Achnatherum contractum

(B.L. Johnson) Barkworth
Common names: Contracted ricegrass
Synonyms: Oryzopsis contracta
Treatment appears in FNA Volume 24. Treatment on page 141.
Please click on the illustration for a higher resolution version.
Illustrator: Cindy Roché

Copyright: Utah State University

Plants tightly cespitose, not rhizomatous. Culms 30-50 cm tall, 1-1.3 mm thick, glabrous; nodes 3-4. Sheaths glabrous; collars puberulent, hairs about 0.2 mm, sometimes the margins with poorly developed tufts of hair to 0.5 mm; ligules 1.8-5 mm, broadly to narrowly acute, glabrous; blades 0.5-1.5 mm wide, flat or convolute, abaxial surfaces smooth, adaxial surfaces scabridulous. Panicles 6-25 cm long, 7-15 cm wide; branches ascending to strongly divergent, longest branches 5-8 cm; pedicels appressed to the branches, paired, unequal, shorter pedicels in each pair usually less than 1/2 as long as the longer pedicels. Spikelets confined to the distal 1/2 of the branches. Glumes saccate below, tapering at midlength, glabrous, midveins sometimes scabridulous, apices acuminate; lower glumes 5.5-7 mm long, 0.9-1.5 mm wide; upper glumes about 0.3 mm shorter; florets 2.5-3.5 mm long, 0.7-1.5 mm thick, fusiform to obovoid; calluses 0.3-0.5 mm, blunt; lemmas densely pilose, hairs at midlength and on the apices similar, 1.2-2 mm, apical lobes 0.5-0.6 mm; awns 6.5-9 mm, readily deciduous, scabrous; paleas similar to the lemmas in length, texture, and pubescence, distal hairs exceeding the paleal apices, apices rounded, flat; anthers about 1.5 mm, penicillate, dehiscent, well-filled. Caryopses 1.5-2.5 mm, globose to obovoid. 2n = 48.

Discussion

Achnatherum contractum grows in rocky grasslands in eastern Idaho, southwestern Montana, and Wyoming. It is a fertile derivative of a Piptatherum micranthum x Achnatherum hymenoides hybrid (Shechter and Johnson 1968; Shechter 1969). Immature specimens of A. hymenoides are sometimes confused with A. contractum because they have contracted panicles with appressed branches and pedicels; they differ in having pedicel pairs in which the shorter pedicel is more than half as long as the longer pedicel.

Selected References

None.

Lower Taxa

None.

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

... more about "Achnatherum contractum"
membranous +  and scarious +
penicillate +
1.5 cm15 mm <br />0.015 m <br /> (?) +
awned +, bifid +, bilobed +  and entire +
0 cm0 mm <br />0 m <br /> (0.7 cm7 mm <br />0.007 m <br />) +
Mary E. Barkworth +
(B.L. Johnson) Barkworth +
1 (?) +  and 3 (?) +
flexuous +
subterminal +  and eccentric +
usually scabrous +  and scabridulous +
not once-geniculate +
0.65 cm6.5 mm <br />0.0065 m <br /> (0.9 cm9 mm <br />0.009 m <br />) +
keeled +  and rounded +
pseudopetiolate +  and branching +
intravaginal +, extravaginal +, branching +  and basal +
swelling +
not evident +
convolute +  and flat +
0.5mm;1.5mm +
flexuous +  and straight +
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 />) +
Contracted ricegrass +
branching +  and not branching +
perennial +  and annual +
30 cm300 mm <br />0.3 m <br /> (50 cm500 mm <br />0.5 m <br />) +
intravaginal +  and basal +
10 cm100 mm <br />0.1 m <br /> (250 cm2,500 mm <br />2.5 m <br />) +
not woody +
0.1 cm1 mm <br />0.001 m <br /> (0.13 cm1.3 mm <br />0.0013 m <br />) +
Mont. +, Colo. +  and Wyo. +
1/5 +  and 1/3 +
liquid +, soft +  and hard +
capillary +
pistillate +  and staminate +
0.25 cm2.5 mm <br />0.0025 m <br /> (0.35 cm3.5 mm <br />0.0035 m <br />) +
sometimes longer +
fusiform +  and obovoid +
1-10-veined +
subtending +
tapering +
membranous +
divergent +  and distributed +
uncinate +
0.12 cm1.2 mm <br />0.0012 m <br /> (0.2 cm2 mm <br />0.002 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 +
0.18 cm1.8 mm <br />0.0018 m <br /> (0.5 cm5 mm <br />0.005 m <br />) +
membranous +
membranous +
inconspicuous +
not lobed +
5 cm50 mm <br />0.05 m <br /> (8 cm80 mm <br />0.08 m <br />) +
0.55 cm5.5 mm <br />0.0055 m <br /> (0.7 cm7 mm <br />0.007 m <br />) +
0.9mm +  and 1.5mm +
scabridulous +
concealed +  and prominent +
3 +  and 4 +
2 +  and 1 +
pubescent +  and glabrous +
well-developed +
not keeled +
reduced +
pubescence +
6cm +  and 25cm +
7 cm70 mm <br />0.07 m <br /> (15 cm150 mm <br />0.15 m <br />) +
dry +  and fleshy +
not prolonged +
1 +  and 60 +
unisexual +  and bisexual +
laterally compressed +  and terete +
1 (?) +  and 3 (?) +
simple +  and compound +
Oryzopsis contracta +
Achnatherum contractum +
Achnatherum +
species +
membranous +
0 cm0 mm <br />0 m <br /> (0.05 cm0.5 mm <br />5.0e-4 m <br />) +
0.3 cm3 mm <br />0.003 m <br /> (?) +
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 +