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Sep 05 2012

It Doesn’t Take a Genus to Guess This Mystery Plant

By Dr. John Nelson

What type of plant is this? (Photo by Allison Weakley).

The concept of the genus as a taxonomic category really came into play among botanists in the late 17th century. A genus is recognized as a convenient way to group closely related species. The dictionary definition of this word suggests “group” or “kind,” generally involving the notion of close relationships among its constituent members. Considered from the other perspective of grouping, a number of different but related genera (the plural of genus – don’t ever say “genuses”!) are placed in a family. For instance, there are several species of huckleberry and they all belong to the genus Gaylussacia. The huckleberries are related to blueberries, which are placed in the genus Vaccinium. Both genera, Gaylussacia and Vaccinium, belong to the family that we have named Ericaceae.Two Mystery Plants at once! These two species will serve nicely as a consideration of what we call a “genus.”

Our two mystery plants both belong to the genus Hypericum, which contains about forty different species found in North America. Hypericum is just one of the several genera placed in the Hypericaceae, or “St. John’s Wort” family. Various species of Hypericum may be stout and shrubby, or low and herbaceous, and with flowers bearing either four or five petals. Nevertheless, these species share enough features, especially those involving the flower parts, that they are all considered reasonably close relatives. Some members of this genus have been highly prized for medicines as these species commonly harbor some interesting organic compounds. You have probably heard of the alleged anti-depressant qualities made from extracts from St. John’s Wort (Hypericum perforatum). Other species of Hypericum are valued as ornamental plants. Still others are known as annoying weeds. They aren’t any good to eat, as far as I know.

The big-flowered mystery plant, on the left in the photograph, is a shrub with bluish-green foliage that grows about waist-high with peeling bark. It is native to high ground and cedar glades from Georgia to Tennessee and Pennsylvania, as well as the Midwest and Texas. Its bright gold flower is really showy and 400-500 stamens are commonly present, forming a conspicuous crown. This species is grown widely in cultivation and sometimes escapes into surrounding countryside. Its small-flowered cousin, on the right, is an herb that is mostly at home in damp places and is fairly common from Quebec to Florida. It is often in ditches, floodplain forests, or even in floating mats of vegetation on quiet lakes. It’s a comparatively humble flower with tiny, somewhat copper-colored petals with only about a dozen stamens present. Several differences exist between the two species, but they still have a lot in common.

John Nelson is the curator of the Herbarium in the Department of Biological Sciences at the University of South Carolina. As a public service, the Herbarium offers free plant identifications. For more information, visit www.herbarium.org or call 803-777-8196.

Answer: On the left, “Blue leaf hypericum,” Hypericum frondosum. On the right, “Dwarf hypericum,” Hypericum mutilum.

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