Synonym(s): Achnatherum clandestinum (Hack.) Barkworth,
Stipa clandestina Hack.
Duration and Habit: perennial Grass
Forms mats, dense tufts, or tussocks, with knotty, rhizomatous bases. Culms 50–90 cm tall, 1–2.9 thick, erect, glabrous; nodes usually 3. Leaves mostly basal, conspicuously 2-ranked. Blades erect, 10–50 cm long, usually with edges rolled or folded, and, 2–4 mm wide when flat, with sharp brown point, especially when dry. Stems with inflorescence less than 1 m tall. Inflorescence stem carries a single, terminal dense slender spike-like panicle or raceme, with its branches contracted; frequent presence of cleistogamous (hidden) panicles in the axils of its basal leaf sheaths. Panicles 10–20 cm long, 1–5 cm wide, bases sometimes included in the leaf sheaths. Awns 11–23 mm, usually twice-geniculate (bent twice) Seeds about 3 mm long, 1–1.4 mm thick, with smooth longitudinal ribs. [modified from Arriaga and Barkworth, in http://herbarium.usu.edu/webmanual/ and Bogler http://eol.org/data_objects/6657865]
Ecological Threat: Cattle avoid A. clandestine (and other Amelichloa) because of its sharply pointed leaves. This can lead to livestock compacting the soil and trampling the vegetation around the tussocks. In addition, it spreads by both the open and hidden seeds. Taken together, this means that it could become a serious problem in rangelands.
Biology & Spread: By seeds. In addition to seeds in the panicles, there are “hidden” seeds in the basal leaf sheaths.
History: First recorded in the U.S. in Texas in 1987; likely established in San Saba River Valley in the 1960s (Barkworth, Valdes-Reyna and Landers 1988).
U.S. Habitat: Disturbed and heavily grazed areas, along roadsides and fence lines.
U.S. Nativity: Non-native
Native Origin: Native from northern Mexico to Colombia. It has been accidentally introduced to pastures and roadsides in Texas, and is now established there. Barkworth, Valdes-Reyna and Landers (1988) offer some hypotheses for how it arrived in Texas. May also be established in CA, but likely has been misidentified as A. brachychaeta (Ariaga and Barkworth 2006).
U.S. Present: (CA), TX
In California, resembles Amelichloa brachychaeta, having spikelets that have a single floret that bears a single, terminal awn, but its awns are twice-geniculate (bent twice) whereas those of A. brachychaeta are once-geniculate (Ariaga and Barkworth 2006).
Physical: Mowing favors establishment and spread because it does not eliminate, and may disperse, the “hidden seeds” (cleistogenes). The species is eaten by goats. Horses will eat in winter if necessary because it remains green, as they know how to avoid the sharp tips of the leaves. (Barkworth, Valdes-Reyna and Landers 1988)
Chemical: Actively growing plants can be killed by applying a foliar spray of either glyphosate or hexazinone (Barkworth, Valdes-Reyna and Landers 1988). The related Amelichloa caudata was mentioned on page 34 of a document from Australia covering the use of herbicides for particular species of weeds, in which flupropanate and/or glyphosate were used. (http://www.pir.sa.gov.au/__data/assets/pdf_file/0009/187686/Full_Document_Final_Weeds.pdf)
Arriaga, Mirta O., and Mary E. Barkworth. 2006. Amelichloa: a new genus in the Stipeae (Poaceae). Sida, vol. 22, no. 1. 145-149.
Barkworth, Mary E., Valdes-Reyna, Jesús, and Landers, Jr., Roger Q. Stipa clandestina: New Weed Threat on Southwestern Rangelands. Weed Technology Vol. 3, No. 4 (Oct. - Dec., 1989), pp. 699-702. http://www.jstor.org/stable/3987568
Barkworth, Mary E., Capels, Kathleen M., Long, Sandy, Anderton, Laurel K. and Piep, M.B., eds. Flora of North America,Volume 24: Magnoliophyta: Commelinidae (in part): Poaceae, part 1: North of Mexico. 05 March 2007. 944 Pages. Viewed at http://herbarium.usu.edu/webmanual on 27 Oct 2014.
Bolger, R. 2010. http://eol.org/data_objects/6657865
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