Studies on the bennettitalean fructification Williamsonia Carruthers

摘要

The genus Williamsonia was instituted on the basis of study of the specimens collected from the Secondary rocks of Yorkshire (Britain). More than 80 species of this genus are known from the world and over a dozen from the Indian sub-continent. This seed bearing cone has a conical/hemispherical receptacle covered by a compact layer of seminiferous and interseminal scales. In some species (W. gigas), the apical portion of the receptacle is naked and without scales. Each fertile scale has an orthotropus ovule with a long micropylar canal. 5-8 sterile scales surround an ovule which has an uneven, non-vascularised integument and free nucellus with a long nucellar stalk. Seed is endospermic with a dicot embryo. Linear, little curved bracts protect the compact layer of scales. Relationship of Williamsonia with allied taxa of Bennettitales (Cycadeoidea, Williamsoniella and Amarjolia) is discussed and made use in tracing the phylogeny of Williamsonia and origin of angiosperms.