By V. A. Krassilov
This article encompasses a description of the morphological grades and their linking types; a dialogue of seed plant evolution; an outline of early angiosperms and their environments; and a n research of morphological tendencies in separate organs and their implications for angiosperm phylogeny.
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Extra info for Angiosperm Origins: Morphological and Ecological Aspects
A p h y l o g e n e t i c significance of Dinophyton lies in the c o m b i n a t i o n of the gnetalean and p t e r i d o s p e r m o u s characters. T h e former include the d e c u s s a t e perianth bracts both in the pollen c o n e s and seed organs and the 4-lobed bracteolate c u p u l e containing a solitary erect ovule, w h e r e a s the structure of the latter is like in the h y d r o s p e r m a l e a n Lyrosperma, and the leafy shoots show transitional c a u l o m e - p h y l l o m e characters, as in the c a l a m o p y t i a c e a n foliar branch systems.
T h e p o l l e n g r a i n s w e r e m o n o protosaccate, with a bilobed saccus. T h e pollen wall infrastructure was alveolate (Zavada & Crepet, 1986). T h e g y n o c l a d e s w e r e pinnately b r a n c h e d with the lateral ovuliphores bent toward one side, consisting of a short stalk bearing a spherical cupule. T h e latter was fleshy, strongly cutinized, lacking stomata, vascularized, with the tracheary ele ments s h o w i n g bordered pits ( R e y m a n o w n a , 1974). A slit-like e x o s t o m e occurred at the base of the cupule, w a s subtended by a short a p p e n d a g e ("lip"), and w a s connected to the ovules by a series of channels ( T h o m a s , 1925).
T h e integuments d e v e l o p in acropetal succession (Takaso & B o u m a n , 1986), the inner laid d o w n as an a n n u l a r ridge, the outer as two decussate knobs. T h e vascular bundles extend to the level of splitting of the nucellus from the inner integument. T h e pollen grains s o m e t i m e s g e r m i n a t e in the m i c r o p y l a r cana* that is later sealed with papillae. T h e m e g a s p o r e tetrad is linear. T h e m e g a g a m e t o p h y t e is tetrasporic or m o n o s p o r i c , nuclear until a 1000-1500-nucleate stage.