“Sokonashi-ike” on Nakano-shima, one of the Tokara Islands, Kagoshima Prefecture, is a small lake dammed by lava from active volcano O-take and not a crater in its origin. The water plants collected in this lake in June of 1953 are 12 species, 3 of which are all the same to those from Hondo, viz.
Trapa japonica FLEROW,
Sparganium japonicum ROTH and
Polygonum nippon ense MAK. There occur no peculiar species related to those of the Liukiu Islands and Formosa.
Trapa of this lake somewhat differs in the shape of its fruit from that of the same species from any of the remote ialands. The body of water which has
Trapa and is nearest to Sokonashi-ike is Homan-ike, a pond on the Island of Tanega-shima, some 150 km north-east of Nakano-shima.
Trapa of this pond is, however, different from that of Sokonahi-ike in less thick basal part of its fruit. This may suggest that the dispersal of
Trapa to Sokonashi-ike from any northern area of its distribution had not taken place by way of Honan-ike and had arrived to the former lake until the latter pond had been born. The water of the latter pond is deeper and clearer than the former lake.
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