Scattered through the families of bees are several large species complexes for which the current generic classification is arbitrary and will probably be revised in the near future. I am not referring here to the many differences of opinion on rank—should a given group of species be regarded as a species group or be given subgeneric status, should a taxon be a subgenus or a separate genus, or should a taxon be regarded as a tribe or a subfamily? Such problems are perpetual; they have no right or wrong solutions. I refer instead to cases where the taxa to be recognized are uncertain, either because of conflicting character complexes or the existence of intermediates between largely separable taxa. The following list includes the largest of such complexes.
Leioproctus and Lonchopria in the Colletinae (Sec. 39).
Evylaeus and Dialictus and other groups in the genus Lasioglossum in the Halictini (Sec. 66).
Hoplitis, Osmia, Atoposmia, Hoplosmia, etc., in the Osmiini (Sec. 81).
Megachile, including subgenera Chalicodoma and Creightonella, in the Megachilini (all placed in the genus Megachile) (Sec. 84).
Eucera (Synhalonia) and Tetraloniella in the Eucerini (Sec. 112).
Within each of these complexes, intermediates exist among the taxa. Sometimes they are intermediates only on the basis ofkey characters, which break down in probably derived taxa. In such cases the current classification may be suitable with some changes in key characters. Other intermediate forms, like Lonchopria (Loncho-prella), which connects Leioproctus and Lonchopria, are probably basal taxa. Phylogenetic studies have not been made, or at least are not yet reliable, for any of these groups. Molecular studies should provide an infusion of many new characters. I believe that the development of sounder classifications should in each case await both morphological and molecular studies, although I doubt that they will solve all the problems.
Each of the problem groups listed above, and numerous other problems, are explained in some detail in the systematic part of this book, Sections 36 through 121. The enormous number of similar subgenera of Andrena contrast sharply with the quite divergent subgenera of some other genera, for example Leioproctus. Such inconsistencies are numerous and are not likely to be solved in the near future.
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