indicates that it may have 3 ovules per locule. This broad interpretation does not agree with 

 the most recent treatment by RoUins (1993) which recognizes these taxa as separate, or the 

 earlier taxonomic research of Mulligan (1967). We recognize these treatments in which P. 

 brassicoides is endemic to the Great Plains. 



Physaha brassicoides 

 . Rydberg Doubis Twinpod 



Montana distribution: Dom (1984) listed 

 Physaria brassicoides as "expected" in 

 southeast Montana but it was not verified in 

 the state until 1 994 when it was collected from 

 Carter County by Keith Dueholm (Heidel and 

 Dueholm 1995). To date, all known Montana 

 occurrences are in Carter County. 



Carter County distribution: Two locations 



were found in 1994 on the Custer National 



Forest in the Ekalaka Hills and the Long Pines 



units (Heidel and Dueholm 1995). In 1997 the species was collected twice from BLM land 



in northeastern Carter County in the vicinity of Chalk Buttes (Newberry Knob) and in the 



badlands out the Powderville Road on the western edge of the county. 



HABITAT: Rollins (1993) describes habitat throughout its range as "bare hillsides, dry gravel and 

 clay soil, badlands, clay knolls and banks." All Montana populations oi Physaria brassicoides occur 

 on sparsely vegetated, steep, eroding, south-facing slopes of highly dissected breaklands and 

 badlands. Substrate parent materials are both sandstone and shale. Three of the sites are at the 

 contact zone of sandstone overlying shale, with both parent materials influencing topography and 

 erosion processes; the upper horizons at these sites are sandy. The Powderville Road site is on the 

 sides of gullies eroded in soft shale. These eroding slopes do not support stable vegetation 

 communities and have 80-90% exposed substrate. Immediately associated plant species at two or 

 more sites include the shrubs skunkbush sumac {Rhus aromatica) and yucca {Yucca glauca), the 

 grasses Indian ricegrass {Oryzopsis hymenoides) and little bluestem {Schizachyrium scoparium; syn. 

 Andropogon scoparius), and the forbs Douglas" dusty maiden {Chaenactis douglasii) and white 

 prairie clover {Dalea Candida). In addition to these, yellow buckwheat {Eriogonumflavum), hairy 

 goldenaster {Heterotheca villosa), alpine bladderpod (Lesquerella alpina), and plains muhly 

 {Muhlenbergia cuspidata) have also been noted as common associates (North Dakota Natural 

 Heritage Program 1990). 



SPECIES BIOLOGY: Estimates of Montana population numbers range from 20 to 100 plants. 

 Highest number of plants observed was at the BLM site near Newberry knob at the north end of the 

 Chalk Buttes. Only about 20 plants were observed at the Powderville Road BLM occurrence, 

 however, potential habitat here is extensive but extremely difficult to traverse and a complete survey 

 was not conducted. The Newberry Knob population extends across about 1 acres while the other 

 occurrences cover 1 acre or less. In 1997, seed production was high in the Newberry Knob 

 population, but most plants had aborted fruits at the Powderville Road site. Small population size 

 may be attributed to sporadic seed production and poor competitive ability of the species. 



101 



