The sparkling Thames

The Thames at Goring

It all started last week with Adrian asking 'What is the Goring Gap'? As geographical questions go it's not quite in the same league as 'What did the Caspian Sea?' but it's not bad.  I explained that the Goring Gap is the point at which the River Thames cuts through the low chalk hills of the Chilterns, and alongside it goes Brunel's Great Western Railway, carried over the river on a rather attractive bridge. It's no tremendous gorge, but a very pleasant bit of scenery and I suggested that we went to see it on our way to lunch at my parents' on Easter Monday.

The journey turned into something of a refresher course on the upper and mid-Thames valley and associated drainages, though missing out the Wiltshire section. In the Cotswolds we crossed the upper reaches of the rivers Churn, Coln, Leach and  later the Windrush, all draining eastwards to the Thames. We reached and first crossed the Thames proper at Newbridge in Oxfordshire and then again at Abingdon, travelling south on the Oxfordshire side to Goring.

At this point I should confess that I had an ulterior motive in undertaking this mobile geography lesson. Just outside Goring is the Berkshire, Buckinghamshire and Oxfordshire Wildlife Trust's Hartlock Reserve, a scrap of Chiltern chalk grassland that has avoided being ploughed or fertilized; as you go along on the train it's the only bit of grey-looking grassland to be seen in the whole Thames valley - grey is always good, amid the lush green of fertilized but non-flowery fields. For decades Hartslock has been the only site outside Kent known for the Monkey Orchid, Orchis simia, which was once widely found in the Chilterns. From the low point in 1950, when only a tiny number of plants were known, the population has been carefully managed and last year 448 plants were counted (according to Bill Temple in the January 2011 Journal of the Hardy Orchid Society). Unfortunately, despite the earliness of the season, the Monkey Orchids were not in flower yesterday, visible only as still-furled inflorescences.

Orchis purpurea

The conservation of the Monkey Orchid was a great success story. Then, perhaps about ten years ago now, a specimen of a Lady Orchid, Orchis purpurea, appeared at Hartslock. This is the most handsome, and largest, of our native Orchis species, with a flower that suggests a lady in a dress and poke bonnet. It is comparatively common in Kent, but very rare anywhere else. It was soon rumoured that it had been planted there, and DNA analysis has since confirmed that it is from a French population. As nobody has owned-up and it is just conceivable that it blew in as seed, the plant was allowed to remain, and very beautiful it was when I first saw it in 2004. The Lady Orchids - there are now several - were in peak flower yesterday, so the journey was certainly not wasted.

Orchis x angusticruris

Orchids being as promiscuous as plants can be, it was not long before the Monkeys mated with the Lady, and hybrids started to appear. Given the unattractive name 'Lonkey' Orchids, they are formally known as Orchis x angusticruris and are the first known occurrence of this hybrid in Britain. They are extremely striking plants, large and vigorous, unlike the very diminutive Monkey Orchids at Hartslock, with richly coloured flowers. BUT - they are also fertile and are increasing rapidly (309 in 2010), and I fear for the long term survival of the native genepool represented by the original Orchis simia at Hartslock. There has been much learned debate about this, and eminent authorities have declared that it is a natural experiment in progress, so the interlopers have been tolerated. The DNA evidence again shows that the Hartslock Monkeys share DNA with the other Chiltern speciality, Orchis militaris, and are therefore not pure to begin with - though my view is that they are the plants indigenous to the area, whatever their genetic background, and that the 'natural' experiment would be much better if it it was being carried on somewhere else.

A Hartslock hybrid - Orchis x angusticruris (O. purpurea x O. simia)

Having admired both the orchids and the glorious view of the river and the Goring Gap, we realised we had three minutes to be at lunch, so had to go the fastest way to go the thirty miles to Maidenhead, crossing the Thames from Goring to Streatley, following it along past Pangbourne to Theale and there abandoning the river, opting for a speedy journey along the M4. To complete the circuit, however, we returned by the scenic route, first crossing the river at Henley, and then crossing and recrossing at Wallingford, Shillingford, Oxford and Swinford - on bridges of course - and so home.

Orchids at Hartslock: the bare patch is erosion
caused by photographers