Chaetobromus Nees
From the Greeek chaeto (bristle) and Bromus; the spikelets look like those of Bromus, but the lemmas have longer awns and bristles.
Habit, vegetative morphology. Perennial; rhizomatous (sometimes), or caespitose, or decumbent. Culms 15–75 cm high; herbaceous; to to 0.3 cm in diameter; branched above (but not profusely). Culm nodes black, glabrous. Culm internodes hollow. Plants unarmed. Young shoots intravaginal. Leaves not basally aggregated; non-auriculate (but hairy at the auricle positions). Leaf blades linear to linear-lanceolate; narrow; 1–5 mm wide; flat, or folded; without cross venation; persistent; a fringe of hairs.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets.
Inflorescence. Inflorescence paniculate (rarely racemose, in depauperate plants); open, or contracted (sometimes with few spikelets); with capillary branchlets, or without capillary branchlets. Inflorescence with axes ending in spikelets. Inflorescence espatheate. Spikelet-bearing axes persistent. Spikelets solitary; not secund; pedicellate (the pedicels articulated).
Female-fertile spikelets. Spikelets 10–17 mm long; compressed laterally; falling with the glumes (the hairs on the persistent pedicel allowing the spikelet to move in only one direction); ultimately disarticulating between the florets (i.e., disarticulation occurring in the pedicel, above the glumes, and between the florets). Rachilla prolonged beyond the uppermost female-fertile floret; hairy; the rachilla extension with incomplete florets. Hairy callus present (comprising the bearded upper part of pedicel, and the rachilla below the glumes). Callus long.
Glumes two; more or less equal; about equalling the spikelets, or exceeding the spikelets; long relative to the adjacent lemmas; free; hairy (puberulous), or hairless; scabrous (on the keels); pointed; awnless; carinate; similar (subherbaceous, with scarious margins, the upper narrower). Lower glume 5–10 nerved. Upper glume 3–5 nerved. Spikelets with incomplete florets. The incomplete florets distal to the female-fertile florets. The distal incomplete florets merely underdeveloped. Spikelets without proximal incomplete florets.
Female-fertile florets (2–)3–4(–6). Lemmas less firm than the glumes to similar in texture to the glumes (membranous); not becoming indurated; incised; 2 lobed; deeply cleft; awned (but the L1 sometimes with a reduced awn or awnless). Awns 1, or 3; median, or median and lateral (the lateral lemma lobes sometimes being bristle-tipped); the median different in form from the laterals (when laterals present); from a sinus (mostly), or apical (sometimes, in the L1); geniculate (and twisted below); hairless; much longer than the body of the lemma; entered by one vein. The lateral awns when present, shorter than the median (and straight). Lemmas hairy (mostly), or hairless (L1); non-carinate; 7–9 nerved. Palea present; relatively long; apically notched (obscurely 3-notched); awnless, without apical setae; textured like the lemma; not indurated; 2-nerved; 2-keeled. Lodicules present; free; fleshy; glabrous. Stamens 3. Anthers 5–6 mm long; not penicillate; without an apically prolonged connective. Ovary glabrous. Styles free to their bases (short). Stigmas 2; rusty red pigmented.
Fruit, embryo and seedling. Fruit tightly enclosed by lemma and palea; longitudinally grooved; compressed laterally (slightly). Hilum long-linear.
Ovule, embryology. Micropyle not noticeably oblique. Outer integument covering no more than the chalazal half of the ovule; more than two cells thick at the micropylar margin. Inner integument discontinuous distally; not thickened around the micropyle. Synergids haustorial (strongly developed); exhibiting large, globular starch grains.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells markedly different in shape costally and intercostally (the intercostals fusiform, the costals rectangular). Mid-intercostal long-cells fusiform; having markedly sinuous walls and having straight or only gently undulating walls (and the costals with sinuous walls). Microhairs absent (but panicoid type present adaxially). Stomata common (but apparently confined to two lateral files per intercostal zone); 36–42 microns long. Subsidiaries low dome-shaped, or parallel-sided. Guard-cells overlapping to flush with the interstomatals. Intercostal short-cells common; in cork/silica-cell pairs; silicified. Intercostal silica bodies often crescentic. Costal short-cells conspicuously in long rows. Costal silica bodies horizontally-elongated crenate/sinuous, or ‘panicoid-type’ (predominantly ‘panicoid type’, but the undulations sometimes amount to crenation).
Transverse section of leaf blade, physiology. C4 (in C. involucratus, according to carbon isotope ratio - H. Ziegler, pers. comm.), or C3 (seemingly, judging from the poor material seen of C. dregeanus, though the lateral cell count is low between all but a few bundles); XyMS+ (C. dregeanus). Mesophyll without adaxial palisade. Leaf blade adaxially flat (with marked abaxial ribs only). Midrib not readily distinguishable (the bundle and keel only very slightly larger); with one bundle only; with colourless mesophyll adaxially (in the form of a wide bundle-sheath extension). Bulliforms present in discrete, regular adaxial groups; in simple fans (the groups large). Many of the smallest vascular bundles unaccompanied by sclerenchyma (and these ‘inserted’ between the large veins, as in panicoid C4 leaves). Combined sclerenchyma girders absent (the large bundles with adaxial strands and girders, linked to the bundles by colourless sheath extensions). Sclerenchyma all associated with vascular bundles.
Special diagnostic feature. Pedicels articulated and bearded with long hairs at and above the joint. Female-fertile lemmas with a bent awn, the awn twisted below.
Cytology. Chromosome base number, x = 6. 2n = 12, 24, 36, 48, 54, 72.
Taxonomy. Arundinoideae; Danthonieae.
Distribution, ecology, phytogeography. 1 species; southern Africa. Xerophytic; halophytic, or glycophytic. Commonly coastal, generally on sandy soil.
Paleotropical and Cape. African. Namib-Karoo.
References, etc. Leaf anatomical: this project.
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).
