STRUCTURAL CORRELATIONS AMONG WOOD, LEAVES AND PLANT HABIT

Abstract

Within the phylogenetically unrelated genera Hibbertia and Erythroxylum multiple correlations among woody anatomy, plant stature, and details of leaf morphology and anatomy are clearly environmentally related. Xeric radiants typically have undergone plant and leaf size reductions, along with the development of foliar xeromorphy, deciduousness, and xeromorphic xylem specializations. Mesic radiants have evolved an increased plant stature and leaf size as well as retaining a primitively mesomorphic xylem structure. Clinal variation patterns are much more extreme and apparent in Hibbertia whereas Erythroxylum species possess more subtle degrees of habitat related variability. In species of both genera, modifications in leaf morphology and anatomy and the existence of deciduousness, appear to buffer the xylem and permit rather primitive and mesomorphic wood anatomy to exist within seasonally or permanently dry locations. The extent of the buffering influence of leaves upon the xylem tissues is presumably determined by the complex interrelationships between various climatic variables and such features as leaf size, duration, type and degree of scleromorphy, as well as non-foliar characteristics such as architectual forms, degree of stem succulence, and the nature of the root system. In this regard the foliage constitutes perhaps the most significant component of the plant hydrovascular system. Biological and evolutionary interpretations of wood anatomy within an ecological context, therefore, are ill-advised in the absence of correlative leaf structural data.