Achnatherum diegoense |
Poaceae tribe Stipeae |
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San Diego County needlegrass, San Diego needlegrass |
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Habit | Plants cespitose, not rhizomatous. | Plants usually perennial; usually tightly to loosely cespitose, sometimes rhizomatous. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Culms | 110-140 cm tall, 2.5-4 mm thick, internodes densely and retrorsely pubescent for 3-9 mm below the nodes, particularly the lower nodes, glabrous or retrorsely puberulent elsewhere; nodes 3, pubescent or glabrate. |
annual or perennial, not woody, branches 1 to many at the upper nodes. |
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Leaves | basally concentrated to evenly distributed; sheaths open, margins not fused, sometimes ciliate distally, basal sheaths sometimes concealing axillary panicles (cleistogenes), sometimes wider than the blade; collars sometimes with tufts of hair at the sides extending to the top of the sheaths; auricles absent; ligules scarious, often ciliate, cilia usually shorter than the base, ligules of the lower and upper cauline leaves sometimes differing in size and vestiture; pseudopetioles absent; blades linear to narrowly lanceolate, venation parallel, cross venation not evident, cross sections non-Kranz, without arm or fusoid cells; epidermes of adaxial surfaces sometimes with unicellular microhairs, cells not papillate. |
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Panicles | 21-25 cm long, (2)4-8 cm wide; branches strongly divergent to ascending, straight, lower branches 5-7 cm. |
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Inflorescences | usually terminal panicles, occasionally reduced to racemes in depauperate plants, sometimes 2-3 panicles developing from the highest cauline node. |
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Spikelets | appressed to the branches. |
usually with 1 floret, sometimes with 2-6 florets, laterally compressed to terete; rachillas not prolonged beyond the base of the floret in spikelets with 1 floret, prolonged beyond the base of the distal floret in spikelets with 2-6 florets, prolongation hairy, hairs 2-3 mm; disarticulation above the glumes and beneath the florets. |
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Glumes | subequal, 8-11.5 mm; lower glumes 0.5-1 mm wide, 3-5-veined; upper glumes 3-veined; florets 5.5-7.5 mm long, 0.7-1 mm thick, fusiform, terete; calluses 0.25-1.2 mm, acute; lemmas evenly hairy, hairs at midlength and at the apices 0.5-1 mm, apical lobes 0.2-0.4 mm, membranous, flexible; awns 20-50 mm, persistent, twice-geniculate, all segments scabrous to scabridulous, terminal segment straight; paleas 2.6-3.8 mm, 1/2 - 3/4 as long as the lemmas, pubescent, hairs not extending beyond the apices, veins terminating below the apices, apices rounded; anthers 2.5-4 mm, dehiscent, not penicillate. |
usually exceeding the floret(s), always longer than 1/4 the length of the adjacent floret, 1-10-veined, narrowly lanceolate to ovate, hyaline or membranous, flexible; florets usually terete, sometimes laterally or dorsally compressed; calluses usually well-developed, rounded or blunt to sharply pointed, often antrorsely strigose; lemmas lanceolate, rectangular, or ovate, membranous to coriaceous or indurate, 3-5-veined, veins inconspicuous, apices entire, bilobed, or bifid, awned, lemma-awn junction usually conspicuous, awns 0.3-30 cm, not branched, usually terminal and centric or eccentric, sometimes subterminal, caducous to persistent, not or once- to twice-geniculate, if geniculate, proximal segment(s) twisted, distal segment straight, flexuous, or curled, not or scarcely twisted; lodicules 2 or 3; anthers 1 or 3, sometimes differing in length within a floret; ovaries glabrous throughout or pubescent distally; styles 2(3-4)-branched. |
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Caryopses | ovoid to fusiform, not beaked, pericarp thin; hila linear; embryos less than 1/3 the length of the caryopses. |
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Basal | sheaths mostly glabrous or puberulent, margins ciliate distally; collars glabrous or with hairs, hairs mostly to 0.5 mm, sides with tufts of 1.5-2 mm hairs; ligules 0.4-2 mm, rounded to acute, abaxial surfaces hairy, hairs to 0.5 mm; upper ligules 1-3 mm, similar in structure and pubescence; blades 1-3.5 mm wide, abaxial surfaces smooth or scabrous, adaxial surfaces prominently ribbed, hairy, hairs 2-3 mm. |
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x | = 7, 8, 10, 11, 12. |
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2n | = unknown. |
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Achnatherum diegoense |
Poaceae tribe Stipeae |
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Distribution |
CA
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Discussion | Achnatherum diegoense grows in chaparral and coastal sage scrub, on rocky soil near streams or the coast, at 0-350 m, on the Channel Islands of Santa Barbara County, California, and, on the mainland, in Ventura and San Diego counties south into Baja California, Mexico. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
The tribe Stipeae includes about 15 genera and approximately 500 species. It grows in Africa, Australia, South and North America, and Eurasia. In Australia, South America, and Asia, it is often the dominant grass tribe over substantial areas. It is not present in southern India, and is represented by only one native species in southern Africa. Most species grow in arid or seasonally arid, temperate regions. Morphological considerations have led to the Stipeae being placed in three different subfamilies (Pooideae, Bambusoideae, and Arundinoideae) in the past, and even to recognition as a subfamily. Molecular data support its treatment as an early diverging lineage within the Pooideae (Soreng and Davis 1998; Grass Phylogeny Working Group 2001) that is more closely related to the Meliceae than the core pooid tribes. Decker (1964) suggested including Ampelodesmos in the Stipeae on the basis of the cross sectional anatomy of its leaf blades. His suggestion is supported, not always strongly, by molecular studies (Soreng and Davis 1998; Grass Phylogeny Working Group 2001; Jacobs et al. 2006). The usual alternative is to treat Ampelodesmos as the only genus of a closely related, monospecific tribe, the Ampelodesmeae (Conert) Tutin, because it is so distinct from other members of the Stipeae, being, for example, the only member of the tribe with more than 1 floret in its spikelets and rachillas that are prolonged beyond the base of the terminal floret in a spikelet. The lowest chromosome number known in the Stipeae is 2n =18 (Prokudin et al. 1977), suggesting that all members of the tribe are ancient polyploids. The wide range of base numbers listed is based on numbers for the various genera. The primary basic chromosome number for the tribe is probably 5 or 6, with higher numbers reflecting ancient euploidy. (Discussion copyrighted by Flora of North America; reprinted with permission.) |
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Key |
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Source | FNA vol. 24, p. 131. | FNA vol. 24, p. 109. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Parent taxa | Poaceae > subfam. Pooideae > tribe Stipeae > Achnatherum | Poaceae > subfam. Pooideae | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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Name authority | (Swallen) Barkworth | Dumort. | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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