section, but the suitable microhabitat is magnitudes less extensive. A tracing 

 of the wetlands in a high-density section is provided in Figure 6. The origin 

 of these extensive wetland systems has not been studied. 



C. Biological characteristics. 



1. Vegetation physiognomy and community structure: All Montana 

 occurrences are within broad, open or semi-open intermontane valleybottoms 

 with grassland. In these settings, the occurrences are restricted to discrete 

 zones sporadically distributed along abandoned meandered wetlands. Most 

 occurrences are in broken bands along the outer margins of wetland channels 

 and a couple are also across the bottom of wet meadow swales. The occupied 

 habitat within these shallow wetland settings have emergent vegetation of 

 relatively sparse cover and short stature compared to other wetland vegetation 

 in the wetland meanders. 



2. Regional vegetation types: There is no published mapping of the potential 

 natural vegetation of intermontane valleys in Montana at a scale finer than the 

 Kuchler map (1964). This map shows Intermountain shrub-steppe grassland 

 across the foothills and valleys vsithout a discrete valleybottom vegetation in 

 the ancient floodplains. 



Landscapes containing Spiranthes diluvialis are small vegetation inclusions 

 in the vmdescribed valleybottom matrix, i.e. patches within the larger open 

 grasslands. The patches are dominated by the alkali sacaton plant association 

 (Sporobolus airoides p.a.). Buffaloberry (Shepherdia argented) contributes 

 more than trace coverage, particularly along the edge of the meandered 

 wetlands. Robbins milkvetch {Astragalus robbinsii) is common in alkali 

 sacaton uplands, and is often locally abundant at the wetland edges. 

 Cottonwoods (Populus spp.) and willows (Salix spp.) are intermittent or 

 absent on-site, though they are found along the nearby river banks. Water 

 birch (Betula occidentalis) is occasionally present in or near the same settings 

 as Spiranthes diluvialis. The Gallatin County upland vegetation has western 

 wheatgrass (Elymus smithii; syn. Agropyron smithii) as codominant with 

 alkali sacaton, and a discrete association apparently dominanted by 

 Muhlenbergia racemosa is also present. Halophytic vegetation types are 

 sometimes present in the nearby landscape, including the Sarcobatus 

 vermiculatus p.a. 



Alkali sacaton p.a. is the surrounding upland vegetation at Montana's 

 Spiranthes diluvialis sites. This is different from associated upland vegetation 

 in the rest of its range, though many of the associated wetland species are 

 similar. Halophytic species also are present at Spiranthes diluvialis sites of 

 Nebraska (Hildebrand 1998) and Washington (Gamon pers. commun.) . 



22 



