Floral anatomy of the plant Psittacanthus schiedeanus (Loranthaceae)
Anatomía floral de la planta Psittacanthus schiedeanus (Loranthaceae). Loranthaceae hemiparasitic family comprises 76 genera and about 1 050 species distributed in temperate and tropical regions. The subtribe Psittacanthinae contains 14 genera of neotropical mistletoe including Psittacanthus with over 120 species, characterized by large, brightly colored (red, orange, yellow) flowers that are mostly pollinated by hummingbirds. During the 20th century, a number of morphological and embryological studies were conducted mainly on Old World Loranthaceae genera. More recently, attention has been focused on neotropical Psittacanthinae where among the 14 genera, floral anatomy has been examined in only seven. The aim of this study is to describe the floral anatomy of Psittacanthus schiedeanus and compares the results with those derived from related mistletoe, interpreting the variation of the floral characters of the calyculus, nectary, gynoecium and from floral dissections and serial histological sections, detailing the structure of androecium and gynoecium and anthers in the context of the new phylogenetic information. Flowers of P. schiedeanus at different developmental stages were examined using stained serial sections visualized with light microscopy. These flowers have a vascularized, cupular pedicel fused to a bracteole, a non-vascularized calyculus, an annular nectary, a unilocular gynoecium with a single central mamelon and an androecium formed by epipetalous septate stamens. The morphological comparison of pedicel, bracteole and calyculus provides support for the interpretation of the calyculus as a reduced calyx. The annular nectary seems to be a character shared by the entire subtribe Psittacanthinae, which distinguishes it from Ligarinae which has stylar nectary. The unilocular gynoecium formed by a single central structure is a character shared with other genera in Psittacanthinae except Tripodanthus. The androecium is composed of dithecal, tetrasporangiate stamens with septate locules that are here considered an adaptation for pollen releasing over an extended time period rather than previous suggestions that they result from evolutionary pressure to reduce anther size or to facilitate the nutrition of microspores in large anthers.