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Almost all flowering plants cannot move by themselves, but they cast their seeds or fruits to get new domain. The geographic distance attained by seed dispersal is generally limited because of the media (winds, water, animal, etc., for example), so that the distribution areas of plants are mostly limited. This is the reason that we meet lots of endemic plants, even in a certain mountain area in Honshu Isl. of Japan. -- The dispersal range is mostly limited in Plants.--
However, some plants have really wide distribution on the earth, and Pantropical Plants with Sea Drifted Seeds (PPSDS) are one of the plants that have most intriguing and extremely wide distribution areas. Ipomoea pes-caprae (Convolvulaceae), Canavalia rosea (Leguminosae), and Hibiscus tiliaceus (Malvaceae) are the top three members of PPSDS. PPSDS are littoral plants that have very wide distribution range in tropics, and perhaps less than 6 species are known in total. The three species listed above and their close allies have almost overlapping distribution range in the coastal areas of tropics and subtropics on the earth. Imagine this. How can a plant species that grow in the beautiful sandy beach of Rio de Janeiro interact with the one in Okinawa Isls. in Japan? The geographic distance between the two localities is about 20,000km! This is the problem we are currently working on. We focus on these three species and collect materials from their populations in tropics world wide, and to reveal the level of gene flow than are maintained by Sea-Drifted seeds. Our goal is to figure out the level of recurrent gene flow by sea-drifted seeds to maintain the unity of a species in the distribution area around the earth in tropics.
Leguminosae ("Bean Family") is the third biggest family of flowering plants. So many legume plants are utilized in various ways in our daily life, especially as crops. We do not live on legume crop alone, but our life without legumes must be very hard. To understand the phylogenetic relationships of Leguminosae, we use molecular phylogenetic method. This modern method using nucleotide sequences of DNA can provide us objective ways to infer phylogenetic relationships of living organisms. In the field of legume study, many researchers are working on various taxonomic groups using various methods. I myself did phylogenetic study on whole Legume family using chloroplast rbcL gene collaborated with Jeff Doyle of Cornell University. I am working now on tribe Desmodieae that includes ca. 400 species.