In Search of the Earliest Flowers: Introduction

Abstract

On the occasion of the sixtieth birthday of Else Marie Friis, an international symposium, ‘‘In Search of the Earliest Flowers,’’ was held at the Swedish Museum of Natural History, Stockholm, on June 2–3, 2007. Else Marie Friis has made classic, innovative, and groundbreaking contributions to the understanding of angiosperm evolution through her work on Cretaceous angiosperm reproductive structures. Her discovery of a major mesofossil flora from the Late Cretaceous at the Asen locality in Scania, southern Sweden, in the 1980s is a milestone in paleobotanical research. The Asen Flora includes thousands of flowers, fruits, and seeds that are mostly preserved as charcoal and show great diversity in floral organization and structure. In the wake of this discovery, numerous other Cretaceous mesofossil floras around the globe have been described, and our knowledge about the early evolutionary history of the angiosperms has massively increased. Mesofossil studies have documented the presence of numerous lineages of extant angiosperms in the Cretaceous and have strongly influenced our view of early floral evolution. Prevailing ideas on the floral structure of earliest angiosperms at the time of the discovery of the first mesofossil floras usually assumed that flowers were relatively large with numerous floral parts. The fact that Cretaceous floras comprise almost exclusively tiny flowers, with a limited number of floral organs, came as a surprise. Now it is widely accepted that the earliest angiosperms most likely had small flowers. The symposium brought together paleobotanists and neobotanists whose research focuses on the evolution of angiosperms. The goal was to provide a platform for discussions on various aspects of early angiosperms, including such issues as early floral morphologies and the geological context for understanding interactions between vegetation and environmental changes during the emergence of early angiosperms. In this special section, the origin of the angiosperm flower is addressed by J. A. Doyle, who demonstrates that inferences on its origin require consideration of other seed plants and particularly of fossil taxa. He emphasizes analytical difficulties caused by uncertainties in phylogenetic relationships among living and fossil seed plant lineages and by insufficient understanding of critical fossils. A complementary study by P. K. Endress presents the perianth structure and behavior of basalmost extant angiosperms. His findings lead to a better understanding of the perianth of extant angiosperms and help in the correct interpretation of fossil floral structures. O. Eriksson explores the evolution of seed size and biotic seed dispersal in angiosperms using paleoand neoecological evidence. His findings indicate that changes in vegetation structure (open vs. closed) were probably a primary driving force for the evolution of seed size and dispersal mechanisms. Based on their studies of fossils from a newly discovered mid-Cretaceous locality in Germany, A. Viehofen, C. HartkopfFroder, and E. M. Friis describe a new species of the extinct genus Mauldinia (Lauraceae). Mauldinia is now known from several localities in the Northern Hemisphere, indicating that the genus was an important element in Cretaceous vegetation. From the Early Cretaceous of Virginia, USA, M. von Balthazar, K. R. Pedersen, P. R. Crane, and E. M. Friis describe Carpestella lacunata, a fossil flower with affinities to both Nymphaeaceae and Illicium (Illiciaceae); this fossil may represent an extinct lineage among basal angiosperms. M. Takahashi, E. M. Friis, P. R. Herendeen, and P. R. Crane describe Late Cretaceous flowers and fruits from Japan as Archaefagacea. These fossils’ structure links them to extant and fossil Fagales. They seem to fall outside the core fagalean group and provide a link between the earliest occurrence of the group and extant basal Fagales. Another taxon from Late Cretaceous Japan, Futabanthus asamigawaensis, is described by M. Takahashi, E. M. Friis, K. Uesugi, Y. Suzuki, and P. R. Crane. The multipartite construction of Futabanthus and the form of the stamens indicate placement near the base of Annonaceae (Magnoliales). The fossil provides the earliest record of the family and documents the presence of Annonaceae in eastern Eurasia during the early Late Cretaceous. New reconstructions of complete plants based on fossil foliage, fruits, seeds, flowers, in situ pollen, and wood are presented by Z. Kva cek. He discusses the difficulty of whole plant reconstructions but explains the importance of this approach for paleoecological, phytostratigraphic, and paleobiogeographical studies.