The grass genera of the world
Habit, vegetative morphology. Perennial; caespitose. Culms 70–90 cm high; herbaceous; unbranched above. Culm nodes glabrous. Young shoots intravaginal. Leaves auriculate (with long sheath auricles). Leaf blades narrow; setaceous; rolled (pungent); without cross venation. Ligule an unfringed membrane; truncate, or not truncate; 1–4 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence few spikeleted; paniculate (spiciform); contracted; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets paired; not secund; pedicellate.
Female-fertile spikelets. Spikelets 12–19 mm long; not noticeably compressed; disarticulating above the glumes. Rachilla prolonged beyond the uppermost female-fertile floret; the rachilla extension with incomplete florets. Hairy callus present. The callus hairs white (long). Callus short (1–1.2 mm long); blunt.
Glumes two; very unequal, or more or less equal; (the longer) long relative to the adjacent lemmas; hairless; pointed (acuminate); awned, or awnless; non-carinate; similar (membranous). Lower glume 7–9 nerved. Upper glume 7–9 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.
Female-fertile florets 2–3. Lemmas similar in texture to the glumes; not becoming indurated; incised; 2 lobed; deeply cleft (notched); awned. Awns 1 (but with short setae terminating the lateral lobes); median; from a sinus (the notch deep); geniculate; hairless (scabrid); about as long as the body of the lemma to much longer than the body of the lemma. Lemmas hairy (beneath the insertion of the awn); non-carinate; without a germination flap; 7 nerved. Palea present; relatively long; apically notched; awnless, without apical setae (but apically ciliate); 2-nerved; 2-keeled. Lodicules present; 3; free; membranous (stipoid, the posterior smaller); glabrous; not toothed; heavily vascularized (the anterior pair). Stamens 2. Anthers 1.5–2 mm long. Ovary apically hairy. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Hilum long-linear. Embryo small; with an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins overlapping.
Abaxial leaf blade epidermis. Costal/intercostal zonation lacking. 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 (thick, pitted). Microhairs absent. Stomata absent or very rare. Intercostal short-cells common; mostly in cork/silica-cell pairs; silicified. Costal short-cells predominantly paired. Costal silica bodies rounded, or tall-and-narrow, or crescentic (mostly rounded, tall-and-narrow or crescentic, but the silica cells often cross- to dumb-bell shaped); not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with radiate chlorenchyma; without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs; with the ribs very irregular in sizes. Midrib not readily distinguishable; with one bundle only. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles); forming figures (all bundles). Sclerenchyma not all bundle-associated. The extra sclerenchyma in a continuous abaxial layer.
Cytology. Chromosome base number, x = and chromosome size seemingly unknown.
Classification. Watson & Dallwitz (1994): Stipoideae, or Pooideae, or Arundinoideae; if pooid, Poodae; Aveneae; if stipoid, Stipeae; if arundinoid, Danthonieae. Soreng et al. (2015): Pooideae; Phaenospermateae. 1 species.
Distribution, phytogeography, ecology. Mexico.
Species of open habitats. Stony hillsides.
References, etc. Morphological/taxonomic: Tateoka 1964b; Conert 1960; Clayton 1985. Leaf anatomical: this project.
Special comments. A taxonomic puzzle - cf. Danthoniastrum? The embryo structure as described by Tateoka (1964) is emphatically not pooid, the lodicules are stipoid, and the leaf anatomical evidence (see above) is ambiguous. Reliable taxonomic assignment requires that adaxial leaf epidermis, glumes, lemmas and lodicules be examined for microhairs, and that cytological information be obtained. Illustrations. • M. mexicana, abaxial epidermis of leaf blade: this project. • M. mexicana, 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: 13th November 2017. delta-intkey.com/grass’.