Pennisetum polystachion (L.) Schultes

Family: Poaceae,  Tribe: Paniceae

Common names:  mission grass, thin napiergrass

Disseminule 

Fertile floret or involucre of bristles enclosing single sessile spikelet; disarticulation below involucre.

Description

Spikelets subtended by involucre of unfused bristles, bristles plumose and/or antrorsely barbed, 4-12 mm long, with 1 conspicuously longer bristle, 6-25 mm long. Spikelets of 1 fertile floret and 1 basal sterile floret. Spikelets lanceolate, mildly dorsally compressed; 2-5 mm long, 0.6-0.9 mm wide. Lower glume absent or a vestigial scale; upper glume and sterile lemma membranous, as long as spikelet, 5-nerved. Sterile lemma tri-lobed, ciliate. Fertile floret cream to light brown, narrowly lanceolate, 2-3 mm long, ca. 0.5-0.6 mm wide; fertile lemma and palea coriaceous, glossy, with truncate-ciliate apices, fertile lemma 5-nerved.

Identification remarks

Pennisetum polystachion belongs to a unique section of the genus with a trilobed sterile lemma. The spikelet is solitary and sessile in the involucre, the lower glume is minute or small. See

Pennisetum clandestinum Hochst. ex Chiov.

Pennisetum macrourum Trin.

Pennisetum pedicellatum Trin.

Distribution

Tropical Africa, India to Southeast Asia, Australia, New Zealand, and the Pacific Islands; Mexico, tropical South America, United States.

Native to tropical Africa.

Habitat

Tropical scrublands; a weed of roadsides, waste places, arable lands and disturbed sites.

General information

Pennisetum polystachion is an annual or perennial grass, to 200 cm tall, that has been widely introduced as a fodder grass. It reproduces solely by seed, yet production of the highly viable grains is prolific, enabling the grass to quickly invade cultivated fields. Disseminules are dispersed by water, by clinging to animals, or as hay and grain contaminants. This grass has become a dominant weed in cleared forest lands in Southeast Asia and the Pacific Islands.

Portion of inflorescence

Spikelets enclosed by involucres

Spikelet enclosed by involucre of bristles

Spikelet

photo by Mark Thurmond

Florets in dorsal view showing lemma (left) and ventral view showing palea (right)

Caryopses in dorsal view (left) and ventral view (right)

photo by Mark Thurmond

A, Involucre of bristles enclosing spikelet; B, spikelet in dorsal view showing upper glume; C, spikelet in ventral view showing sterile lemma; D, floret in ventral view; E, floret in dorsal view; F, caryopsis in ventral view; G, caryopsis in dorsal view

drawing by Lynda E. Chandler