Henbit Deadnettle is a semi-erect annual to biennial forb, growing from 6 to 12 inches high with 4-angled purple tinged stems which are usually without hair. The plant may branch from the base. The flowering part of the stem is usually erect.
The leaves are of two types: Lower stalked leaves and upper stem leaves that are without stalks or clasping the stem. Leaves are opposite on the stem, egg-shaped to circular with crenations or shallow lobes that have crenations. The stem leaves subtend a set of smaller green bracts of the inflorescence. The lower stalked leaves are similar. All have a reticulated vein pattern with surface hair - dense on the underside.
The flowers of this species are are two types. Those that form an open flower are called "chasmogamous" (open marriage) [CH flowers] and those that never open are called "cleistogamous" (closed marriage) [CL flowers]. Both types are bisexual (perfect) and set seed but at different times - with CL flowers later if plants have both types as some plants will have only CH or only CL. (1) Various reasons have been put forth for CL flowers but studies indicate environmental reasons predominate (2) but a lack of pollinators has been noted in one study as being more important than environment resource availability - i.e. temperature, moisture, soil, etc (3)
The Spring inflorescence is a series of well spaced verticillasters containing chasmogamous flowers. 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. Plants that have died back in the heat of Summer but recover in Autumn may produce non-opening cleistogamous flowers which produce seed.
The individual chasmogamous flowers are bilaterally symmetrical, tubular with a short green calyx that is hairy and have 5 long-pointed lobes. The flowers have a pinkish-purple corolla that forms a long tube and then flares out into an upper and lower lip. The upper lip is notched at the center and rises to form a hood-like structure over the stamens. The sides of the tube flare outward just a bit between the upper lip and the larger two-lobed lower lip, which looks somewhat heart-shaped. The outside of the corolla is hairy; the inside of the lips is usually whitish but some flowers can be pinkish, but always with darker pink large spots. There are 4 stamens, in pairs of different length. The style has a bifurcated tip. Neither style nor stamens are exserted from the corolla but are visible in the throat. Corolla and calyx are up to 1 inch long. Flowers contain for their size, much nectar.
The cleistogamous flowers, if formed in late Summer or Autumn, resemble flower buds that do not open. They self fertilize and only open once the seeds are ripe.
Seed: Fertile flowers usually produce a cluster of 4 nutlets that are sharply 3-angled, ovoid shaped, dark brown flecked with white dots. Seeds are long-lived.
Habitat: Henbit has adapted to wide range of habitats, soil conditions, temperatures and moisture conditions. It can go through the entire Spring growing season without rainfall. It is a cool season plant, dying back in Summer heat, but can redevelop in the cool of Autumn when it can produce the second set of seeds in the cleistogamous flowers. It is found in waste places, agricultural fields, and areas not being disturbed as it must set seed to propagate. The root has a slender taproot and fibrous roots.
Names: The genus Lamium is exclusively assigned to the Deadnettle plants and is derived from the Latin word for the plant - Labiatae. The species amplexicaule means 'stem clasping', coming from two separate words. Amplexi referring to clasping and caule referring to a stem. The author name for the plant classification 'L.' refers to Carl Linnaeus (1707-1778), Swedish botanist and the developer of the binomial nomenclature of modern taxonomy.
The common name of Deadnettle refers to a plant resembling a nettle but without stinging hairs - thus 'dead'. That resemblance came from Lamium album, the White Deadnettle, where the leaves resemble those of our common stinging nettle. Henbit does not have those leaves.
Comparison: In most parts of the midwest, the plant most closely resembling Henbit is our blessed Creeping Charlie, or Ground Ivy, Glechoma hederacea, where the stems also trail but the leaves are all on stalks, the flowerers purplish-blue instead, and the flower has more noticeable side lobes.
Above: The inflorescence is a separated group of verticillasters along the upper stem. Drawing from Britton, N.L., and A. Brown. 1913. An illustrated flora of the northern United States, Canada and the British Possessions.
Below: The stems frequently are decumbent with just the flowering end erect. This plant shows multiple stems from the root with up to four verticillasters on some stems. Note the stalked lower leaves.
Below: 1st photo - the stem leaves are opposite, stalkless to clasping, hairy. 2nd photo - looking down at the verticillaster, nutlets are visible.
Below: 1st photo - the vertillicaster at the top of the stem, not all flowers open at once. 2nd photo - the seeds are brown with white spots; 3-angled. 3rd photo - the root develops a slender taproot.
Below: Three views of the flower. 1st photo - the corolla tube is long and tubular. 2nd photo - 2 petals from an upper hood-like lip, 2 slightly flaring side lobes and a much larger lower lip of two-lobes. The two pair of stamens are tucked under the upper lip. 3rd photo - the calyx is short with 5 awl-like lobes.
Notes: Henbit was introduced to the Wildflower Garden by Eloise Butler on Sept. 8, 1919 when she got plants from Lyndale Gardens, a nursery in Minneapolis. The plant was known to her from Maine and Massachusetts and was one of those species she thought should have a place in the new Wildflower Reserve. Martha Crone did not list it on her 1951 Garden census.
Henbit is found in all of North America except the far northern Canadian Provinces. In many areas it has not made extensive inroads but in a number of states in the west and south it is extensively found and is a serious agricultural pest. In was introduced from Europe, some sources say probably no longer ago than the 1920s, but Ada George already had it in her book A Manual of Weeds (Ref. #6b) in 1914 and listed extensive U.S. distribution. In Minnesota the DNR surveys have found populations in Carver and Dakota Counties. It is the only species of Lamium the DNR reports in Minnesota although the U of M Herbarium reports a collection of Lamium album, White Deadnettle, in Ramsey County. There are 5 known species of Lamium in North America.
(1): Sato, Takakura, Nishida, Nishida, 2013, International Scholarly Research Notices. Dominant Occurrence of Cleistogamous Flowers in Lamium amplexicaule.
(2): Plastic adaptive cleistogamy in Lamium amplexicaule, Annals of Botany, May 12, 2016.
(3): Season-dependent effect of cleistogamy in Lamium amplexicaule, Stojanova, Maurice, Cheptou, Jan 2020 Botanical Society of America.
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"