Nassella trichotoma

Name and classification

Nassella trichotoma (Nees) Hack. ex Arech.
Family Poaceae, Tribe Stipeae

Common names

serrated tussock

Disseminule

floret; disarticulation above the glumes

Description

Spikelets of 1 fertile floret. Glumes similar, narrowly lanceolate, very long-tapered, hyaline, with 3 scabridulous nerves, up to 3½ times as long as floret; 4–10 mm long. Floret laterally compressed; outline obovate, with truncate apex; lemma coriaceous, rolled up longitudinally, concealing palea, surface tuberculate, crown 0.5 mm long; callus bearded with hairs half as long as floret; lemma awn off-center, 15–35 mm long, straight to geniculate and twisted, antrorsely barbed. Caryopsis laterally compressed, narrowly obovate to oblong or rhombic, 1.2–1.6 mm long, hilum linear.

Identification considerations

Similar species

Nassella exserta Phil. (=Nassella gigantea (Steud.) Muñoz-Schick) [no image available] (non-FNW)

Distribution

Africa: South Africa; Europe: United Kingdom, France, Italy; Oceania: Australia, Tasmania, New Zealand; South America: Argentina, Brazil, Chile, Peru, Uruguay

native to South America

Habitat

subhumid, subtropical, and warm-temperate regions, rocky hillsides

General information

Nassella trichotoma is a perennial tussock-forming grass, to 60 cm tall. In its native range, it is heavily grazed by cattle, horses, and sheep, but in Australia, it is a serious weed, primarily responsible for the reduced carrying capacity of pasture. Sheep will eat it non-preferentially, but they lose weight, and may be injured by the awns. Dense infestations of tussocks form, eventually eliminating other plants. Propagation is by grain alone, and these remain viable after passing through animals and in the soil for up to 15 years. The florets are dispersed by wind, and cling to wool and clothing.

florets

florets

spikelet; photo by Mark Thurmond

spikelet; photo by Mark Thurmond

spikelets

spikelets

nearly full length spikelet and floret

nearly full length spikelet and floret

caryopses in side view

caryopses in side view

two marginal views showing hilum and embryo

two marginal views showing hilum and embryo

A, spikelet; B, floret; C, caryopsis in side view; drawing by Lynda E. Chandler

A, spikelet; B, floret; C, caryopsis in side view; drawing by Lynda E. Chandler