Forked three-awned grass (Aristida basiramea) COSEWIC assessment and status report: chapter 3

Species Information

Name and Classification

Aristida basiramea Engelm. ex. Vasey. The type specimen was collected near Minneapolis, Minnesota by W. Upham in 1883 and published in the Botanical Gazette the following year. A. basiramea Englemann var. curtissii (A. Gray) was recognized by Shinners in 1940. Previously it had been described as A. dichotoma var. curtissii by Asa Gray in 1890, and subsequently as A. curtissii by Nash in 1901 (Shinners, 1940; Vaughn, 1981; The New York Botanical Garden, 2001). In the draft Flora of North America (FNA) treatment by Allred (2001) it is again recognized as A. dichotoma var. curtissii. In the FNA Aristida basiramea is accorded full species status, with a cautionary note from Allred that further study may show that A. basiramea and A. dichotoma should in fact also be treated as conspecific varieties.

All Canadian collections are referrable to the nominate variety, matching the ‘long lateral awn’ character of A. basiramea, and are clearly distinct from A. dichotoma. The collection from Cazaville was verified by Stuart Hay; the collection from Rainy River District was verified by M.J. Oldham; that from Anten Mills by M.J. Oldham; the Beausoleil Island collection was determined by Dr. J. Goltz; and the stations at Macey Lake and Christian Island have previously been determined as distinctly A. basiramea (Reznicek, 1984).

English common names include: Three-awn, Forked Aristida, Tufted Triple-awn, Forktip Three-awn, Arrowfeather Threeawn, and Branching Needle-grass. The French common name is Aristide.

Description

The generic name is from the Latin arista, which means “an awn”, while the specific epithet basiramea means “branching from base”. The species is an annual, usually freely branching at the base, sparingly so above, and reaches 30 to 50 cm in height (Figures 1, figure4). The culms are wiry and often rough, and grow in tufts or dense clumps. Leaves are flat, 5 to 15 cm long and very narrow (about 1 mm) wide, with rolled-in margins at the tip. The panicle is slender, to 10 cm long, more or less loose, the lower included in the sheaths, which can be smooth or rough. The glumes are prolonged into a very acute point, are 1-nerved and unequal, the second being 1.2 to 1.5 cm long, the first about 2/3 as long. The lemma is rough on the keel and about 1 cm long, excluding the awns. The lateral awns are 5 to 13 mm long, and are erect or spreading, and delicate; while the central awn is divergent, coiled at the base in 2 to 3 loose spirals, 1 to 1.5 cm long, and is often loosely spiraling when dry. The anthers are very reduced and difficult to observe, but when rarely detected are 2.6 to 3.1 mm long and purplish-brown.

In his 1972 key, Voss uses the length of the lemma, the middle and lateral awns, and the length of the glume to differentiate A. basiramea from other Aristida species. He notes that the glumes are clearly unequal, the first usually equalling or shorter than the body of the lemma. Allred (2001) differentiates from the very similar A. dichotoma on the basis of the length of the lateral awns, with dichotoma being 1-4 mm long, and basiramea 5-13 mm long.

Figure 1. Aristida basiramea

  1. Habit
  2. Sheath, with ligule
  3. Spikelet (from Mohlenbrock, 1973)

 

Aristida basiramea a. Habit. b. Sheath, with ligule. c. Spikelet. (from Mohlenbrock, 1973)

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