10.08 HESPEROSTIPA (M.K. Elias) Barkworth
Mary E. Barkworth
Plants perennial; cespitose, not rhizomatous. Culms 12–110 cm, erect, not branching at the upper nodes; prophylls shorter than the sheaths. Leaves not overwintering, not basally concentrated; cleistogenes not developed; sheaths smooth; auricles absent; ligules membranous, frequently ciliate; blades 4–40 cm long, 0.5–4.5 mm wide, usually tightly involute, adaxial surfaces conspicuously ridged, apices narrowly acute, not sharp. Inflorescences terminal panicles, contracted or open. Spikelets 15–60 mm, with 1 floret; rachillas not prolonged beyond the base of the floret; disarticulation above the glumes and beneath the floret. Glumes 15–60 mm long, 2–4 mm wide, tapering from near the base to a hairlike tip; florets 7–25 mm, narrowly cylindrical; calluses 2–6 mm, sharp, densely strigose distally; lemmas indurate, smooth, margins flat, slightly overlapping at maturity, the upper portion fused into a papillose, ciliate crown, awned, lemma-awn junction distinct; awns 50–225 mm, persistent, twice-geniculate, often weakly so, lower segments twisted and scabrous to pilose, terminal segment not twisted, usually scabridulous or pilose; paleas equal to the lemmas, flat, pubescent, coriaceous, 2-veined, veins terminating at the apices, apices indurate, prow-tipped; anthers 3, 1.2–9 mm. Caryopses fusiform, not ribbed. x = 11. Name from the Greek hesperos, ‘west’, and the generic name Stipa.
Hesperostipa is a North American endemic that resembles the Eurasian Stipa sensu stricto in overall morphology, but is more closely related to the primarily South American genera Piptochaetium and Nassella. It differs from Stipa sensu stricto in its indurate palea apices and its lemma epidermal patterns. There are five species in the genus, four of which are found in the Flora region. The fifth species, from southern Mexico, is known only from the type specimen.
SELECTED REFERENCES Barkworth, M.E. 1977. A taxonomic study of the large-glumed species of Stipa (Gramineae) in Canada. Canad. J. Bot. 56:606–625; Barkworth, M.E. and J. Everett. 1987. Evolution in the Stipeae: Identification and relationships of its monophyletic taxa. Pp. 251–264 in T.R. Soderstrom, K.W. Hilu, C.S. Campbell, and M.E. Barkworth (eds.). Grass Systematics and Evolution. Smithsonian Institution Press, Washington, D.C., U.S.A. 473 pp.; Elias, M.K. 1942. Tertiary Prairie Grasses and Other Herbs from the High Plains. Geological Society of America Special Paper No. 41. The [Geological] Society [of America, New York, New York, U.S.A.]. 176 pp.; Misra, K.C. 1961. Geography, morphology, and environmental relationships of certain Stipa species in the northern Great Plains. Ph.D. dissertation, University of Saskatchewan, Saskatoon, Saskatchewan, Canada. 141 pp.; Misra, K.C. 1963. Phytogeography of the genus Stipa L. Trop. Ecol. 4:1–20 [reprint pagination]; Thomasson, J.R. 1979. Late Cenozoic Grasses and Other Angiosperms from Kansas, Nebraska, and Colorado: Biostratigraphy and Relationships to Living Taxa. Kansas Geological Survey, Bulletin No. 218. University of Kansas, Lawrence, Kansas, U.S.A. 68 pp.
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1. Awns pilose on all segments, the terminal segment with hairs 1–3 mm long ... H. neomexicana
1. Awns scabrous to strigose on the first 2 segments, the terminal segment scabridulous ... 2
2. Lemmas usually evenly white-pubescent, sometimes glabrous immediately above the callus; lower ligules often lacerate ... H. comata
2. Lemmas unevenly pubescent with brown to beige hairs; lower ligules not lacerate ... 3
3. Florets 8.5–14(17) mm long; awns 50–105 mm long; lower nodes usually glabrous, occasionally evenly pubescent ... H. curtiseta
3. Florets 15–25 mm long; awns 90–190 mm long; lower nodes usually with lines of pubescence ... H. spartea
1. Hesperostipa comata (Trin. & Rupr.) Barkworth
Culms 12–110 cm; lower nodes glabrous or pubescent. Lower sheaths glabrous or pubescent, not ciliate; ligules of lower leaves 1–6.5 mm, scarious, usually acute, sometimes trun-cate, often lacerate; ligules of upper leaves to 7 mm; blades 0.5–4 mm wide, usually invol-ute. Panicles 10–32 cm, contracted. Glumes 16–35 mm, 3–5-veined; lower glumes 18–35 mm; upper glumes 1–3 mm shorter; florets 7–13 mm; calluses 2–4 mm; lemmas evenly pubescent, hairs about 1 mm, white, sometimes glabrous immediately above the callus; awns 65–225 mm, first 2 segments scabrous to strigose, hairs shorter than 1 mm, terminal segment scabridulous.
Hesperostipa comata is found primarily in the cool deserts, grasslands, and pinyon-juniper forests of western North America. The two subspecies overlap geographically, but are only occasionally sympatric. Both are primarily cleistogamous.
