The Flowers in Extant Basal Angiosperms and Inferences on Ancestral Flowers

Abstract

This is a combination of a review and original data on floral structure, development, and biology of representatives of all families of the ANITA grade and, in addition, Chloranthaceae and Ceratophyllaceae. Since the ANITA grade has been identified as the basalmost grade of extant angiosperms based on molecular studies by a number of authors, it has become possible to search for potential plesiomorphies among flowers of extant basal angiosperms. They may include the following traits: flowers small, pollination by small insects (dipters, thrips, moths); flowers with moderate or low number of floral organs, in spiral (or whorled) arrangement, with a tendency to form organ series in Fibonacci numbers (3, 5, 8); flowers bisexual (but easily becoming unisexual because of low level of synorganization between organs), protogynous; tepals (in spiral flowers) with gradual transitions between bractlike, sepal‐like, and petal‐like forms; stamens with short filaments, anthers with a connective tip, with more or less bulging disporangiate thecae; thecae opening by a longitudinal slit and not by valves. Carpels free, styleless, extremely ascidiate, with one or only few anatropous ovules, sealed by secretion and not by postgenital fusion; stigmas wet, with multicellular protrusions. Among members of the ANITA grade, there is a trend to form extragynoecial compita. In those taxa with the relatively most complicated gynoecium architecture (including an extragynoecial compitum), there is a concomitant trend to have less strongly ascidate to almost plicate carpels (Nymphaeaceae, Schisandraceae, Illiciaceae).