Abstract
Asplenium cheilosorum Kunze is a triploid obligate apogamous fern growing in Darjeeling-Sikkim Himalayas and Ceylon. The cytological details of apogamy are worked out. In 16-celled sporangium the meiotic chromosome number is 2n=3x=108. Premeiotic mitosis fails in the archesporial cells at 8-celled stage, resulting in the formation of only 8 mother cells, each showing 108 ‘auto-bivalents’ at meiosis and producing 32 viable spores with zygoid chromosome number. Quite often double pre-meiotic divisions fail leading to the formation of four giant mother cells with 216 auto-bivalents at meiosis. Some of these 4 or 8 mother cells undergo irregular cytokinesis, consequent on irregular lobing and cleavage of the nucleus, as a result of which unequal cells are formed which show variable number of autobivalents. It is concluded on the basis of pairing phenomenon in 16-celled sporangia that the species is a hybrid between two parents with diverse genomic constitution.
