2005 Volume 56 Issue 3 Pages 231-240
Ceratopteris thalictroides has been reported to contain three cryptic species, called the south type, the north type and the third type. To obtain a clear understanding of these cryptic species, the somatic and meiotic chromosomes were examined in 18 sporophytes from different localities and three hybrids synthesized among the three types. The examinations revealed that the north type and the third type are tetraploids with 2n=156 and n=78 chromosomes, whereas the south type is a hypotetraploid with 2n=154 and n=77 chromosomes. Several peculiar configurations were occasionally observed at diakinesis in all three types: single rope-shaped bivalents with acrosyndesis, split bivalents with acrosyndetic connections, and quadrivalent or quadrivalent-like configurations. Occasional quadrivalents indicate the presence of several homologies within the genomes of the three types. Many univalents were observed at metaphase I in the hybrid between the south and north types, whereas only a few univalents were occasionally observed in the hybrids between the third and north types, for which a partial cross-sterility had been reported. This suggests that the chromosomal structure has differentiated little between the genomes of the third type and the north type and that the partial cross-sterility is mostly due to genic differentiation between them.
