The grass genera of the world
Habit, vegetative morphology. Perennial; caespitose. The flowering culms leafy (but differing from the non-flowering culms in having elongated internodes). Culms 30–60 cm high (usually erect, sometimes decumbent to ascending); herbaceous; to 0.26 cm in diameter; unbranched above (seemingly). Leaves not basally aggregated; auriculate; with auricular setae (or at least, the auricles pilose). Leaf blades linear; narrow; 2–3.1 mm wide (and 3–7 cm long); flat, or rolled (inrolled or involute); not pseudopetiolate; without cross venation; persistent (the senescent tips becoming spirally coiled). Ligule present; a fringed membrane.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; contracted (spikelike, with short, rigid, closely appressed primary branches); spicate; spatheate; a complex of partial inflorescences and intervening foliar organs (in that the lowermost spikelets of primary branches are often subtended by a 0.5–3.5 mm scale). Spikelet-bearing axes persistent. Spikelets solitary; not secund.
Female-fertile spikelets. Spikelets 8–16 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets; with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret; hairless.
Glumes two; more or less equal (subequal, the G1 being slightly longer); shorter than the adjacent lemmas; hairless; awnless; seemingly non-carinate (but the nerves protruding abaxially); similar (pale green, chartaceous, with hyaline margins). Lower glume 7 nerved, or 9 nerved. Upper glume 7 nerved, or 9 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets, or both distal and proximal to the female-fertile florets (the lowemost floret staminate or perfect, the upper florets male or neuter). The distal incomplete florets usually several; merely underdeveloped. The proximal incomplete florets when present, 1; when present, paleate; when present, male. The proximal lemmas awnless; 7 nerved, or 9 nerved; exceeded by the female-fertile lemmas; similar in texture to the female-fertile lemmas (rigid, chartaceous); not becoming indurated.
Female-fertile florets 1, or 2 (the second, and sometimes the third). Lemmas similar in texture to the glumes (rigid, chartaceous, with hyaline margins); not becoming indurated; entire; awnless; glabrous except for a tuft near the callus; non-carinate (seemingly, though the nerves prominent); without a germination flap (or at least, no flap mentioned); 7 nerved, or 9 nerved. Palea present; relatively long to conspicuous but relatively short (subequal with to 3mm shorter than the lemma); apically notched (the teeth 0.3–0.4 mm long); awnless, without apical setae; texture unstated; not indurated; 2-nerved; sharply 2-keeled. Lodicules present; 2; free; glabrous; regularly 3-lobed; not or scarcely vascularized (obscurely 3 nerved). Stamens 1 (anterior to the pistil). Anthers 1.5–2.1 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Stigmas 2; red pigmented.
Fruit, embryo and seedling. Fruit small (about 3 mm long); compressed laterally (ovate to triangular in section). Hilum short (probably, but unstated). Pericarp fused (yellow brown above, golden brown below). Embryo small (1/5 of the caryopsis length); with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the costals much narrower). Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; panicoid-type. Stomata common. Subsidiaries triangular. Intercostal short-cells absent or very rare (seemingly). Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type; cross shaped and dumb-bell shaped.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma; seemingly without arm cells; without fusoids. Leaf blade with distinct, prominent adaxial ribs to nodular in section. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures. Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 12. 2n = 24. 2 ploid.
Classification. Watson & Dallwitz (1994): Centothecoideae; Centotheceae. Soreng et al. (2015): Panicoideae; Chasmanthieae. 1 species.
Distribution, phytogeography, ecology. Mexico.
Xerophytic; species of open habitats. In desert scrub.
References, etc. Morphological/taxonomic: Valdés, Morden and Hatch 1986.
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’.