Willowherb is a native erect perennial growing 2 to 4 feet tall on stems that usually have many branches above the middle. The stems are smooth, except within the inflorescence. Stem shape may vary from round to square, often reddish at the stem nodes and completely reddish in the Autumn.
The leaves are mostly opposite but can be alternate along the stem. They are oblong to lance-like in shape with irregular toothed margins, smooth on both sides with a taper toward the base and pointed tips. They may be a short stalk on lower leaves but most upper leaves are stalkless. In the fall, in full sun, the color can turn purplish - particularly in the leaf veins.
The inflorescence consists of many short branching open flower clusters rising from either the leaf axils or the tips of the upper branches.
Flowers are 4-parted, on short stalks and with a very long, thin, calyx tube that is hairy. The tube terminates in 4 green lance-shaped sepals that sometimes have a color tint of pink to purple at their tips. Like other members of the genus Epilobium The long calyx tube and is attached to the top of the ovary. Slightly longer than the sepals are the 4 petals that have notched tips and vary in color from white to light pink. The petals, which have a darker color veining acting as nectar guides, are deeply notched at the tips. The width of the flower at the petals is about 1/3 inch. There are eight stamens with yellow anthers that surround the single white style which has a knobby tip. Calyx tubes and upper stems can take on a purplish color cast.
Seed: Fertile flowers mature to an elongated (1-1/2 inch) seed capsule that splits from the tip into 4 segments and releases tiny 1/32 inch long seeds with brownish hairy tufts attached to one end for wind dispersion. These small seeds require light for gemination plus 60 days of cold stratification.
Habitat: Willowherb is a plant of wet meadows, stream banks and marsh edges - all where the soil is wet to moist, in partial shade to full sun. The root system produces rhizomes and the plant spreads vegetatively via the rhizomes in addition to seed propagation.
Names: The genus name, Epilobium, is from 2 Greek words - epi meaning 'upon' and lobos, meaning 'a pod', and refer to the flower and capsule being together - that is, the corolla tube sits on the end of the ovary. The species name, coloratum, means 'colored'. The author name for the plant classification, ‘Biehler’ is for Johann Friedrich Theodor Biehler (1785-1850). A German botanist, he described a number of species, including E. coloratum, in his main publication of 1807 - PLANTARUM NOVARUM EX HERBARIO SPRENGELII CENTURIAM, SPECIMINIS LOCO INAUGURALIS.
Comparisons: The other Willowherb noted in the Garden is Northern Willowherb, Epilobium ciliatum Raf. subsp. glandulosum. This species has leaves that are only sometimes toothed, has less branching and the hairy pappus on the seeds is white. Another Epilobium that has similar characteristics and which some references apparently mistake for E. coloratum is Epilobium angustifolium L. known as Fireweed or Great Willowherb.
Above: The branching inflorescence of Willowherb. 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 - The long calyx tube can have a purplish tone and the tips of the sepals can also take on a purplish tone. 2nd photo - Note the white knobby style tip and the notched tips on the petals.
Below: 1st photo - The long calyx tube and 4 the sepals show fine hair. 2nd photo - The buds show the fine hair on the sepals and the irregular teeth is seen on the small upper leaves.
Below: 1st photo - The leaf has a irregularly toothed margin and depressed veins while on the underside (2nd photo) the veining is very prominent.
Below: 1st photo - Toward fall when seed pods begin to form a pinkish tone is noted in the branches. 2nd & 3rd photos - Leaves and stems take on a purplish color when in full sun in the fall.
Below: 1st photo - The seed pods split along 4 sides and present a visual jungle. 2nd photo - Each small seed has an attached long fine pappus (hair), brownish in Willowherb and white in Northern Willowherb.
Notes: Willowherb, E. coloratum, should be considered indigenous to the Garden. While Eloise Butler did not list the plant on her first Garden inventory in 1907, she noted it in blossom on Aug. 16, 1915. The indigenous species she did list was E. palustre, the Marsh Willowherb, but that is no longer present. Martha Crone reported planting Willowherb in 1947 but did not give a specific species. However on her 1951 census she listed both E. palustre and E. strictum (Downy Willow-herb). She had planted the latter in 1933, but what she planted in 1947 is unknown. E. coloratum is found in the U.S. from the central states eastward to coast and in Canada from Ontario eastward. Within Minnesota, this species is found in about one half of the counties, mostly on the eastern side of the state. Seven species of Willowherb are native to Minnesota, two of those are not widespread.
Epilobium is a world-wide genus and a number of species have 'Willowherb' in their name. Some were used for medicinal purposes but there is no literature on this particular species used as such.
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"