Nature on our doorsteps: Parasitic plants

Rosaleen Dwyer is the County Heritage Officer at South Dublin County Council – every week she gives us an insight into the natural heritage around us and the beautiful biodiversity of the plants and creatures

Two very different plants in our wildflower meadows share a similar technique to help them grow and thrive. Both are parasitic plants, feeding off their neighbours.

The Broomrape family of plants are unusual in that they do not contain any chlorophyll. Chlorophyll is the compound that gives plants their green colour.

Plants use it to convert energy from the sun into chemical energy to drive the process by which plants make the sugars that they need to grow (photosynthesis).

Without green chlorophyll, Broomrape cannot make its own food. It therefore has evolved to tap into the roots of other plants and steal what it needs from them.

Different Broomrape species feed on different host plants. The Broomrape species in Tymon Park’s meadows feeds on the roots of Clover, while those found along the banks of the River Liffey feed on the roots of Ivy.

Broomrape grows as a short spike of very pale yellowish flowers, sometimes tinged with purple.

Plant parasites in flower, Broomrape (left) and Yellow Rattle (right)

When the spike is mature, it turns brown, dry, and papery. It can remain standing like this amongst the vegetation for some time.

Yellow Rattle is also a parasitic plant. It is termed a hemi-parasite, however, meaning it is only partly parasitic.

Unlike Broomrape, Yellow Rattle has chlorophyll and so it is capable of making its own food. When the opportunity arises, however, Yellow Rattle gets an added boost by taking nutrients from its neighbours, mostly from the roots of nearby grasses.

Yellow Rattle is a useful plant in a flowering meadow as it reduces the growth and vigour of surrounding grasses.

As grass growth declines, the reduced competition gives wildflowers more space to grow, flower, and set seed.

Yellow Rattle gets its name from the sound that its big, round, seed pods make when they are full of ripened seed.

They rattle loudly when disturbed by passing animals.

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