The grass genera of the world
Including Colobanthium (Reichenb.) Taylor, Colobanthus (Trin.) Spach, Reboulea Kunth
Habit, vegetative morphology. Perennial (usually), or annual; caespitose. Culms 30–120 cm high; herbaceous. Culm internodes hollow. Leaves not basally aggregated; non-auriculate. Leaf blades narrow; mostly flat; not pseudopetiolate; without cross venation; rolled in bud. Ligule an unfringed membrane; truncate; 0.5–4 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; open, or contracted; with capillary branchlets, or without capillary branchlets; espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 1.5–5 mm long; compressed laterally; falling with the glumes; not disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret (as a bristle); the rachilla extension naked. Hairy callus absent.
Glumes present; two; very unequal to more or less equal; long relative to the adjacent lemmas; awnless; carinate; very dissimilar (rather leathery with thin margins, the G1 narrow-lanceolate and acute, the G2 broader and oblanceolate or obovate). Lower glume 1–3 nerved. Upper glume 3–5 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets distal to the female-fertile florets. Spikelets without proximal incomplete florets.
Female-fertile florets (1–)2(–3). Lemmas similar in texture to the glumes; not becoming indurated; entire; pointed; awnless, or mucronate, or awned. Awns when present, 1; dorsal; from near the top; geniculate; hairless (scabrid); much shorter than the body of the lemma to about as long as the body of the lemma. Lemmas hairless; non-carinate (dorsally rounded); without a germination flap; 3–5 nerved. Palea present; relatively long; gaping; thinner than the lemma; not indurated (hyaline); 2-nerved; 2-keeled. Lodicules present; free; membranous; glabrous; toothed, or not toothed; not or scarcely vascularized. Stamens 3. Anthers 0.3–0.7 mm long. Ovary apically glabrous. Styles free to their bases. Stigmas 2.
Fruit, embryo and seedling. Embryo small. Endosperm liquid in the mature fruit. Embryo with an epiblast; without a scutellar tail; with a negligible mesocotyl internode. Embryonic leaf margins meeting.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (costals shorter); of similar wall thickness costally and intercostally. Mid-intercostal long-cells rectangular and fusiform; having straight or only gently undulating walls. Microhairs absent. Stomata common (in files adjoining the veins); 27–33 microns long. Subsidiaries low dome-shaped, or parallel-sided. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare. Rows of prickles present costally. Costal short-cells neither distinctly grouped into long rows nor predominantly paired (the rows interrupted by prickles). Costal silica bodies abundant, horizontally-elongated crenate/sinuous; not sharp-pointed.
Transverse section of leaf blade, physiology. C3; XyMS+. Mesophyll with non-radiate chlorenchyma. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Bulliforms present in discrete, regular adaxial groups; in simple fans. All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present. Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 7. 2n = 14. 2 ploid.
Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Aveneae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Aveninae. 5 species.
Distribution, phytogeography, ecology. North America, West Indies.
Helophytic, or mesophytic, or xerophytic; shade species, or species of open habitats; glycophytic. Woodland, marshes, prairies.
Hybrids. Intergeneric hybrids with Trisetum.
Rusts and smuts. Rusts Puccinia. Taxonomically wide-ranging species: Puccinia graminis and Puccinia striiformis.
References, etc. Leaf anatomical: studied by us - S. obtusata (Michx.) Scribner.
Illustrations. • S. obtusata, as Reboulea gracilis: Kunth (1835). • S. obtusata: Hitchcock and Chase (1950)
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’.