Illustration of hypotheses on evolution of Phytophthora and associated changes in sporangial papillation: (a) species producing papillate sporangia evolved from non-papillate ancestors. Semi-papillation is considered as intermediate between non-papillation and papillation (Blackwell 1949, Cooke et al. 2000, Erwin & Ribeiro 1996); (b) some semi-papillate species, exemplified by P. primulae in the group III of Waterhouse (1963), are primitive and evolved to be non-papillate and papillate through two evolutionary paths, by Brasier (1983); (c) papillate species evolved from non-papillate ancestors. Semi-papillate species have been considered as morphological variants of papillate or non-papillate species, by Cooke et al. (2000); (d) a new hypothesis developed in this study that non-papillate ancestors evolved directly to either papillate or semi-papillate species. Some semi-papillate species further evolved to be papillate, or vice versa.