HOW TO RECOGNISE GIANT HOGWEED

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Giant hogweed - Heracleum mantegazzianum, has been a naturalized plant in the United Kingdom since the 19th century when Victorian gardeners first brought it in from its native regions of central Asia the Caucasus region for its ornamental value. Despite looking similar to our native and innocuous cow parsley - Anthriscus sylvestris, the giant hogweed has some fairly serious phototoxic properties and as such is considered to be a noxious weed in this country.

It is the sap of the giant hogweed which is the problem and can come into contact with the skin by merely brushing past the plant. The sap causes phytophotodermatitis which results in skin burns, significant and multiple blisters, and long-lasting scars. These symptoms can also re-appear in subsequent years when the affected skin is exposed to sunlight, even though fresh contact with giant hogweed has not been made. In worst cases, excessive contact with the sap can cause death, and even a small amount of sap in the eyes can cause temporary or permanent blindness. These serious reactions are due to the furocoumarin derivatives that are found within the leaves, roots, stems, flowers, and seeds of the plant.

So what does giant hogweed look like?

While the giant hogweed may look similar to our native cow parsley it is a significantly larger plant growing to approximately 2–5.5 m tall. It has deeply incised, serrated compound leaves which can grow to between 1–3 m in width. The leaves also have bristles on the underside. One of its most identifiable features are its stout, bright green stems which are often marked by dark red spots, usually covered with sharp hairs and will vary from 3–8 cm in diameter, although they have been recorded as being up to 10 cm wide. Each red spot on the stem surrounds a hair, and large coarse white hairs also emerge at the base of the leaf stalks.

The giant hogweeds flowering heads branch frequently, forming clusters of several flowering heads, each one more than 80 cm across. The blooms are upwards facing and mostly white, although pink forms sometimes appear.

Giant hogweed usually forms a rosette of jagged leaves in the first year before sending up a flower spike in the second year before going to seed. However research has shown that the giant hogweed can also have a recognized perennial life cycle as well as the accepted bi-annual cycle.

For related articles click onto the following links:
COLD HARDY PLANTS WITH GIANT LEAVES
HOW TO RECOGNISE GIANT HOGWEED
WHAT IS GIANT HOGWEED