The grass genera of the world
~ Cathestechum, Bouteloua sensu lato
Habit, vegetative morphology. Short, erect, delicate perennial; caespitose. Culms about 40–50 cm high; herbaceous; unbranched above. Culm nodes minutely hairy. Leaves mostly basal; non-auriculate. Leaf blades linear; narrow; about 1–2 mm wide (and 5–6 cm long); flat; without abaxial multicellular glands; without cross venation. Ligule a fringe of hairs.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets (at least the first floret of the central spikelet of the triplet being usually hermaphrodite), or without hermaphrodite florets. The spikelets of sexually distinct forms on the same plant to all alike in sexuality; hermaphrodite, or hermaphrodite and male-only, or hermaphrodite, male-only, and sterile, or female-only, male-only, and sterile (the lateral spikelets of the triplets tending to be staminate or sterile, the central one hermaphrodite or occasionally female); homomorphic.
Inflorescence. Inflorescence a false spike, with spikelets on contracted axes (a raceme of spikes, each reduced to three spikelets). Inflorescence axes not ending in spikelets (the main branches bare-tipped, the clusters with the rachis prolonged as a short, sometimes winged awn). Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes disarticulating; falling entire (the triplets falling). Spikelets subtended by solitary bristles (i.e. by the rachis prolongation); in triplets; secund (the main branches on one side of the culm).
Female-fertile spikelets. Spikelets 2–2.5 mm long; compressed laterally; falling with the glumes (the triplets falling whole); disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret; hairy; the rachilla extension with incomplete florets. Hairy callus present (constituted by the hairy axis of the triplet).
Glumes two; very unequal (but the G1 longer than in Cathesticum sensu stricto); shorter than the spikelets; (the upper) long relative to the adjacent lemmas; hairy (the G1 hirsute); pointed (G1 acuminate, G2 trullate); awnless; very dissimilar (G1 acuminate, G2 trullate). Lower glume about 0.7 times the length of the upper glume; 1 nerved (?). Upper glume 1 nerved (?). Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets (the first floret being female or hermaphrodite, the second hermaphrodite or male or sterile, the remaining 2–3 florets sterile). The distal incomplete florets 2–4; clearly specialised and modified in form (for dispersal); awned (the terminal florets being reduced to multiple-awned lemmas).
Female-fertile florets 1–2. Lemmas similar in texture to the glumes (thin); not becoming indurated; incised; 3 lobed; deeply cleft to not deeply cleft (less deeply than in the upper, sterile florets); awned, or mucronate. Awns 3, or 5 (the lowermost lemma 3 awned, the others 3 to 9 awned, the awn number increasing with the degree of sterility); median and lateral; the median similar in form to the laterals; apical; non-geniculate; much shorter than the body of the lemma. The lateral awns shorter than the median. Lemmas hairy (with a few scattered hairs); non-carinate; 3 nerved. Palea present; relatively long; apically notched; with apical setae, or awned; not indurated; 2-nerved; 2-keeled. Palea keels wingless. Lodicules present; 2; free; fleshy; glabrous. Stamens 0, or 3. Ovary apically glabrous. Stigmas 2.
Fruit, embryo and seedling. Fruit ellipsoid; compressed dorsiventrally. Hilum short. Pericarp fused. Embryo large; with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins meeting.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent (?). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhair basal cells 15–18 microns long. Microhair total length/width at septum 5–6. Microhair apical cell/total length ratio about 0.4. Stomata common. Subsidiaries mostly dome-shaped (?). Intercostal short-cells not paired. Intercostal silica bodies absent. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; saddle shaped.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4. PCR sheath outlines even. 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. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (these linked with traversing columns of colourless cells). The lamina margins with fibres.
Cytology. Chromosome base number, x = 10; 2 ploid.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae. 1 species (G. multifidum).
Distribution, phytogeography, ecology. Mexico.
Xerophytic; species of open habitats. Dry scrub.
References, etc. Morphological/taxonomic: Pierce 1978. Leaf anatomical: Pierce 1978.
Illustrations. • Spikelet cluster, spiklets, lemmas (G. multifidum): Pierce, 1978
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’.