After spending 16 years studying the ginkgo tree (Ginkgo biloba), whose leaf extracts are used to treat cardiovascular disease, an Academia Sinica research team yesterday said it had finally found evidence confirming that ginkgo and seed plants called cycads are sister groups.
The Ginkgo tree is a living fossil that is believed to have grown all over the world until 150 million years ago, when the extremely cold climate of the Pleistocene epoch killed off many of the trees except the ones in China, the research team said.
The species was introduced to Europe and the US in the late 17th century and has prospered since because can withstand severe air and soil pollution and its trunk is pest-resistant, the team added.
The research team said the classification of ginkgo — the only living representative of a plant lineage similar to fossils dating back more than 200 million years — and its evolutionary relationship to other seed plants have long been debated.
While six different placements for gingko have been proposed in relation to other divisions of non-flowering seed plants, distinguished research fellow Chaw Shu-miaw (趙淑妙) thought that the prehistoric tree could be a sister of the cycads group and finally confirmed her hypothesis after 16 years of research.
The team led by Chaw established the largest and most diverse gymnosperm chloroplast genome database to date, including 25 gymnosperm chloroplast genomes with 35,994 nucleotides and 11,998 amino acids. Using the database, the team found that the phylogenetic position of the ginkgo is significantly influenced by five factors, leading them to conclude the gingko group and the cycad group are closely linked.
Their research result was published last month in the journal Genome Biology and Evolution.