Evolution of leaf forms among palms

Abstract

Among the three basic types of palm leaves- the palmate, costapalmate and the pinnate. The palmate form is considered to be the most primitive, the pinnate most advanced and the costapalmate intermediate. Ontogenetic leaf sequences in seedlings indicate that the pinnate form could have been derived from the costapalmate or directly from the palmate type. Persistent, broad and green reins are primitive while the ephemeral and colourless ones are advanced. The hastula of the palmate leaves could be an excrescence as Eames considered it or the remnant of the ventral lobe of an ancestral peltate lamina. The shedding of a large part of the laminal tissue as haut in Phoenix is interpreted as a trend towards specialisation of the intercostal lamina as the sole photosynthetic area of the leaf.