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By V. A. Krassilov

This article incorporates a description of the morphological grades and their linking kinds; a dialogue of seed plant evolution; an outline of early angiosperms and their environments; and a n research of morphological developments in separate organs and their implications for angiosperm phylogeny.

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Extra resources for Angiosperm Origins: Morphological and Ecological Aspects

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T h e m i c r o p y l e is short, indis­ tinctly lobed. T h e integument is single, glabrous, thinly cutinized. T h e nucellus is free. T h e m e g a s p o r e m e m b r a n e was not observed. T h e shed c u p u l e s are empty, filled with rock matrix. T h e pollen grains sticking to the c u p u l e are anasulcate, asaccate, of the Cycadopitys type. T h e associated leaves are simple, lobed, of the Nilssonia type. T h e paired c u p u l e s oiDirhopalostachys s e e m derivable from the peltate ovuliphores of the Nilssoniales {Beania) by involution of the peltae bearing t w o inverted ovules (Krassilov, 1975a).

T h e pollen organs w e r e catkin-like strobili, with the lateral s p o r a n g i o p h o r e s arranged spirally or p s e u d o w h o r l e d , consisting of a slender, apically reflexed stalk bearing an adaxial s y n a n g i u m . T h e latter w a s 4-lobed, spreading at d e h i s c e n c e , each lobe vascularized by a branch of a single pedicellar bun­ dle. T h e g y n o c l a d e s w e r e terminal on short shoots, with scale leaves at base, loose, branching spirally, with the lateral ovuliphores distant or o v e r l a p p i n g , consisting of a stalk and a terminal bivalved cupule (Harris, 1951b; Krassilov, 1969).

T h e perianth consists of t w o decussate pairs of bracteoles the inner of which are c o n n a t e to half their length. T h e y form an open cupule that contains six sporangiophores arranged radially around the apical ovule, the latter extended into a papillate corona, p e r h a p s glandular. T h e sporangiophore stalks are connate basally, bent toward the central ovule, each bearing 3-locular synangia. T h e pollen grains are ribbed, as in Ephedra, but with a single or several colpous apertures between the ribs.

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