Mark Olson, Ph.D.
Recieved from: Washington University, 2001
Missouri Botanical Garden Graduate School
Drs. Peter H. Raven and Barbara A. Schaal
Plants come in an incredible profusion of different shapes and sizes. How have plants come to display such diversity? My research examines the role that changes in the timing of developmental events may play in producing the wide array of plant form. I am using the small but wonderfully diverse family Moringaceae as a study system. To find out what makes the Moringaceae wonderful, visit the Moringa Home Page.
Before coming to the Missouri Botanical Garden, I worked with
vernal pools and other vulnerable habitats, many of which occur
on land that is prized for development, ranching, or agriculture.
Click here to see my CV, which lists
some of these projects. This work made me interested not only
in the detailed inventory efforts that are necessary to document
changes in biodiversity, but also the relationship of scientists
with those that own and use the land.
My dissertation research on the Moringaceae: Heterochrony in the dry tropics
This map shows tropical rainforests in green. The heavy black line is the equator, and the lighter lines are the tropics. Most of the land area within the tropics is not rainforest, and experiences some form of annual drought. Painting © 1996 Barbara Alongi.
While rainforests support the highest diversity of species on earth, tropical dry habitats may exhibit the highest diversity of plant life forms (Medina, 1995). This painting shows examples of some life forms from the dry tropics of the world. Bottle tree: Chorisia sp. (spiny trunk at right; Bombacaceae, South America); Brachychiton sp. (thick tree in left rear; Sterculiaceae, Australia). Slender, water-storing tree: Amphipterygium adstringens (bent tree at right; Julianiaceae, North America). Tuberous shrub: Adenia sp. (green prickly stems in middle front; Passifloraceae, Africa); Erythrina sp. (red flowers; Fabaceae; mostly tropics). Other life forms are represented by Celtis sp. (shrub in left foreground; Ulmaceae, tropics and temperate); Bouteloua sp. (grass at right; Poaceae; North America); Selaginella sp. (green tufts in middle foreground; Selaginellaceae, tropics and temperate); Acacia sp. (slender tree at left middle; Fabaceae; mostly dry); Alluaudia sp. (slender grey columns in background; Didieriaceae, Madagascar); Pilosocereus sp. (green columns in background; Cactaceae, South America). Painting © 1996 Mark Olson and Barbara Alongi.
How did this diversity of habit in the dry tropics arise? How can one family be represented in one area by bottle trees, slender trees in the next, and tuberous herbs in another? The small size of the Moringaceae, its range of life form from giant bottle tree to small tuberous shrub, and its ease of cultivation make it easily one of the most amenable groups for the study of this issue. Click to visit the Moringa Home Page. to see the family's diversity for yourself, find out where they grow, how to cook them, and follow links to the best moringa sites on the web!
One clue to the mechanisms that might be acting to produce the array of forms seen in Moringa is found is their life history: The adult stages of some Moringas seem to resemble intermediate stages exhibited by other members of the genus. Are changes in the timing of developmental events (a phenomenon called heterochrony) involved in generating this pattern of life forms, which is seen repeated in other families throughout the dry tropics? I am growing Moringas in the greenhouse and have collected samples of stem and roots from the wild to try to answer this question. Now, I'm finding out how the timing of events in development compares between species. Illustration © 1996 Mark Olson and Barbara Alongi.
Studies of heterochrony are built upon the phylogenetic assumptions used. Whether or not a species is considered an ancestor or a descendant determines how any heterochronic change is interpreted. Therefore, one of the most important aspects of my thesis research is a hypothesis of the relationships within the Moringaceae and its relationship to other families. I'm using evidence from DNA and other sources to construct my hypothesis. So far, phylogenetic reconstructions show pachycaul, actinomorphic-flowered species as basal, with the tuberous shubs with zygomorphic flowers in more derived positions.
Here are a few relevant References:
The following papers tell the surprising story of the familial relationships of the Moringaceae:
©1999 Mark E Olson