ABSTRACT
The higher abundance, greater diversity, and earlier appearance of angiosperm pollen types in the Cretaceous of Africa and South America indicate that this area (Northern Gondwana) was the most active center of early diversification and spread of angiosperms. Improved data on pollen ultrastructure, studies of fossil angiosperm flowers with in situ pollen from other areas, and phylogenetic analyses of living primitive angiosperms, based particularly on molecular data, are allowing the broad pattern of angiosperm spread to be dissected into the histories of individual lines. Among magnoliids, Winteraceae (Walkeripollis tetrads, possibly Afropollis and/or Schrankipollis) apparently originated in the Northern Gondwana tropical zone and later spread south. Chloranthaceae (Clavatipollenites and related forms) were nearly worldwide, but some possible members (Tucanopollis) were centered in Northern Gondwana. The basically tricolpate eudicot clade may have originated in Northern Gondwana, but most surviving basal lines, such as those leading to Platanus, Nelumbo, and Trochodendraceae, spread north into Laurasia and became significant members of the flora there, while dying out in Africa. However, Buxaceae (originally with striate-reticulate tricolpate pollen) survived in both areas, while Proteaceae (with triporate pollen) spread south. Tricolpodiorates (Hexaporotricolpites) may be related to the Malagasy endemic Didymeles, which has been linked with Buxaceae; if so, this is a Northern Gondwanan line that later died out in Africa but survived in Madagascar, as did Chloranthaceae and Winteraceae.
