Does the Monocot Mode of Leaf Development Characterize all Monocots?

Abstract

Patterns of early leaf development in monocots are analyzed in a phylogenetic context. Recent developmental and phylogenetic studies enable this reevaluation of the leaf base model of the developing monocot leaf. Two questions are addressed: a) is the presence of the Vorläuferspitze (fore-runner tip) invariably correlated with development of the lamina from the lower leaf zone? and b) was the ancestral monocot characterized by the leaf base mode of development? Scanning electron microscopic observations are made of young primorida using the mold and cast method. These data are combined with data from the literature and examined in a phylogenetic context using parsimony analysis. The results suggest that in some taxa the Vorläuferspitze may be associated with a lamina that is derived from the upper leaf zone, and that the ancestral monocot may not have been characterized by the leafbase mode of development. It is concluded that the leaf-base model, in a strict sense, may apply to a nested subset, but not all, of the monocotyledons.