Achnatherum hendersonii

(Vasey) Barkworth
Common names: Henderson's needlegrass
Synonyms: Stipa hendersonii Oryzopsis hendersonii
Treatment appears in FNA Volume 24. Treatment on page 139.
Please click on the illustration for a higher resolution version.
Illustrator: Cindy Roché

Copyright: Utah State University

Plants tightly cespitose, not rhizomatous. Culms 10-35 cm tall, 0.3-0.9 mm thick, pubescent below the nodes, glabrous or sparsely puberulent elsewhere; nodes 1-2. Basal 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. Panicles 4-12 cm long, 2-5 cm wide, erect; branches and pedicels straight, appressed to strongly ascending, longest branches 2-7 cm. Glumes 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. Caryopses 2.5-4 mm. 2n = 34.

Discussion

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.

Selected References

None.

Lower Taxa

None.

"decumbent" is not a number."prolonged" is not a number.

... more about "Achnatherum hendersonii"
membranous +  and scarious +
penicillate +
2.5 cm25 mm <br />0.025 m <br /> (?) +
awned +, bifid +, bilobed +  and entire +
Rounded (?) +  and Acute (?) +
0 cm0 mm <br />0 m <br /> (0.7 cm7 mm <br />0.007 m <br />) +
Mary E. Barkworth +
(Vasey) Barkworth +
1 (?) +  and 3 (?) +
flexuous +
subterminal +  and eccentric +
usually scabrous +  and scabridulous +
not geniculate +
0.6 cm6 mm <br />0.006 m <br /> (1 cm10 mm <br />0.01 m <br />) +
keeled +  and rounded +
pseudopetiolate +  and branching +
intravaginal +, extravaginal +, branching +  and basal +
swelling +
not evident +
convolute +  and folded +
0 cm0 mm <br />0 m <br /> (0.1 cm1 mm <br />0.001 m <br />) +
thick;wide +
appressed;strongly ascending +
spikelike +
well-developed +
0.03 cm0.3 mm <br />3.0e-4 m <br /> (0.05 cm0.5 mm <br />5.0e-4 m <br />) +
Henderson's needlegrass +
branching +  and not branching +
perennial +  and annual +
10 cm100 mm <br />0.1 m <br /> (35 cm350 mm <br />0.35 m <br />) +
intravaginal +  and basal +
puberulent +, glabrous +  and pubescent +
10 cm100 mm <br />0.1 m <br /> (250 cm2,500 mm <br />2.5 m <br />) +
not woody +
0.03 cm0.3 mm <br />3.0e-4 m <br /> (0.09 cm0.9 mm <br />9.0e-4 m <br />) +
Idaho +, Wash. +  and Oreg. +
1/5 +  and 1/3 +
liquid +, soft +  and hard +
capillary +
pistillate +  and staminate +
0.35 cm3.5 mm <br />0.0035 m <br /> (0.45 cm4.5 mm <br />0.0045 m <br />) +
sometimes longer +
compressed +  and fusiform +
1mm +  and 1.5mm +
3.5mm +  and 5.5mm +
subtending +
obtuse +, acute +  and acuminate +
subequal +
membranous +
1mm +  and 1.5mm +
divergent +  and distributed +
uncinate +
0.2 cm2 mm <br />0.002 m <br /> (0.3 cm3 mm <br />0.003 m <br />) +
solid +  and hollow +
basally concentrated +  and evenly distributed +
0 cm0 mm <br />0 m <br /> (0.6 cm6 mm <br />0.006 m <br />) +
ovate +, rectangular +  and lanceolate +
coriaceous +
pubescent +  and glabrous +
0.04 cm0.4 mm <br />4.0e-4 m <br /> (0.1 cm1 mm <br />0.001 m <br />) +
membranous +
membranous +
inconspicuous +
not lobed +
2 cm20 mm <br />0.02 m <br /> (7 cm70 mm <br />0.07 m <br />) +
concealed +  and prominent +
1 +  and 2 +
2 +  and 1 +
pubescent +  and glabrous +
well-developed +
not keeled +
reduced +
3 cm30 mm <br />0.03 m <br /> (?) +
4cm +  and 12cm +
2 cm20 mm <br />0.02 m <br /> (5 cm50 mm <br />0.05 m <br />) +
appressed +  and strongly ascending +
dry +  and fleshy +
not prolonged +
1 +  and 60 +
unisexual +  and bisexual +
laterally compressed +  and terete +
1 (?) +  and 3 (?) +
simple +  and compound +
Stipa hendersonii +  and Oryzopsis hendersonii +
Achnatherum hendersonii +
Achnatherum +
species +
membranous +
rounded +  and obtuse +
0-1 mm +  and subequal +
inconspicuous +
0.1 cm1 mm <br />0.001 m <br /> (0.3 cm3 mm <br />0.003 m <br />) +
plant +  and cespitose +
aquatic +  and terrestrial +