Giant hogweed

Giant hogweed is an umbrella term given to cover a number of closely related species found in Britain, such as Heracleum mantegazzianum (originating from Asia), Heracleum sosnowskyi (from eastern Caucasus) and Heracleum persicum (from the Middle East). The most commonly found species in the UK is Heracleum mantegazzianum.

Giant hogweed can be identified by the following:

• Stems: hollow, purple (or green speckled with purple) and covered in fine hairs.

Figure 1: Giant hogweed stems

• Leaves:  dark green, coarsely toothed and measuring up to 2 metres across. Like the stems, they too are hairy.
• Flowers: emerge in mid to late summer on top of the stems in umbrella-like clusters. The numerous individual flowers are small and white, and it is common to find more than 80,000 of them on a single plant.

Figure 2: Giant hogweed flowers emerging

• Seeds: at the end of the summer, each individual flower is replaced by a single large seed. Seeds can remain dormant but viable for several years. Seeds are easily dispersed by water and Giant hogweed can often be found colonising the banks of waterways.

Figure 3: Giant hogweed seeds