GRASSES OF THE COLUMBIA BASIN OF BRITISH COLUMBIA
Heather Stewart, Richard Hebda
Major Groups of Grasses
Table of Contents
Glossary

Piptatherum is a genus of 30 species, most of which are Eurasian. The name comes from the Greek word pipto, meaning fall, and ather, meaning awn. Originally most of the members in this treatment were included in Oryzopsis, but Barkworth (1998) has separated them. Piptatherum has a blunt to sharp callus that is less that 1/5 the length of the flower. This separates the members from Stipa. Leaf blades of Piptatherum are more than 0.5 mm wide, the awns are weakly to strongly bent and the callus is round rather than pointed. There are three species of Piptatherum in the Columbia Basin region.

Piptatherum exiguum (Thurber) Barkworth Oryzopsis exigua Thurb.

Little Ricegrass

Plant: Piptatherum exiguum is a native species that grows to 10-30 cm tall. It is a strongly tufted perennial with a spikelike flowerhead, and short, twisted awns.

Leaves and Stem: The smooth to slightly rough sheath is open and there are no auricles. The ligule is 3-4 mm high and pointed. The inrolled leaves are less than 1 mm wide.

Flowerhead and Flowers: The narrow flowerhead is 3-6 cm long and has short upward-pointing branches that are pressed tight to the stem. The glumes are broad and vary from blunt to somewhat pointed. They are equal in length. The hardened lemma is equal to or longer than the glumes. The lemmas have short hairs scattered over the back. The awn is 4-6 mm long and slightly twisted.

Habitat: Little Ricegrass grows in the steppe to the montane zone on dry talus slopes and ridges such as Mount Festubert, Grizzly Gulch and Horseshoe Ridge.

Similar Species: Little Ricegrass resembles Small-flowered Ricegrass (Piptatherum micranthum). However, Little Ricegrass differs by having twisted awns and flowerhead branches that are pressed close to the stem, whereas Small-flowered Ricegrass has branches that spread out from the stem axis.

Piptatherum micranthum (Trin. & Rupr.) Barkworth Oryzopsis micrantha (Trin. & Rupr.) Thurb.

Small-flowered Ricegrass

Plant: Piptatherum micranthum is a native species that grows to 30-70 cm tall. It is a strongly tufted, perennial with a moderately open, spikelike flowerhead.

Leaves and Stem: The open sheath is smooth to slightly hairy with fine, short hairs. The ligule is 0.5 mm long, blunt and finely hairy along the edge. The flat or slightly inrolled leaf blades are 1-2 mm wide.

Flowerhead and Flowers: The flowerhead is 7-15 cm tall, appears spikelike, but has branches that are slightly diverging. The equal glumes are papery, transparent and sharply pointed. The lemma is hairless or occasionally covered in fine hairs. A lemma awn is 6-8 mm long, straight, stiff and longer than the flower.

Habitat: Small-flowered Ricegrass grows on dry, rocky slopes or open forests in the steppe or montane zone. In the Columbia basin region it occurs at Yoho National Park, Canal Flats and Armstrong Bay.

Similar Species: Small-flowered Ricegrass resembles Short-awned Ricegrass (Piptatherum pungens), but differs by having a spreading flowerhead, and branches and awns that remain after maturity. The awns of Short-awned Ricegrass fall off shortly after maturity.

Piptatherum pungens (Torrey) Barkworth Oryzopsis pungens (Torr.) A.S. Hitchc.

Short-awned Ricegrass

Plant: Piptatherum pungens is a native species that grows to 15-40 cm tall. It is a tufted perennial with a spikelike flowerhead.

Flowerhead and Flowers: The flowerhead is 2-6 cm long, spikelike and consists of branches that are tightly pressed against the spike axis. Hairless glumes are blunt or rounded and have a transparent edge. The lemma is as long as the glumes and covered in fine hairs. The awn is 1-2 mm long and falls off at maturity, so that most flowers appear awnless.

Habitat: Short-awned Ricegrass grows on moist slopes in the montane zone in Yoho National Park.

Similar Species: Short-awned Ricegrass is unique in that it is the only species of Piptatherum in which the awn falls off at maturity.