upper with a minutely-toothed apex, the lower pointed. Lower glume 1 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 1; clearly specialised and modified in form (the terminal sterile floret reduced to the three long awns and the lobes tiny compared with the L1, the lower part strongly adnate to the back of the palea).

Female-fertile florets 1. Lemmas decidedly firmer than the glumes (firmly membranous or leathery); becoming indurated; incised; 4 lobed (the lobes hyaline); deeply cleft; awned. Awns 3; median and lateral; the median non-geniculate; hairless (scabrid); much longer than the body of the lemma. The lateral awns shorter than the median (somewhat, arising from the inner sides of the outermost lobes). Lemmas hairy; somewhat carinate; without a germination flap; 3 nerved. Palea present (strongly winged above, bowed out below); relatively long; deeply bifid; awnless, without apical setae; not indurated (but very firm, cf. the lemma); 2-nerved; 2-keeled. Palea keels strongly winged (the wings projecting above the bases of the lemma awns). Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 0. Ovary apically glabrous. Styles fused (the ovary asymmetrically beaked, and saccate to fit the palea). Stigmas 2; white (?).

Fruit, embryo and seedling. Fruit small (about 1 mm long); ellipsoid; compressed laterally. Hilum short. Pericarp rather tough; free. Embryo large.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally; of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls (thick, pitted). Microhairs present; elongated; clearly two-celled; panicoid-type (rather large, the apical cell very thin-walled, about equalling the basal cell in length). Microhair apical cell wall thinner than that of the basal cell and often collapsed. Microhairs (45–)54–60(–69) microns long. Microhair basal cells 30 microns long. Microhairs (6.6–)7.2–8.4(–9) microns wide at the septum. Microhair total length/width at septum 6.4–8.2. Microhair apical cells (22.5–)28.5–31.5(–35.4) microns long. Microhair apical cell/total length ratio 0.5–0.53. Stomata common; 24–25.5–27 microns long. Subsidiaries low to medium dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies imperfectly developed; mainly crescentic (small). Costal short-cells predominantly paired. Costal silica bodies present throughout the costal zones to present in alternate cell files of the costal zones; crescentic (mainly), or saddle shaped (especially over the main veins), or tall-and-narrow (some); not sharp-pointed.

Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.

C4; XyMS+. PCR sheaths of the primary vascular bundles interrupted; interrupted abaxially only. PCR sheath extensions absent. Leaf blade adaxially flat. Midrib conspicuous (with a large anchor-shaped girder abaxially, and bulliform epidermis adaxially); with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans and associated with colourless mesophyll cells to form deeply-penetrating fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (one primary bundle towards the margin on each side, the rest (except the midrib) with scanty adaxial and abaxial strands); forming ‘figures’ (the two aforementioned). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.

Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Boutelouinae (as a synonym of Bouteloua). 1–2 species (O. bracteata, O. stolonifera).

Distribution, phytogeography, ecology. Southern Mexico, Cuba.

Species of open habitats. Shallow soils on dry hillsides.

References, etc. Leaf anatomical: studied by us - O. stolonifera Presl.

Illustrations. • Opizia stolonifera: Hitchcock (1936).

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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