| Abstract: | The present paper aims at discovering the characters of embryological development
of Circaeaster agrestis, which makes up a monotypic genus, Circaeaster, to establish the phylogenetic relationships of the genus. The different opinions on its systematic position among botanists are briefly explained.
The embryological studies show that the most important advanced characters of the genus
are as follows. The ovule is amphitropous, unitegmic and tenuinucelar; the embryo sac formation is in accordance with the Polygonum type; endosperm formation is of the cellular type, the
primary endosperm nucleus dividing to form two cells and the first wall vertical; embryo
formation follows the variation of the Caryophyllad type; at the early stage of development of
embryo, the integument has been already atrophied and at last disappeared, so that the seed coat
is absent in the mature fruit.
On the basis of the embryological and some morphological evidence, the authors consider
that a close relationship between the genus and Ranunculaceae and its related families seems to
be unlikely. The affinities of the genus Circaeaster are still uncertain. |
