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The grass genera of the world

L. Watson, T.D. Macfarlane, and M.J. Dallwitz

Rhizocephalus Boiss.

From the Greek rhiza (root) and cephale (head), re the almost sessile heads of spikelets.

Habit, vegetative morphology. Dwarf annual. Culms 1–3 cm high (i.e., almost without culms); herbaceous. Leaves mostly basal; non-auriculate. Leaf blades linear-lanceolate; narrow; 1–4 mm wide; flat, or folded; without cross venation. Ligule an unfringed membrane; not truncate; 2 mm long.

Reproductive organization. Plants bisexual, all with bisexual spikelets; with hermaphrodite florets. The spikelets all alike in sexuality.

Inflorescence. Inflorescence paniculate; contracted; capitate; espatheate (but the head-like panicles partly concealed among the leaves); not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund (?); shortly pedicellate.

Female-fertile spikelets. Spikelets 3–7 mm long; not noticeably compressed; falling with the glumes. Rachilla terminated by a female-fertile floret. Hairy callus absent.

Glumes two; more or less equal; shorter than the adjacent lemmas; shortly hairy (with clavate hairs); pointed (acute); awnless; non-carinate; similar (thinly learthery). Lower glume 3 nerved. Upper glume 3 nerved. Spikelets with female-fertile florets only; without proximal incomplete florets.

Female-fertile florets 1. Lemmas acuminate; decidedly firmer than the glumes; not becoming indurated; entire; pointed; awnless, or mucronate; hairy; carinate; without a germination flap; 5 nerved (the lateral nerves much thickened). Palea present; relatively long; entire (lanceolate); awnless, without apical setae; thinner than the lemma; not indurated (hyaline); 2-nerved; 2-keeled, or keel-less. Lodicules absent. Stamens 2. Anthers 0.5–0.8 mm long; not penicillate; without an apically prolonged connective. Ovary apically glabrous. Styles fused. Stigmas 2.

Fruit, embryo and seedling. Fruit small (about 2 mm long); ellipsoid (rostrate); compressed dorsiventrally. Hilum short. Embryo small.

Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells fairly similar in shape costally and intercostally (the costals smaller); of similar wall thickness costally and intercostally to differing markedly in wall thickness costally and intercostally (the costals somewhat thicker walled). Mid-intercostal long-cells rectangular and fusiform; having markedly sinuous walls to having straight or only gently undulating walls (heavily pitted, the sinuosity fine, more apparent at lower levels of focus). Microhairs absent. Stomata common (in quite deep depressions between the interstomatals, the guard-cells quite sausage-shaped); (33–)36–42(–45) microns long. Subsidiaries non-papillate; parallel-sided. Guard-cells overlapped by the interstomatals. Intercostal short-cells absent or very rare. With a few blunt costal prickles. Costal short-cells neither distinctly grouped into long rows nor predominantly paired (mostly solitary). Costal silica bodies present and well developed; horizontally-elongated crenate/sinuous and horizontally-elongated smooth (numerous, often quite irregular).

Transverse section of leaf blade, physiology. C3; XyMS+. Leaf blade with distinct, prominent adaxial ribs; with the ribs more or less constant in size. Midrib conspicuous to not readily distinguishable (fairly obvious from the infolding of the blade, but scarcely so from bundle size or sclerenchyma layout); with one bundle only. The lamina symmetrical on either side of the midrib. Bulliforms not present in discrete, regular adaxial groups (no bulliforms apparent). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent (each bundle limited to small abaxial and adaxial strands). Sclerenchyma all associated with vascular bundles.

Cytology. Chromosomes ‘large’.

Classification. Watson & Dallwitz (1994): Pooideae; Poodae; Aveneae. Soreng et al. (2015): Pooideae; Poodae; Poeae; Poinae. 2 species.

Distribution, phytogeography, ecology. Southwest and central Asia.

Xerophytic; species of open habitats. Arid places.

References, etc. Leaf anatomical: this project.

Illustrations. • R. orientalis: Fl. Iraq, 1968

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.’.