On the Relationship of the Apocynaceae and Periplocaceae

Abstract It is generally agreed that the Periplocaceae arose from apocynaceous ancestors. Whether these ancestors were from the Plumerioideae, Cerberoideae or Apocynoideae has long been in dispute. This investigation is a comparative study of the pollen morphology and floral structure of selected genera of Apocynaceae and Periplocaceae. The examinded genera of the Plumerioideae and the Cerberoideae have 3-colporate, smooth to sculptured pollen grains. In the Apocynoideae there are single, smooth, 2–3-porate pollen grains or 3-to multiporate grains loosely united in tetrads of variable size and shape. The exine consists of an outer thick, homogeneous stratum subtended by a very thin, granular-fibrillar stratum, and globules; the internal septa are double-layered due to partial fusion of the tecta of the individual grains. The genera of Periplocaceae have pollen grains united in elongated, rhomboidal to rounded, or tetrahedral and decussate tetrads with few to many pores, pairwise, opposite or irregularly a...