Spores from the liverwort Podomitrium phyllanthus. This liverwort is one of many plant species scientists are studying as part of the National Science Foundation (NSF)-supported "Tree of Life" initiative. The goal of the initiative is to reconstruct the evolutionary history of early land plants, as well as to answer such questions as how multicellular aquatic plants evolved, what plants first colonized land, how are the early plant lineages related to each other, and what genetic, cellular and structural changes did they undergo. (Year of image: 2002)
Image Credit: Photo by Karen Renzaglia; courtesy Dan Nickrent.