Wednesday, 10 November 2010

Yew berries and their dispersers

Taxus baccata 'Fastigiata'
The female Yews (Taxus baccata) here have had a huge crop of 'berries' this year; although they are quite reliable in producing a good crop this  year's seems exceptional. What is generally called the berry is formed of a single seed that develops from the naked ovule characteristic of gymnosperms, produced on the twigs in about March. As it grows it becomes surrounded by a red fleshy aril, which develops from the disc on which the ovule is borne. The ovules are not usually noticed when receptive in early spring, unlike the male strobili or cones which are conspicuously pale and can release huge clouds of pollen in the right climatic conditions: the trees are either male or female, though occasional hermaphrodites are known.

Badger dropping containing Yew seeds
The aril, which is stickily sweet, is the only non-toxic part of a Yew (although susceptibility to the toxins varies with species). The red colour attracts birds, which act as the dispersal agent for the species - the poisonous seed has a thick coat and passes unharmed through the gut. At the moment the trees here are full of Redwings (Turdus iliacus), busily scoffing the fruits. More surprising is the heavy consumption of the fruits by Badgers. We know this because a Badger has taken to using a gravel path as its regular latrine, leaving behind copious masses of droppings mainly composed of semi-digested Yew berries: not at all a pleasant sight. The most conspicuous have been covered over, but this picture shows the general effect, plus a large number of Yew seeds. It will be interesting to see if we get a crop of seedlings there next spring. Even more interesting would be to see the beast harvesting them: it must have to stand on its hind legs to do so, as there are not many fruits close to the ground. At least while so occupied it is not digging in the lawn for worms...

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