Diheteropogon (Hack.) Stapf
Habit, vegetative morphology. Annual, or perennial (slender); caespitose. Culms 15–230 cm high; herbaceous (to woody at the base); mainly unbranched above. Culm internodes solid. Leaves not basally aggregated. Sheath margins free. Leaf blades greatly reduced (sometimes, to their midribs in D. filifolius), or not all greatly reduced; linear, or linear-lanceolate; broad to narrow; cordate, or not cordate, not sagittate; flat, or acicular; without cross venation; an unfringed membrane; not truncate.
Reproductive organization. Plants bisexual, with bisexual spikelets; with hermaphrodite florets. The spikelets of sexually distinct forms on the same plant (all male or sterile at the bases of the ‘racemes’, heterogamous above); hermaphrodite and male-only, or hermaphrodite and sterile; overtly heteromorphic; in both homogamous and heterogamous combinations (the 3–9 proximal pairs homogamous, imperfect, hardly heteromorphic).
Inflorescence. Inflorescence of spicate main branches, or paniculate (of paired ‘racemes’, terminal or in a scanty false panicle); spatheate; a complex of ‘partial inflorescences’ and intervening foliar organs. Spikelet-bearing axes ‘racemes’; paired (not deflexed the bases terete); with substantial rachides; disarticulating; disarticulating at the joints. ‘Articles’ non-linear (thickened and hollowed at the summit); not appendaged; disarticulating obliquely; densely long-hairy to somewhat hairy. Spikelets paired; sessile and pedicellate; consistently in ‘long-and-short’ combinations; in pedicellate/sessile combinations. Pedicels of the ‘pedicellate’ spikelets free of the rachis. The ‘shorter’ spikelets hermaphrodite (save at the base of the raceme). The ‘longer’ spikelets male-only, or sterile (?).
Female-sterile spikelets. The pedicelled spikelets awnless or aristulate, larger, callus glabrous.
Female-fertile spikelets. Spikelets 5–9 mm long; compressed dorsiventrally (subterete); falling with the glumes (or with a slight tendency to disarticulate above them). Rachilla terminated by a female-fertile floret. Hairy callus present. Callus long; pointed.
Glumes two; more or less equal; G2 with ciliate margins; awnless; carinate (G2), or non-carinate (G1); very dissimilar (somewhat leathery, G1 bicarinate and grooved between the keels, G2 not bicarinate). Lower glume two-keeled; sulcate on the back; not pitted; relatively smooth; many nerved. Upper glume 3 nerved. Spikelets with incomplete florets. The incomplete florets proximal to the female-fertile florets. Spikelets with proximal incomplete florets. The proximal incomplete florets 1; epaleate; sterile. The proximal lemmas awnless; 2 nerved; more or less equalling the female-fertile lemmas; similar in texture to the female-fertile lemmas (thin); not becoming indurated.
Female-fertile florets 1. Lemmas less firm than the glumes (hyaline); not becoming indurated; incised; awned. Awns 1; median; from a sinus; twice geniculate; hairless (scabrid), or hairy; much longer than the body of the lemma (and sturdy). Lemmas with ciliate lobes; non-carinate; without a germination flap; 1 nerved (?). Palea present; conspicuous but relatively short (small); entire; awnless, without apical setae (ciliolate); not indurated (hyaline); 2-nerved; keel-less. Lodicules present; 2; free. Stamens 3. Ovary glabrous. Stigmas 2.
Fruit, embryo and seedling. Fruit free from both lemma and palea.
Abaxial leaf blade epidermis. Costal/intercostal zonation conspicuous. Papillae absent. Long-cells of similar wall thickness costally and intercostally. Mid-intercostal long-cells mostly rectangular; having markedly sinuous walls, or having straight or only gently undulating walls. Microhairs present; panicoid-type. Stomata common. Subsidiaries dome-shaped and triangular. Intercostal short-cells common; in cork/silica-cell pairs, or not paired (some solitary); silicified, or not silicified. Intercostal silica bodies infrequent and variable in shape. Crown cells absent. Costal short-cells conspicuously in long rows, or conspicuously in long rows and predominantly paired. Costal silica bodies ‘panicoid-type’; cross shaped.
Transverse section of leaf blade, physiology. Leaf blades consisting of midrib, or ‘laminar’.
C4; XyMS–. PCR sheath extensions absent. PCR cell chloroplasts centrifugal/peripheral. Mesophyll traversed by columns of colourless mesophyll cells. Leaf blade (when the blade not acicular and reduced almost to its midrib) with distinct, prominent adaxial ribs, or adaxially flat; when present, with the ribs more or less constant in size. Midrib conspicuous (or the blade reduced to the midrib); with one bundle only, or having a conventional arc of bundles; with colourless mesophyll adaxially. Bulliforms present in discrete, regular adaxial groups, or not present in discrete, regular adaxial groups (the adaxial part of the leaf extensively colourless in D. filifolius, the adaxial epidermis of irregularly grouped bulliform cells in D. amplectens). Many of the smallest vascular bundles unaccompanied by sclerenchyma. Sclerenchyma all associated with vascular bundles.
Phytochemistry. Leaves containing flavonoid sulphates (1 species).
Cytology. Chromosome base number, x = 10. 2n = 20 and 40. 2 and 4 ploid.
Taxonomy. Panicoideae; Andropogonodae; Andropogoneae; Andropogoninae.
Distribution, ecology, phytogeography. 5 species; tropical Africa. Helophytic; species of open habitats; glycophytic. Savanna.
Paleotropical. African and Madagascan. Sudano-Angolan, West African Rainforest, and Namib-Karoo. Sahelo-Sudanian, Somalo-Ethiopian, South Tropical African, and Kalaharian.
References, etc. Morphological/taxonomic: Stapf 1922. Leaf anatomical: Metcalfe 1960 (Andropogon amplectens); photos of D. filifolius and D. amplectens provided by R.P. Ellis.
Special comments. Fruit data wanting.
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).
