Hitching a free ride

Roy McGhie – Conservation Project Assistant

You might remember at least something about photosynthesis from school – it’s the chemical process by which plants absorb light energy, which reacts with carbon dioxide and water, and produces glucose and oxygen. Photosynthesis provides food/energy for plants, which ultimately provide food/energy for every animal on the planet. It’s also the reason most plants are green – photosynthesis occurs in chloroplasts within plant cells, which contain the green chlorophyll that absorbs the light energy.

However some plants have evolved ways to get the energy they need without having to photosynthesise. Instead, they do it by parasitising other plants. Orobanchaceae is one such family of parasitic plants. There are varying levels of parasitism within the family, ranging from those that are hemiparasitic (only deriving some of their nutrients from other plants) to those that are holoparasitic (obtaining all of their nutrients from a host plant).

Toothwort is an example of a holoparasitic plant. I’ve found some particularly nice specimens of Common toothwort (Lathraea squamaria) growing on our doorstep in Helmsley. Note the lack of green colouring because the toothwort doesn’t photosynthesise, and also the resemblance to teeth. Toothwort feeds off the roots of woody plants, such as hazel, elm alder, and also walnut. There is a particularly fine walnut tree close by.

Common toothwort - NYMNPA Office, Helmsley. Copyright Roy McGhie, NYMNPA.

Common toothwort, also sometimes known as the Corpse Flower - NYMNPA Office, Helmsley. Copyright Roy McGhie, NYMNPA.

As I mentioned above, hemiparasitic plants are those that derive only some of their nutrients from the host plant but photosynthesise as well. Examples include Yellow rattle, Eyebright, Bartsia, Lousewort and Birds-nest orchid. We’ve commended Yellow rattle (Rhinanthus minor) before on this blog. Yellow rattle can photosynthesise but also parasitizes grasses and other plants nearby. Because of its parasitic nature it can be a useful plant to reduce the vigour of grasses which in turn allows other wildflowers better opportunity to thrive. A recognised technique for establishing a wildflower meadow is to sow Yellow rattle initially to help ensure the grasses don’t out-compete everything else during the establishment phase. But it’s important to remember that Yellow rattle is an annual and like most annuals, it shouldn’t be cut or grazed until late July so it has had time to set seed and so has the chance to grow again next year.

Yellow rattle - copyright NYMNPA.

Plant relationships definitely aren’t as straightforward as you might think – and we haven’t yet featured the carnivorous sundews or butterworts (a future blog post). So the next time you’re out and about where ever you are have a closer look at what’s growing around you – it may not be as innocent as it seems!

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