Pennisetum L.C. Rich. in Pers., Syn. Pl. 1:72. 1805. Boiss., Fl. Or. 5:444. 1884; Hook.f., Fl. Brit. Ind. 7:82. 1896; Blatter & McCann, Bombay Grasses 177. 1935; Sultan & Stewart, Grasses W. Pak. 1:61. 1958; Bor, Grasses Burma Ceyl. Ind. Pak. 341. 1960; Bor in Towns., Guest & Al-Rawi, Fl. Iraq 9:494. 1968; Bor in Rech.f., Fl. Iran.70:499. 1970; Tzvelev, Poaceae URSS 680. 1976; Clayton in Tutin et al., Fl. Eur. 5:264. 1980.
Annuals or perennials. Leaf-blades linear to lanceolate, flat or convolute; ligule a line of hairs, rarely membranous. Inflorescence a cylindrical to subglobose spike-like panicle terminal on culms and branches, rarely axillary and then often gathered into a leafy false panicle, each spikelet or cluster of spikelets subtended by a deciduous involucre of 1-many slender bristles free throughout; rhachis rounded or angular, with or without short peduncle stumps, occasionally the involucre shortly stipitate below the insertion of the bristles. Spikelets narrowly lanceolate to oblong, dorsally compressed, glabrous or almost so; lower glume up to two-thirds the length of the spikelet, sometimes suppressed; upper glume varying from very small to as long as the spikelet; lower floret male or barren, its lemma of variable length, membranous; upper lemma as long as the spikelet or a little shorter, membranous to coriaceous, its margin covering ± half the palea; anther tips smooth or sometimes with a minute tuft of hairs. Caryopsis oblong and dorsally compressed to subglobose.
A genus of about 70 species in the tropics and subtropics; 6 species occur in Pakistan, one of them in cultivation only.
The involucral bristles of Pennisetum are apparently derived from the much modified branches of a panicle (Sohns in J. Wash. Acad. Sci. 45:135-143. 1955). The lower spikelet scales are often extremely variable and easily confused with one another, so that the spikelet parts are best elucidated by working backwards from the upper lemma. Habit, though difficult to describe unambiguously, is of taxonomic value in this genus, and often seems more reliable than the traditional characters derived from inflorescence and spikelet.
The term involucre, as employed here, refers to that portion of the inflorescence, enclosing one or more spikelets, that is deciduous from the rhachis. While in most cases there is no problem with its interpretation, in Pennisetum lanatum it is not so easy. In this species the branching system is not fully condensed, so that the bristles themselves are branched. It often appears as though each spikelet is subtended by an involucre comprising a single, much branched bristle, with several such spikelets falling together. In the context of this account those bristles enclosing a group of spikelets that fall together as a unit are considered to represent a single involucre. Thus, in Pennisetum lanatum there are 2-4 spikelets in each involucre and not 1 as stated by Bor (1970).
Pennisetum purpureum K. Schum., Beskr. Guin. Pl. 44. 1827, a native of tropical Africa, is widely grown for fodder under the names “Elephant” and “Napier” grass. It is said to have been introduced into Sind, but its presence there has not been confirmed. It differs from Pennisetum orientale in having no lower glume. The involucres are sessile or shortly pedunculate and if the latter then, on falling, they leave short stumps on the rhachis. It grows very rapidly and if cut before full grown it yields an excellent hay. When mature the leaves are razor-sharp on the margins and therefore unpopular with cattle at this stage. Pennisetum purpureum (a perennial) can be crossed with Pennisetum glaucum (an annual), the hybrids being sterile but resembling Pennisetum purpureum with ± persistent spikelets. The amphidiploid is a useful fodder grass in South Africa.
Pennisetum polystachion (Linn.) Schult., Syst. Veg., Mant. 2:146. 1824 (Panicum polystachion Linn., Syst. Nat., ed. 10, 2:870. 1759) is found throughout the tropics and is widely grown for fodder. It is probably not native in India or Sri Lanka and although reported to have been introduced into Sind, its occurence there has not, to date, been confirmed. It differs from other species of Pennisetum in Pakistan by having an angular rhachis with sharp decurrent wings below the scars of the fallen involucres.