The grass genera of the world
~ Bouteloua sensu lato
Habit, vegetative morphology. Small perennial; stoloniferous (and mat forming). Culms herbaceous; unbranched above. Culm nodes glabrous. Plants unarmed. Young shoots intravaginal. Leaves mostly basal; non-auriculate. Leaf blades narrow; about 2 mm wide; not setaceous (but enrolling); without abaxial multicellular glands; without cross venation; persistent. Ligule a fringe of hairs.
Reproductive organization. Plants monoecious with all the fertile spikelets unisexual; without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; female-only and male-only. The male and female-fertile spikelets in different inflorescences (the staminate spikelets in 4 or 5 short spikes on a long projecting peduncle, the pistillate spikelets clustered in the radical rosette).
Inflorescence. Inflorescence of spicate main branches (male), or a false spike, with spikelets on contracted axes (contracted, headlike, with 2–5 glomerules, female). Inflorescence with axes ending in spikelets. Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes disarticulating; falling entire (the glomerules shed). Spikelets 3–5 spikelets in each glomerule; secund (male inflorescence), or not secund (female inflorescence).
Female-sterile spikelets. Male spikelets 2–4 mm long, 1-flowered, rachilla not prolonged, stamens 3. Rachilla of male spikelets terminated by a male floret. The male spikelets with glumes; without proximal incomplete florets; 1 floreted. Male florets 1; 3 staminate.
Female-fertile spikelets. Spikelets 4 mm long (excluding the awns); compressed dorsiventrally; falling with the glumes (in the glomerules). Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets.
Glumes two; more or less equal; long relative to the adjacent lemmas; hairy; pointed; awned (the G2 acuminate into its short awn, the G1 reduced almost to its awn); non-carinate; very dissimilar (the G1 very narrow, the G2 lanceolate and tapering into its awn). Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets (the empty lemmas each hairy, more dissected than L1, the lowermost having about 15 awns, the uppermost 3). The distal incomplete florets 2–3; clearly specialised and modified in form (constituting a multi-awned tip to the spikelet).
Female-fertile florets 1. Lemmas decidedly firmer than the glumes (membranous or cartilaginous); not becoming indurated; incised; 3 lobed; deeply cleft (to 1/3 or more of its length, at each side); awned. Awns 2, or 3; median and lateral, or lateral only (two short lateral awns and a median mucro); the median (when present) similar in form to the laterals (but smaller); non-geniculate; hairless (scabrid). The lateral awns exceeding the median (the median awn reduced to a mucro, the laterals longer than the median, but shorter than the body of the lemma). Lemmas sparsely hairy; non-carinate; without a germination flap; 3 nerved. Palea present (sparsely hairy apically between the keels); relatively long; apically notched; awnless, without apical setae; not indurated (membranous); 2-nerved; 2-keeled. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 0 (3 staminodes only). Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small (about 2 mm long); ellipsoid; compressed dorsiventrally. Hilum short. Pericarp 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 (and pitted). Microhairs present; elongated; clearly two-celled; panicoid-type. Microhair apical cell wall thinner than that of the basal cell and often collapsed. Microhairs 39–42–51 microns long. Microhair basal cells 24 microns long. Microhairs 7.5–8.4–9.6 microns wide at the septum. Microhair total length/width at septum 5–5.6. Microhair apical cells (15–)16.5–19.5(–21) microns long. Microhair apical cell/total length ratio 0.38–0.46. Stomata common; 25.5–30 microns long. Subsidiaries dome-shaped (mostly), or triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies present and perfectly developed; tall-and-narrow, acutely-angled, and oryzoid-type. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; saddle shaped to crescentic; 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. Mesophyll traversed by columns of colourless mesophyll cells. Leaf blade adaxially flat. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (these linked with traversing colourless columns). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (mostly with adaxial and abaxial strands). 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 species (P. stolonifera).
Distribution, phytogeography, ecology. Mexico.
Species of open habitats. Dry calcareous plains.
References, etc. Leaf anatomical: studied by us.
Illustrations. • P. stolonifera, abaxial epidermis of leaf blade: this project
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: 11th December 2017. delta-intkey.com/grass’.