The grass genera of the world
Habit, vegetative morphology. Perennial; caespitose. Culms herbaceous. Leaves non-auriculate. Sheath margins free. Leaf blades narrow; setaceous; without cross venation. Ligule present; an unfringed membrane; truncate; 0.5 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; open; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund.
Female-fertile spikelets. Spikelets 10–15 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 absent.
Glumes present; two; more or less equal; long relative to the adjacent lemmas (exceeding the L1); pointed (acute); awnless; non-carinate; similar. Lower glume 3 nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets.
Female-fertile florets 2–5. Lemmas similar in texture to the glumes; not becoming indurated; incised; awned. Awns 1; median; from a sinus; non-geniculate; entered by one vein. Lemmas hairless; non-carinate; without a germination flap; 5 nerved. Palea present; relatively long; 2-nerved; 2-keeled. Lodicules present; 2; free; membranous; glabrous; toothed; not or scarcely vascularized. Stamens 3. Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Fruit small (5 mm long); deep purple; compressed dorsiventrally. Hilum long-linear. Embryo small. Endosperm hard; with lipid; containing compound starch grains. Embryo with an epiblast.
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 (walls thick, conspicuously pitted). Microhairs absent. Stomata absent or very rare. Intercostal short-cells common; in cork/silica-cell pairs (in H. fragilis), or in cork/silica-cell pairs and not paired (commonly solitary, in H. livida); silicified. Intercostal silica bodies tall-and-narrow, or crescentic, or oryzoid-type, or rounded. Costal short-cells predominantly paired (in H. fragilis), or neither distinctly grouped into long rows nor predominantly paired (mostly solitary but some paired, in H. livida). Costal silica bodies rounded (H. fragilis), or tall-and-narrow (especially H. livida), or crescentic (conspicuous in IH. fragilis), or oryzoid (tall-and-narrows expanded top and bottom, in H. livida).
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll without adaxial palisade. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (most with a small adaxial strand in the top of the overlying rib, and none in contact with the abaxial fibres). Sclerenchyma not all bundle-associated. The extra sclerenchyma in abaxial groups, or in a continuous abaxial layer (this 2–3 cells thick); (when non-continuous) abaxial-hypodermal, the groups isolated (opposite the furrows).
Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Poeae. Soreng et al. (2015): cf. Pooideae; Poodae; Poeae; Loliinae. 2 species.
Distribution, phytogeography, ecology. Mexico, Venezuela.
References, etc. Morphological/taxonomic: Alekseev 1984. Leaf anatomical: 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’.