The grass genera of the world
Habit, vegetative morphology. Arenicolous perennial; rhizomatous. Culms 50–120 cm high; herbaceous. Leaves not basally aggregated; non-auriculate. Leaf blades linear (to filiform); narrow; tapering to a fine point; rolled; without abaxial multicellular glands; not pseudopetiolate; without cross venation. Ligule present; a fringe of hairs; 1 mm long.
Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate (up to half the length of the culm); open; with capillary branchlets (these flexuous); espatheate; not comprising partial inflorescences and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 5–8 mm long; cuneate; compressed laterally; disarticulating above the glumes; disarticulating between the florets. Rachilla prolonged beyond the uppermost female-fertile floret. Hairy callus present (silky-pilose).
Glumes two; more or less equal (to somewhat unequal); shorter than the spikelets; shorter than the adjacent lemmas; hairless; glabrous; pointed; awnless; similar (narrow lanceolate, acuminate). Lower glume not two-keeled; 1 nerved. Upper glume 1 nerved. Spikelets without proximal incomplete florets.
Female-fertile florets 2–5. Lemmas not becoming indurated (papery); entire, or incised (sometimes tridentate); when incised not deeply cleft; awnless, or mucronate (the nerves sometimes excurrent, forming 3 minute teeth); hairless (but with a basal, hairy callus); carinate (compressed); without a germination flap; 3 nerved. Palea present; relatively long (as long as the lemma); 2-nerved. Lodicules present; 2; fleshy. Stamens 3 (?). Ovary apically glabrous. Stigmas 2.
Fruit, embryo and seedling. Fruit free from both lemma and palea; ellipsoid. Hilum short. Pericarp fused. Embryo large; with an epiblast; with a scutellar tail; with an elongated mesocotyl internode. Embryonic leaf margins overlapping.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous (the intercostal zones hidden in deep grooves). Papillae absent. Long-cells differing markedly in wall thickness costally and intercostally (the intercostals thinner walled). Mid-intercostal long-cells having straight or only gently undulating walls. Microhairs present; elongated; clearly two-celled; chloridoid-type. Microhair apical cell wall of similar thickness/rigidity to that of the basal cell. Microhairs 42–45 microns long. Microhair basal cells 33 microns long. Microhairs 9.6–12 microns wide at the septum. Microhair total length/width at septum 3.6–4.4. Microhair apical cells 6.9–10.5 microns long. Microhair apical cell/total length ratio 0.2–0.24. Stomata common; 18–21 microns long. Subsidiaries triangular. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells seemingly absent or very rare. Intercostal silica bodies absent. Costal short-cells conspicuously in long rows. Costal silica bodies present in alternate cell files of the costal zones; abundant, predominantly saddle shaped; not sharp-pointed.
Transverse section of leaf blade, physiology. Lamina mid-zone in transverse section open.
C4. The anatomical organization somewhat unusual, in that the PCR sheaths are often bifurcated in the outer parts of the adaxial ribs, by intrusion of the adaxial sclerenchyma girder. XyMS+. PCR sheath outlines even. PCR sheaths of the primary vascular bundles interrupted; interrupted laterally. PCR sheath extensions present. Maximum number of extension cells 12 (or more, not uniseriate but in the form of an adaxial block of PCR cells which is either partially or completely interrupted by the sclerenchyma girder). PCR cell chloroplasts centripetal. Mesophyll traversed by columns of colourless mesophyll cells (in each intercostal zone). Leaf blade nodular in section; with the ribs more or less constant in size (tall, somewhat hollowed at the sides). Midrib not readily distinguishable; with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms present in discrete, regular adaxial groups; associated with colourless mesophyll cells to form deeply-penetrating fans (these linking with the traversing columns of colourless cells). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders present; forming figures (all the bundles with a large I or anchor, though in many the adaxial sclerenchyma mass is interrupted by PCR tissue). Sclerenchyma all associated with vascular bundles.
Classification. Watson & Dallwitz (1994): Chloridoideae; main chloridoid assemblage. Soreng et al. (2015): Chloridoideae; Cynodonteae; Muhlenbergiinae (as a synonym of Muhlenbergia). 1 species (R. flexuosa).
Distribution, phytogeography, ecology. Central U.S.A..
Xerophytic; species of open habitats. Inland sandhills.
Rusts and smuts. Rusts Puccinia. Smuts from Tilletiaceae. Tilletiaceae Tilletia.
References, etc. Leaf anatomical: studied by us.
Illustrations. • R. flexuosa: Lamson-Scribner, American Grasses (1897). • R. flexuosa: 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’.