The grass genera of the world
Habit, vegetative morphology. Annual, or perennial; caespitose. Culms herbaceous; unbranched above. Culm nodes glabrous. Culm internodes solid. Leaves not basally aggregated; non-auriculate. Leaf blades broad; without cross venation; persistent. Ligule a fringed membrane; truncate; 1.5 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; without hermaphrodite florets (the second floret being female-only).
Inflorescence. Inflorescence of spicate main branches; open. Inflorescence axes not ending in spikelets. Rachides hollowed. Inflorescence espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets subtended by solitary bristles (each subtended and exceeded by a single, sticky bristle). The bristles persisting on the axis. Spikelets solitary; secund (the branches dorsiventral).
Female-fertile spikelets. Spikelets 3.5 mm long; abaxial; compressed dorsiventrally; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.
Glumes two; very unequal; (the longer) long relative to the adjacent lemmas (almost equalling the spikelet, the lower much shorter); dorsiventral to the rachis; hairless; glabrous; pointed; awnless; non-carinate; similar (herbaceous). Lower glume 3 nerved. Upper glume 11 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets (the latter being female-only). The proximal incomplete florets 1; paleate. Palea of the proximal incomplete florets fully developed; becoming conspicuously hardened and enlarged laterally (hyaline at first, then developing expanded leathery flanks and winged keels clasping the upper floret). The proximal incomplete florets male. The proximal lemmas awnless; 5 nerved; decidedly exceeding the female-fertile lemmas; less firm than the female-fertile lemmas (cartilaginous); not becoming indurated.
Female-fertile florets 1. Lemmas decidedly firmer than the glumes; minutely striate; not becoming indurated (tough); mucronate; hairless; non-carinate; having the margins inrolled against the palea; with a clear germination flap; 5 nerved. Palea present (firm, rugulose between the veins); relatively long; tightly clasped by the lemma (enclosed by it at its tip); 2-nerved; 2-keeled. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 0. Ovary apically glabrous. Styles basally fused. Stigmas 2; red pigmented.
Fruit, embryo and seedling. Fruit free from both lemma and palea; small (about 3 mm long); compressed dorsiventrally. Hilum short. Embryo large; waisted. Endosperm hard.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally; of similar wall thickness costally and intercostally. Intercostal zones exhibiting many atypical long-cells (many being quite short). Mid-intercostal long-cells intercostal long-cells variable - some rectangular, some fusiform, many short; having markedly sinuous walls. Microhairs present; panicoid-type; 49–51 microns long; 8.4–9 microns wide at the septum. Microhair total length/width at septum 5.7–6.1. Microhair apical cells 31.5–36 microns long. Microhair apical cell/total length ratio 0.62–0.71. Stomata common; 37.5–48 microns long. Subsidiaries mostly dome-shaped. Guard-cells overlapped by the interstomatals, or overlapping to flush with the interstomatals. Intercostal short-cells absent or very rare. Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type; short butterfly shaped and dumb-bell shaped, or cross shaped.
Transverse section of leaf blade, physiology. C4; XyMS (median midrib bundle XyMS+, the rest XyMS-). Leaf blade nodular in section; with the ribs more or less constant in size. Midrib conspicuous; having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups (in places, but the epidermis mostly irregularly bulliform); occasionally in simple fans. Many of the smallest vascular bundles unaccompanied by sclerenchyma. Combined sclerenchyma girders present.
Classification. Watson & Dallwitz (1994): Panicoideae; Panicodae; Paniceae. Soreng et al. (2015): Panicoideae; Panicodae; Paniceae; Cenchrinae. 2–3 species.
Distribution, phytogeography, ecology. Mexico.
Species of open habitats. Weedy places.
Rusts and smuts. Rusts Puccinia. Taxonomically wide-ranging species: Puccinia chaetochloae.
References, etc. Leaf anatomical: studied by us - I. unisetus (Presl) Schlecht.
Illustrations. • I. unisetus: Hitchcock (1936). • Germination flap of I. unisetus: this project. Ixophorus unisetus. Plateau-like germination flap. • I. unisetus, 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: 11th December 2017. delta-intkey.com/grass’.