The grass genera of the world
~ Bouteloua sensu lato
Habit, vegetative morphology. Annual, or perennial; stoloniferous, or decumbent. Culms 10–40 cm high; herbaceous; branched above, or unbranched above. Culm internodes solid. Plants unarmed. Young shoots intravaginal. Leaves mostly basal; non-auriculate. Leaf blades linear; narrow; 0.5–2 mm wide; setaceous, or not setaceous; without abaxial multicellular glands; without cross venation; persistent. Ligule present; a fringe of hairs (dense).
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets (the lower floret of the central spikelet commonly hermaphrodite), or without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant; hermaphrodite, male-only, and sterile, or female-only, male-only, and sterile (in triplets, the two lower spikelets usually male or neuter, the central one female-fertile). The male and female-fertile spikelets mixed in the inflorescence. The spikelets usually overtly heteromorphic (the laterals more or less rudimentary).
Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (a raceme of cuneate spikes, each reduced to three spikelets). Inflorescence axes not ending in spikelets (in that the ostensibly terminal triplet is subtended by a more or less bifid bristle of a quarter to half its length). Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes disarticulating; falling entire (the triplets fall entire, leaving the short pedicel on the rachis). Spikelets subtended by solitary bristles (i.e. the rachis prolongation). The bristles deciduous with the spikelets. Spikelets in triplets; pedicellate; consistently in long-and-short combinations (the lateral spikelets shorter pedicelled, the central longer-pedicelled); unequally pedicellate in each combination. The shorter spikelets male-only, or sterile. The longer spikelets hermaphrodite, or female-only.
Female-sterile spikelets. The lower two spikelets of each triplet male or neuter. These with two florets, the lower often having three stamens with apiculate thecae, the upper usually much reduced. The male spikelets 2 floreted. Male florets 3 staminate.
Female-fertile spikelets. Spikelets about 4 mm long; compressed laterally; falling with the glumes (i.e. the triplets falling). Rachilla prolonged beyond the uppermost female-fertile floret; hairy; the rachilla extension with incomplete florets. Hairy callus present (the axis of the triplet being densely hairy, constituting a callus at the disarticulation).
Glumes two; very unequal; shorter than the spikelets; (the upper) long relative to the adjacent lemmas (approximately equalling them); hairy (G2 only, the G1 being glabrous); pointed (G2 mucronate), or not pointed (G1); awned (G2 sometimes awn-tipped), or awnless; carinate (G2), or non-carinate (G1); very dissimilar (G1 short, truncate, flabellate, glabrous; G2 narrow, awn-tipped or lanceolate, hairy). Lower glume to about 0.25 times the length of the upper glume; 0 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets (the lowermost of the three florets hermaphrodite or female-only, the upper two male or neuter). The distal incomplete florets 2; awned (but without the multiple awning of Griffithsochloa). Spikelets without proximal incomplete florets.
Female-fertile florets 1. Lemmas similar in texture to the glumes (thin); not becoming indurated; incised (the apical, sterile lemmas usually more deeply lobed); usually 4 lobed; deeply cleft (usually 4-partite); awned (the nerves usually extending into short awns). Awns 3; median and lateral; the median similar in form to the laterals; from a sinus; non-geniculate; hairless (scabrid); much shorter than the body of the lemma to about as long as the body of the lemma. The lateral awns shorter than the median to about equalling the median. Lemmas hairy (finely pilose on the back); non-carinate; without a germination flap; 3 nerved. Palea present; relatively long; apically notched; with apical setae to awned; not indurated (thin); 2-nerved; 2-keeled. Lodicules present; 2; free; fleshy; glabrous. Stamens 0, or 3. Ovary apically glabrous. Styles free to their bases (the stigmas densely plumose). Stigmas 2.
Fruit, embryo and seedling. Fruit ellipsoid.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls (pitted). Microhairs present; elongated; clearly two-celled; chloridoid-type (but thin walled, tending to collapse). Microhair apical cell wall thinner than that of the basal cell but not tending to collapse to of similar thickness/rigidity to that of the basal cell. Microhair basal cells 21–36 microns long. Microhair total length/width at septum 3–5. Microhair apical cell/total length ratio 0.3–0.4. Stomata common (in deep grooves). Subsidiaries dome-shaped. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs and not paired; silicified. Intercostal silica bodies present and perfectly developed; tall-and-narrow. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; very consistently saddle shaped.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+ (mestome sheath cells thick walled). 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 nodular in section to adaxially flat (large, rounded abaxial ribs); with the ribs more or less constant in size. 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. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (adaxially with strands only, but abaxially with big anchor-shaped girders). Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 10. 2n = 60.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Boutelouinae (as a synonym of Bouteloua). 6 species.
Distribution, phytogeography, ecology. Southern U.S.A., Mexico.
Species of open habitats. Scrub on dry hills.
Rusts and smuts. Rusts Puccinia. Taxonomically wide-ranging species: Puccinia cacabata and Puccinia boutelouae. Smuts from Tilletiaceae. Tilletiaceae Tilletia.
References, etc. Morphological/taxonomic: Griffiths 1912. Leaf anatomical: this project.
Special comments. Fruit data wanting. Illustrations. • Spikelet details. • Spikelet details. • C. erectum, TS 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: 13th November 2017. delta-intkey.com/grass’.