Japanese Hedge Parsley is an erect biennial invasive plant, growing on ridged branched stems 2 to 4 feet in height. Stems are covered with appressed stiff hair. The basal rosette develops the first year, staying green until late fall and the flowering stem develops in the second year.
The leaves are alternate and pinnately divided, fern-like, slightly hairy, up to 5 inches long and 4 inches wide. They attached to the main stem with a small sheath. On the larger leaves, the tips of the leaf branches and the upper branches of the leaf are not fully divided (are pinnatifid). Upper leaves will be small and less divided (completely pinnatifid) than the larger lower stem leaves.
The inflorescence is a small loosely branched compound umbel, the base of which will have several linear green bracts. The individual umbellets will also have very small linear bracts. Stalks all have appressed stiff hair.
Flowers are each about 1/8 inch wide and have 5 white petals of unequal length that are notched on their rounded tips. Bases of the petals are much narrowed. There are 5 spreading stamens that alternate with the petals (are arranged in-between them), and a creamy-white central receptacle disc with 2 styles. The disc sits above a 2-part ovary. The stamens have white filaments, the anthers turn darker yellow at maturity of the pollen. There are also 5 sepals that are very small. Flowers open from the edge to the center of the umbellet.
Seed: Mature flowers develop a dry 2-part ribbed oblong seed that is surrounded with up-curved sticking hair. The seed, 4 to 5 mm long, splits into 2 halves, flat on the split and more rounded on the remainder.
Habitat: Japanese Hedge Parsley grows from a thick taproot that develops during the first year of growth. It takes root in exposed disturbed sites, waste sites, path edges, in various soils, sandy preferred, in moist to dry conditions. A report by the Aldo Leopold Foundation in Wisconsin covers their experience with the plant. (pdf download).
Names: The genus, Torilis is a Latin word, the meaning of which today is considered obscure. The species, japonica, means 'of Japan'. As to the author names of the plant classification, Japanese Hedge Parsley was originally described in 1777 by ‘Houtt.’, which refers to Martinus Houttuyn (1720-1798), Dutch naturalist who published many books on natural history. His work was amended by ‘DC’, which is for Augustin Pyramus de Candolle (1778-1841), Swiss botanist, who influenced Charles Darwin. He studied plants, began a systematic catalogue and has 2 genera named for him.
Comparisons: There are several plants in Minnesota that have flower umbels somewhat resembling this plant. However, the unequal length white petals, the appressed hair all over the plant, and the form of the leaf should be sufficient to separate out this species. For comparison look at another non-native plant, Fool's Parsley, Aethusa cynapium; and then two native plants - Water Hemlock, Cicuta maculata; and Bulblet Water Hemlock, Cicuta bulbifera.
Above: The inflorescence. Illustration courtesy of Kurt Stüber's Online Library.
Below: 1st photo - The inflorescence is a small loosely branched compound umbel. 2nd photo - Flowers have 5 white petals of unequal length that are notched on their rounded tips. Bases are much narrowed.
Below: 1st photo - The underside of the flower umbel showing all the stalks with stiff appressed hair. 2nd photo - An upper leaf that is less divided than the lower stem leaves as shown below.
Below: The bi-pinnate larger lower leaf. The lower (and larger) sections are more divided (pinnate) while the leaflets of the tips and of the upper sections are not completed separated (pinnatifid).
Below: 1st photo - Stems and stalks have ridges and stiff appressed hair. 2nd photo - Fertile flowers on the umbellets produce a 2-parted seed capsule covered with up-curved sticking hairs.
Below: 1st photo - The 2-parted seed capsule covered with up-curved sticking hairs. 2nd photo - When mature the 2-parted seed splits longitudinally into 2 viable seeds.
Notes: Japanese Hedge Parsley has established itself in about half the states of the U.S. and in several Canadian Provinces. As it is an invasive spreader, moving via the sticky seeds attaching themselves to fur and clothing, it can show up anywhere but is most likely to spread within the area where people and animals have contacted it. Cutting it prior to flower maturity provides control if cut just near maturity. If cut too early it will regenerate flower stems. It is found in Minnesota in several sites.
Medicinal uses: Japanese Hedge Parsley contains a substance, a guaiane-type sesquiterpene known as 'torilin', that has been used in pharmacological studies for its effect on cancer. In Korea, Japan and China the plant has been used to treat cough, hemorrhoids and to break fever. (Ref: Medicinal Plants of China and its Neighborhood, CRC Press 2012)
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"