Berkshire: Cookham Area

31 July 2015

All day                                                             OS Map Explorer 172 Chiltern Hills East

This walk concentrated on wetland plants after brief exploration of chalk-based woodland and grassland.  The variety of wetland plants seen was quite remarkable in one relatively small area, although increasingly dry weather over the years must be a threat to these, as the marshes were visibly drier than we have ever known them.  Although a break for lunch in Cookham on this route is possible, we in fact took a light lunch with us and returned there to eat in the early evening.

We began by parking on the eastern edge of Quarry Wood, on the edge of Cookham Dean, and walked along the upper part of wood south-westerly before going down the steep slope to the path back NW along the bottom of the wood.  The wood is on clay at the top, but the very steep slope (down to the River Thames) is chalk rubble.  Although once good beechwood with old records of many rare plants (including five different helleborines), it has been extensively worked and modified, and although now managed by the Woodland Trust it has few large trees remaining and little of the interesting vegetation.  The main management now seems to be dedicated to providing horse-riding routes.  A good view across the Thames to Marlow can be obtained from the top of the wood.

View from Quarry Wood to Marlow

Upper path through Quarry Wood - mainly young secondary growth trees

Our list of plants from the main part of the wood included only minor indicators of ancient chalk woodland - yellow pimpernel Lysimachia nemorum, remote & wood sedges Carex remota & sylvatica, enchanter's nightshade Circaea lutetiana, woodruff Galoium odoratum, wood spurge Euphorbia amygdaloides, wood speedwell Veronica montana and three St John's-worts: hairy, common and square-stemmed Hypericum hirsutum, perforatum & tetrapterum.  The best sighting was of white helleborine Cephalanthera damasonium (now in seed) alongside the upper path.

Moth Endotricha flammealis on ragwort, Quarry Wood

Having crossed the road that snakes up the hill through the wood, we entered a north-easterly extension of the wood solely on the lower steep chalk slope that once went right down to the Thames.  Unfortunately this was much too valuable river-frontage and the river is inaccessible because of a continuous line of very large houses, although one can still walk above, with the wooded slope on the right (although this bridleway is under threat of development).  More characteristic survivors of the woodland grow along here - dark mullein Verbascum nigrum, vervain Verbena officinalis, wall lettuce Mycelis muralis, nettle-leaved bellflower Campanula trachelium, traveller's joy Clematis vitalba and wood barley Hordelymus europaeus.

Vervain

Dark mullein

These were of course mixed with garden escapes like stinking hellebore Helleborus foetidus, garden yellow archangel Lamiastrum galeobdolon argentatum and green alkanet Pentaglottis sempervivum.

          Eventually the path leads to the top of Winter Hill, where a steep chalk slope with grassland and scrub descends to the wet bottom known as Cock Marsh, which takes the form of a series of shallow ponds surrounded by wet meadow, eventually becoming arable land bordering the Thames.  This hillside runs for about a kilometre and provides extensive semi-natural habitat.  The upper slope has typical dry chalk grassland species like harebell Campanula rotundifolia, crested hair-grass Koeleria cristata, glaucous sedge Carex flacca, lady's bedstraw Galium verum, dwarf thistle Cirsium acaule, mouse-ear hawkweed Pilosella officinarum, salad burnet Poterium sanguisorba, quaking grass Briza media, wild thyme Thymus polytrichus, burnet saxifrage Pimpinella saxifraga and musk thistle Carduus nutans.

Harebell

The lower steeper part of the slope has more interesting calcicolous species like rock-rose Helianthemum nummularium, squinancywort Asperula cynanchica, fairy flax Linum catharticum, small scabious Scabiosa columbaria, carline thistle Carlina vulgaris, common and chalk eyebright Euphrasia nemorosa & pseudokerneri, and clustered bellflower Campanula glomerata.  All of these were frequent and attracted a range of butterflies and moths, including brown argus and six-spot burnet.

6-spot burnet on small scabious	Carline thistle
Squinancywort		Chalk eyebright

It is the marshland at the bottom, however, which has a particularly extensive and varied suite of flowers that is unrivalled anywhere in the region.  Common species we saw included water mint Mentha aquatica, great water dock Rumex hydrolapathum, brooklime Veronica beccabunga, blue water speedwell Veronica anagallis-aquatica, water plantain Alisma plantago-aquatica, purple loosestrife Lythrum salicaria, marsh cudweed Gnaphalium uliginosum, lesser spearwort Ranunculus flammula, creeping Jenny Lysimachia nummularia, common spike-rush Eleocharis palustris, marsh foxtail Alopecurus geniculatus, toad rush Juncus bufonius, marsh bedstraw Galium palustre, fool's watercress Apium nodiflorum, marsh yellow-cress Rorippa palustris, water and creeping forget-me-nots Myosotis scorpioides & secunda, and bulrush Typha latifolia. 

But there was an equally long list of much rarer species.  The feathery leaf rosettes of water violet Hottonia palustris were everywhere on the wetter mud, but we were disappointed not to see any fruiting spikes (the flowers would by now have been over).  Tubular water-dropwort Oenanthe fistulosa were scattered but not as abundant as we have seen them here on previous visits.  Strawberry clover Trifolium fragiferum (in flower and fruit) became increasingly common in the drier parts as we walked eastwards.  Others of note were marsh speedwell Veronica scutellata, the rare least water-pepper Persicaria minor (infrequent and inconspicuous among abundant redleg Persicaria maculosa), cyperus & hairy sedges Carex pseudocyperus & hirta, marsh stitchwort Stellaria palustris, and the sweet-grass Glyceria declinata.

