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.) At 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 four stamens in pairs of different length. The longer pair are exserted from just beneath the upper lip. Anthers are dark purple at maturity. There is a longer single white style, also exserted, with a two-lobed stigma.

Seed: Fertile flowers produce a open capsule containing 4 ovoid nutlets. The seeds require 60 days of cold stratification for germination.

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. It is a woodland plant.

Names: The genus, Blephilia, is Greek for eyelash and is derived from the Greek blepharon, meaning 'eyelid' and then cilia, referring the fine short marginal hairs and together refer to the hairy fringes on the flower bracts and calyx teeth. 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 (finer and shorter) hair - less on the leaves and stem hair is shorter and usually appressed. Leaf margin teeth are variable, from coarse on lower stem leaves to poorly defined on the upper. Leaves are either sessile or have short stalks. 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.