Structural development of the fruits and seeds in three mistletoe species of Phoradendron (Visceae: Santalaceae)

Abstract

Phoradendron is a New World genus of chlorophyllous hemiparasite plants with the distribution extending from the United States to Argentina, including the West Indies. The names given to the fruits within the Visceae are variable and include a viscous berry or pseudoberry bearing a single seed lacking the testa. Here, it was performed an anatomical study about the development of fruit and seed of three species of Phoradendron. During the fruit development the structure of the mesocarp undergoes intense activity of cell division, and it differentiates onto two new mesocarpic regions: the parenchyma and the viscid layer. In its maturity, the seed is ategmic, presenting the embryo entirely embedded within a chlorophyllous endosperm. The occurrence of chlorophyll in the endosperm may be associated to absence of integuments on the seed, which allows the light to reach the seminal tissues throughout the somewhat transparent pericarp. In addition, the Pomaceous fruit, "viscidio" type is proposed as an alternative classification for Phoradendron fruits.