Multipartite Flowers with a Distinct Floral Cup and Multiovulate Carpels: An Early Cretaceous Angiosperm of Probable Lauralean Relationship

Abstract

Premise of research. Typically, the small coalified mesofossil flowers known from the Early Cretaceous have character combinations that are unknown among extant angiosperms, highlighting that many extinct lineages, which will be important for understanding the early diversification of angiosperms, are currently unrecognized. The fossils studied here provide a further example of an early angiosperm flower with an unusual combination of features of extant Laurales and other magnoliids. Methodology. Mesofossils were extracted from the sediments, cleaned using standard methods, and investigated using scanning electron microscopy and synchrotron radiation X-ray tomographic microscopy. Comparisons with extant and fossil taxa, and a phylogenetic assessment using the existing Doyle and Endress data set for extant angiosperms, were used to assess potential relationships. Pivotal results. Racheliflora is named as a new Early Cretaceous flower based on floral buds with an obconical floral cup. The perianth has about six whorls, each of four tepals. Tepals borne on the outside of the floral cup are bract-like, while inner tepals are more petallike and borne on the rim of the floral cup. The androecium comprises two whorls of four bulky, partly laminar stamens that are also borne on the rim of the floral cup. The gynoecium is apocarpous with three free carpels, each of which contains many ovules borne along two ventral placentae. Conclusions. Racheliflora is most closely related to extant magnoliids but possesses a combination of characters that is unknown among extant taxa. It has several carpels borne in a distinct floral cup, as in pluricarpellate members of Laurales, but the multiovulate carpels and bulky, laminar stamens are unknown in Laurales and more like features seen in other groups of magnoliids.