PARVILEGUMINOPHYLLUM-COLORADENSIS, A NEW COMBINATION FOR MIMOSITES-COLORADENSIS KNOWLTON, GREEN RIVER FORMATION OF UTAH AND COLORADO

The purported ash samara, Fraxinus flexifolia (Lesquereux) Brown (1940) from the middle Eocene Green River Formation, is shown to be the same as small inequilateral legume leaflets identified as Mimosites coloradensis Knowlton. Because the name Mimosites Bowerbank is restricted to legume pods with mimosoid affinities, the new combination Parvileguminophyllum coloradensis (Knowlton) Call and Dilcher is proposed for the previously supposed samara, here recognized as a leaflet, and for leaflets currently placed in M. coloradensis. A lectotype is designated from among Knowlton's original specimens. The transfer of Brown's so-called Fraxinus samara to Parvileguminophyllum coloradensis (Knowlton) Call and Dilcher comb. nov. removes Fraxinus fruits from the list of macrofossil remains presently recognized in the Green River flora. The distribution of Fraxinus samaras in Paleogene assemblages from North America is briefly discussed. The paper concludes with a discussion of nomenclatural problems that may arise when two or more fossil organ types are united under a common name. We argue that this practice should be avoided except when the organs are found in organic connection, or when other indisputable evidence of their conspecificity is preserved, such as shared anatomical or biochemical features. By itself, the co-occurrence of disassociated fossil organs at different localities is only circumstantial evidence of their conspecificity.