Resources plant studies on the natural forest in subtropical Okinawa, 7: About plant distribution on the main islands of the Ryukyus [Okinawa, Japan]

Within the frame work of a series of plant resource studies on the natural forests in the subtropical Okinawa, the present study was undertaken to clarify the distribution of forest plant for both indigenous and exotic species on the Ryukyu Islands, especially for the 4 main Islands, i.e. Okinawa, Miyako, Ishigaki and lriomote Islands in the Ryukyus based on the database of the five reference books. The considerable difference was found for the total number of species among the references. The plants distributed in the entire Ryukyu Islands were 238 families, 1,688 genera and 5,473 species based on Flora of the Ryukyus, Southern of Amami Island (FRSAI), which had the highest number of species, while Flora of Okinawa and Southern Ryukyu Island (FOSRI, 1976) recorded 239 families, 1,061 genera and 2,560 species. According to Check List Vascular Flora of the Ryukyu Islands (CLVFR), 200 families, 949 genera and 2,275 species were present. Flora of the Ryukyus (FR) recorded the least species with a total of 182 families, 863 genera and 2,142 species. The methods of the handling of plant distribution to the exotic species may be responsible for the obvious differences in the main factor on the total number of species among these references. For the composition of the indigenous species, in Okinawa Island, 1,451 (FR), 1,445 (FRSAI) and 1,404 (CLVFR) species were recorded; 1,099(FR), 1,132 (FRSAI) and 1,119(CLVFR) species in Ishigaki Island; 1,151(FR), 1,139 (FRSAI) and 1,142(CLVFR) species in lriomote Island. No obvious differences were found among the 3 references. Moreover, for the abovementioned indigenous species, the order of species number were Okinawa Iriomote Ishigaki Miyako. As for the least value of indigenous species in Miyako Island, it is thought that the greater part of the Island is covered with the limestone of the upheaval coral reef, and the mountainous forest plant is less than other Islands because of its smooth landform on the Island. Each reference recorded a lot of endemic plants in the Okinawa Island, with 16 species recorded in VJOO, 15 species in FR, and 33 species in CLVFR, while Iriomote Island had the second highest value for endemic plants with 13 species recorded in VJOO, 10 species in FR and 9 species in CLVFR. In Miyako or Ishigaki Islands, few endemic plants were present with a range of 1-3 only.