A good year for a rare parasite

http://www.theguardian.com/environment/2015/jul/18/greater-broomrape-parasite-new-forest

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The grapevine is important. We were about to leave for Ireland when the call came in. “The plant you told us about in your talk is showing through.” No time to check it out before we departed, but we did go to look soon after our return. Nationally scarce and in decline, greater broomrape is uncommon throughout Hampshire. The one colony in the New Forest where it has some strength is possibly the largest in Britain.

In the weeks we have been away, most of the plants have flowered, gone over, and stand as tan-brown sentinels among gorse bushes. A few are in more open ground along root runs. A few still hold their florets with down-turned yellowish-pink lips tinged with purple, and a brightly coloured stigma that looks like two close-set yellow eyes peering out from under the upper hood. Some plants are no more than 10cm tall, others reach nearly a metre.

Broomrape seed are tiny. Chemical reactions trigger germination and draw the seed’s root towards the host plant. Once alongside, it taps in and draws up the sap passing along the system more efficiently than the host plant itself can do. The broomrapes shed their ability to create life-giving resources of their own long ago and the whole family are now totally dependent on other species for their livelihood. They don’t kill their hosts, but they do weaken them and reduce their ability to flower and set seed.

Aptly named, greater broomrape gains all its nourishment from broom or gorse. This colony has been here for many years but, as the gorse is spreading, so too are the parasites, which appear to have a distinct preference for younger bushes. Altogether we counted many hundreds of spikes and certainly missed some. It’s a mystery how it became established on the slopes of these old gravel workings. Records show that it has been present since at least 1986, when it was first noted, and that its numbers fluctuate. This year seems to have suited it very well.