VAMPIRE PLANTS IN BRITAIN

You might think parasitic plants are only the stuff of steamy jungles and horror movies, but you’d be wrong. We have several plants in Britain that live entirely or partly off other plants and there are thought to be 4000 such species worldwide. Those that steal all their nourishment from a host, and cannot survive unless they do, are known as obligate parasites, whilst those that just pinch some of another species’ nutrients are known as hemiparasitic. These latter may be meroparasites which have chlorophyll and photosynthesize but augment their supply of nutrients by feeding on their host: mistletoe Viscum album is an example that many of us look for at this time of year. Other hemiparasites can survive for at least part of their lives without a host, often as a seed, before attaching to another species, usually their roots, to take nutrients. The eyebrights Euphrasia spp. are an example, as is lousewort Pedicularis sylvatica and yellow-rattle Rhinanthus minor agg.

Although mistletoe can photosynthesise, it does not do so very well so infiltrates the xylem of its host to acquire supplementary nutrients and, importantly, water. Host trees do not appear to suffer from even quite large populations of mistletoe although I have known it seemingly overcome a very old apple – which to be fair would probably have died anyway soon, mistletoe or not

Mistletoe is pollinated by insects and you won’t find berries on every plant because it is dioecious (has separate male and female plants).  Its sticky seeds are famously spread by mistle thrushes (Turdus viscivorus – the specific scientific name means mistletoe-eating). The seeds form a holdfast, a primary haustorium, and overwinter to germinate in spring as illustrated in Tony’s photo. It is a long-lived species, surviving as long as its host in fact.

British obligate plant parasites include the broomrapes (Orobanche spp. – nine native and one introduced), toothworts (Lathraea spp. – one native and one introduced) and dodders (Cuscuta spp. – two native and one introduced). They all tend to be rare, sporadic and only occasionally, and very locally, common. It is therefore always a thrill to find one.

Betts Ecology use hemiparasitic plants in our seed mixes to reduce the vigour of meadows and grasslands which helps prevent coarse, competitive species take over and reduce species-richness. Yellow-rattle is particularly good at this in its weakening of coarse grasses, and it can be found in abundance on many of our sites. We also promote mistletoe because it is a foodplant for several interesting invertebrates as well as famously providing berries, not just for humans at Christmas, but for mistle thrushes and other wildlife.

We are also always excited to see some of the true parasites, which are uncommon, such as toothwort, broomrapes and dodder. Do please let us know if you find any of these in our greenspaces.

Seasonal best wishes to everyone.

© Betts Ecology