Achnatherum diegoense
Achnatherum hendersonii
San Diego County needlegrass, San Diego needlegrass
Henderson's needlegrass, Henderson's rice grass
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.
10-35 cm tall, 0.3-0.9 mm thick, pubescent below the nodes, glabrous or sparsely puberulent elsewhere;
nodes 1-2.
21-25 cm long, (2)4-8 cm wide;
branches strongly divergent to ascending, straight, lower branches 5-7 cm.
4-12 cm long, 2-5 cm wide, erect;
branches and pedicels straight, appressed to strongly ascending, longest branches 2-7 cm.
appressed to the branches.
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.
subequal, 3.5-5.5 mm long, 1-1.5 mm wide, 5-veined;
lower glumes obtuse, apices rounded to acute;
upper glumes rounded to obtuse, subequal or to 1 mm shorter than the lower glumes;
florets 3.5-4.5 mm long, 1-1.5 mm wide, fusiform, laterally compressed;
calluses 0.3-0.5 mm, blunt;
lemmas coriaceous, glabrous, shiny, apical lobes about 0.2 mm long, thick;
awns 6-10 mm, readily deciduous, not geniculate, scabrous;
paleas about 3 mm, from3/4 as long as to equaling the lemmas, indurate, glabrous, apices rounded, flat;
anthers about 2.5 mm, dehiscent, penicillate.
2.5-4 mm.
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.
sheaths completely or mostly glabrous, margins sometimes ciliate distally;
collars glabrous;
ligules 0.4-1 mm, hyaline, glabrous or pubescent, rounded;
blades tightly folded or convolute, to 1 mm wide or thick, abaxial surfaces scabrous, adaxial surfaces pubescent.
= unknown.
= 34.
Achnatherum diegoense
Achnatherum hendersonii
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.)
Achnatherum hendersonii grows in dry, rocky, shallow soil, in sagebrush or ponderosa pine associations. It is known from only three counties: Yakima and Kittitas counties, Washington, and Crook County, Oregon. Maze (1981) noted that, at one site, A. hendersonii was restricted to areas subject to frost heaving, although under cultivation, it can grow without such disturbance. He hypothesized that its survival in such sites is attributable to a competitive advantage gained by the structure of its root system. Unlike Poa secunda, which grew in the surrounding, undisturbed areas, the outer cortex and epidermis of the roots of A. hendersonii form a sheath around the stele and inner cortex. When the roots are pulled, this sheath slips and breaks but the internal structures remain intact. In Poa secunda, the outer part of the root is attached to the central core and, when the roots are pulled, they break. Achnatherum hendersonii also differs from P. secunda in having relatively few (9-12), evenly distributed roots that extend to 30 cm.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
CA
WildflowerSearch
iNaturalist
USDA Plants Database
OR
WA
Flora NW
PNW Herbaria
