Achnatherum nelsonii

(Scribn.) Barkworth
Synonyms: Stipa williamsii Stipa occidentalis var. nelsonii Stipa nelsonii
Treatment appears in FNA Volume 24. Treatment on page 123.
Please click on the illustration for a higher resolution version.
Illustrator: Cindy Roché

Copyright: Utah State University

Plants cespitose, not rhizomatous. Culms 40-175 cm tall, 0.7-2.4 mm thick, lower cauline internodes usually glabrous, sometimes slightly pubescent below the lower nodes; nodes 2-5. Basal sheaths glabrous or sparsely to densely pubescent, margins sometimes ciliate; collars glabrous or somewhat pubescent, without tufts of hair on the sides, collars of the flag leaves glabrous or sparsely pubescent; basal ligules 0.2-0.7 mm, membranous, truncate to rounded, usually not ciliate; upper ligules 1-1.5 mm, acute; blades (0.5) 1.2-5 mm wide. Panicles 9-36 cm long, 0.8-2 cm wide; branches ascending to appressed, straight. Spikelets appressed to the branches. Glumes 6-12.5 mm long, 0.7-1.1 mm wide; lower glumes exceeding the upper glumes by 0.2-0.8 mm; florets 4.5-7 mm long, 0.6-0.9 mm thick, fusiform; calluses 0.2-1 mm, blunt to sharp, dorsal boundary of the glabrous tip with the callus hairs almost straight to acute; lemmas evenly hairy, hairs at midlength 0.5-1 mm, hairs at the apices to 2 mm, erect to ascending, apical lobes 0.1-0.4 mm, membranous, flexible; awns 19-45 mm, persistent, twice-geniculate, first 2 segments scabrous or with hairs shorter than 0.5 mm, terminal segment straight; paleas 2-4 mm, 1/3 – 2/3 as long as the lemmas, pubescent, hairs usually not exceeding the apices, veins terminating before the apices, apices rounded; anthers 2-3.5 mm, dehiscent, not penicillate. Caryopses 3-4 mm, fusiform. 2n = 36, 44.

Distribution

Ariz., Colo., N.Mex., Tex., Utah, Calif., Oreg., Mont., Wyo., Wash., Alta., B.C., Sask., Yukon, Nev., Idaho, S.Dak.

Discussion

Achnatherum nelsonii grows in meadows and openings, from sagebrush steppe and pinyon-juniper woodlands to subalpine forests, at 500-3500 m. It flowers in late spring to early summer, differing in this respect from A. perplexum. It is sometimes sympatric with A. lettermanii, from which it differs in its shorter paleas and wider leaves, and its tendency to grow in deeper or less disturbed soils. It differs from A. lemmonii in having wider leaf blades, shorter paleas, and membranous lemma lobes, and from A. nevadense and A. occidentale in its scabrous awns and the truncate to acute boundary of the glabrous tip of the callus with the callus hairs.

The two subspecies intergrade to some extent. There is also intergradation with Achnatherum occidentale, possibly as a result of hybridization and introgression.

Selected References

None.

Key

1 Calluses blunt, dorsal boundary of the glabrous tip and the callus hairs almost straight to rounded; awns 19-31 mm long Achnatherum nelsonii subsp. dorei
1 Calluses sharp, dorsal boundary of the glabrous tip and the callus hairs acute; awns 19-45 mm long Achnatherum nelsonii subsp. nelsonii

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

... more about "Achnatherum nelsonii"
membranous +  and scarious +
not penicillate +
0.2 cm2 mm <br />0.002 m <br /> (0.35 cm3.5 mm <br />0.0035 m <br />) +
awned +, bifid +, bilobed +  and entire +
Rounded (?) +  and Acute (?) +
0 cm0 mm <br />0 m <br /> (0.2 cm2 mm <br />0.002 m <br />) +
0 cm0 mm <br />0 m <br /> (0.7 cm7 mm <br />0.007 m <br />) +
Mary E. Barkworth +
(Scribn.) Barkworth +
1 (?) +  and 3 (?) +
flexuous +
subterminal +  and eccentric +
usually scabrous +  and scabridulous +
not once-geniculate +
1.9 cm19 mm <br />0.019 m <br /> (4.5 cm45 mm <br />0.045 m <br />) +
keeled +  and rounded +
glabrous or +  and sparsely densely pubescent +
pseudopetiolate +  and branching +
intravaginal +, extravaginal +, branching +  and basal +
swelling +
not evident +
involute +, convolute +  and flat +
1.2mm;5mm +
ascending;appressed +
spikelike +
well-developed +
acute +, blunt +  and sharp +
0.02 cm0.2 mm <br />2.0e-4 m <br /> (0.1 cm1 mm <br />0.001 m <br />) +
pubescent +  and glabrous +
branching +  and not branching +
perennial +  and annual +
40 cm400 mm <br />0.4 m <br /> (175 cm1,750 mm <br />1.75 m <br />) +
intravaginal +  and basal +
10 cm100 mm <br />0.1 m <br /> (250 cm2,500 mm <br />2.5 m <br />) +
not woody +
0.07 cm0.7 mm <br />7.0e-4 m <br /> (0.24 cm2.4 mm <br />0.0024 m <br />) +
Ariz. +, Colo. +, N.Mex. +, Tex. +, Utah +, Calif. +, Oreg. +, Mont. +, Wyo. +, Wash. +, Alta. +, B.C. +, Sask. +, Yukon +, Nev. +, Idaho +  and S.Dak. +
1/5 +  and 1/3 +
liquid +, soft +  and hard +
capillary +
pistillate +  and staminate +
0.45 cm4.5 mm <br />0.0045 m <br /> (0.7 cm7 mm <br />0.007 m <br />) +
sometimes longer +
fusiform +
6mm +  and 12.5mm +
subtending +
obtuse +, acute +  and acuminate +
membranous +
0.7mm +  and 1.1mm +
divergent +  and distributed +
erect +  and ascending +
uncinate +
0.5 cm5 mm <br />0.005 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 +
stiffly membranous +  and coriaceous +
pubescent +  and glabrous +
membranous +
membranous +
inconspicuous +
not lobed +
concealed +  and prominent +
2 +  and 5 +
2 +  and 1 +
pubescent +  and glabrous +
well-developed +
1/3 +  and 2/3 +
not keeled +
reduced +
0.2 cm2 mm <br />0.002 m <br /> (0.4 cm4 mm <br />0.004 m <br />) +
9cm +  and 36cm +
0.8 cm8 mm <br />0.008 m <br /> (2 cm20 mm <br />0.02 m <br />) +
dry +  and fleshy +
not prolonged +
1 +  and 60 +
unisexual +  and bisexual +
laterally compressed +  and terete +
1 (?) +  and 3 (?) +
simple +  and compound +
Stipa williamsii +, Stipa occidentalis var. nelsonii +  and Stipa nelsonii +
Achnatherum nelsonii +
Achnatherum +
species +
membranous +
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 +