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Brigham Young University Science Bulletin, Biological Series

Abstract

This revision discusses seven closely related species of Eriogonum (Polygonaceae) found in the western United States of North America. One of the two major species, E. microthecum, is composed of nine varieties which range over a wide area of the Far West. The other major species, E. effusum, is found over a more restrictive geographical range mainly east of the Continental Divide. The remaining five species are primarily restricted to the Colorado-Green river drainage basin of Utah, Colorado, New Mexico, and northern Arizona. Together these entities form the core of a group of plants known as Section Corymbosa. The new varieties proposed are E. microthecum var. corymbosoides and var. johnstonii from southern California; E. microthecum var. lapidicola of eastern California, southern Nevada, and perhaps adjacent Utah; and, E. microthecum var. alpinum from the Sierra Nevada of east-central California. The following new combinations are proposed: E. ericifolium var. pulchrum and E. microthecum var. foliosum. Detailed distribution maps are provided for each taxonomic element recognized, and the variation in E. microthecum and E. effusum is illustrated.

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