First report of laticifers in lianas of Malpighiaceae and their phylogenetic implications

Abstract

Premise: Laticifers have evolved multiple times in angiosperms and have been interpreted as a key innovation involved in plant defense mechanisms. In Malpighiaceae, laticifers were previously known from a single lineage of trees and shrubs, the Galphimia clade, but with detailed anatomical analyses here, we show that their distribution is broader in the family, also encompassing large clades of lianas. Methods: From 15 genera, 70 species of Malpighiaceae were surveyed through careful anatomical ontogenetic analysis of roots, stems, and leaves and detailed histochemical tests to elucidate the nature of laticifers and latex in the family. Results: Articulated anastomosing laticifers were encountered in roots, stems, and leaves of two distantly related megadiverse genera of Malpighiaceae lianas: Stigmaphyllon (stigmaphylloid clade) and Tetrapterys s.s. (tetrapteroid clade). From the apex downward, in Stigmaphyllon the laticifers are derived from the procambium and from the cambium during its early activity and are present in the outermost part of the vascular cylinder of stems and leaves and in the pericycle of roots, whereas in Tetrapterys s.s. they are derived from the ground meristem, procambium, and cambium throughout the plant body and are present in the cortex and pith, either the pericycle in roots or the outermost part of the vascular system in stems and leaves, and the primary and secondary phloem. Conclusions: Laticifers seem to have evolved at least three times independently in Malpighiaceae, once in a lineage of trees and shrubs and twice in two distantly related megadiverse lianescent lineages. Laticifer evolution in Malpighiaceae is homoplastic and may be related to increases in species diversification.