Pennisetum polystachion

Name and classification

Pennisetum polystachion (L.) Schultes
Family Poaceae, Tribe Paniceae

Common names

mission grass, thin napiergrass

Disseminule

fertile floret, or fascicle consisting of bristles enclosing a single sessile spikelet; disarticulation below fascicle and at base of fertile floret

Description

Fascicle consists of unfused bristles; outer bristles 13–30, 1.2–5 mm long, antrorsely scabrous; inner bristles 6–14, 4.3–11.5 mm long, long ciliate; primary bristle solitary, conspicuously longer than other bristles, to 25 mm, long ciliate. Spikelets solitary, sessile, lanceolate, mildly dorsally compressed; 2–5 mm long, 0.6–0.9 mm wide; consisting of 1 fertile floret and 1 basal sterile floret. Lower glume absent or a vestigial scale; upper glume 3–4.5 mm long, glabrous, trilobed. Sterile lemma membranous, as long as spikelet, 5–7-nerved, trilobed, ciliate; sterile palea 2.9–3.7 mm long. Fertile floret cream to light brown, narrowly lanceolate, 1.7–3 mm long, ca. 0.5–0.6 mm wide; fertile lemma and palea coriaceous, glossy, with truncate-ciliate apices, lemma 5-nerved.

Identification considerations

Pennisetum polystachion belongs to a unique section of the genus with a trilobed sterile lemma. The spikelet is solitary and sessile in the fascicle, 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

portion of inflorescence

spikelets enclosed by fascicles

spikelets enclosed by fascicles

spikelet enclosed by fascicle of bristles

spikelet enclosed by fascicle of bristles

spikelet; photo by Mark Thurmond

spikelet; photo by Mark Thurmond

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

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

caryopses in dorsal view (left) and ventral view (right); photo by Mark Thurmond

A, fascicle 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

A, fascicle 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