Upright Hedge-Parsley

Appearance

Japanese hedge parsley typically grows between 2–4 feet tall during its second year of growth. The leaves of Japanese hedge parsley are fern-like, alternate, divided pinnately, and have very slim stems that support each leaf. The plant doesn't flower until its second growth year in June–August and the flowers are white with five petals in multiple broad domed umbels. The flowers are bisexual in the epicenter and a stamen is located at the margins of the umbels. There are five stamens that alternate with the petals of the flowers and the ovary is located below. Japanese hedge parsley can be described as unspecialized and self-fertile, and very attractive to pollinators.

Each plant produces easily distributable bristle-textured, rosy or white/green fruits that eventually turn brown when mature. The fruits are schizocarps and then mericarps when split into two. The schizocarpic fruits are dry, remain closed until maturity, and have two pollen-containing chambers. Each mericarp of the fruit is five-ribbed, making its dispersal highly effective and competitive towards native vegetation.

Naming

The major threat from Japanese hedge parsley is its ability to grow vigorously and disperse rapidly. Japanese hedge parsley was first introduced to North America in 1917 and has been considered invasive since its introduction. Reasons for its introduction are unknown, but it is assumed it was for medicinal purposes because it is not considered ornamental. The plant's current distribution as an invasive species is in southern parts of Canada and in the Midwestern, Eastern, Southern parts of the US, and Oregon.

In Wisconsin, the Department of Natural Resources found that this plant tends to establish itself along roadsides, edge habitats, or open areas and then spread to grasslands, prairies, savannahs, and forests. A 1979 study revealed that Japanese hedge parsley seeds showed the most promising degree of survival in harsh and disturbed soils, which revealed its overall resilience and threatening ability to invade. Also, the plant can produce seeds that do not germinate until the following autumn of the next year, allowing seeds to build up in the seed bank and increase elimination difficulty. This strategy gives Japanese hedge parsley an advantage in areas where native vegetation fails to grow or becomes disturbed. Mowing of the initially-established habitats encourage population density growth when brown fruits are present, which could be the reason for its initial ability to spread over a short period of time.

This species has been commonly misidentified with other species within the genus "Torilis", which has inhibited knowledge of its range and overall seriousness as a threat to biodiversity. Researchers have not determined why this plant is invasive in North America while exhibiting not invasive tendencies as an agricultural weed in Europe. The species is clearly highly adaptive to its biogeographic location, utilizing certain strategies more than others depending on the environment in which it is found. Studies have shown that seed dormancy and germination differ greatly across the US and across the globe. This limiting the scientific understanding on management strategies. To date, there are no documented studies on Japanese hedge parsley's effect on native vegetation communities in relation to the possible response to climate change or eutrophication.

Distribution

Despite "japonica" meaning “of Japan”, the native range of Japanese hedge parsley spans from Western Europe to central Asia, northern Japan, and Mediterranean parts of northern Africa. In Europe, "T. japonica" is a summer annual/biennial. In its United States invasive range, it is considered a summer biennial. In Japan, it is considered a winter annual.