Science

• Current Initiatives
  • Biodiversity of the Hengduan Mountain region, China
  • Botanical diversity and biogeography of peninsular Thailand
  • Center for Tropical Forest Science-Arnold Arboretum Asia Program
  • Hemlock Hill management and research
  • Molecular biology and evolution of phytochrome systems
  • Phylogeny and biogeography of woody plants
  • Plant hydraulics - Zwieniecki lab
  • Tree of Life
• Fellowships
  • Mercer Research Fellowships in plant biology
  • Putnam Fellowships in plant science
  • Curatorial Fellowship
  • Deland Award for Student research
• Staff
• Herbaria

Tree of Life Project

Scientists at the Arnold Arboretum are investigating the origins and phylogenetic relationships of seed plants through a three-million dollar grant awarded by the National Science Foundation. The award to investigate the diversity of this major clade of plants is supported by NSF’s Assembling the Tree of Life (ATol) Program. The aim of the program is to support teams working across institutions and disciplines to produce a genealogical map, or phylogeny, for all lineages of life on earth. Arboretum Sargent Fellow Sarah Mathews has assembled a team to focus specifically on gymnosperms, plants such as conifers and cycads that bear seeds but have no flowers. Together with Senior Research Scientist Jianhua Li, Mathews heads a team of scientists from twelve other American and Canadian institutions, including experts in molecular phylogenetics, paleobotany, and bioinformatics.

Gymnosperms first appeared about 360 million years ago and, together with ferns, were the dominant land plants during the age of dinosaurs. Their decline coincided with the rise of the flowering plants (angiosperms), 140-190 million years ago, so that today seed plants comprise the angiosperms (approximately 300,000 species) and the relictual gymnosperms: conifers (approximately 700 species), cycads (approximately 300 species), Ginkgo (one species), and Gnetales (approximately 90 species). Gymnosperms include not only the tallest plants on earth—the giant sequoias—but also the oldest living organisms, the bristlecone pines of California (up to 5,000 years old) and a Norway spruce discovered in Sweden (about 9,550 years old). The seed plant lineages diverged from one another so long ago and so many of the gymnosperms are now extinct that it is particularly challenging to reconstruct seed plant evolutionary history. Thus, we are still vexed by a problem that puzzled Charles Darwin 130 years ago, the “abominable mystery” surrounding the rapid rise and diversification of the flowering plants. Resolving the ambiguities along this branch of the tree of life is the first step toward understanding the origin of important plant components like seeds, wood, and flowers.

The study, which is slated for completion in 2010, relies heavily on DNA data from living plants, including samples derived from the living collections of the Arboretum. The team will extract one set of DNA sequences from every living gymnosperm species, including core species representing the major branching points along the seed plant segment of the tree of life. Additionally, since seventy to eighty percent of the major lineages of seed plants that have ever existed are extinct, the team will devote considerable time to studying fossil records to assess the morphological connections between living and extinct taxa. All of the data in the study will be made easily accessible on standardized databases using an enhanced version of the web-based informatics tool TOLKIN (Tree Of Life Knowledge and Information Network).