Aristida basiramea
Author: Engelm. ex Vasey

Forktip three-awn

Poaceae (Grass Family)

Close up of Aristida basiramea by Rich Scully.
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Close up of Aristida basiramea by Rich Scully.
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Close up of Aristida basiramea by Pamela Smith.
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Ranks and Status

Global rank: G5
State rank: S1
Federal protection status: None
State protection status: None

[+] Description and Phenology

Illustration of Aristida basiramea from USDA-NRCS PLANTS Database, Britton and Brown 1913. 
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General description:

Annual grass that grows 25 to 50 cm tall. It is branched at the base and grows in tufts or dense clumps. The stems are wiry and often rough; the leaves are 5 to 15 cm long and less than 1 mm wide. The root system is shallow. Plants produce mostly cleistogamous flowers in Colorado. Ligules are about 0.3 mm long.  Inflorescences are racemose or paniculate, 2-10 cm long, 1-2 cm wide, with few spikelets. Glumes are 1-veined, acute, and awned; awns are 1-2 mm, and brown to purplish; upper glumes are 10-12+ mm; lower glumes are 1-2+ mm shorter; lemmas are 8-18 mm, light gray, and mottled; awns are erect to divergent; central awns are 10-35 mm long, with 2-3 spiral coils at the base; lateral awns are 5-10 mm, not coiled but often curved and twisted basally, and strongly divergent distally. The flowers have 3 anthers, about 3 mm, and are purplish-brown. The coiled central awn and the curved, strongly divergent lateral awns are distinctive (FNA 2003, Shaw, 2008, Scully 2015, Weber and Wittmann 2012, Ackerfield 2015).

Look Alikes: Similar to A. dichotoma, but A. basiramea has lateral awns that are curved and widely divergent, whereas A. dichotoma lateral awns are straight and erect (Weber and Wittmann 2012).


[+] Herbarium Photos

Images of Aristida basiramea housed at the Colorado State University Herbarium.

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[+] Habitat

Habitat of Aristida basiramea by Rich Scully.
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Habitat of Aristida basiramea by Rich Scully.
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Habitat of Aristida basiramea by Pamela Smith
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In Colorado, Aristida basiramea has been observed on several kinds of sandy substrates, including sandy soil of an outwash mesa, and rock outcrops of Fox Hills sandstone, Dakota sandstone, Lyons sandstone, Ingleside sandstone, and Silver Plume granite. On rock outcrops it grows in crevices and gentle slopes where loose sand has accumulated (Scully 2015). Associated species include Pinus ponderosa, Cercocarpus montanus, Andropogon gerardii, Juniperus scopulorum, Ribes cereum, Aristida purpurea, Lycurus setosus, Piptatherum micranthum, Heterotheca villosa, Aster porteri, Opuntia pheacantha, O. polyacantha, Solidago nemoralis, Penstemon virens, Gaillardia aristata, Sedum lanceolatum, and Selaginella densa (Colorado Natural Heritage Program 2017.)

Elevation Range: 5,102 - 6,522 feet (1,555 - 1,988 meters)

[+] Distribution

Distribution of Aristida basiramea in Colorado according to mapped land ownership/management boundaries (CNHP 2017, COMaP).
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Distribution of Aristida basiramea in Colorado.
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Colorado endemic: No
Global range: Known from most states in the central and eastern parts of the United States, and north into Canada (USDA NRCS 2017).
State range: Jefferson, Boulder, and Larimer counties in CO (USDA NRCS 2016).

[+] Threats and Management Issues

In Colorado, urban expansion, extraction of sand, and use by all-terrain vehicles present the biggest concerns. The suppression of disturbances such as fire, and the planting of conifers, are also altering the nature of some of the existing habitat (Scully 2015). Colorado climate scenarios for 2050 suggest temperature will increase by 3-7 F and precipitation may decrease or increase. The impact to any given rare plant habitat is likely to vary. Long-term monitoring that includes weather and soil moisture data is critical to understanding climate impacts.

[+] References

    • Ackerfield, J. 2015. Flora of Colorado. Brit Press, Botanical Research Institute of Texas, Fort Worth, TX. 818 pp.
    • Britton, N. L. and A. Brown. 1913. An Illustrated Flora of the Northern United States and Canada. 3 vol. Dover Publications, Inc., N. Y. 2052 pp.
    • Colorado Natural Heritage Program and the Geospatial Centroid. 2017. The Colorado Ownership and Protection Map (COMaP). Colorado State University, Ft. Collins, CO.
    • Flora of North America Editorial Committee. 2003a. Flora of North America North of Mexico. Vol. 25. Magnoliophyta: Commelinidae (in part): Poaceae, part 2. Oxford Univ. Press, New York. xxv + 781 pp.
    • Kartesz, J.T. 1994. A synonymized checklist of the vascular flora of the United States, Canada, and Greenland. 2nd edition. 2 vols. Timber Press, Portland, OR.
    • Scully, R. 2015. Survey for Aristida basiramea, Forktip Threeawn Grass, on Jefferson County Open Space Lands. Unpublished report prepared for the Colorado Natural Areas Program.
    • Shaw, R.B. 2008. Grasses of Colorado. University Press of Colorado. Boulder, CO. 650 pp.
    • USDA, Natural Resources Conservation Service, PLANTS Database [USDA PLANTS]. Accessed 2017.
    • Weber, W. A. and R. C. Wittmann. 2012. Colorado Flora, Eastern Slope, A Field Guide to the Vascular Plants, Fourth Edition. Boulder, Colorado. 555 pp.

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