By V. A. Krassilov
This article includes a description of the morphological grades and their linking kinds; a dialogue of seed plant evolution; an summary of early angiosperms and their environments; and a n research of morphological traits in separate organs and their implications for angiosperm phylogeny.
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Extra resources for Angiosperm Origins: Morphological and Ecological Aspects
Cell walls are laid down after the first division of the zygote. T h e e m b r y o produces a haustorial feeder, like in Gnetum, and two unequal cotyledons with the axillar buds that overtop the primary apex. Typical gnetalean characters a p p e a r in the Triassic genera Dinophyton and Sanmiguelia that can be considered as protognetalean. T h e y can then be traced through the Jurassic Heerala to the even m o r e definitely gnetalean Crttactous Leongathia, Drewria and Eoantha and the recently found pollen inflorescences of the Baisian A s s e m b l a g e .
10. : (1, 2 ) juvenile and ripe cupules with bracts, ( 3 ) ovule with a trilobed nucellus, (4) involute phyllomic struc ture, (5) pollen cone with bracts, (6) sporangiophore (after Krassilov & Ash, 1988). s p o r a n g i u m or a g r o u p of three apparently fused sporangia that are basifixed, dehiscing in t w o valves. T h e pollen grains are bisaccate. T h e ovuliphores are 4-lobed pedicellate cupules borne on shoots of different orders, with a 4-lobed cross-like perianth formed of two decussate pairs of bracts and fused to the base of the cupule, persistent as a propeller in the fruit-like diaspora.
Several distal bracts are empty. Fig. 5. Semionogyna hracteata Krassil. , a protocycadean plant from the Early Cretaceous of Transbaikalia: ovulate spikes with juvenile and ripe ovules subtended by the bracts, with distal bracts empty, compared to extant Cycas revoluta (right), (after Krassilov & Bugdaeva, 1988c). Young ovules are shorter than bracts and are protected by the bract bases, protruding at maturity, with the bracts pendent and eventually shed. T h e ovules are large, sessile, erect, r a d i o s p e r m i c .
Angiosperm Origins: Morphological and Ecological Aspects by V. A. Krassilov