Comments: Aase's onion is restricted to a narrow range of habitat conditions. It occurs on open, relatively barren, xeric, gentle to very steep, sandy slopes, generally with a southerly aspect, but ranging from east to west. It is usually associated with relatively sparsely vegetated bitterbrush (Purshia tridentata) or bitterbrush/sagebrush (Artemisia tridentata) communities. One or several bunchgrasses such as red threeawn (Aristida longiseta), bluebunch wheatgrass (Agropyron spicatum), squirreltail (Sitanion hystrix), needle-and-thread (Stipa comata), Sandberg's bluegrass (Poa sandbergii), Indian ricegrass (Oryzopsis hymenoides) and sand dropseed (Sporobolus cryptandrus) are often closely associated. Aase's onion sites are often bordered by Artemisia tridentata ssp. wyomingensis or ssp. tridentata/bunchgrass- dominated communities. Commonly associated species Eriophyllum lanatum, Balsamorhiza sagittata, Achillea millefolium, Phacelia heterophylla, and Eriogonum ovalifolium. A number of exotic species may be abundant, especially Bromus tectorum, Erodium cicutarium and Taeniatherum caput-medusae. Allium aaseae populations in the Boise Foothills often occur in close proximity to Astragalus mulfordiae, and/or Lepidium papilliferum, two other rare, regional endemic plants. These three rare species largely share the same conservation concerns and problems. On a local scale, Allium aaseae can be very common. At some sites it is one of the dominant forbs in early spring. When considering its sagebrush-bitterbrush/steppe and foothill grassland habitats rangewide, however, it is a minor constituent. Most populations are restricted to the alluvial soils of the Glenns Ferry Formation. This sandy substrate is of granitic origin and typically coarse textured, well-drained and relatively deep (Packard 1979; Prentice 1988). In the Boise Foothills, all populations occur on one of three sand-dominated geologic units - Pierce Gulch Formation Sand, Terteling Springs Formation Sand and Sandstone, and Terteling Springs Formation Sandy Sediments (Beck 1988). A large majority of Boise Foothill populations occur on three soil mapping units of Beck (1988): Quincy-Lankbush complex, Payette-Quincy complex, and Haw-Lankbush complex. Rarely, populations or portions of populations occur on other soil types, namely, Lankbush-Brent sand loam, Ada gravelly sand, and Searless-Rock outcrop complex. All known populations except for the two in Cartwright Canyon occur between 2700-4300 feet elevation, with the great majority below 3700 feet. Cartwright Canyon populations occur at 4950 and 5100 feet, and possibly indicate that soil characteristics such as texture are more important than elevation in determining the distribution of Allium aaseae (McNeal 1993).
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