The Problem of Generic Delimitation when Conflict Exists between Molecular and Morphological Data

Abstract

Congruent molecular and morphological data present few problems for generic delimitation; the diagnostic morphological synapomorphies can be used in keys and generic descriptions, and these characters provide reliable means for field identification and generic assignment of new species. Problems arise when evolution results in drastic modification of the floral and fruit characters in one species (or its resulting clade) such that the diagnostic features of the group are no longer discernible due to the pattern of subsequent modification. If the pattern of subsequent modification is sufficiently extensive, the historical information needed to reconstruct the true phylogeny may not be represented in the morphological features, and a morphologically-based analysis may yield a false reconstruction. In some cases, molecular data may retain the historical information needed to reconstruct the true phylogeny, and from this, the pattern of morphological modification can be inferred, but such conflicts between data sets present problems for morphologically-based generic delimitation in a monophyletic system.