New PDF release: An introduction to gymnosperms, cycas, and cycadales

By Pant, D.D. and Osborne, R. and Birbal Sahni Institute of Palaeobotany

ISBN-10: 8186382011

ISBN-13: 9788186382011

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1989) and Moresnetia zalesskyi (FaironDemaret, 1986) from the Upper Devonian or those of Genomosperma kidstOllii (Long, 1961) from the Lower Carboniferous (see also Rothwell & Scheckler, 1988). The integuments of these seeds are not at all like an envelope but made up of a ring of 4 to 10 linear sterile lobes which are fused only at the base of the seeds and free all round the nucellus (Figs. 4A, a). The apical ends of the lobes spread out beyond the level of the nucellar beak and the seeds have no micropyles.

ID .. c . ~. J • Fig. 12. COlllniasperma remyi. A, reconstruction of the seed-like body with two lobes removed to expose the megasporangium, B,diagrammatic longisection. CoG, successive transections of levels indicated by lines c-g (all redrawn after Galtier & Rowe, 1991). The Sui Generis Theory believes that the ovule is a new organ, which is unassignable to any fundamental categories like root, stem or leaf. The Foliolar Theory compares the ovule to a three-lobed leaflet. It believes that the nucellus is an emergence formed by the terminal lobe of the leaflet and the integument is formed by the two lateral lobes.

Karkeniaceae ? 3. Pseudotorelliaceae? Order 5. 1. 2. Leptostrobaceae Iraniaceae ? Order 6. 1. 3. ) Order 4. Cycadeoideales) Bennettitales (= 1. Bennettitaceae (Cycadeoideaceae) 2. Williamsoniaceae Order 5. Gnetales Gnetaceae Order 6. 1. Welwitschiales Welwitschiaceae Class Ephedrales Pinopsida (= C;;oniferopsida) Order 1. ) 2. ) 3. ) Order 2. Buteoxylaceae Trigonocarpales (= Trigonocarpaceae Cordaitanthales 1. Lagenostomales (=Lyginopteridales) Lagenostomaceae Order 2. Medullosales) 1. Cycadaceae Pentoxylales Note: This family is in need of further subdivision, taking into account the number of seeds in the cupule and its symmetry, the microsporoclad characters and stelar organization.

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An introduction to gymnosperms, cycas, and cycadales by Pant, D.D. and Osborne, R. and Birbal Sahni Institute of Palaeobotany


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