Thursday, October 21, 2010

A Tree-Spotter's Guide to Fruits and Seeds: Part 2

Yew Taxus baccata, one of only three native conifers in Britain (the others are Scots pine and juniper) is a conifer that doesn't produce cones. The vast majority of its relatives carry seeds on the surface of whorls of woody bracts that form a cone, but yew produces single seeds surrounded by a red fleshy aril. In the picture above you can see an aril that has yet to swell and envelope its seed, just above and to the right of the seed in the centre of the image. Thrushes are particularly fond of the succulent aril. All parts of the tree are very poisonous apart from this conspicuous coat but the thick hard wall of the poisonous seed (which can take two years to germinate) means that it can pass through the bird's gut with no ill effects. There are separate male and female yew trees, so any that are not bearing seeds at this time of year are probably male. There is a rare mutant of yew (which I have never seen) known as var. lutea that bears yellow arils. In Sussex you can find one of the finest of all yew forests, at Kingley Vale National Nature Reserve, filled with venerable trees whose dense shade prevents anything from growing beneath them -well worth a visit if you are ever in that part of the country. Some churchyard yews in various parts of Britain are reputed to be over 2000 years old.

Usually privet Ligustrum vulgare grows as a shrub and is often clipped into a neat hedge, but it it's allowed to grow unchecked it will grow into a small tree, flowering prolifically, attracting butterfly and bee pollinators and producing these rather attractive indigo-hued berries. It's a member of the olive family (Oleacea), as is ...

... the common ash Fraxinus excelsior. Ash trees can be either male, female or hermaphrodite and it's only the latter two forms that bear these familiar ash 'keys', in large bunches. Ash seeds are dormant and can take up to 18 months to germinate. They begin to fall in late autumn and require a winter chill before any will germinate - and even then only a small percentage of the crop sprouts in spring. The rest are immature and the embryos inside continue to develop throught the summer, on the tree or on the ground, and will not germinate until the following spring.

Some potential ash seeds never mature, if the flowers are attacked by a microscopically-small gall-mite called Eriophyes fraxinivorus (also known as Aceria fraxinivorus). Trees like this one alongside the River Tyne at Wylam can become completely infested and produce few seeds.

For more posts on tree ID click here


12 comments:

  1. Absolutely fascinating stuff this - I know where to find some privet (I think) and shall be seeking it out asap. Didn't know about the bloom on 'bullies' either. Will there be a part three?

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  2. I've noticed the Eriophyes fraxinivorus investation, often wondered what caused it, now I know.......thanks.

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  3. Fascinating Phil. Educated there on Yew and Ash; didn't know about the seed development of either.

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  4. This is a fascinating account of the three trees, Phil. Even though I bought a Collins Complete Guide to British Trees this summer, it's quite difficult to separate the native trees from all the imports, which caused me to make my own index which I keep inside the cover. I'll take a closer look at the Common Ash when I next see one.

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  5. That's the best view of Yew seeds that I've ever seen, thank you Phil. There are so many Ash trees in my area and their seedlings are many, causing gardeners much effort to uproot them. I've not noticed any that have been attacked as in your last shot.

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  6. Used to have a lone 200+ year old ash tree which had reached the end of its life. Some keys were germinating more than ten years after the tree had gone. Amazing the way plants time things to increase the chances of successful new growth.

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  7. Thanks Mark, the berries are at their best now... latter, if the birds don't get them, they become blacker..

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  8. It seems to me that the gall-mite infestations are becoming commoner Adrian.

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  9. We have some lovely old yews in churchyards here in the North East, Keith....

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  10. I know what you mean Emma - there are a lot of non-native relatives of our native trees that are planted, that can be tricky to identify - like some of the more exotic whitebeams and hawthorns, for example.

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  11. Hi Toffeeaple, I spend a lot of time every year pulling ash seedlings out of my garden too 9along with Norway maple, which can also be pretty invasive...

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  12. It's surprising how far ash keys travel too John. I once stood in the snow about 100 yards downwind of an ash tree on a moderately windy winter day and there were ask keys everywhere in the snow..

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