March 2006

Why are flowering plants, or angiosperms, important in the evolution of our planet?

By studying floral genetics, we may be able
to understand the origin of the flower.
Photograph: Oksana Hlodan.

Soltis: Currently the angiosperms are by far the largest group of plants and the most important from an ecological standpoint. They inhabit all sorts of environments. They make up the majority of a lot of different habitats, such as grasslands (all the grasses are flowering plants), most forests except for the boreal forests, and most terrestrial habitats on the face of the planet. They provide food sources and shelters for the organisms that live in these habitats. On a more personal note to humans, they provide us with most of our food and, in certain areas, a lot of our shelter materials.

Your research is based on the idea that most plants as well as some other species have originated more than once. How did you arrive at this idea?

Soltis: There is one mechanism of speciation that is very prominent in flowering plants, and that is called polyploidy. [Polyploid cells or organisms have one or more extra sets of chromosomes.] Polyploidy is beginning to be recognized as an important evolutionary process in groups of organisms other than plants. In fact, even vertebrates are now thought by most people to be ancient polyploids. So a process that occurs in a lot of different groups of organisms has been sort of perfected in the flowering plants, or at least it’s very common.

The way that we have determined that a lot of flowering plant species are of multiple origin is through molecular techniques. For example, a polyploid species is one that has undergone a genome duplication event. Typically these polyploid species have arisen through hybridization between two species, which means there would be two parental species that would have given rise to a single polyploid derivative species. That polyploid derivative species would have the combined genetic markers of both of its parents. Through molecular studies we have been able to determine that different populations of the same polyploid species have different genetic markers that correspond to the parental species in a particular area. This allows us to infer that the polyploid species has arisen multiple times in different locations from genetically different parental species. If we extrapolate what we have seen on a local scale, for example, in an area of the Pacific Northwest where we have done a lot of research, it may be that half or more of all flowering plant species that have originated by this mechanism may also be of multiple origins. This tells us that there may in fact be a lot more genetic diversity in polyploid species than some of our botanical predecessors thought. For a while it was perhaps considered an evolutionary dead end. We now know that there are ways to get a lot of genetic diversity into a polyploid species.

You and your husband Douglas are principal investigators of the Floral Genome Project. What are you hoping to achieve through that project?

Soltis: This is a really fun project that is a large collaboration with other researchers at the University of Florida and with folks at Cornell and Penn State Universities. We also have a number of collaborators in Europe. We are hoping to understand the genetic architecture of the flower. What I mean by that is what are the most important sets of genes that control the formation of the flower? This is a fundamental feature of all the angiosperms, the flowering plants. By studying the floral genetics of the most ancient flowering plant lineages, we may be able to understand the origin of the flower. This has been an extremely important and interesting question for a long period of time.

Deep Time is another one of your team projects. What is the purpose of this project?

Soltis: The Deep Time Project is what the National Science Foundation calls a research coordination network. It is designed to bring people from different fields together, in our case, for example, paleobotanists and angiosperm systematists, to discuss areas of overlap and differences and to develop new ways of looking at how flowering plants may have evolved. For too long paleobotanists have generally gone in their own direction, kind of ignoring what is being done in molecular systematics, and molecular systematists and morphologists have tended, for the most part, to ignore a lot of paleobotany. With the phylogenetic trees or the reconstructions of evolutionary history that have been undertaken over the last decade or so it seems like a good time to try and bring the fossil record into all of that. Along with David Dilcher and my husband, who are also at the University of Florida, and Patrick Herendeen at George Washington University, we developed this network of paleobotanists, phylogenetecists, and morphologists. We meet once or twice a year, sponsor symposia, hold workshops, and offer training opportunities for graduate students and undergraduates, all with the idea of developing new ways of coordinating research and activities. Lots of collaborations, symposia, and papers have resulted from just getting people together. It is a great idea.

How is it that without angiosperms we would not have cotton or aspirin?

Soltis: Cotton is a fiber that is derived from the seeds of the cotton plant. There are a number of species in the cotton genus that produce fibers that are then used to make our cotton fabric. Plants of the cotton genus are flowering plants, in the rosid group. There would be no such thing as a T-shirt or cotton swab without flowering plants.

The same thing is true of aspirin. Aspirin is a chemical compound found in willows, a flowering plant. It is made synthetically, but it was originally identified through analysis of willows. There are so many compounds and so many products derived from the 250,000 to 300,000 species of flowering plants that we would just be without if they didn’t exist.

Why is such knowledge of evolutionary relationships vital to modern research?

Soltis: There are many ways that understanding the evolutionary history of groups of plants can help us. Many of our medicines and other chemical substances have been identified by looking at relatives of plants. A wonderful example, and this isn’t from the flowering plants but from the gymnosperms, is Taxol (paclitaxel), a natural derivative that holds promise in the treatment of cancer. Taxol was identified from the bark of the Pacific yew. People started looking for other sources of Taxol because it was not feasible to get sufficient Taxol from the Pacific yew. They looked to the closest relatives of the species. Understanding something about evolutionary history can certainly help us in bioprospecting for medicines or any other sorts of important compounds.

Another important use of evolutionary information in an applied sense is in agriculture. Wild relatives of our crop plants, or any of our domesticated animals, are the best sources of improvement for those organisms. If we want to improve a crop and improve its disease resistance, we go first of all to the wild relatives. If we didn’t know how the species are related, it would be very difficult to know where to begin. Agricultural biologists have been studying this aspect of plants for a long time.

How has human activity disrupted plant diversity today?

Soltis: What humans are doing to the environment is causing a lot of problems. Habitat destruction, just to name one right off the bat, has accounted for a lot of extinctions. I live in Florida where there is so much development it really threatens a lot of the state’s natural biodiversity. Florida is one of the top 10 or 20 areas for biodiversity on the globe, particularly from the panhandle down into the rest of the peninsula. There are so many species that are either recently extinct or are declining now as a result of changes in land use.

Members of our lab study a number of species from a conservation genetics perspective. A number of these studies occur in the Lake Wales Ridge in central Florida. This is an area that was originally a kind of scrub habitat that was then used for orange orchards and has more recently been converted to golf courses and retirement communities. As a result, one plant species that occurs nowhere else in the world other than Lake Wales Ridge has now been reduced to about five populations. This species is unisexual so plants can’t persist if there is only one sex in the population. We have been working with ecologists to try and develop a method for remedying that problem.

On a larger scale I think this same sort of thing happens repeatedly. There are lots of species on a global scale that are very restricted in their distributions so that they only occur in one limited location. There are other sorts of larger scale threats, for example, in the tropics. Destruction of large tropical regions has a huge impact on the biology of the organisms that live there. There is a fairly large body of research now on the genetics of tropical trees, and this research suggests that the populations become so fragmented that gene flows are cut off in what used to be a contiguous population. Members of the population become isolated, and isolated members can’t reproduce any longer.

Also, plants serve as habitat for a host of other organisms, like this one example from central Florida that I mentioned. Anytime you lose a species there is a potential effect on the rest of the ecosystem. Our knowledge of how the ecosystems used to be is so rudimentary at this point that we don’t necessarily know what the exact effects of any particular species loss would be. But there are predictions that we could make about ultimate effects, and depending on the type of species that is lost from the ecosystem, that effect could be very large.

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