A Numerical and Nomenclatural Analysis of Morpho-Geographic Taxa of Humulus

Abstract

In an attempt to alleviate extensive confusion regarding infra-specific variation of H. lupulus (s.l.), numerical taxonomic analyses were conducted on 783 herbarium collections of this species. A method combining alternating cycles of principal coordinate analysis and canonical analysis was used to generate morphologically defined groups, the taxonomic acceptability of which was judged on the basis of geographical homogeneity. This technique produced 5 groups, formally recognized as varieties. H. lupulus var. neomexicanus occupies western North America, especially the Cordillera and is largely allopatric. H. lupulus var. pubescens (var. nov.) inhabits the American Midwest. H. lupulus var. lupulus occurs in Europe, where it is allopatric and is introduced elsewhere, especially in eastern North America, where it comprises half of the herbarium plants from this region. H. lupulus var. lupuloides (var. nov.) occurs in the eastern part of North America and intergrades with the other 3 varieties populating North America, wherever it is sympatric with them. H. lupulus var. cordifolius is found in eastern Asia, mainly in Japan. Attempts to cluster these variants hierarchically did not reveal an unambiguous pattern of relationship, although several of the techniques used produced the intuitively satisfying separation of the 3 North American taxa from the Asian variety and the European variety. H. japonicus, a distinctive relative, does not manifest comparable geographical differentiation. H. yunnanensis, a Chinese endemic species first described in 1936, was almost universally unappreciated and identified as H. lupulus, which it resembles superficially. However, it is more similar to H. japonicus. Two contrasting genetic systems are perceivable in the 4 spp. comprising the Cannabaceae: Cannabis sativa and H. japonicus seem to have general purpose genotypes adapted to cosmopolitan distribution. H. yunnanensis and the varieties of H. lupulus appear comparatively specialized for localized habitation.