North Carolina Cactus for a Hot Summer Day
This is an excerpt of the current issue of the North Carolina Botanical Garden Newsletter, which is available in printed or digital format to members of the Botanical Garden Foundation. For more information, or for back issues, see our Newsletter page.
You can say you read it here: North Carolina, despite its humidity and rainfall, has native cactuses! There are three species, of which one is common — the Eastern prickly pear, Opuntia humifusa (some references call it Opuntia compressa), also known as Hardy Prickly Pear (it is native all the way to Cape Cod, Massachusetts), Devil’s Tongue (from the shape of the “pads” and the prickles), Beaver Tail (also from the shape of the “pads”), and Indian Fig (from the edible fruits). The other two species are rare and found on coastal dunes.
As I write these words, North Carolina’s prickly pear is in full bloom — dazzling yellow flowers — in the Native American section of the Mercer Reeves Hubbard Herb Garden. Some wild types of this species have a red flower center, a characteristic that has been selected as a horticultural form. The plant can be grown from seed and makes a low-growing specimen plant for sunny, dry places in your yard.
I stand by the proposition that every plant can be a door to a deeper understanding and enjoyment of this green world. All plants have a story to tell. Cactuses, with their succulent stems and vestigial leaves, tell a clear evolutionary story: the reduction of surfaces through which water evaporates, and the decrease in surface area relative to volume — features that make for survival in deserts. By my count, Arizona, at roughly similar latitudes to North Carolina but with one-tenth the rainfall, has 83 species of cactuses compared to our three. Environmentalists are experimenting with North Carolina’s prickly pear on green roofs — to reduce runoff from roofs by promoting retention and evaporation. Green roofs are thin-soiled, sunny, hot, and well-drained: a good description of Opuntia’s habitat.
You may find it curious that Native American Indians valued the prickly pear fruits as food, and that many people eat them today. In fact, cactus fruits outsell strawberries globally! Did you know that tomatoes (originally from South America), when first introduced to Italy, were shunned because they are related to the poisonous European plants Deadly Nightshade and Belladonna? John Harriot, the earliest person to write about Carolina natural history, in 1580 recorded that prickly pear was abundantly cultivated by Native Americans. We take for granted the “normalcy” of our diets even though what was strange can later become common.
I should here note that the invasive species issue is not just a problem of the importation of risky plants — it is also an export problem. Our prickly pear is a pest in Africa and Australia! The mixing of the world’s flora and fauna has another dimension in this case. A moth from South America was imported to Australia as a biocontrol agent to reduce Optunia infestations. It did such a great job that it has become the textbook example of biocontrol. But now that same moth has been inadvertently introduced to North America and is beginning to threaten North Carolina’s cactuses as well as the many rare Arizona species. Beware the law of unexpected consequences when it comes to biocontrol!
Years ago, as a student, I was intrigued that New England had a native cactus and traveled to Nantucket to find this plant in the wild. Now you can hunt, too. We have no official herbarium specimens of Opuntia humifusa from Orange County, but Elisha Mitchell wrote that he saw prickly pear on the dry slopes above Morgan Creek in or near what is now the land of the Garden (see my previous description, in the May-June Newsletter, of UNC Geology Professor Elisah Mitchell and his botanical wanderings around Chapel Hill in the 1820s). If you are inclined, look for Opuntia on dry, sunny, rocky or gravelly places, on south- or west-facing upper slopes. We might doubt the written word in other cases, but Mitchell could hardly have mistaken this plant for any other! Much has changed since 1820, but somewhere in our area, North Carolina’s prickly pear lies in the warmth and sun of a summer day.
Peter White, Director
North Carolina Botanical Garden
Published on December 15, 2011 at 02:02:23 am.