Giant hogweed – Heracleum mantegazzianum

Plants of the genus Heracleum are umbelliferous (Apiaceae) and very large. They can grow tall: more than three metres and even up to five metres in a lush location. In Finland, the most common species is giant hogweed (Heracleum mantegazzianum), and Persian hogweed (Heracleum persicum) has also been found here. There are also some observations of Sosnowsky’s hogweed (Heracleum sosnowskyi), but the findings have not been verified. Alien Heracleum group plants have been imported as garden plants, and they are especially found in built-up areas, as well as on roadsides, wastelands and courtyards in sparsely populated areas, but also in nature, including beach groves.

Giant hogweed and Sosnowsky’s hogweed are biennial, or they die after flowering. Persian hogweed is perennial and can flower several times, but it is able to reproduce not earlier than the third year. Heracleum group species can only reproduce through seeds, and they can spread to new habitats with garden waste or soil contaminated with seeds. Their seeds generally germinate well and remain incubated in the soil for several years, which is why new populations may come as a surprise.