Format: ORAL

Gongle Shi 1, Fabiany Herrera 2, Patrick S. Herendeen 3, Elizabeth G. Clark 4, Peter R. Crane 5,6

1 Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing, China 2 Field Museum of Natural History, Chicago, USA 3 Chicago Botanic Garden, Glencoe, USA 4 University of California Berkeley, Berkeley, USA 5 Oak Spring Garden Foundation, Upperville, USA 6 Yale University, New Haven, USA

The Mesozoic seed ferns, a loose group of extinct seed plants with cupulate ovulate reproductive organs, have long been considered to be key for understanding the origin of angiosperms. Traditionally this group has included Caytonia, Petriellaea, corystosperms, peltasperms and several other closely related groups of plants. However, most of these plants are known based on compression or impression fossils, hindering a detailed understanding of the structure and homology of their reproductive organs, and resulting in several distinct interpretations regarding the relationships of Mesozoic seed ferns with other extant and extinct seed plants. Recent discoveries and careful documentation of similar cupulate ovulate structures from the Early Cretaceous of Canada, Mongolia and China based on three-dimensionally preserved, lignified specimens, and anatomically preserved, permineralized material, have significantly enriched our knowledge of the anatomy, structure and homology of these cupules. Careful comparisons suggest that the recurved cupules of Caytonia, Doylea, Jarudia, Geminispermum, Kannaskoppia, Ktalenia, Petriellaea, Reymanownaea, Umkomasia are all fundamentally the same. Differences among these Mesozoic seed plants in the number of cupules per lateral unit, the number of seeds per cupule and the degree of seed enclosure probably reflect differences in their pollination ecology and/or seed dispersal strategies. These recurved cupules are fundamentally comparable with the second integument of an anatropous angiosperm ovule. Phylogenetic analyses suggest that the likely stem relatives of angiosperms are among these Mesozoic plants, which has important implications for continuing efforts to understand the phylogeny of seed plants and the origin of angiosperms.