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Date of Award


Document Type

Thesis - Pacific Access Restricted

Degree Name

Master of Science (M.S.)


Biological Sciences

First Advisor

Dale McNeal

First Committee Member

Alice S. Hunter

Second Committee Member

Eric Thomas


This investigation was undertaken to determine if there were morphologic characters that would allow rapid field identification of Allium tribracteatum Torrey and A. obtusum Lemmon, or if, in the absence of such characters, it would be possible to separate the two species on the basis of plant associations that might be unique to each. Allium tribracteatum is restricted or nearly restricted to volcanic soils of the Mehrten Formation in Tuolumne County, California and is a species of concern to the United States Forest Service because of this restricted distribution. Allium obtusum, on the other hand, is found both on the Mehrten Formation and on other soil types in the Sierra Nevada and has a much wider geographic distribution.

I found that the only reliable way to differentiate the two species morphologically was by the cell pattern on the bulb coats, a difficult characteristic to ascertain in the field. However a number of species of vascular plants were found that were associated only with one or the other of the species in question and were reliable indicators of the Allium species identity.

Environmental impacts facing Allium tribracteatum include winter recreation activities, illegal off highway vehicles, power line maintenance, seasonal wood cutting, some livestock grazing, and activities associated with the Bald Mountain Helitack fire base. Currently, these activities have minimal impacts on the Allium tribracteatum populations.



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