London Natural History Society The place for wildlife in London

London Natural History Society - The place for wildlife in London

This article was first published in the Newsletter of the London Natural History Society, No. 240 February 2016

On a mild, grey and moist but precipitation-free December day 18 folk met with John Poland to look at the trees of Holland Park in their winter state. The park covers 22 hectares and has a wide selection of trees, some native species but many more introduced ones.

We started with an Ash Fraxinus excelsior, which John used as a model to demonstrate character-istics used for winter twigs, including shape, size and colour of the terminal bud, number of bud scales, distribution of lateral buds, presence or not of an interpetiolar ridge, shape and size of leaf scar, number and distribution of vascular bundle scars, form of the girdle scar (the one left by abscission of the scales as the buds burst in spring), presence or not of stipule scars, and twig thickness and indumentum.

He pointed out that the appearance of the bark should be used with discretion because, as with people, the bark on a young plant may be smooth and delicate but as they age it becomes more corrugated and tough. This Ash was typical, with a mitre-shaped, black, terminal bud, crescentic leaf scars and many vascular bundle scars tightly-packed in a row, corresponding with the many leaflets of the pinnate Ash leaf.

The next tree was a Persian Ironwood Parrotia persica, an introduction that flowers in late winter, from woodland south of the Caspian Sea. It has flaky bark and hairy buds, many of which would have been flower buds, but, as in most species, those of leaves and flowers are similar. These twigs did have stipule scars, not always present even in stipulate species because they may be attached to the petiole, so disappear when the leaf falls.

We then looked at Pedunculate Oak Quercus robur. All oaks have clustered terminal buds, as did this one, and twigs that are pentagonal in cross-section.

We moved on to a White Mulberry Morus alba, with slender twigs. In general, but not always, trees with small leaves have slender twigs and those with large leaves have thicker ones, as with the Ash seen previously. Mulberries also produce a latex, seen as a white exudate when the twig is cut; latex is held in lactifers and is not the same as sap. The generic name Morus is the Latin for mulberry, as stated in Gledhill’s The Names of Plants, and also the generic name for Gannets. I know of no equivalent Names of Birds to explain the homonymy. Nearby was a Beech Fagus sylvativa, another tree with small leaves and slender twigs. Its buds are very distinctively long and slender with many bud scales, so the girdle scar is very clear. The profile of trees seen from a distance can be a good clue to the species and the fine twigs and branchlets (the previous year’s growth) of Beech are upswept in a way that is characteristic but hard to easily describe (I like to occasionally split infinitives).

As any fule kno, conifers are evergreen, but as any bottinist kno, it’s with the exception of those in the genera Larix, Pseudolarix, Taxodium, Glyptostrobus and the one we were now looking at, Dawn Redwood Metasequoia glyptostroboides, a name to match that of Dragon’s-teeth Tetragonolobus maritimus for labial exercise. The genus was known only as fossils until living trees were discovered in China in the 1940s so all trees in the British Isles are less than 70 years old, as am I. The profile of the tree so far is an elegant spire and the bark, even on young twigs, is a finely-stringy reddish-brown. Its opposite leaves and winter buds distinguish it from the superficially similar Swamp Cypress Taxodium distichum, which we didn’t see on the day.

We looked at shrubs as well as trees. Guelder Rose Viburnum opulus has opposite buds and crescentic leaf-scars, each with three prominent vascular bundle scars. John told us that three is the default number for most species, but that they are almost always in odd numbers, as you might expect with a symmetrical leaf plus one for the midrib.

We saw characteristics of many other species, including the long purple-green buds of Flowering Currant Ribes sanguineum, a Foxglove Tree Paulownia tomentosa with very thick twigs and abundant spikes of large fruit capsules, and a young Paperbark Maple Acer griseum with, as you may have divined, bark like peeling brown paper. Typical for the genus, a whitebeam of some sort Sorbus sp. had shed all its leaves except for a small piece of red tissue at the base of each petiole, but this too will fall in the course of the winter.

Trees in the Juglandaceae­, such as the Walnut Juglans regia we were now looking at, have chambered pith, but to demonstrate it we needed a twig. They were all out of reach, but that was corrected with the help of Irene’s walking-stick and the prize twig cloven lengthwise to expose the pith.

Many trees in Fabaceae with pinnate leaves lose the leaflets first, then the bare petiole, demonstrated on a Pagoda Tree, now called Styphno-lobium japonicum.

After lunch in the comfort of the café we looked at an Italian Alder Alnus cordata. The December warmth meant that it still had most of its leaves but we could still see the stalked buds characteristic of the genus. Irene told us that Venice is built on piles made from the timber of this species because it attains a reasonable size and is very durable, especially under water.

A rapid succession of trees followed: Hazel Corylus avellana with asymmetrical buds, stipule scars and glandular hairs, Elder Sambucus nigra with corky bark, Crimson Glory Vine Vitis coignetiae with forked tendrils which are absent from every third node, Cappadocian Maple Acer cappadocica with pruinose purple twigs and latex on cutting, Rowan Sorbus aucuparia red-black at the base of the leaf scar and 3–5 bud scales, and much more besides.

John gave us information on far more trees than I have space to include and we thank him for his expertise and the time and effort he put into leading the meeting. His Winter Key to Trees and Shrubs is due for publication in September 2016 and if it’s as good as The Vegetative Key to the British Flora it will be a masterpiece.

George Hounsome