The grass genera of the world
Habit, vegetative morphology. Perennial; with thick rhizomes. Culms 150–300 cm high (often floating and thickened); herbaceous. Culm internodes solid. Rhizomes pachymorph. Plants unarmed. Leaves mostly basal; non-auriculate. Leaf blades broad; 10–26 mm wide (?-up to 2.6 cm broad and 80 cm long); without abaxial multicellular glands; without cross venation; persistent. Ligule a fringed membrane. Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence of spicate main branches and paniculate (a narrow panicle of numerous spike-like branches, tending to verticils); espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes spikelike; disarticulating, or persistent; if deciduous falling entire. Spikelets solitary; not secund; pedicellate.
Female-fertile spikelets. Spikelets 6–15 mm long; adaxial; compressed laterally; falling with the glumes and disarticulating above the glumes (falling with the pedicels, but the rachilla also disarticulating tardily); not disarticulating between the florets (or only tardily so). Rachilla prolonged beyond the uppermost female-fertile floret; hairless; the rachilla extension with incomplete florets. Hairy callus absent.
Glumes two; more or less equal; long relative to the adjacent lemmas; dorsiventral to the rachis; hairless (minutely scabrid); pointed (lanceolate-acuminate); awned (acuminate into the straight awns); carinate; similar. Lower glume 1 nerved. Upper glume 1 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped.
Female-fertile florets 2–20. Lemmas similar in texture to the glumes; not becoming indurated (leathery); entire; pointed; awnless (but cuspidate); hairless; glabrous; carinate; without a germination flap; 3 nerved. Palea present; relatively long; entire; awnless, without apical setae; not indurated (leathery or membranous); 2-nerved; 2-keeled. Lodicules present (minute); 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 3. Anthers very small; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles fused. Stigmas 2.
Fruit, embryo and seedling. Fruit subterete. Hilum short (presumably). Pericarp fused (presumably). Embryo large.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular; having markedly sinuous walls. Microhairs present; more or less spherical to elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs (27–)28.5–30(–33) microns long. Microhair basal cells 21 microns long. Microhairs 12.6–15.6 microns wide at the septum. Microhair total length/width at septum 1.8–2.3. Microhair apical cells 6–9 microns long. Microhair apical cell/total length ratio 0.22–0.29. Stomata common (very abundant, closely packed); 18–21 microns long. Subsidiaries dome-shaped (mostly), or triangular (a few). Guard-cells overlapping to flush with the interstomatals (but the ends of the subsidiaries tending to be overlapped by the corners of the interstomatals). Intercostal short-cells common; in cork/silica-cell pairs and not paired; silicified. Intercostal silica bodies present and perfectly developed; saddle shaped. Costal short-cells predominantly paired (and in short rows), or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies present in alternate cell files of the costal zones; saddle shaped (mostly), or crescentic (a few, over the larger veins); not sharp-pointed.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4; XyMS+ (the mestome sheath cells very thick-walled). PCR sheaths of the primary vascular bundles interrupted; interrupted both abaxially and adaxially. PCR sheath extensions present. Maximum number of extension cells 6. Mesophyll traversed by columns of colourless mesophyll cells. Leaf blade adaxially flat. Midrib conspicuous (with adaxial lacunae); having a conventional arc of bundles (several); with colourless mesophyll adaxially (and lacunae). Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (these linking with traversing columns of colourless cells). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures (anchors). Sclerenchyma not all bundle-associated. The extra sclerenchyma in abaxial groups.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae. 1 species (M. wightiana).
Distribution, phytogeography, ecology. Indo-China, Thailand, Malay Peninsula, Indonesia, also India, Burma and Ceylon.
Hydrophytic to helophytic; halophytic (in brackish water and tidal river margins).
References, etc. Leaf anatomical: studied by us.
Illustrations. • M. wightiana, 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’.