Carter County distribution: The five Carter County occurrences represent the majority in 

 the state. Most are in the northern end of the county. Prior to 1997, two populations were 

 known in the Custer National Forest on the Chalk Buttes and Long Pines units (Heidel and 

 Dueholm 1 995), and one population was known at Medicine Rocks State Park. Two 

 additional populations were found on BLM land in 1 997, one near Mill Iron in the northern 

 part of the county, and one in the Little Powder River drainage in the southwest part of the 

 county. 



HABITAT: All Montana populations ofAsclepias stenophylla grow on grassy uplands with sandy 

 soils, often with scattered Pinus ponderosa. It is possible that its distribution on BLM lands in the 

 county corresponds with that of the Fox Hills Sandstone Formation (Ross et al. 1955), though there 

 are other settings with sandy soils in the county. The grasslands represent sandy range sites typically 

 dominated by needle-and-thread with threadleaf sedge plant associations {Stipa comata-Carex 

 filifolia p.a./ Other dominants may include prairie sandreed (Calamovilfa longifolia) and little 

 bluestem {Schizachyrium scopahum; syn. Andropogon scoparius). At the BLM sites, the populations 

 are near the ecotones of open stands of ponderosa pine {Pinus ponderosa). Associated forbs include 

 purple coneflower {Echinacea angustifolia), spiderwort {Tradescantia occidentalis), and green 

 milkweed {Asclepias viridiflora), species which are characteristic of sandy soils. Known Montana 

 sites are at 3100-3900 ft. 



SPECIES BIOLOGY: All Montana populations are relatively small, the largest being those at 

 Medicine Rocks State Park and at the Rosebud County site, with around 1 00 plants each. Twenty- 

 six plants were found at the BLM Mill Iron site while only ten plants were found in the Little 

 Powder River population. Both areas were thoroughly surveyed, indicating that these are probably 

 small, isolated populations. All plants in these populations were in flower at the survey dates in early 

 July. Both of the Custer National Forest populations are extremely small, consisting of just six 

 plants in each observed in 1994. Fruit production has not been observed in Montana populations. 

 Reproduction in these small isolated populations may be limited by pollination, as the species, like 

 all milkweeds, is adapted to cross-pollination by insects. 



OTHER COMMENTS: The habitats of the BLM populations are grazed by sheep at the Mill Iron 

 site, and by cattle at the Little Powder River site. Some species of Asclepias are known to be 

 poisonous to livestock, especially sheep, but the plants are reportedly rarely eaten if other forage is 

 available (Great Plains Flora Association 1986). However, browsing of plants to the ground, 

 probably by sheep, was observed at the Mill Iron site. Range condition in the vicinity of the 

 populations was at the low end. The Mill Iron site is on a small, isolated BLM tract surrounded by 

 private ranchlands. Due to few populations, small population size, and presence of potential threats, 

 we recommend that current BLM Watch status be changed to Sensitive status for this species. 



This is one of several sand-loving species in the coimty that are often found with other species of 

 special concern where the habitat is extensive and/or in good condition. 



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