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(American Journal of Botany. 1998;85:1289-1300.)
© 1998 Botanical Society of America, Inc.

Reconstruction of the Jurassic conifer Sewardiodendron laxum (Taxodiaceae)1

Xuanli Yao5,a, Zhiyan Zhoub and Bole Zhangc

a Department of Biology, University of San Francisco, San Francisco, California 94117; b Nanjing Institute of Geology&Palaeontology, Academia Sinica, Nanjing, Jiangsu 210008, China; and c Qingdao Research Institute of Geotechnical Prospecting and Surveying, Qingdao, Shandong 266030, China

Compressed seed cones and pollen cones of Sewardiodendron laxum are described from the Middle Jurassic of Yima, Henan, central China. They are either organically attached to or associated with leafy shoots. Seed cones are terminally borne. Each cone is ovate to elongated, up to 6.5 cm long and 3.5 cm wide, and consists of a stout axis and numerous helically arranged bract–scale complexes. The bract protrudes beyond and is partially fused with the reduced ovuliferous scale. The ovuliferous scale bears approximately six inverted, small, and flattened seeds. Pollen cones are borne in terminal clusters. Microsporophylls are helically arranged, each bearing three abaxial, basally fused pollen sacs. Pollen is assaccate, rounded, and with an inconspicuous pore. Morphological, structural, and cuticular features of seed cones, pollen cones, and leafy shoots of S. laxum are compared with those of fossil and extant conifers. S. laxum is included in Taxodiaceae and believed to have its closest affinities with a Mesozoic conifer Elatides and a group of Cunninghamia-like conifers. It is reconstructed as a half-evergreen tree that lived in a humid, warm-temperate climate.

Key Words: Cunninghamia • Elatides • Jurassic • pollen cone • seed cone • Sewardiodendron • S. laxum • Taxodiaceae






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