Sunday, May 20, 2012

Way down yonder in the pawpaw patch




Species name: Asimina triloba

Common name: Pawpaw

Location: Ontario

This species of tree is at the most northern part of its range in Southwestern Ontario. It is native to the Carolinian Forest of North America, which extends from the Carolinas (d'uh) up to southern Ontario, east to Nebraska and Missouri and northwest up to Pennsylvania. It is part of the breadfruit family, along with other fruits of tropical origins like soursop, ylang-ylang, custard-apple, and cherimoya. I've heard that pawpaw fruit are delicious, but I've never had the opportunity to try one -- even through the tree on campus produces flowers, it has yet to produce fruit. Perhaps I'll go track a pawpaw down in South Carolina in September/October when the fruit is ripe. Because of climate change, the habitat in Southwestern Ontario should become more hospitable to these trees, where winters are less harsh and so less stress on the trees themselves. Unfortunately, due to habitat destruction, Southwestern Ontario is actually becoming less hospitable for this species even taking into account climate change (current warming and projected values).

The flowers of pawpaw trees are a very dark red or maroon, and, true to the "flower rules," smell like rotting meat. They are certainly not pleasant! One of the great benefits of planting pawpaw trees on suburban properties is that all of the plant tissues contain a potent chemical called acetogenin. This acts as a natural pesticide against all sorts of pests: insects, bacteria, fungi, deers and rabbits. The chances of this plant being destroyed by herbivorous predators is pretty slim! The fruits themselves would attract bears (if you happen to be in bear country), foxes, racoons, opossums, and squirrels. The leaves are the only food source for the zebra swallowtail butterfly. This confers a major benefit to the butterfly larvae and the future mature butterflies in that the acetogenins remain in trace amounts in the insect's tissues which make them unpalatable to predators.

Acetogenins from this plant are currently being produced en masse in organic fertilizer labs across North America for use in organic gardening. Pawpaw trees are relatively fast-growing and can grow new shoots off their root systems and so are great plants in their native range to control erosion.