Morphological Variation and Speciation

Abstract

Developmental factors (e.g., canalization, plasticity, epistasis) weaken the integration of genomic and morphological diversification. Numerous non-lethal morphological mutations and several cases of substantial morphological differentiation associated with negligible isozymic di- vergence have been documented. These observations suggest that evolution of plant form often may be punctuational. Patterns of morphological variation observed within and among plant pop- ulations indicate that morphology can diverge in apparently random directions. A comparison of characters in which intraspecific (racial) and interspecific divergence has occurred suggests that adaptation, which is frequently an important component of ecotypic differentiation, may often be a less important factor in speciation. These observations converge to suggest that the differentiation of morphological plant species is frequently rapid and random in direction.