Molecular taxonomic study and revision of the three Japanese species of Asplenium sect. Thamnopteris

The Bird-Nest Fern Asplenium sect. Thamnopteris or A. nidus L. complex is d efined by the synapomorphic character peculiar to Aspleniaceae, an anastomo sing vein near the margin of the simple lamina. Thus, it is easily recogniz able and its monophyly is quite clear. In spite of its naturalness as the w hole group, species delimitation is very confusing. Three species of sect T hamnopteris, A. antiquum Makino, A. australasicum (J. Smith) Hooker and A. nidus L have been recognized in Japan, but the naturalness of each species is still not clear because their morphology is too simple to find good qual itative taxonomical characters. In the present work, we examined the intras pecific variation of allozymes and rbcL sequences in the Japanese plants of sect Thamnopteris and compared them with those from other paleotropical lo calities in order to recognize natural units in such morphologically simple plants. We found a large amount of genetic variation in this section and i nferred that A. antiquum is a species of ancient origin, though morphologic ally it is not so different from other species of the sect Thamnopteris. a was also discovered that the so called "A australasicum" in Japan has a ver y different rbcL sequence from A. australasicum sensu Holttum, which is dis tributed in Australia and South Pacific Islands. Based on these molecular d ata, we described the Japanese "A. australasicum" as a new species, Aspleni um setoi N. Murak. et Seriz.