The grass genera of the world
Habit, vegetative morphology. Erect perennial; rhizomatous, or caespitose. Culms 50–150 cm high; herbaceous; sparsely branched above, or unbranched above. Culm nodes glabrous. Culm internodes hollow. Young shoots extravaginal. Leaves not basally aggregated; non-auriculate; without auricular setae. Leaf blades linear to lanceolate; broad; 10–20 mm wide (and 7 to 20 cm long); flat, or folded; not pseudopetiolate; without cross venation; persistent; rolled in bud. Ligule a fringed membrane; truncate. Contra-ligule absent.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets; exposed-cleistogamous, or chasmogamous.
Inflorescence. Inflorescence few spikeleted to many spikeleted; paniculate, or of spicate main branches (the primary branches reduced to racemes); open, or contracted; non-digitate; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets morphologically conventional, or unconventional (in having supernumerary proximal sterile lemmas); 5–35 mm long; cuneate; markedly compressed laterally; disarticulating above the glumes (or above the sterile lemmas); disarticulating between the florets; with conventional internode spacings. Rachilla prolonged beyond the uppermost female-fertile floret. Hairy callus present, or absent. Callus absent, or short.
Glumes two; very unequal to more or less equal; shorter than the spikelets; shorter than the adjacent lemmas; hairless (apart from the keel); pointed (acute, acuminate, or rarely mucronate); awnless; carinate; similar (rigid, compressed). Lower glume 3–7 nerved. Upper glume 3–7 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets, or both distal and proximal to the female-fertile florets. The distal incomplete florets merely underdeveloped. Spikelets with proximal incomplete florets. The proximal incomplete florets 1–6; paleate, or epaleate; sterile. The proximal lemmas awnless; 5–11 nerved (?); exceeded by the female-fertile lemmas; similar in texture to the female-fertile lemmas; not becoming indurated.
Female-fertile florets 2–12 (or occasionally reduced to one, in few-spikeleted inflorescences). Lemmas acute to acuminate; less firm than the glumes to similar in texture to the glumes (papery); not becoming indurated; entire; pointed; awnless; hairless; glabrous; carinate (sometimes markedly flattened); without a germination flap; 7–11 nerved. Palea present (rigid, bowed at the base); relatively long; entire; awnless, without apical setae; textured like the lemma; 2-nerved; 2-keeled. Palea keels narrowly winged, or wingless. Lodicules present; 2; free; fleshy; glabrous; not or scarcely vascularized. Stamens 1(–3); with free filaments. Ovary apically glabrous. Styles free to their bases. Stigmas 2; red pigmented.
Fruit, embryo and seedling. Fruit free from both lemma and palea (loosely enclosed); dark brown to black; compressed laterally. Hilum short. Embryo large. Endosperm hard; without lipid; containing only simple starch grains. Embryo with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.
First seedling leaf with a well-developed lamina. The lamina 7 veined.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Mid-intercostal long-cells rectangular, or rectangular and fusiform; having markedly sinuous walls, or having markedly sinuous walls and having straight or only gently undulating walls (in C. laxum). Microhairs present; panicoid-type; 42–54 microns long; 4.5–6 microns wide at the septum. Microhair total length/width at septum 7–11.3. Microhair apical cells 21–24(–33) microns long (C. latifolium), or 15–18 microns long (C. laxum). Microhair apical cell/total length ratio 0.31–0.33 (C. laxum), or 0.47–0.61 (C. latifolium). Stomata common; 15–21 microns long. Subsidiaries dome-shaped, or dome-shaped and triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common (fairly), or absent or very rare; not paired (solitary); not silicified. Costal short-cells conspicuously in long rows. Costal silica bodies panicoid-type.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with adaxial palisade, or without adaxial palisade (this not apparent in the two species seen); without arm cells; without fusoids. Leaf blade with distinct, prominent adaxial ribs to adaxially flat. Midrib conspicuous (conspicuously keeled or not); with one bundle only (larger than the rest), or having a conventional arc of bundles (the large median accompanied by small laterals); with colourless mesophyll adaxially (e.g. C. laxum), or without colourless mesophyll adaxially (e.g. C. latifolium). Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present (with all the bundles); forming figures (all the bundles with conspicuous anchors). Sclerenchyma all associated with vascular bundles.
Culm anatomy. Culm internode bundles in one or two rings, or scattered.
Cytology. Chromosome base number, x = 12. 2n = 24. 2 ploid. Nucleoli persistent.
Classification. Watson & Dallwitz (1994): Centothecoideae; Centotheceae. Soreng et al. (2015): Panicoideae; Chasmanthieae. 6 species.
Distribution, phytogeography, ecology. Southeastern U.S.A. and northern Mexico.
Shade species; glycophytic. Moist woodland to semiarid scrub.
References, etc. Morphological/taxonomic: Yates 1966b. Leaf anatomical: this project.
Illustrations. • C. laxum, as Uniola gracilis: Kunth (1835). • C. latifolium: Nicora & Rúgolo de Agrasar (1987)
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’.