Fine structure of mistletoe pollen. I. Eremolepidaceae, Lepidoceras, and Tupeia

Abstract

An examination of pollen morphology and ultrastructure of Eremolepidaceae (Antidaphne, Ixidium, Eremolepis, Eubrachion) and Lepidoceras by light and scanning and transmission electron microscopy reveals a close relationship among the taxa. Pollen of Eremolepidaceae is typically echinate, tricolporate, and oblate-spheroidal. Eubrachion is unique within the family, exhibiting shallowly reticulate pollen. Ultrastructurally, all Eremolepidaceae exhibit a similar exine structure. The sculptural ektexinous elements (spines or 'muri') are never contiguous with the basal ektexine but rest on a thin granular zone. Pollen characters of Lepidoceras are particularly close to those of Ixidium and Eremolepis. The porate (por(or)ate) aperture type, completely spherical shape, and reduced granular ektexine of Lepidoceras pollen indicate an advanced position within the complex. The relationship of Tupeia to Eremolepidaceae is more obscure as pollen of the genus exhibits both eremolepidaceous (echinate sculpturing, shape in polar and equatorial views) as well as loranthaceous characters (simple apertures, ektexine organization). Palynologically Eremolepidaceae and related genera show no particular close relationship to Olacaceae or Santalaceae. Though Eremolepidaceae et al. do share a number of pollen features with Viscaceae (echinate sculpturing, compound apertures, exine organization) the strong nonpalynological differences between the two families suggest that these pollen features may have arisen independently.