No one could describe Norwich’s Northern Distributor Road (NDR) as pretty but recently Tall Willowherb, Epilobium brachycarpum, has been brightening up the central reservation between Norwich Airport and the A140 Cromer Road. As I cycled north from Norwich in early September, crossing the dual carriageway with the help of a pedestrian refuge, I stopped to take some photos of the plant.

Tall Willowherb, Epilobium brachycarpum, by Norwich’s Northern Distributor Road. 6th September 2023.

Tall Willowherb, Epilobium brachycarpum, has pink flowers but by the time of my visit in early September the plant was mostly a reddish haze of stems and seed pods.

Tall Willowherb is a thin, gangly annual plant which normally grows up to one metre (39 inches) tall, though it can occasionally reach twice this height. Its leaves are narrow, curving and pointed. The pink flower petals have darker pink veins. There are four petals per flower but they are so deeply notched they almost look like eight. The red fruit capsule is 1 to 3 centimetres (0.4 – 1.8 inches) long.

Tall Willowherb, Epilobium brachycarpum. Detail of flower and fruit capsule.

Epilobium brachycarpum, is also known as Panicled Willowherb, Tall Annual Willowherb and Tall Fireweed. It is a member of the family Onagraceae, like Great Willowherb, which I wrote about in August 2022.

Tall Willowherb was first recorded by the NDR in 2019. It is a native of North America, where it grows in varied open and woodland habitats in Canada and the northern and western United States and parts of Mexico. It has been introduced into Wisconsin and Kentucky, Argentina in South America and parts of Europe (Belgium, Czech Republic and Slovakia, France, Germany, Great Britain, Netherlands and Spain).

A Recent Arrival

Epilobium brachycarpum is a recent arrival in the British Isles and was first found in 2004 in gravel workings near Colchester in Essex. It has since been found in Kent, Surrey and Norfolk (note 1). The BSBI Plant Atlas describes its habitat in the British Isles as “open ground on nutrient-poor sandy and gravelly substrates, including quarries, railway sidings and other brownfield sites“.

North American Tall Willowherb plants have 4-lobed stigmas and are usually out-crossing but British plants have clavate stigmas and appear to self-pollinate.

Tall Willowherb produces masses of viable seed, enabling it to spread very rapidly. The BSBI Plant Atlas predicts that the plant “is highly likely to spread further over the coming decades“, so keep a look out for it.

Identifying willowherbs can be very difficult but Mike Crewe’s Flora of East Anglia website has useful photographs of willowherbs for comparison (he uses the name “Tall Annual Willowherb” for Epilobium brachycarpum). Epilobium brachycarpum is “a very different plant to any of our native species“. The gallery tab on the BSBI Plant Atlas website has plenty of good photographs of the plant, as has the Burke Herbarium website (University of Washington).

Bob Leaney’s article (note 2) provides a lot of help if you want to identify willowherbs. Luckily Epilobium brachycarpum is “easily recognised by its panicled flowers with tiny, deeply bifid petals, minute linear leaves, short, slightly curved fruits and exceptionally fine, wiry stems“.

Looking west: Tall Willowherb, Epilobium brachycarpum, by Norwich’s Northern Distributor Road. 6th September 2023.

Multiple Introductions

Epilobium brachycarpum was first found in Europe in 1978. A 2016 study looked at populations of Epilobium brachycarpum in Germany and northern France and found that the plant had been introduced into Europe more than once. More invasive Tall Willowherb plants came from high mountain areas in North America and a less invasive and smaller German population came from lowland areas but suffered from frost damage, making its permanent establishment doubtful (note 3).

Notes

Note 1 – This was the second time I’d seen Tall Willowherb in my local area. My previous encounter was on the edge of a pavement by a building site in King Street in Norwich in June 2022.

Thanks to Chris Lansdell for telling me about the King Street plants. They had been spotted by champion plant hunter Louis Parkerson, who also found the Stinking Fleabane that I wrote about in October 2021.

Note 2 – Bob Leaney (2020), “Common problems with identification in Epilobium (willowherbs)”. BSBI News Vol. 144, pp5 – 13.

Note 3 – K. Nierbauer, J. Paule and G. Zizka (2016), “Invasive tall annual willowherb (Epilobium brachycarpum C. Presl) in Central Europe originates from high mountain areas of western North America”. Biological Invasions Vol. 18. Available as a PDF at https://www.researchgate.net/publication/304917418_Invasive_tall_annual_willowherb_Epilobium_brachycarpum_C_Presl_in_Central_Europe_originates_from_high_mountain_areas_of_western_North_America.