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

Once about 15 of us had assembled at Boxhill and Westhumble station, then proceeded in enough cars to the free car park on Ranmore Common, our leader and tutor George Hounsome had fruits of Sweet Chestnut Castanea sativa, Beech Fagus sylvatica and Oak Quercus robur spread out on the bonnet of his car, and used them to distinguish between the nuts (chestnut, mast and acorn) with a shell derived from the carpel wall and the nut(s) inside the shell. These are all members of the Beech family Fagaceae, with an involucre of more or less fused bracts, spiny-backed in the case of Sweet Chestnut and Beech, but forming a scaly cup round the base of the nuts.

First we went downhill slightly into the woodland on Clay-with-Flints, making the path muddy after recent rain. A crown of Male Fern Dryopteris filix-mas was the occasion for a mini-lecture on the alternation of generations, lacking only a sample gametophyte. Sanicle Sanicula europaea was the first of a number of Carrot family Apiaceae members, some more easily distinguished in fruit than in flower. And so it went on, with frequent reference to a four-side handout with a list of definitions, a list of dispersal methods, a list of species ‘very roughly in the order we hope to see them’ which has been of great utility to me in writing this report, other ‘fruits which we might come across’ and drawings of seed structure, online sources acknowledged.

It was a bright day and we were glad to get to the sunny grassland alongside the road eastward. Here we were supposed to look at the cypselas of Common Knapweed Centaurea nigra with their short pappus, but the capitulum I examined had only a sawfly grub in it. Creeping Thistle Cirsium arvense might have been a better bet, but most of the fruits with their feathery pappus had already been dispersed anemochorously (by the wind, as in list of dispersal methods). That was on the other side of the road, where we were walking on a vague track in the middle of the wide verge, evidently used by horse riders, though the only hazard for us was a cyclist who seemed to enjoy the rough ground. A feature along here was the abundance of Fragrant Agrimony Agrimonia procera, which we could compare with the common species A. eupatoria seen earlier. With George’s help, it became a little easier to understand how these plants, whose fruit are small, hard and dry, and dispersed by hooks attaching them to passing animals (an example of epizoochory), could be in the same family as apples and pears.

It took quite a long time to reach the other, unfree, car park on the Common, due to the frequent pauses to examine other fruits: the drupes of Holly Ilex aquifolium, the naked seeds of the gymnosperm Yew Taxus baccata surrounded by a fleshy aril, the only part of the tree which is not poisonous, the flattened mericarps of Hogweed Heracleum sphondylium with unusually visible oil-canals, and many more, so we were more than ready to sit and eat at the picnic tables provided by the National Trust. Lunchtime conversation included a short informal quiz – “Which of the fruit types on the handout is a banana? ... a cucumber? ... an orange?” – answer in each case a berry. Priscilla had brought a book, The Complete Book of British Berries by David Lang, and showed it to George, but there was no time for him to make the judgment that the title should be something like ‘Berries and similar fruits’ – berries being succulent fruit with seeds bounded by their testa, the outer layer of seed (I’m reading the handout again), unlike drupes, which are also succulent fruit, but the hard coat of the seeds is derived from the endocarp which is the inner layer of the pericarp.

From here we went downhill and onto the Chalk of the North Downs, with a fine view south to the tower on Leith Hill. I was looking forward to seeing what happened when the Centaurea nigra met the chalk-tolerant Slender Knapweed C. debeauxii (would there be a zone of intermediates, or an abrupt change from one to the other?) but the latter wasn’t there. The change of habitat provided plenty of new fruit types: Small Scabious Scabiosa columbaria, with a fruit too complicated to describe here, Vervain Verbena officinalis, with a fruit of four nutlets much like those of the many plants of the Dead-nettle family Lamiaceae considered during the day, though the enclosing calyx is different, Common Centaury Centaurium erythraea with a two-valved capsule, Glaucous Sedge Carex flacca with its nuts completely enclosed in a utricle and Common Rock-rose Helianthemum nummularium with a three-valved capsule. Dogwood Cornus sanguinea was not one George had prepared for, but he examined it by halving a fruit with his teeth, decided it was a drupe and checked that in a book. He also hadn’t listed Common Gromwell Lithospermum officinale in the handout, having missed it in his recce, but knew not to try biting its nutlets which are indeed as hard as stone. Paul produced a stem of White Helleborine Cephalanthera damasonium with the seed already dispersed, showing how the fruit opened by the splitting of the thin surface stretched between three thick longitudinal ribs. Then George went down the hill a little way and returned with a stem of Great Mullein Verbascum thapsus held upright; back amongst us he shook a couple of thousand tiny seeds out of their capsules into the palm of his other hand, distributing many so that their sculpturing could be admired under hand lenses, and throwing the rest to the ground. There will be many rosettes of mullein leaves there next spring.

A gentle climb took us back up to the wood, and with only a few species left in the sequence the choice of route was designed to take us back to the car park without any road walking as much as to link together a many additional interesting fruits. The ‘explosive’ capsules of Indian Balsam Impatiens glandulifera did not detain us long; probably we all knew about them already. Mario provided a diversion with some interesting fungi, conveniently close to each other, Yellow Stagshorn Calocera viscosa, a Marasmius species probably Collared Parachute Marasmius rotula and Crested Coral Clavelina cristata. Perhaps it was a sign of tiredness that George’s funny remarks, such as Deschampsia cespitosa having nothing to do with cesspits, were getting worse. Almost at the end he redeemed himself by finding a nice plant of Hairy Wood-rush Luzula pilosa, its three-seeded capsules ready for examination.

It was a most rewarding day, and George was warmly thanked by all for his well-prepared instruction.

Rodney Burton