Holt Island Nature Reserve in St Ives features rare plant

There is an invader in the stinging nettles on the nature reserve.

It is winding itself up stems and between plants, and sucking the juices from its victims, the nettles.

No need to panic—it is, in fact, a fascinating parasitic plant called Greater Dodder Cuscuta europaea, which is related to the convolvulus family.

It is only one of a number of dodders, all of which rely on particular plant species for their development.

Without leaves, they have no chlorophyll and cannot convert the sun’s light energy to chemical energy, like most plants, by the process called photosynthesis.

Each spring, the warmer weather encourages germination of dodder seeds lying dormant in the soil.

Minute roots anchor a threadlike pink shoot, which rotates as it grows through the surface layer of organic matter.

This shoot recognises a young, tender stem of the nettle and grows towards it, encircling it and growing up in an upward spiral.

The small store of energy in the dodder seed is rapidly depleted, and it must quickly plug into the host plant’s vascular system to get nutrients and water.

It does this by forming specialised suckers, and at this point, the small root withers away.

The dodder threads or tendrils grow quickly, spiralling upwards and branching.

They are caught in the breeze to land on adjacent nettle plants to wind around these too.

Once the dodder is established and nourished, it forms many more suckers which adhere firmly to the host stem.

Small pinkish flowers form in spherical groups, making the threads look like a string of beads.

When conditions favour the plant, it produces a huge number of these flowers and plentiful dusty pollen grains.

With pollination likely through insect or wind dispersal, large numbers of tiny seeds are produced.

Sometimes the growth of dodder is so prolific, the strands resemble candyfloss above the nettle beds.

Host plants bearing dodder seeds then drop into the soil to lie dormant overwinter.

Worldwide, dodders cause significant reduction in the yield of arable crops, although locally, and on Holt Island, our dodder is regarded more as a curiosity.

Why not come and see for yourself?