5. Reports having ambiguous or incomplete locality information: 



a. Montana: None. Herbaria in the state, including MONTU and 



MONT, have been searched for specimens of Spiranthes diluvialis 

 which might be misidentified as S. romanzoffiana, and none were 

 found. 



6. Locations known or suspected to be erroneous reports: 



a. Montana: None. 



C. Biogeographical and phylogenetic history: Spiranthes diluvialis is intermediate 

 between its putative parent species, hooded ladies '-tresses {S. romanzoffiana) and 

 Great Plains ladies'-tresses (5. magnicamporum). It is an allotetraploid (2n=74; 

 Sheviak 1984) which possesses a combination of alleles found within the putative 

 diploid parent species {S. romanzoffiana 2n=44 and S. magnicamporum 2n=30; 

 Sheviak 1984). It hypothesized to have evolved when the two parent species were 

 sympatric or parapatric during a relatively cool, wet Pleistocene pluvial period 

 (Sheviak 1984). These climatic conditions may have shifted the overall distribution 

 of 5. romanzoffiana relatively low in its elevation range on the Rocky Mountains, 

 and the distribution of 5". magnicamporum relatively far west across what are the 

 driest segments of the Great Plains, bringing the distribution of the two species into 

 overlap or proximity. 



Genetic research on Spiranthes dilvialis in Colorado and Utah indicates that it 

 evolved from at least two separate hybridization events (Arft 1995a). The Montana 

 populations in the headwaters of the Missouri River may have a separate origin from 

 those in the rest of its range. Genetic analysis of the species at the northern and 

 eastern ends of its range are proposed for conservation planning purposes. 



6. General environment and habitat description. 



A. Concise statement of general environment and habitat: Spiranthes diluvialis is 

 restricted to a small, sporadic microhabitat represented by calcareous, wet-mesic, 

 temporarily-inundated meadow in shallow wetlands. The shallow meandered 

 wetlands are in alluvial fans (Boast & Shelito 1989) that correspond with two 

 imcommon soils series. They are part of broad, flat, arid, open, low-elevation valley 

 bottoms. The meandered wetlands include narrow channels and broader swales, both 

 of which parallel the existing river courses, and most are set back over a mile from 

 the river and without surface-water connections to the river. The valley cross- 

 sections where it occurs are depicted in Figure 5. 



15 



