Centropodia Reichenb.
Including Asthenatherum Nevski
Habit, vegetative morphology. Annual, or perennial (with glaucous stems and leaves); caespitose to decumbent. Culms 3–150 cm high; herbaceous; unbranched above (but often branched near the base). Culm nodes hairy, or glabrous. Culm internodes solid. Plants unarmed. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate. Leaf blades linear-lanceolate; narrow; 1–5 mm wide; flat, or rolled (convolute, stiff, pungent); without cross venation; persistent; a fringe of hairs; about 1.5 mm long. Contra-ligule absent.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate; contracted; spicate; enclosed by spathe-like upper leaf sheaths; not comprising ‘partial inflorescences’ and foliar organs. Spikelet-bearing axes persistent. Spikelets not secund; pedicellate.
Female-fertile spikelets. Spikelets 7–10 mm long; compressed laterally; disarticulating above the glumes; disarticulating between the florets; with a distinctly elongated rachilla internode between the glumes. Rachilla prolonged beyond the uppermost female-fertile floret; hairless. Hairy callus present. Callus long; pungently pointed.
Glumes two; more or less equal; exceeding the spikelets; long relative to the adjacent lemmas (enclosing the spikelet); hairless; pointed; awnless; carinate, or non-carinate; similar (papery to leathery). Lower glume much exceeding the lowest lemma; 5–11 nerved. Upper glume 5–11 nerved. Spikelets with female-fertile florets only, or with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped; awned. Spikelets without proximal incomplete florets.
Female-fertile florets 2–5. Lemmas similar in texture to the glumes (papery); not becoming indurated; incised; 2 lobed; deeply cleft; awned. Awns 1, or 3; median, or median and lateral (by small straight extensions from the lobes); the median different in form from the laterals (when laterals present); from a sinus; geniculate; much shorter than the body of the lemma to about as long as the body of the lemma; entered by one vein. The lateral awns shorter than the median (and straight). Lemmas hairy. The hairs in tufts (6 to 8 bristle-tipped tufts); in transverse rows (with a transverse row of tufts level with the base of the awn, as well as longitudinal rows of hairs). Lemmas non-carinate; without a germination flap; 7–11 nerved; with the nerves non-confluent. Palea present; relatively long (almost equalling the lemma); entire to apically notched; awnless, without apical setae; somewhat thinner than the lemma; not indurated; 2-nerved; 2-keeled. Palea keels winged (below); minutely scaberulous. Lodicules present; 2; free; fleshy; glabrous. Stamens 3. Anthers 0.7–1.2 mm long; not penicillate; without an apically prolonged connective. Ovary glabrous. Styles free to their bases. Stigmas 2; brown.
Fruit, embryo and seedling. Fruit free from both lemma and palea; longitudinally grooved; compressed dorsiventrally. Hilum short. Embryo large.
Ovule, embryology. Micropyle oblique. Outer integument extensive, being absent only from the micropylar region; two cells thick at the micropylar margin. Inner integument continuous, the micropyle constricted; thickened around the micropyle. Synergids not haustorial; without large, globular starch grains.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent (but mimicked by prickle bases, especially in the costal zones). Mid-intercostal long-cells rectangular; having markedly sinuous walls, or having straight or only gently undulating walls. Microhairs present (but very hard to find - obscured by macrohairs and seemingly very rare), or absent; when seen panicoid-type to chloridoid-type (with short, rounded but thin-walled apical cells); in C. forskalei 36 microns long; 21 microns wide at the septum. Microhair total length/width at septum 1.7. Microhair apical cells 12 microns long. Microhair apical cell/total length ratio 0.33. Stomata common; about 27 microns long. Subsidiaries dome-shaped, or dome-shaped and triangular. Intercostal short-cells absent or very rare. Costal short-cells conspicuously in long rows, or neither distinctly grouped into long rows nor predominantly paired. Costal silica bodies tall-and-narrow, or ‘panicoid-type’.
Transverse section of leaf blade, physiology. C4; biochemical type biochemical type and ultrastructure need investigating, in view of the peculiarity of other C4 arundinoids and especially in view of the variation in PCR sheath form; XyMS+. PCR sheath outlines uneven (e.g. C. mossamedense), or even (e.g. C. glaucum). PCR sheath extensions present (eg C. mossamedense), or absent. Maximum number of extension cells 2. PCR cell chloroplasts centripetal. Mesophyll with radiate chlorenchyma. Leaf blade ‘nodular’ in section; with the ribs more or less constant in size. Midrib not readily distinguishable; with one bundle only. Bulliforms present in discrete, regular adaxial groups; in simple fans (each group with a large, deeply penetrating median cell, cf. many chloridoids). All the vascular bundles accompanied by sclerenchyma. Combined sclerenchyma girders absent. Sclerenchyma all associated with vascular bundles.
Cytology. Chromosome base number, x = 12. 2n = 24. 2 ploid. Chromosomes ‘small’.
Taxonomy. Arundinoideae, or Chloridoideae (?); if arundinoid, Danthonieae; if chloridoid, main chloridoid assemblage.
Distribution, ecology, phytogeography. 4 species; North Africa, South and South West Africa and Middle East. Xerophytic; species of open habitats.
Holarctic, Paleotropical, and Cape. Tethyan. African and Indomalesian. Irano-Turanian. Saharo-Sindian, Sudano-Angolan, and Namib-Karoo. Indian. Sahelo-Sudanian and South Tropical African.
Rusts and smuts. Rusts — Puccinia.
Economic importance. Important native pasture species: C. forsskalii.
References, etc. Morphological/taxonomic: Conert 1962. Leaf anatomical: this project; photographs of Asthenatherum (=Centropodia) glaucum and A. mossamedense provided by R. P. Ellis; Ellis 1984a.
Illustrations. • General aspect
Cite this publication as: Watson, L., and Dallwitz, M. J. (1992 onwards). ‘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.’ http://biodiversity.uno.edu/delta/. Version: 18th August 1999. Dallwitz (1980), Dallwitz, Paine and Zurcher (1993 onwards, 1998), and Watson and Dallwitz (1994), and Watson, Dallwitz, and Johnston (1986) should also be cited (see References).