1. Terminal awn segment 40–120 mm long, sinuous to curled at maturity; lower cauline nodes usually concealed by the sheaths; panicles often partially enclosed in the uppermost sheath at maturity ... subsp. comata
1. Terminal awn segment 30–80 mm long, straight; lower cauline nodes usually exposed; panicles usually completely exserted at maturity ... subsp. intermedia
Hesperostipa comata (Trin. & Rupr.) Barkworth subsp. comata
Lower cauline nodes usually concealed by the sheaths. Panicles often partially included in the uppermost sheath at maturity. Awns 75–225 mm, terminal segment 40–120 mm, sinuous to curled. 2n = 38, 44, 46.
Hesperostipa comata subsp. comata grows on well-drained soils of cool deserts, grasslands, and sagebrush associations, at elevations of 200–2500 m. It is widespread and often abundant in western and central North America, particularly in disturbed areas. It is similar to H. neomexicana, differing primarily in having awns that are either not hairy or have hairs that are no more than 0.5 mm long, and in having thinner, longer ligules. Intermediates to H. neomexicana exist but are not common.
Hesperostipa comata subsp. intermedia (Scribn. & Tweedy) Barkworth
Lower cauline nodes usually exposed. Panicles usually fully exserted at maturity. Awns 65–130 mm, terminal segment 30–80 mm, straight. 2n = 44–46.
Hesperostipa comata subsp. intermedia is found in pinyon-juniper woodlands, at elevations of 2175–3075 m, in the Sierra Nevada and Rocky Mountains, from southern Canada to New Mexico. It resembles H. curtiseta, but differs in its evenly pubescent lemmas and its often lacerate ligules.
2. Hesperostipa neomexicana (Thurb.) Barkworth
New Mexican Needlegrass
Culms 40–100 cm; lower nodes glabrous. Lower sheaths glabrous or puberulent, not ciliate; ligules of lower leaves 0.5–1 mm, thickly membranous, rounded; ligules of upper leaves to 3 mm, scarious, acute; blades 0.5–1 mm wide. Panicles 10–30 cm. Glumes subequal, 30–60 mm; florets 15–18 mm; calluses 4–5 mm; lemmas evenly pubescent, hairs shorter than 1 mm; awns 120–220 mm, first 2 segments hairy, hairs mostly 0.2–1 mm, terminal segment flexible, pilose, hairs 1–3 mm. 2n = 44.
Hesperostipa neomexicana grows in grassland, oak, and pinyon pine associations, from 800–2400 m, usually in well-drained, rocky areas in the southwestern United States and adjacent Mexico. It is similar to H. comata subsp. comata, differing in its longer awn hairs and shorter ligules.
3. Hesperostipa curtiseta (Hitchc.) Barkworth
Culms 24–65 cm; lower nodes usually glabrous, sometimes evenly pubescent, often con-cealed by the lower sheaths. Lower sheaths usually glabrous; ligules of lower leaves 0.2–1 mm, truncate to rounded, often highest at the sides, stiff; ligules of upper leaves to 3.5 mm, usually acute to rounded, sometimes truncate; blades 1.3–3 mm wide. Panicles 6–24 cm. Glumes subequal, 15–30 mm; florets 8.5–14 mm; calluses 3–5 mm; lemmas unevenly pubescent, densely pubescent on the margins, more sparsely pubescent elsewhere on the lower portion of the lemmas, usually glabrous distally, hairs brown at maturity; awns 50–105 mm, scabrous to scabridulous throughout, terminal segment straight. 2n = 46.
Hesperostipa curtiseta grows on light to clay loams in the prairies and northern portion of the central plains and northern intermontane grasslands, at elevations from 750–2050 m, extending primarily from British Columbia to Manitoba and North Dakota. It resembles H. comata subsp. intermedia, but differs in having unevenly pubescent lemmas and non-lacerate ligules. It is also very similar to H. spartea, differing in its smaller size, usually glabrous or evenly pubescent culm nodes, usually glabrous sheaths, and shorter florets. Misra (1961) argued that its shorter florets and awns restrict H. curtiseta to more mesic sites than H. spartea.
4. Hesperostipa spartea (Trin.) Barkworth
Culms 45–90 (145) cm; lower nodes usually crossed by lines of pubescence, occasion-ally glabrous. Lower sheaths usually with ciliate margins; ligules of lower leaves 0.3–3 mm, stiff, truncate to rounded, usually entire; ligules of upper leaves 3–7.5 mm, thin, acute, often lacerate; blades 1.5–4.5 mm wide. Panicles 10–25 cm. Glumes 22–45 mm, subequal; florets 15–25 mm; calluses 3.5–6 mm; lemmas unevenly pubescent, densely pubescent on the margins and in lines on the lower portion of the lemmas, glabrous distally, hairs brown at maturity; awns 90–190 mm, terminal segment straight, scabridulous. 2n = 44, 46.
Hesperostipa spartea grows at elevations of 200–2600 m, primarily in the grasslands of the central plains and southern prairies of the Flora region. In its more northern locations, it tends to grow on sandy soils. The southern and western specimens from outside its primary range may represent introductions. It was once a common species, but its habitat is now intensively cultivated. It differs from H. curtiseta in its larger size, unevenly pubescent culm nodes, usually ciliate lower sheaths, and longer florets. Misra (1961) argued that its longer florets and awns enabled H. spartea to survive in drier sites than H. curtiseta. Native Americans used bundles of the florets for combs.