A Tree-Spotter's Guide to Bark: Part 4

The success of London plane Planatus x hispanica as a street tree owes a lot to its propensity to slough off flakes of bark frequently, shedding pollutants along with it - and leaving an attractive abstract pattern of pastel coloured patches.

Marooned in a sea of of concrete and asphalt and assailed by exhaust fumes; it's a small miracle that plane trees like this not only survive but thrive in the urban jungle.

On a sunny day, it's pretty obvious how redwoods got their name. This is the giant sequoia Sequoiadendron giganteum, a species that was introduced into Britain in 1853. The bark is incredibly thick, soft and fibrous and, it is said, has been adopted as a roosting site by treecreepers that hollow out small depressions where they spend the night. Where did treecreepers roost before 1853, I wonder? The tree is sometimes known as Wellingtonia, named after the Duke of Wellington who died the year before it was introduced, but attempts to formalise this name as Wellingtonia gigantea - an act of imperialistic arrogance - upset the Americans. It was, after all, their tree so they countered with the name Washingtonia, to commemorate their national hero.... but there was already a palm species with the same name. Thankfully, it turned out that it was a cousin of the coast redwood Sequoia sempervirens and so could also be called Sequoia, circumventing any further taxonomic squabbling. It became Sequoiadendron in 1939, when detailed examination revealed that it was sufficiently distinct to be placed in a genus of its own. 

Horse chestnut Aesculus hippocastanum becomes flaky with age but isn't easily shed - so it often acquires a veneer of green algae on the northern, shady side of the trunk.

Elder Sambucus nigra rarely lives long enough to develop tree proportions but when it does the deeply fissured corky bark can be very attractive.

When common hawthorn Crataegus monogyna grows as a tree, rather than as a regularly cut hedgerow shrub, it tends to branch from low down from an early age and this produces a trunk that resembles vertical branches welded together - which is what they are, I suppose.

For more information on tree identification click here

Purple

I found this exquisite little purple toadstool on my lunchtime walk in Durham today, growing beside the footpath near Blaid's Wood to the south of the city. I'm pretty sure it's a violet webcap Cortinarius violaceus (unless anyone out there knows better???). Without doubt the most intensely purple pigmented toadstool I've ever seen. It doesn't have much of a 'web' but what remains of it is the white patch on the flank of the cap and the wispy white threads around its rim.

For pictures of fungi on this blog click here

A Tree-Spotter's Guide to Fruits and Seeds: Part 7

I've always been partial to pickled walnuts and the key thing to remember if you are going to pickle them is to time the harvest just right, before the coat of the developing seed inside begins to become woody, which you can test by pushing in a long needle. The soft outer fruit wall produces a black dye (which is why pickled walnuts are black) and after you've harvested them your hands go black too - it can take a couple of days for the dye to fade from your skin.

These are sitka spruce Picea sitchensis cones, which are often at the top of the tree and out of camera range, but this tree was growing on a cliff ledge and the cones were at eye level from the top of the cliff. Like so many conifers, sitka spruces are attractive trees when they are given space to develop their natural shape but all too often they are only seen crowded into dense commercial plantations. The tree a native of the west coast of North America, from Alaska to Northern California.

In comparsion to sitka spruce, the 4 cm.-long cones of giant redwood Sequoiadendron giganteum are diminutive and the seeds are minute - only about three millimetres across, including their papery wing - which is remarkable when you consider that the tree that they produce grows to a height of 100 metres and lives for over 3000 years.

The cones may be small but they do have an interesting pattern on the end of their scales........

... and are quite decorative when they ripen.

A familiar sight on the streets of the capital in winter - leafless branches of London plane Platanus x hispanica decorated with the dangling, ball-shaped fruits that break up to release small hairy seeds. The tree's only real link with London is that it's the commonest street tree there - it's actually a hybrid between Oriental plane Platanus orientalis from eastern Europe and north west Asia and the American plane (aka American sycamore) P. occidentalis. In nature the parents of the hybrid are separated by the Atlantic Ocean but they hybidised when they were grown together in Europe (possibly first in Spain - hence hispanica). The offspring of the union is a vigorous and pollution tolerant urban tree that rarely seems to be planted in the countryside.

For more on tree identification click here