Comparative studies on number of leaflets, venation, and epidermal structure in the genus Lathyrus

Abstract

A comparison of endemic Lathyrus species of different continents has been carried out with regard to venation, epidermal cell structure, and number of leaflets to apply the information so obtained to phylogenetic considerations. Morphologically primitive Lathyrus species have several leaflets with pinnate venation, and epidermal cells with undulate walls. This type is represented by all the North American endemic species and by some Eurasian ones. Most Eurasian and North African species, however, have only 1 pair of leaflets, parallel venation, and epidermal cells with undulate walls. The South American species are the furthest advanced in evolution. They have 2 leaflets with parallel venation, and epidermal cells with straight lateral walls. The endemic species of South and North America thus differ sharply with regard to the characteristics examined while Eurasian and North African species show relationship to species of both South and North America. The distribution of the leaf characteristics studied and evolution of species within this genius might have its cause in historical geology.