Ovular Morphology and the Classification of Dicotyledons

Abstract

Four types of ovule are defined by integument number and nucellar thickness. Their distribution throughout the dicotyledons is summarized and their importance in defining major subclasses is advocated. In particular, those families with ovules having a single integument are considered to form a complex of orders and families which includes most sympetalous and several polypetalous groups (including Cornales, Araliales, Escalloniaceae and Pittosporaceae). This complex (provisionally referred to as the Unitegminae) is believed to comprise the modern representative of a distinct evolutionary line within the dicotyledons.