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T. C. Kane, T. C. Barr, Jr., and G. E. Stratton 
Trechus exceeds all other carabid genera in taxonomic diversity (Barr 
1985a). Nearly 55 Trechus taxa are known from the region at present; a 
great majority of them are alpine endemics isolated at elevations above 
1,350 m. Much of the diversity in this genus is a result of lineage 
vicariance associated with fluctuating climatic regimes during the 
Pleistocene. Presumably ancestral Trechus species were more continuously 
distributed at lower elevations during colder, wetter climates associated 
with glacial maxima. However, the warmer, drier interglacial climates 
made lowlands inhospitable to most trechines and resulted in vertical 
contraction and fragmentation of ranges. The present insular pattern of 
distribution of alpine Trechus taxa is a direct result of the recent 
climatic regime (Barr 1962, 1979, 1985a). 
Evolution in Appalachian Trechus has also been influenced by the 
Asheville basin, a major lowland drained by the French Broad and 
Pigeon rivers. The two subgenera represented in the region, Trechus, s. 
str. (males with two protarsomeres enlarged, dentate, and setose beneath), 
and Microtrechus (males with only one protarsomere so modified), are 
essentially separated by the Asheville basin and the French Broad River. 
Microtrechus , endemic to the Unaka mountain province, appears to 
have evolved west of the basin, in isolation from subgenus Trechus, s. 
str., to the east (Barr 1962, 1979). However, occurrence of a limited 
number of Microtrechus species east of the French Broad River and a 
few Trechus, s. str., species west of the river suggests that the barrier has 
recently been breached (Barr 1985a). In general, the area southwest of 
Asheville exhibits greater endemicity and diversity in many groups of 
carabids, and carabids in the mountains northeast of Asheville are 
taxonomically much closer to carabid species and genera in the mountains 
of western Virginia and eastern West Virginia (see Barr 1969 for 
summary). The eyeless, wingless, edaphobitic species of Arianops 
(Coleoptera: Pselaphidae) also show much the same pattern (Barr 1974; 
for a detailed discussion of the evolutionary impact of the Asheville 
lowland, see Barr 1985a). 
Morphological differences between closely related isolates of Trechus 
are often subtle, involving quite minor, though consistent, characters. 
The taxonomy of the isolates belonging to the vandykei species group of 
Microtrechus has proven especially difficult. Twelve upland isolates — all 
more or less morphologically distinct and strictly allopatric — are known 
from western North Carolina and eastern Tennessee (Fig. 1. shows all 
known localities except Joanna Bald, in the Snowbird Mountains). 
Beetles in this group are quite small (total length means <3 mm) and 
characteristically inhabit the superficial layers of moist or wet litter in 
the forest floor and carpets of loose, wet, fluffy mosses. Local populations 
