In the Garden:
Middle South
August, 2012
Regional Report

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Many native plants, such as this maypop, are a valuable resource for indigenous wildlife.

Native or Naturalized?

A midsummer bike ride on Greenville's Swamp Rabbit Trail provided a good opportunity to take inventory of plants that grow along local roadsides. I found many natives, including trumpet vine (Campsis radicans), pokeweed (Phytolacca americana), elderberry (Sambucus canadensis) and Joe-Pye weed (Eupatorium fistulosum). I also saw several naturalized plants -- nonnative interlopers that have established themselves as a part of the flora of our region -- such as Queen Ann's lace (Daucus carota), woolly mullein (Verbascum thapsus), and spotted knapweed (Centaurea maculosa).

Though gardeners welcome and admire many naturalized plants, sometimes they're a bad thing. If a naturalized plant spreads without help and defies eradication, then it is pegged with the pejorative label "invasive." Invasive plants are unwelcome because they crowd out the native plants that evolved with indigenous wildlife. Spotted knapweed, beautiful though it may be, is among the worst.

Introduced to the United States in the late 1800s, spotted knapweed is a pioneer species that takes hold in recently disturbed sites, and once established, spreads to surrounding areas. It out-competes native plants in three ways: with a long taproot that deprives surrounding plants of water, copious seed production, and low palatability (which makes it less likely to be consumed by wildlife). Some experts believe the knapweed is also allelopathic, or has the ability to produce a chemical that harms nearby species.

While not all naturalized plants are invasive, conservationists believe native plants are preferable because they help preserve the balance of local ecosystems. Natives are adapted to local conditions and, when properly sited, grow with minimal use of water, fertilizers, and pesticides. They also provide indigenous wildlife with the most nutritious food and the best places to live and hide.

When I returned to the area recently with my camera, I found a different collection of plants in bloom. Among that group was Johnson grass (Sorghum halepense), a 3 to 7 foot tall aggressive perennial grass that flowers in loose, purplish panicles. But I saw some spectacular natives too, including the exotic-looking maypop (Passiflora incarnata).

Sometimes called passion flower, this indigenous vine blooms with intricate, 2 to 3 inch flowers comprised of sepals and petals topped with a fringe of crimped filaments (the corona) and a tri-forked stigma surrounded by five stamens. The name passion flower is derived from the crucifixion story, with some seeing the ten petal-like parts as the disciples (excluding Peter and Judas), the five stamens as the wounds Jesus received, the three segments of stigma as the nails, and the fringe as the crown of thorns.

The more common name, maypop, comes from the sound made by the lemon-sized fruits when crushed. Though said to have been a favorite snack of colonial settlers and Native Americans, the fruits are a seedy and inferior substitute for those of the related species (P. edulis) that gives Hawaiian Punch its distinctive taste.

The fruits are a resource for many small mammals, however. Equally important, the foliage is a valuable larval food for several butterflies, including the zebra longwing and the Gulf fritillary.

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