keys to the vascular plants of east texas - Botanical Research ...

828 POACEAE/ARISTIDA
AA large homogeneous genus of 250–300 species found nearly throughout the world, but particularly
frequent in warm, semi-arid environments (Allred & Valdés-Reyes 1995; Allred
2003d). The species are characterized by C4 photosynthesis (Watson & Dallwitz 1992). “The
divergent awns aid in wind and animal transportation of the florets and, by holding the florets
and the caryopses they contain at an angle to the ground, in establishment” (Allred 2003d).
However, according to Yatskievych (1999), the long awns reduce the value of the species as forage
and can cause injuries to the noses, eyes, mouths, and intestines of grazers. In addition, the
sharp calluses can be problematic for livestock and are irritating when in shoes and socks.
Aristida species are “notorious for their taxonomic difficulty” (Allred & Valdés-Reyes 1995).
(Latin: arista, a beard or awn) (subfamily Aristidoideae, tribe Aristideae)
REFERENCES: Hitchcock 1924, 1935; Holmgren & Holmgren 1977; Allred 1984a, 1984b, 1985a,
1985b, 1986, 2003d; Sutherland 1986; Tucker 1990; Allred & Valdés-Reyes 1995.
1. Lateral awns of lemma much reduced, 1–2(–4) mm long, erect; central awn of lemma 3–8 mm
long, deflexed, with a spiral coil at base like a corkscrew ________________________________ A. dichotoma
1. Lateral awns of lemma usually well-developed, (2–)4 mm or more long (often much longer),
erect to spreading, horizontal, or even deflexed; central awn of lemma (5–)10–36 mm long, deflexed
to erect, without a spiral coil at base (but may have a semicircular bend) OR in 1 rare
species (A. basiramea) with a spiral coil at base.
2. Awns of lemma, at least central one, spirally coiled at base like a corkscrew OR with a distinct
semicircular bend at base.
3. Lemma (8–)14–25 mm long (to base of awn); lower glume 3–7-veined, 11–20 mm long,
the upper glume longer, usually 16–25 mm long (including awn); lateral awns of lemma
very short, 0–7 mm long ___________________________________________________ A. ramosissima
3. Lemma 4–10 mm long (to base of awn); lower glume 1-veined, the glumes � equal, 17
mm or less long (including awn); lateral awns of lemma 4–30(–35) mm long.
4. Central and lateral awns of lemma ca. equal, 20–30(–35) mm long, the central awn with a
semicircular bend at base; awn column with a well-defined joint at base, separating at
the joint at maturity (check mature spikelets); glumes 10–17 mm long; culms (30–)45–
80 cm tall ______________________________________________________________ A. desmantha
4. Central and lateral awns of lemma different in length, the lateral awns 4–10 mm long,
the central awn 9–15 mm long, spirally coiled at base like a corkscrew; awn column not
jointed basally and not separating at maturity; glumes ca. 8–12 mm long; culms 45 cm
or less tall ______________________________________________________________ A. basiramea
2. Awns of lemma nearly straight or curved, but neither spirally coiled basally nor with a distinct
semicircular bend.
5. Lemma usually 16–28 mm long to base of awn; central and lateral awns ca. equal (laterals
at least 3/4 as long as central); lower glume 3–7-veined _____________________________ A. oligantha
5. Lemma 15 mm or less long to base of awn; central and lateral awns ca. equal OR not so;
lower glume 1–2-veined.
6. Leaf sheaths (at least lower ones) lanate, the hairs cobwebby, kinked, and intertwined
__________________________________________________________________________ A. lanosa
6. Leaf sheaths not lanate, varying from glabrous to pilose, the hairs, if present, � straight,
not cobwebby, and usually appressed.
7. Panicles open, at least the lower branches spreading.
8. Awns of lemma 4–10+ cm long; upper glume usually 14–25 mm long; lemma 12–
16 mm long (to base of awns) ________________________________ A. purpurea var. longiseta
8. Awns of lemma 3–4.5 cm long; upper glume usually 15 mm or less long; lemma
usually 10–12 mm long (to base of awns) _____________________ A. purpurea var. purpurea
7. Panicles contracted, the branches usually all stiffly appressed along the main axis.
9. Lemma narrowing into a slender twisted awn column (sometimes called a beak)
ca. 0.1 mm wide and 1–4 mm long _____________________________ A. purpurea var. nealleyi