Investigations of North American cycadeoids: Microsporangiate structures and phylogenetic implications

Abstract

The microsporangiate structure of cycadeoid cones seems to have been composed of a fleshy portion, continuous and cup-shaped below and with separate distal members, each with a fleshy appendage at the distal region. This microsporangiate structure was probably derived from a phyletic fusion of separate sporophylls, the tips of which are still free, although compactly appressed to each other. Such an interpretation brings the cycadeoid cone closer to the williamsonian cone structure. Furthermore, certain cycadeoids seem to have had monosporangiate fruiting structures, including a cone described in this paper with only microsporangia, - another parallel with the williamsonias.