Abstract
Veinlet sheathing of twenty-six species ofPancheria is described and illustrated. Within the genus foliar vein sheathing varies from almost completely lacking to abundant, and individual sheath cells show much variation in cell wall composition and structure. The topographical distribution of sheath cells along the vein system, when coupled with the structure of individual sheathing elements, can be utilized to distinguish three anatomical groups of species. Although the evolutionary sequence and ecological significance of the diverse sheath types are at present unresolved, features of vein sheathing appear to be of systematic significance and may provide an additional basis for a better understanding of infraspecific relationships within this genus.
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