Novel reports of laticifers in Moraceae and Urticaceae: revisiting synapomorphies

Abstract

In this study, we reassessed the morphology and distribution of laticifers present in the inflorescences of nine Moraceae and three Urticaceae species and compared the substances found in their latices. Reproductive meristems and inflorescences at different developmental stages were collected, fixed and processed for light microscopy analysis. In Moraceae, laticifers occur in almost all inflorescence organs. In Urticaceae, the presence of laticifers in the inflorescence axis and sepals is a novelty, since the family is characterized by having laticifers only in the bark. The laticifers of Moraceae and Urticaceae show a thin pectocellulosic cell wall and are articulated and branched, although they are currently classified as non-articulated branched in Moraceae and non-articulated unbranched in Urticaceae. The latex contains proteins and alkaloids. Lipids are common in Moraceae latex, whereas phenolic compounds occur in the Urticaceae latex. Polysaccharides occur in the majority of the species studied, an unprecedented finding for the group. Thus, we found that the non-articulated type of laticifer may not consist of a synapomorphy for Moraceae and Urticaceae. Moreover, the laticifer branching in the inflorescences of Urticaceae indicates that its distribution and ramification as acknowledged in the literature (restricted to the bark and unbranched) should be reevaluated and may not constitute synapomorphies for this family either. The adaptive value of laticifers for Moraceae and Urticaceae is high, since they occur widely in the plant body of their representatives. The presence of proteins and alkaloids in the latex and the absence of starch grains are probably conserved traits in the urticinean rosids.