Hairy Mountain Mint
Pycnanthemum pilosum
Mint family (Lamiaceae)

Description: This native perennial plant is 2-4' tall. It has green or brown stems that are four-angled and covered with white hairs. These stems frequently branch and achieve a slender bushy effect. The opposite leaves are up to 3" long and ¾" long. They are light or whitish green, pubescent on both sides, lanceolate in shape, and have smooth edges. The foliage has a mint fragrance.

The small white flowers are in dense clusters toward the apex of the plant. Each flower is about ¼" long, 2-lipped, and usually has small purple dots near the throat. The blooming period occurs during mid- or late summer and lasts about a month. Each flower produces 4 tiny seeds, which are distributed to some extent by the wind. The root system consists of a branching taproot, as well as short rhizomes that cause the plant to form small colonies.

Cultivation: The preference is full or partial sun and moist to slightly dry conditions. Growth is best in fertile loamy soil; it also flourishes in rocky soil. Sometimes transplanted plants become afflicted with rust, but these leaves soon fall off and are replaced by healthy leaves. During summer droughts, the leaves of stressed-out plants may become afflicted with rust, or the lower leaves may turn yellow and fall off their stems. Generally, this plant is easy to grow, especially if it receives adequate water during summer droughts or some protection from the afternoon sun.

Range & Habitat: Hairy Mountain Mint occurs occasionally in central Illinois, but is uncommon or absent in the southern and northern regions of the state (see Distribution Map). Habitats include mesic black soil prairies, rocky upland forests, thickets, and limestone glades. It is not normally observed in disturbed areas.

Faunal Associations: The flowers are very attractive to many kinds of long-tongued bees, short-tongued bees, wasps, and flies. To a lesser extent, butterflies, skippers, and beetles are attracted to the flowers. These insects seek nectar, although Halictine bees also collect pollen. Because of the frequent visitors to the flowers, the parasitic Macrosiagon spp. (Wedge-Shaped Beetles) are especially likely to be found on the flowers. These insects lay their eggs on the flowers, and the larvae attach themselves to bees or wasps and hitch-hike a ride back to the brood chamber, where they feed on the immature larvae and food stores of the host insect. The seeds are too small to have much value to birds. Mammalian herbivores also display little interest in this plant, probably because of the strong minty fragrance of the foliage.

Photographic Location: The photographs were taken at the webmaster's wildflower garden in Urbana, Illinois.

Comments: Some authorities refer to this plant as Pycnanthemum verticillatum var. pilosum. The appearance of Hairy Mountain Mint is similar to other members of the genus, but it has hairier leaves and stems. The common name 'Mountain Mint' is something of a misnomer, as the majority of Pycnanthemum spp., including this one, are usually found in prairies or woodland areas that aren't particularly hilly or mountainous. The leaves of this plant can be boiled in water to make an excellent mint tea.

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