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Published In: Species Plantarum 1: 82. 1753. (1 May 1753) (Sp. Pl.) Name publication detailView in BotanicusView in Biodiversity Heritage Library
 

Project Name Data (Last Modified On 7/9/2009)
Acceptance : Accepted
Project Data     (Last Modified On 7/22/2009)

 

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13. Aristida L. (three‑awn)

(Allred, 1986)

Plants with C4 photosynthesis, annual or perennial, without noticeable rhizomes, forming tufts or clumps. Flowering stems erect or ascending, usually branched, sometimes only near the base. Leaf sheaths open most of their length, the ligule a fringe of short hairs, sometimes from a minute, membranous base. Leaf blades narrow, often inrolled. Inflorescences narrow panicles or spikelike racemes (broad panicles with spreading branches elsewhere). Spikelets with 1 fertile floret, disarticulating above the glumes. Glumes 2, the lower occasionally shed early, papery, linear to narrowly lanceolate, with 1, 3, or 5 nerves, often with an awn, in species with multiple nerves the upper glume also with 2 soft lateral awns. Lemmas hardened, linear, wrapped around the palea and fruit, rounded on the back, 3‑nerved, yellowish green or more commonly green mottled with purple, the tip tapered to 3 awns, these sometimes united into a column at the base, the lateral awns sometimes reduced and much shorter than the central awn. Paleas much shorter than the lemmas, usually 2‑nerved, lacking awns. Stamens (1)3. Fruits linear, shed inside the persistent lemmas. About 250 species, worldwide, but most abundant in tropical and warm‑temperate regions.

Although the long, often bent or twisted awns of Aristida species aid in dispersal of the fruits in animal fur or botanists’ socks, they render these grasses relatively uninteresting as forage to livestock and other grazers, which can receive injuries to the noses, eyes, mouths, and intestines when attempting to graze on them.

 

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1 Awns shed eventually, jointed at the tip of the lemma (with a line visible across the base of the awns at the attachment point to the lemma) 3 Aristida desmantha
+ Awns persistent, not jointed at the tip of the lemma (the awns arise as a continuation of the lemma tip, without a cross-line) (2)
2 (1) Lower and young leaf sheaths with woolly or cobwebby patches of grayish white hairs; all or at least the lowermost nodes of the flowering stems with tufts of woolly hairs 5 Aristida lanosa
+ Leaf sheaths and nodes of flowering stems glabrous or hairy, but not with patches or tufts of woolly hairs (3)
3 (2) Lower glume with 3 or 5 nerves; upper glume divided at the tip with the awn arising from between 2 slender teeth (4)
+ Lower glume with 1 nerve; upper glume awnless or with the awn arising from an undivided tip (5)
4 (3) Central awn of lemma (20–)35–70 mm long, straight to somewhat curved outward, but not coiled; awn of upper glume 7–17 mm long 7 Aristida oligantha
+ Central awn of lemma 9–35 mm long, spirally coiled at the base when dry (and thus differentiated from the lateral awns, which are not coiled); awn of upper glume 3–7 mm long 9 Aristida ramosissima
5 (3) Central awn of lemma spirally coiled at the base when dry (and thus differentiated from the lateral awns, which are not coiled) (6)
+ Central awn of lemma straight to sharply curved outward, but not coiled (7)
6 (5) Lateral awns of lemma 1.5–4.0 mm long, erect or nearly so; upper glume 4–10(–12) mm long 4 Aristida dichotoma
+ Lateral awns of lemma 5–12 mm long, spreading; upper glume 10–15 mm long 2 Aristida basiramea
7 (5) Lower glume 1/2 to 2/3 as long as the upper glume; awns of lemma flattened at the base 1 Aristida adscensionis
+ Lower glume about as long as or slightly longer than the upper glume; awns of lemma circular in cross-section, not flattened (8)
8 (7) Plants annual, with a soft base; lateral awns of lemma 1/2 or less as long as the central awn 6 Aristida longespica
+ Plants perennial, with a firm, hardened base; lateral awns of lemma about as long as the central awn 8 Aristida purpurascens
 
 
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