Summertime is the beginning of the fruiting season for some of the trees at Prairie Ridge. One interesting native tree, the Pawpaw (Asamina triloba), can be spotted in several areas on the grounds and are currently working hard to produce fruits.
Pawpaws are small trees or shrubs in the custard apple family Annonaceae, a primarily tropical plant group that includes several fruiting trees that have become popular foods in various parts of the world. Pawpaw trees reach heights of about 35 feet, though many remain shorter depending on whether they are growing in the dappled light in the understory of a forest or in a more open area. They have large simple oval-shaped leaves that are pointed at the tip and smooth along the edges. The leaves reach sizes of 8-12 inches long and 4-5 inches across and are covered in fine hairs on both the upper and lower surface. When fully grown, the leaves are dark green on the top and pale green on the bottom and turn rusty yellow in the autumn.
Pawpaws produce fuzzy brown flower buds in the winter:
…and the flowers bloom in the spring before or just as the leaf buds burst. Pawpaw flowers are pretty spectacular, a deep maroon or purple color with six petals and a yellow center:
The flowers might look pretty, but they certainly don’t smell as nice as they look! The flowers give off a faint smell of rotting meat and attract carrion beetles, blow flies, scavenging fruit flies, and other carrion-loving insects. The trees require cross-pollination, so a pollinator must visit more than one tree to pollinate the flowers. Due to the weak scent of the flowers, the pollination success of the trees is rather low, so few fruits are tyically produced and few seeds are dispersed to new areas. Pawpaws sucker when they are young, so if you see multiple trees growing together, it is more likely that you see a series of clones of a single tree rather than multiple trees grown from seeds.
If a flower is successfully pollinated, either by an insect or by hand pollination in garden or fruit production settings, a fruit will begin to form:
They grow through the summer and ripen in the early fall, changing from green to yellow or brown when they are ready to be consumed. The fruits are readily eaten by a variety of animals, including raccoons, foxes, possums, squirrels, and bears, but they are also a favorite food of many people as well. In fact, George Washington reportedly ate Pawpaw fruits as a dessert and Thomas Jefferson had them planted on his estate at Monticello. Though they are edible with a custardy texture and tasty flavor reminiscent of a blend of banana, pineapple, and mango, you are unlikely to find Pawpaw fruits at your neighborhood grocery store. The fruits ripen very quickly and bruise easily, transforming them from a tasty treat to a rotting mess in just a few days after picking if left at room temperature. However, there are some growers determined to make a place for our largest edible native fruit, so you may start to see them at farmer’s markets and the like eventually.
Pawpaw trees have become popular landscaping trees as they produce edible fruits, attractive (if stinky) flowers, and showy fall foliage, yet require minimal care once they are established. They are also naturally resistant to most insects and mammals such as the deer and rabbits that cause gardeners such heartaches. Pawpaws contain toxic chemicals calls acetogenins that repel many animals that would otherwise consume the leaves and new twigs. There is one notable exception: the caterpillars of the Zebra Swallowtail feed exclusively on the leaves of Asimina species of trees, including the Pawpaw. The caterpillars cause minimal damage to the foliage, however, so they are not considered pests. The caterpillars store the acetogenins internally to protect themselves from predators. Interestingly, these same chemicals that protect both the Pawpaws themselves and the Zebra Swallowtails that eat their leaves might also one day protect humans: they have been shown to be very effective against certain forms of cancerous cell lines and may eventually be used to develop a chemotherapy drug for people with those cancers.
We have Pawpaws growing in several locations on the Prairie Ridge grounds. Look for trees with the large, deep green leaves in the Nature Neighborhood Garden or in the lowlands near the stream on your next visit. Take a look at the leaves and see if you can spot any Zebra Swallowtail caterpillars or look for fruits growing along the branches. The fruits won’t be ripe for a few more months still, but they will eventually make a tasty treat for one of the many animals that call Prairie Ridge home!
Want to get the most up-to-date information about the wildlife at Prairie Ridge? Visit the Museum's blog  for the most recent sightings, or find out more about the natural happenings at Prairie Ridge at our What Time is it in Nature Archive !
(Photo by Chris Goforth)