Three-awn

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Three-awns
Purple Three-awn, Aristida purpurea
Scientific classification
Kingdom: Plantae Phylum: Magnoliophyta Class: Liliopsida Order: Poales Family: Poaceae Subfamily: Arundinoideae Tribe: Aristideae Genus: Aristida L.
Species
About 300, see text

The three-awns are the grass genus Aristida, distinguished by having three awns (bristles) on each lemma of each floret. The genus includes about 300 species, found worldwide, often in arid warm regions. This genus is among those colloquially called "wiregrasses", "speargrasses" or "needlegrasses".

Aristida stems are ascending to erect, with both basal and cauline leaves. The leaves may be flat or inrolled, and the basal leaves may be tufted. The inflorescences may be either panicle-like or raceme-like, with spiky branches. The glumes of a spikelet are narrow lanceolate, usually without any awns, while the lemmas are hard, three-veined, and have the three awns near the tip. The awns may be quite long; in A. purpurea var. longiseta they may be up to 10 cm.

They are characteristic of semiarid grassland. The Wiregrass Region of North America is named for A. stricta. Other locales where this genus is an important component of the ecosystem include the Carolina Bays, the sandhills of the Carolinas and elsewhere, Mulga scrub in Australia, and the xeric grasslands around Lake Turkana in Africa.

On the other hand, a local increase of the amount of "wiregrass" - which is not well-liked by livestock - is a good indicator of overgrazing.

[edit] Selected species

• Aristida adscensionis L.
• Aristida anaclasta
• Aristida basiramea – Fork-tipped Three-awn, Forked Three-awn
• Aristida behriana F.Muell.
• Aristida beyrichiana
• Aristida burkei – bohlanya-ba-pere (Sesotho: "horse-madness grass")
• Aristida calycina R.Br.
• Aristida chaseae
• Aristida contorta F.Muell.
• Aristida dichotoma Michx. – Shinner's Three-awn, "poverty grass"
• Aristida granitica
• Aristida guayllabambensis
• Aristida hygrometrica R.Br.
• Aristida longespica – Slim-spiked Three-awn
  • Aristida longespica var. geniculata – Red Three-awn
  • Aristida longespica var. longespica
• Aristida mutabilis
• Aristida oligantha Michx. – Prairie Three-awn
• Aristida pallens Cav.
• Aristida portoricensis – Pelos del diablo
• Aristida pungens – Drinn
• Aristida purpurascens Poiret – Arrowfeather Three-awn, Purple Needlegrass
• Aristida purpurea – Purple Three-awn
  • Aristida purpurea var. longiseta
• Aristida ramosa R.Br.
• Aristida refracta
• Aristida spiciformis
• Aristida stricta – Pineland Three-awn, "wiregrass"
• Aristida suringarii
• Aristida swartziana
• Aristida tenuifolia
• Aristida vagans
• Aristida vaginata

[edit] See also

• New Mexico State University Botanical Garden has a large collection of local Aristida species
• Puccinia aristidae, a plant pathogenic urediniomycete fungus first described from three-awn grass

[edit] References

• Hickman, James C. (ed.) (1993): The Jepson Manual - Higher Plants of California: 1234-1235.