Hogweed

 Heracleum spondylium

Despite the unattractive sounding popular name, Hogweed is a magnificent plant whose popular name derives from the unpleasant piglike smell of the flowers rather than reflecting a coarse or ugly appearance. It is the largest of the Apiaceae or umbellifers that are to be found in Leazes Park and in high summer the flat discs of flowers can be above my head. Although you seldom find it in its full glory it does put in an appearance at other times of the year. I have found it during New Year plant hunts and I was prompted to start writing this post by a reappearance of the plant in late October 2020.

In spite of the unpleasant fragrance of the mature flowers, the young shoots are supposed to make good eating but I would discourage anyone from eating members of this family harvested from the park. You only have to get it wrong once.....



Taxonomy

Hogweed belongs to the Apiaceae family that was discussed in a previous blog post. Other members of this family that have been discussed are cow parsley, hemlock and wild carrot. The main diagnostic feature of this family is the inflorescence which consists of several rays emanating from the main stem and in turn multiple secondary rays radiating from the primary ray. Each secondary ray is terminated by a flower with an inferior ovary and five small petals. The genus name, Heracleum relates to the legendary strongman Heracles and the species name sphondylium comes from the Greek for vertebra.  The regular joints along the stem and septae within the stem can give that appearance.

Schematic showing an umbel of umbels

General appearance

Hogweed is a robust plant that can reach 200cms in height. As you might expect this sort of structure needs good foundations in the form of a long taproot.  The hollow stem is reinforced externally with longitudinal ridges and internally with horizontal septae. The stem is covered with coarse downward-pointing hairs. Each main stem bears multiple inflorescences that seem to counterbalance each other on opposite sides of the stem.

Leaves

The leaves are 1-pinnate and the terminal leaflet is usually 3-5 lobed. Individual leaflets are coarsely toothed. The petiole sheaths the stem. There are hairs on both sides of the leaf.  The best thing however is to watch the leaves unfolding on successive days in a kind of reverse origami.


Leaf starting to unfurl

Just unfurled

Young basal leaf

Inflorescence and flowers

It is worth taking the time to watch the inflorescence unfolding on successive days or failing that find plants at different stages of maturation. The inflorescence is initially folded into a tight hairy ball, you can see that the primary rays are subtended by bracts most of which drop off as the inflorescence matures. The secondary rays are subtended by bracteoles that are permanent. The primary rays unfurl first then the secondary rays and finally individual flowers. The newly unfurled inflorescence is somewhat globular but soon forms into the characteristic flat plates of flowers up to 15cm across.

A tightly curled up flower about to unfurl.

The primary rays unfurl.

The flowers unfurl from the secondary rays.

The individual flowers are typical of the Apiaceae having 5 notched petals and inferior two-chambered ovary and two stamens. The flowers towards the edge of the umbel tended to be asymmetric with the outer petal being larger than those pointing towards the center of the umbel. The newly minted flowers tend to be pinkish in colour fading to white over time.

Mature umbel of umbels showing asymmetry of petals.

Where to find hogweed in Leazes Park


The best area is the wild area to the north of the lake. Find the 'blue splashes' marking the Florid Burn. To the left of this (with your back to the lake) is a footpath when you enter this path there is a small pond to your right around which hogweed grows in profusion.






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