The grass genera of the world
~ Bouteloua sensu lato
Habit, vegetative morphology. Perennial; stoloniferous. Culms 5–15 cm high; herbaceous; unbranched above. Leaves non-auriculate. Leaf blades narrow; 1–3 mm wide (to 8 cm long); flat; exhibiting multicellular glands abaxially (at the bases of macrohairs). The abaxial leaf blade glands intercostal. Leaf blades without cross venation; persistent. Ligule a fringe of hairs. 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 (racemes straight to curved, pectinate, pedunculate, the female inflorescence prostrate, the male erect); digitate, or subdigitate, or non-digitate. Primary inflorescence branches (1–)2–3. Inflorescence axes not ending in spikelets (often ending in a scabrid bristle). Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes disarticulating (female inflorescence), or persistent (male infloresence); (of the female inflorescence) falling entire. Spikelets unaccompanied by bractiform involucres, not associated with setiform vestigial branches; solitary; secund (pectinate); biseriate; subsessile; not in distinct long-and-short combinations.
Female-sterile spikelets. Male racemes persistent, erect. Glumes equalling the floret, usually 1-nerved; one floreted, the lemma with three awn points. Rachilla of male spikelets prolonged beyond the uppermost male floret (the terminal rudiments, when present, consisting of scabrid awns which are sometimes very long). The male spikelets 1 floreted (with or without rudiments). The lemmas awned. Male florets 1 (anthers bright orange).
Female-fertile spikelets. Spikelets 7 mm long; compressed dorsiventrally; falling with the glumes (and with the rachis: not disarticulating otherwise). Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus with a tuft of hairs at the base of the glumes.
Glumes two; very unequal; (the upper) about equalling the spikelets; (the upper) long relative to the adjacent lemmas; lateral to the rachis; hairy (at the base); pointed; awnless; carinate (G1), or non-carinate (G2); narrow, the G1 hyaline and keeled, the G2 larger, thinly membranous, not keeled. Lower glume 1 nerved. Upper glume (3–)5 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets 3; clearly specialised and modified in form; awned (the rudiments 3-awned, the awns long and scabrid, forming a terminal cluster).
Female-fertile florets 1. Lemmas decidedly firmer than the glumes (cartilaginous); smooth; not becoming indurated; incised; not deeply cleft (briefly triaristate); awned. Awns 3; median and lateral; the median similar in form to the laterals; from a sinus (from a short sinus between the two laterals); non-geniculate; recurving; hairless (scabrid); much shorter than the body of the lemma; entered by one vein. The lateral awns slightly shorter than the median. Lemmas hairless; glabrous; non-carinate (rounded on the back); without a germination flap; 3 nerved. Palea present; relatively long; apically notched (at the pointed tip); awnless, without apical setae (or the nerves slightly excurrent); not indurated (membranous); 2-nerved; 2-keeled. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 0 (but 3 staminodes). Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit small to medium sized (about 4 mm long); ellipsoid; not noticeably compressed. Hilum short. Pericarp fused. Embryo large; waisted; with an epiblast; with a scutellar tail; with an elongated mesocotyl internode; with one scutellum bundle. Embryonic leaf margins meeting.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells similar in shape costally and intercostally (narrow); of similar wall thickness costally and intercostally (walls of medium thickness). Mid-intercostal long-cells rectangular; having markedly sinuous walls (pitted). Microhairs present; elongated; clearly two-celled; panicoid-type (large, with long basal cells; the apical cells round-tipped, variable in length but all longer than in the chloridoid type). Microhair apical cell wall thinner than that of the basal cell and often collapsed. Microhair basal cells 30–42 microns long. Microhair total length/width at septum 5. Microhair apical cell/total length ratio 0.38. Stomata common. 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; crescentic, tall-and-narrow, and saddle shaped. Cushion-based macrohairs present. Costal short-cells conspicuously in long rows (very consistently). Costal silica bodies confined to the central file(s) of the costal zones, or present in alternate cell files of the costal zones; homogeneously saddle shaped.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+. PCR sheaths of the primary vascular bundles interrupted; interrupted both abaxially and adaxially. PCR sheath extensions absent. Mesophyll traversed by columns of colourless mesophyll cells (between all bundles). Leaf blade adaxially flat. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups (between all bundles); associated with colourless mesophyll cells to form deeply-penetrating fans. Combined sclerenchyma girders present (with all the bundles); forming figures (the primaries; minor bundles with scanty girders). Sclerenchyma all associated with vascular bundles. The lamina margins with fibres.
Cytology. Chromosome base number, x = 10 (n = 20). 2n = 40.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Boutelouinae (as a synonym of Bouteloua). 1 species (B. nervatus).
Distribution, phytogeography, ecology. Mexico.
Species of open habitats. Dry slopes.
References, etc. Morphological/taxonomic: Reeder, Reeder and Rzedowski 1965. Leaf anatomical: studied by us.
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’.