Two Mystery Plants at once! These two species will serve nicely for a consideration of what we call a “genus.”

The concept of the genus as a taxonomic category really came into play amongst botanists in the late 17th century. Briefly, a genus was recognized (and still is) 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 many several species of huckleberry, and they all belong to the genus Gaylussacia. The huckleberries are related to blueberries, which are themselves placed in the genus Vaccinium. Both genera – Gaylussacia and Vaccinium – belong to the family that we have named Ericaceae.

Our two mystery plants both belong to the genus Hypericum, which contains about 40 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, sometimes waist-high, with peeling bark and native to high ground and cedar glades from Georgia and Tennessee into Pennsylvania and into the Midwest and Texas. Its bright gold flower is really showy, and 400 to 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, mostly at home in damp places, and is fairly common from Quebec to Florida, often in ditches or floodplain forests or even in floating mats of vegetation on quiet lakes. Its comparatively humble flower features tiny petals, these somewhat copper-colored, 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.

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