Mint family (Lamiaceae)
Description: This herbaceous perennial plant is ½–2½' tall and usually unbranched. The central stem is 4-angled, usually with scattered hairs along the ridges, but not the sides (see Stem Photo). The opposite leaves are up to 3½" long and 1" across. They are usually lanceolate or narrowly ovate, with serrate or crenate margins. The petioles of the lower leaves are about ¼" or slightly longer, while the upper leaves have shorter petioles or are sessile. Both the upper and lower surfaces of the leaves are hairless or nearly so – if hairs are present, they are most likely to occur along the lower mid-vein of the leaves. The central stem terminates in a spike-like inflorescence that has whorls of flowers at intervals along its length. This inflorescence can vary from 2-8" in length. The tubular corolla of each flower is about 1/3" long and divided into 2 lips. The hairy upper lip functions as a protective hood, while the lower lip is divided into 3 lobes (a central lobe and two smaller side lobes), which functions as a landing pad for visiting insects. The flowers are light pink or white, often with rosy pink splotches within the throat. The green calyx is hairless and at least half as long as the tube of the corolla (not including the lips). It is divided into 5 triangular segments that curl outward as the ovaries mature. The blooming period occurs during the summer and lasts about 1-2 months. Each flower is replaced by 4 black nutlets that are oblong in shape. The root system consists of a taproot and rhizomes. This plant often forms vegetative colonies, like many other members of the Mint family.
Cultivation: The preference is partial sun and moist conditions. This plant also tolerates light shade and full sun. The soil should contain sufficient organic material to retain moisture. If this plant dries out, the leaves have a tendency to turn yellow or brown, and the entire plant may die.
Range & Habitat: Smooth Hedge Nettle occurs in most counties of Illinois (see Distribution Map), where it is native. This plant is occasional in southern and central Illinois, but uncommon or absent in the northern counties. Habitats include ravines in floodplain forests, moist meadows along rivers or woodlands, thickets, and various kinds of wetlands, including swamps, seeps, and ditches. It can be found in either high quality habitats or rather degraded sites.
Faunal Associations: Primarily long-tongued bees pollinate the flowers, where they seek nectar primarily. Short-tongued bees sometimes collect pollen, while flower flies feed on the pollen, but they are not very effective pollinators. Occasionally butterflies or skippers may visit the flowers, but they aren't very effective at pollinating the flowers either. The bitter foliage of this and other Stachys spp. is not often consumed by mammalian herbivores.
Photographic Location: A swampy area of Busey Woods in Urbana, Illinois.
Comments: This is a typical member of the Mint family. It is easy to overlook, because this Hedge Nettle sp. tends to be rather small-sized and non-descript, almost looking like a lanky Prunella vulgaris (Self-Heal) at first glance. Identifying Smooth Hedge Nettle correctly can be rather tricky, so here are some of the key features to look for: 1) The calyx is hairless; 2) the petioles of the lower leaves are usually ¼" or longer, and 3) there are hairs on the ridges of the 4-angled central stem, but not on the sides. There is also a hairy form of this plant, referred to as Stachys tenuifolia hispida by some authorities and Stachys hispida by others, that also occurs in Illinois. It has foliage that is more hairy, and there are also some hairs along the edges of the calyx of each flower. However, it is similar to Smooth Hedge Nettle in that the central stem has hairs along the ridges, but not on the sides.