influence of livestock grazing. Hermann (1970) states that 

 this taxon is "excellent" forage for cattle and horses, 

 suggesting that it may be especially susceptible to grazing. 

 This plant should continue to be tracked by the Montana 

 Natural Heritage Program. It should also be nominated for BLM 

 sensitive status and be given high conservation priority. 

 Spring and summer grazing of sensitive meadow habitats should 

 be restricted. Studies to determine the effects of livestock 

 grazing on this species should be conducted. 



Cirsium subniveum Rydb. 



Jackson Hole thistle 



A. DESCRIPTION 



1. General description: This thistle belongs to the sunflower 

 family (Asteraceae) . It is a large, spiny, branching 

 perennial from a taproot. The spine tipped pinnately lobed 

 leaves are basal and alternate along the stem. The pinkish 

 flowers are all tubular with a pappus of feather-like bristles 

 and are borne in a tight head surrounded by several series of 

 spiny bracts. 



2. Diagnostic characters: The following combination of 

 features is used to key out C. subniveum from other species of 

 Cirsium in southwestern Montana (adapted from Dorn 1984) : 



Involucres of largest heads > 1.8 cm 



heads solitary and terminal on branches (not in dense 



clusters) 

 upper leaf surfaces lacking spines 

 leaves decurrent along stem with "wings" > 15mm 

 underside of leaves tomentose 



B. GEOGRAPHIC DISTRIBUTION 



1. Species range: western Wyoming to northeastern Oregon 

 (Hitchcock and Cronquist 1973) . 



2. Montana distribution: Previously known from over 30 

 records in Beaverhead, Madison, and Park counties. 



3. Occurrences in the study area: Seven populations are 

 known, these concentrated in the southern part of the area in 

 the Big Sheep Creek drainage and in the northern part in the 

 vicinity of Johnson Gulch. 



C. HABITAT 



In the Tendoys this species occurs in grasslands, sagebrush 

 steppe and woodlands, especially in soils derived from 

 limestone. The communities are commonly dominated by Artemisia 



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