Hairy Wood Mint is a native erect perennial forb growing with square hairy stems from one to three feet high with little branching.
The leaves are opposite, lance-shaped to egg shaped with hairy surfaces, a few coarse teeth on the margins which usually have marginal hair. Bases are tapered, tips are acute, short-stalked in the upper stem, lower leaves on longer stalks. They have a noticeable aroma when crushed. Each pair of stem leaves is rotated 90 degrees from the adjacent pairs.
The inflorescence is a distinctly separated grouping of 1 to 6 verticillasters in the leaf axils of the upper stem and one at the top of the stem - also on any stem side branches. (A verticillaster, common in the mint family, is where the flowers look like a whorl arrangement but are actually in cymes that rise from the axils of opposite bracts.) A the base of each verticillaster are a pair of bracts - resembling small leaves. Only a few flowers in each cyme open at one time.
The flowers have a short calyx in an irregular tube shape, with 5 pointed teeth - 3 longer on the upper lip and 2 shorter on the lower, and 13 noticeable nerve lines. The corolla is pale purple with darker spots and composed of two lips, the lower lip divided into 3 lobes (and this is where the spots appear) with the center lobe much longer than the two lateral lobes, while the upper lip has two united lobes, looking like one, and acts like a hood. The outside of both the corolla and the calyx is hairy. There are two visible stamens, exerted from just beneath the upper lip and a longer single white style with a two-lobed stigma.
Seed: Fertile flowers produce a open capsule containing 4 ovoid nutlets.
Habitat: Hairy Wood Mint grows from a fibrous and rhizomatous root system which can form good clumps. It prefers richer loamy soils, partial sun to light shade and wet to wet-mesic moisture conditions.
Names: The genus, Blephilia, refers to the hairy fringes on the flower bracts and calyx teeth and is Greek for eyelash. The species name, hirsuta, means covered with hair. The names of the authors of the plant classification are as follows: The first to publish was ‘Pursh’ who is Frederick Traugott Pursh (1774-1820) German-American botanist who wrote A Systematic Arrangement and Description of the Plants of North America, and was the botanist who catalogued and described the plants brought back by the exploring expedition of Lewis and Clark. His work was updated by ‘Benth.’ who is George Bentham, (1800-1884) English botanist, who published many texts of which his Handbook of the British Flora is most famous.
Comparisons: A very closely related species is the Downy Wood Mint, B. ciliata, which has more downy hair - less on the leaves and stem hair is shorter and usually appressed. Leaves usually lack teeth. Flowers may be more bluish and it prefers more sunny drier sites. But that species is not native in Minnesota. A Minnesota species is the Wild Mint, Mentha arvensis; where there is not a verticillaster at the top of the stem, the flowers lack the spots. It is also found in more sunny, but moist, locations.
Above: Flowers form in cymes at separated points along the upper stem, separated by bracts. - a structure known as a 'verticillaster'. Drawing from Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions. 3 vols. Charles Scribner's Sons, New York.
Below: 1st photo - Hairy Wood Mint has a verticillaster at the top of the stem also. 2nd photo - The dark purple dots on the lower lip are characteristic of the flower.
Below: 1st photo - The long exerted style has a bifuricated tip. 2nd photo - Note the hairy leaves, leaf margins and stem.
Notes: Hairy Wood Mint was not included on Martha Crone's 1951 inventory of Garden plants and has been introduced since. It is reported as native to Minnesota but the only populations were in the five counties of the SE corner of the state where it is across the Mississippi River from a reported Wisconsin population. It's range is from Minnesota east to the coast, where in New England several states have listed it as endangered or threatened. In Canada it is reported only in Ontario and Quebec. The Garden population will preserve a plant seldom seen in Minnesota unless purposely planted in a native garden. There are two listed varieties of the species, var. hirsuta and var. glabrata but Minnesota authorities do not distinguish to that level.
The only other member of this genus that is been found in Minnesota is Blephilia subnuda, Cumberland Pagoda-plant, but that species was introduced into several SE counties and is not native.
References: Plant characteristics are generally from sources 1A, 32, W2, W3, W7 & W8 plus others as specifically applied. Distribution principally from W1, W2 and 28C. Planting history generally from 1, 4 & 4a. Other sources by specific reference. See Reference List for details.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"