Downy Wood Mint is an erect native perennial forb, growing 5 inches to 3 feet high on hollow 4-angled stems that have hair ranging from short-fuzzy hair to more dense appressed hair. Stems may be single or multiple from the base, but unbranched.
Leaves are opposite, lance shaped in the upper stem parts and more ovate on the lower stem leaves. The uppers are very short stalked to sessile but can have smaller axillary leaf growth. Lower leaves have slender hairy stalks. Margins vary from coarse forward pointing teeth to almost entire. There is fine hair on the leaf margins and on the underside, especially on veins. The leaves have a minor amount of fragrance when crushed - more so when crushed dry.
The inflorescence is a terminal spike containing a cluster of verticillasters, subtended by a whorl of fringed (ciliate) purplish-green bracts and the lower ones subtended also by a larger pair of ovate green bracts resembling leaves. The verticillasters are separated from each on the spike. A 'verticillaster' is where the flowers look like a whorl arrangement but are actually in cymes that rise from the axils of opposite bracts. Only a few flowers in each cyme open at one time. There can be one to five clusters.
The individual flowers are tubular, from 1/4 to 3/8 inch long, and irregular in form. The petals of the corolla vary in color from whitish to lavender with deeper colored lavender spots. The corolla is called 'bilabiate', that is, forming two lips with the upper lip of the flower just a single lobe while the lower lip is also singular but subdivided into 3 lobes, with the central lobe much larger than the side lobes. There are four stamens, in pairs of different length; the longer pair of which are tucked up under the upper lip but the whitish filaments are well exserted beyond the lip. Anthers are purplish in color. The style also protrudes from the corolla tube and has a bifurcated tip. The inside of the lips are free of hair but the outsides are covered with dense whitish hair. The whitish-green calyx is usually hairy with 13 visible darker veins. The calyx tubes have five lobes, divided again into a two-lobed upper lip and a 3-lobed lower lip. Both lips usually have fine marginal hair.
Seeds: Fertile flowers have 4-sectioned ovary, each section producing a dark brown to black oval seed, 1 mm long, that has a small pointed tip. Seeds weight about 400,000 to the oz and need 60 days of cold stratification to germinate, but are easy to grow.
Habitat: Downy Wood Mint grows best in full sun to partial shade in good soils with moisture conditions mesic to dry. Deep shade will produce sprawling plants with poor flowering. The root system forms clumps from short rhizomes.
Names: The genus, Blephilia, 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 and is Greek for eyelash. The species name, ciliata, is from the Latin cilium, which also means 'eyelash' and refers to the same fine hairs. The author name for the plant classification is two-fold. First to classify - '(L.)' refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy. 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 Hairy Wood Mint, B. hirsuta, which has more robust hair - more on the leaves and the stem hair is longer and not appressed; and leaves may lack teeth or have more coarse teeth. Leaf stalks however are longer and leaves are not sessile. Flowers may be less toward lavender or blue and it prefers more shady and moist sites. Another Minnesota mint 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: Detail of the upper section of the inflorescence: 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: The inflorescence and detail of the flowers and the whorl of bracts subtending the verticillaster.
Below: The leafy bracts under the inflorescence.
Below: Example of lanceolate upper stem leaf (bottom leaf) and more ovate lower stem leaf (top)
Below: 1st photo - Underside of the leaf. 2nd photo - the small seeds.
Downy Wood Mint is not native to Minnesota. We are just north and west of its native range which is east of the Mississippi River from southern Wisconsin south along the Mississippi to the southern states, excluding Louisiana and Florida and including most of the eastern U.S. except New Hampshire and Maine. It is also known in Ontario.
Downy Wood Mint was first reported in the Garden on 2009 census. Date of origin uncertain. It was planted in 2012 and '13 by Susan Wilkins. Only two species of Blephilia are found in Minnesota, B. hirsuta, Hairy Wood Mint; and the introduced B. subnuda, Cumberland pagoda plant.
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.
Identification booklet for most of the flowering forbs and small flowering shrubs of the Eloise Butler Wildflower Garden. Details Here.
Friends of the Wild Flower Garden, Inc. Text and photos are by G. D. Bebeau unless otherwise credited. "www.friendsofthewildflowergarden.org"