Although Darwin figured out that natural selection was general force driving evolution, he knew there were many difficult puzzles left to solve. For example, he called the sudden appearance of flowering plants in the fossil record an “abominable mystery.” Popular accounts of evolution tend to focus on the animal kingdom, but Darwin, throughout his life, looked equally to plants for insights into the diversification of species.
The New York Botanical Garden recently produced a special exhibition that includes a self-guided tour of plants representing major developments in our planet’s biological prehistory. Parts of the exhibition, including a re-creation of Darwin’s own garden, have already closed, but the Web site, Darwin’s Garden: An Evolutionary Adventure continues to have information on the exhibit, including audio recordings from the two-part symposium with leading Darwin scholars, hosted in conjunction with the American Museum of Natural History.
Other botanical gardens around the world have permanent sections, with “living fossils,” plants that trace their lineage back hundreds of millions of year, highlighting the major advances in green evolution, such as club mosses, true mosses, ferns, horsetails, cycads, ginko trees, conifers, and flowering plants. In the Brooklyn Botanical Garden’s Steinhardt Conservatory, you can walk their Trail of Evolution to see plants representing ancient floras. San Diego State University has a Geology Park with a similar theme. In Los Angeles, I have visited the Huntington Gardens’ Rose Hills Foundation Conservatory for Botanical Sciences, which has interactive live plant exhibits, some of which focus on evolution. In England, the Royal Botanical Gardens in Kew has an Evolution House (http://www.kew.org/collections/evolu.html), and the Sheffield Botanical Garden has an Evolution Garden.
If you are interested in cultivating your own garden with an evolutionary theme, you might start ferns, with the Cultivation of Horsetails or perhaps a rare Wollemi pine, a tree known from 90-million-year-old fossils that was thought extinct until it was discovered in 1994 in Australia. Only a hundred or so are alive in the wild, but as of this summer you can buy a sapling via the National Geographic Society.
Many Web pages give an overview of plant evolution, but a good place to start is the University of California Museum of Paleontology’s Introduction to the Plantae. Perhaps knowing that most people interested in paleontology have an animal bias, the site reminds us that “when we think of a particular landscape, it is the plants which first come to mind. Try to picture a forest without trees, or a prairie without grasses. It is the plants which produce and maintain the terrestrial environment as we know it.” Click on the “Systematics” button to learn more about the relationships of the earliest land plants. Here, I learned that charophytes are the branch of green algae from which land plants evolved. It is a great place to get ideas for an evolution garden. Elsewhere at the site, The Virtual Paleobotanical Laboratory allows you to explore the intricacies of plant evolution.
Other sites with a focus on early plants are Toby White’s Palaeos and W. P. Armstrong’s Plants of Jurassic Park, with emphasis on cycads and other dinosaur-era vegetation. Hans Steur in the Netherlands has put together Hans’ Paleobotony Pages, which is well illustrated and organized by geologic periods.
For the serious amateur paleobotonist, there are two more sites that have lots of links to persue: Boggy’s links and Links for Paleobotonists. The latter has a plethora of sites with ancient plant reconstructions.
It’s hard to find places that evoke the time before plants. I remember getting that primordial feeling just once on an island in the Great Salt Lake. It was sunset, and I was looking west towards the sea of brine and distant salt flats. Not a plant in sight. The greening of the land was an interesting time. An article entitled Lush Life by Marylyn Davis in the Southern Illinois University Carbondale’s Perspective, reports on recent progress in reconstructing the early plant lineages. Sorting out the early relationships from fossils has not been easy, but genetic information promises to clear things up. Go to The Conquest of the Land, a site at the University of the West Indies in Barbados, for a quick overview of the ties land plants have to aquatic green algae (they share starch as a food reserve, cell walls made of cellulose microfibrils, and the same photosynthetic pigments) and to learn about the difficulties the first colonizers of dry land had to overcome, such as desiccation, lack of support, and the need for a way to disperse spores through the air.
As for Darwin’s “abominable mystery,” the sudden appearance of the first flowering plants in the fossil record, more new finds will undoubtedly help. Currently the oldest flowering plants are found in China. See the National Geographic article “Dino-Era Fossil—The First Flower?,” which dates the rise of the first angiosperms to 124 million years ago. (Angiosperms became the dominant plants of today and include all our important food crops.) A more recent news brief in the People’s Daily Online makes a claim of 145 million years. Whatever, the date, the prize for most primitive “living fossil” of the flowering plants goes to Amborella trichopoda, a small shrub that, in the United States, can be found only in the arboretum at the University of California in Santa Cruz. See “Rare specimens at the Arboretum declared most primitive living flowering plants,” an article in the university’s magazine, Currents. Amborella has tiny greenish-yellow flowers and red fruit, and grows wild only on the South Pacific Island of New Caledonia. No doubt Darwin would have wanted one in his green house.