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Protologue Kew Bull. 20: 75 (1966). Family Poaceae (Gramineae) Chromosome number 2n= 20, 40 Synonyms Andropogon amplectens Nees (1841), Andropogon diversifolius Rendle (1899). Vernacular names Broadleaf bluegrass (En). Origin and geographic distribution Diheteropogon amplectens is widely distributed in Africa, from Senegal east to Sudan and Kenya, and south to Angola and South Africa. Uses Diheteropogon amplectens is an important forage species in permanent pastures grazed by ruminants. When still young, it is appreciated by all stock, and it makes an acceptable hay. Flowering plants are less willingly browsed because of the long, pungent awns. On sandy clay soils in Sudan, the vegetation co-dominated by Diheteropogon amplectens forms an excellent grass cover for cattle production because it is palatable and readily grazed. In Mozambique, the savanna vegetation with Diheteropogon amplectens has a varying grazing capacity; locally, the sparse cover has a carrying capacity of only 1 animal per 5 ha. The culms are used for thatching and coarse matting. Description Perennial herb up to 200 cm tall, growing in small tussocks, often with underground scaly shoots at base; culms cylindrical, with up to 9 nodes. Leaves alternate, simple; leaf sheath terete, tight, glabrous; ligule 1–1.5 mm long, truncate, membranous, glabrous; blade linear, 15–30 cm long, tapering into a filiform, glabrous to densely hairy, sharp tip, rough to almost smooth at margins; cauline leaves at base rounded-cordate or not and up to 20 mm wide. Inflorescence a paired raceme up to 9 cm long, up to 6 raceme pairs arranged into a scanty spathate false panicle. Spikelets paired, one sessile, the other pedicelled; sessile spikelet cylindrical, 2-flowered, lower floret reduced to a hyaline lemma, callus 1–2 mm long, pungent, lower glume 5–7 mm long, with 2 rounded, 4–7-veined keels, upper lemma 2-lobed at apex, with kneed, pubescent awn 2.5–7 cm long between the lobes; pedicelled spikelet larger, 9–13 mm long, male, often brownish or purplish, sometimes with an awn up to 8 mm long. Fruit a lanceolate caryopsis, hollowed on one face. Other botanical information Diheteropogon comprises 5 species restricted to Africa. It belongs to the tribe Andropogoneae, subtribe Andropogoninae, together with e.g. Andropogon, having close links to sections Piestium and Parahyparrhenia. Andropogon differs in the callus of its sessile spikelet, which is obtuse and usually very short. Two varieties are distinguished within Diheteropogon amplectens: var. amplectens occurring in eastern and southern Africa, which has most leaves basal and few linear, parallel-sided cauline leaves up to 7 mm wide at base, and var. catangensis (Chiov.) Clayton occurring over the whole range of the species, and which has most leaves cauline with a rounded-cordate base up to 20 mm wide. Intermediate forms are common. Growth and development At the beginning of the rainy season culms with inflorescences develop out of a tussock. Flowering is at the end of the rainy season and beginning of the dry season. Regrowth, consisting of dry season basal leaves, takes place after burning in the dry season. Ecology Diheteropogon amplectens occurs in grassland, often on shallow soils on stony hill slopes, and on poor sandy soils in savanna and deciduous bushland in areas receiving 900–1200 mm annual rainfall in western Africa, and 500–1500 mm/year in southern Africa. The altitudinal range is between 300 m in western Africa and 1800 m in eastern and southern Africa. Management Annual fires maintain the vegetation type in which Diheteropogon amplectens occurs. In trials in Zimbabwe, the proportion of Diheteropogon amplectens in grass cover decreased by 17% after cattle grazing during several years (continuous and rotational) – a small reduction in comparison with that of other desirable grasses, such as Hyperthelia dissoluta (Steud.) Clayton (synonym: Hyparrhenia dissoluta (Nees ex Steud.) C.E.Hubb. ex Hutch. & Dalziel) and Melinis repens (Willd.) Zizka (synonym: Rhynchelytrum repens (Willd.) C.E.Hubb.). In a humid highland grassland in South Africa Diheteropogon amplectens was less common in grazed sites than in ungrazed ones. Application of N fertilizer decreased its proportion. Harvesting The stems used for thatching and matting are collected at the beginning of the dry season, before they have dried out. Prospects Diheteropogon amplectens has considerable local value as a forage. In the dry season it seems to be a valuable species with a good nutritional value, and reasonably capable of withstanding grazing pressure. Major references • Burkill, H.M., 1994. The useful plants of West Tropical Africa. 2nd Edition. Volume 2, Families E–I. Royal Botanic Gardens, Kew, United Kingdom. 636 pp. • Clayton, W.D. & Renvoize, S.A., 1982. Gramineae (Part 3). In: Polhill, R.M. (Editor). Flora of Tropical East Africa. A.A. Balkema, Rotterdam, the Netherlands. pp. 451–898. • Rattray, J.M., 1960. The grass cover of Africa. FAO Agricultural Studies No 49. Food and Agriculture Organization of the United Nations, Rome, Italy. 168 pp. + annex. • van der Zon, A.P.M., 1992. Graminées du Cameroun. Volume II, Flore. Wageningen Agricultural University Papers 92.1. 557 pp. Other references • Clayton, W.D., 1972. Gramineae. In: Hepper, F.N. (Editor). Flora of West Tropical Africa. 2nd Edition. Vol.ume III, part 2. pp. 277–574. • Denny, R.P. & Mavedzenge, B.Z., 1983. A comparison of continuous and rotational grazing on open sandveld. Annual Report 1980–1981, Division of Livestock and Pastures, Zimbabwe. pp. 182–185. Sources of illustration • van der Zon, A.P.M., 1992. Graminées du Cameroun. Volume II, Flore. Wageningen Agricultural University Papers 92.1. 557 pp. • Clayton, W.D. & Renvoize, S.A., 1982. Gramineae (Part 3). In: Polhill, R.M. (Editor). Flora of Tropical East Africa. A.A. Balkema, Rotterdam, the Netherlands. pp. 451–898. Author(s)
Editors
Correct citation of this article: van der Zon, A.P.M., 2002. Diheteropogon amplectens (Nees) Clayton. Record from Protabase. Oyen, L.P.A. & Lemmens, R.H.M.J. (Editors). PROTA (Plant Resources of Tropical Africa / Ressources végétales de l’Afrique tropicale), Wageningen, the Netherlands. |
Diheteropogon amplectens – wild
1, basal part of plant; 2, part of culm with leaf; 3, upper part of flowering plant; 4, part of inflorescenceRedrawn and adapted by M.M. Spitteler |