Water violet leaves

Marsh speedwell

Least water pepper

Strawberry clover in fruit

Cyperus sedge

Tubular water-dropwort

Beyond what had until now been National Trust land, managed by occasional cattle grazing, we came across a tall-grass fen owned by local farmers Copas and kept as a reserve.  The variety of species here was much less, but the different habitat provided suitable conditions for additional taller herbs - common valerian Valeriana dioica, the truly native cream-coloured common comfrey Symphytum officinale, water chickweed Myosoton aquaticum, and both marsh and shore horsetails Equisetum palustre & x litorale.

Common valerian

Common comfrey

Water chickweed

Above this fen ran an old field boundary of which the hedge was now reduced to a line of laid hornbeams.

Statuesque line of old hornbeams

The path then leaves the marsh to pass under a railway bridge, where meadow cranesbill Geranium pratense grew at the base and the walls supported a good colony of pale toadflax Linaria repens.

Pale toadflax on railway bridge

We were far from finished with wetland plants, however, for the path then follows a stream to the River Thames, and we could add a number of waterside plants to our list.  By the stream we saw orange balsam Impatiens capensis, hemlock water-dropwort Oenanthe crocata, wild angelica Angelica sylvestris and gypsywort Leucopus europaeus.

Wild angelica with pair of mating soldier beetles Rhagonycha fulva

& young leaf-mines of the fly Phytomyza angelicae

Along the bank of the Thames into Cookham we added yellow iris Iris pseudacorus, hemp-agrimony Eupatorium cannabinum, common fleabane Pulicaria dysenterica, Indian balsam Impatiens glandulifera, marsh woundwort Stachys palustris, water figwort Scrophularia aquatica, and common Michaelmas-daisy Aster x salignus.  In the river were yellow water-lily Nymphoides peltata and the long floating leaves of unbranched bur-reed Sparganium emersum, while red-finned fish swam beneath them - roach or rudd.

Thames near Cookham, with hemp-agrimony & Indian balsam

Common fleabane with leaf-mines of fly Phytomyza conyzae

Yellow water-lily in Thames

We took a path along the west edge of Cookham and continued due south alongside a cornfield.  There was a damson Prunus domestica insititia in the hedgerow dropping its ripe fruit, supplementing our frugal lunch.  The path continued SW to the end of the widened ditch known as Strand Water, beside arable and disturbed land where we saw the introduced cockspur grass Echinochloa crus-galli.  Here, too, I took a photo of black ant alates emerging from their nest.  These flying ants became increasingly frequent as the afternoon wore on, over a wide area, a miracle of timing whereby all the different nests produced their progeny together.  Later, as we passed through the various built-up areas, and when we went to Cookham for an evening meal to round off the day, the streets were crawling with these creatures.

Cockspur grass

Flying ants emerging

We also took a picture of ground beetles Nebria salina unusually crawling up corn-stalks.

Nebria salina on corn-stalks

The area with cockspur grass, near large dung-heaps, included some remarkable fasciation and branching in the flower-spikes of greater plantain Plantago major (below), perhaps encouraged by an excess of nutrients.

 The public footpath continues along the east side of Strand Water, but this gives one little view of the plants because of dense scrub.  We found that there was a horse-riding track on the west side which was worth taking, as it gave a view of plants we would not otherwise have seen.  These included a large colony of native yellow loosestrife Lysimachia vulgaris, common skullcap Scutellaria galericulata and more marsh woundwort, purple loosestrife and hemlock water-dropwort.  Commoner plants were reed Phragmites australis, lesser water parsnip Berula erecta, pendulous sedge Carex pendula, common duckweed Lemna minor, yellow iris, and - a plant we often find in scrub along the Thames - the lianes of hop Humulus lupulus.  We also saw mute swan, heron, moorhen and bullfinch here.

Yellow loosestrife

Common skullcap

Marsh woundwort

We returned to the footpath which, at the end of Strand Water bent eastwards to Widbrook Common, another National Trust property.  This comprises a single large field, a kilometre long, of which the main botanical interest is provided by the stream White Brook running along its southern end to the main road that cuts off the final quarter of the common.  Although we felt that we had already seen most of the wetland plants we might encounter, we still had more to discover here.  Along with the previously recorded water dock, blue water speedwell, orange balsam and water-plantain, we were able to spot greater and ivy duckweeds Spirodela polyrhiza & Lemna trisulca, arrowhead Sagittaria sagittifolia, branched bur-reed Sparganium erectum, flowering rush Butomus umbellatus, lesser marshwort Apium inundatum, celery-leaved buttercup Ranunculus sceleratus, horned pondweed Zannichellia palustris, water fern Azolla filiculoides, hard rush Juncus inflexus, and false fox sedge Carex otrubae.  On top of these were banded demoiselles patrolling such rich pickings.

Greater duckweed

Celery-leaved buttercup

Arrowhead in flower

Flowering rush

Water fern

After this we walked back to Strand Water, west to Cookham Rise and on to Cookham Dean, adding to our list of plants Soapwort Saponaria officinalis, hedgerow cranesbill Geranium pyrenaicum, and Guernsey fleabane Conyza sumatrensis.  With 63 wetland plants recorded in one day (not counting the commonest ones like reed-grass and great willowherb we did not bother to make a note of), we were more than satisfied with this excursion, even if a few rare aquatics known once to have grown at these sites still eluded us and may no longer grow there.