Botanical finds this summer

Botanical activity over the last couple of months has been generating a lot of records and some fantastic finds. Activity has included two recording meetings organised by myself, an 'official' BSBI field outing to Nettlebed Common, as well as numerous other formal and informal recording meetings and other kinds of survey undertaken by local botanists. As it is about time that I posted something, I thought I would blog about some of the highlights.

The biggest surprise of the season (so far) is the double re-appearance of the nationally scarce Althaea officinalis (marsh mallow) in the county, with one site at Otmoor and the other by the Thames near Shiplake. Usually a plant of brackish marshes at coastal sites, A. officinalis was reported by Druce as appearing in a ditch at Long Meadow near Iffley/Oxford in the 1830s, and was more recently recorded as a casual from the Oxford tip. Where these newly recorded plants could have come from is a mystery. The Otmoor plant appeared a few years following the cutting of a hedge by a ditch on the RSPB reserve, and could have appeared from buried seed. Perhaps more plausibly as it is growing by a footpath, it could have been accidentally introduced from a visiting birder (it also grows at RSPB Minsmere). If it were an introduction, it seems odd that it should appear simultaneously with another plant at the other end of the county, but then it has never been known from Otmoor and is the habitat at either site right?

Floodplains were a theme early in the season, with a couple of great finds. During fieldwork for Tanya Smith's master's thesis, in which she is studying the damper meadows of the county's floodplains, a huge hitherto unknown population of the nationally scarce Oenanthe silaifolia (narrow-leaved water-dropwort) was found at a large meadow in the floodplain of the River Cherwell. With the several other sites for this species already known in the county, such as featured previously on this blog, Oxfordshire must surely be among the best places in the country where it can be seen in such spectacular numbers. In contrast in terms of population size, Fay Banks came upon a single plant of Eriophorum angustifolium (common cotton-grass) in a spring on the terrace of the River Thame near Wheatley. Having recently been on holiday in the north-west where this species was everywhere in the hills, Fay did not immediately realise how special a find this was — it had previously been known from only two sites in VC 23! While a seemingly unlikely situation in heavily modified pasture, it was in good company, growing with Galium uliginosum (fen bedstraw), Valeriana dioica (marsh valerian) and other fen plants.

Back in the spring I blogged about some of my recent finds, including a surprising record of the fern Gymnocarpium robertianum (limestone fern). While out recording near Sandford St Martin I came across another fern that is rare in our parts, Cystopteris fragilis (brittle bladder-fern), with numerous plants growing in a limestone wall. This was an exciting record as this fern is included in the list of possible extinctions in the county's recently published rare plants register, Oxfordshire's Threatened Plants. Very gratifyingly, I have had a couple of records this summer of another species to be removed from this list of county extinctions, Fumaria capreolata (white ramping fumitory), seen in Headington and Garsington. It was also seen last year elsewhere in Oxford, so although rare is evidently still holding on in the county.

I can't help but mention a good recent stonewort record made during the meeting at Souldern in July. The extremely clear spring-fed waters of the village pond were much admired, and this was the habitat for the locally rare Chara hispida. Not many botanists tackle this group of algae, but this one is easy to identify on account of its being huge (for a stonewort) and very bristly. Known from only two other sites in VC 23, it is not surprising that it is very rare with us, requiring clean, lime-rich water. It was growing with Ranunculus circinatus (fan-leaved water-crowfoot), another locally rare plant of clean lime-rich water.

Finally, the BSBI meeting at Nettlebed Common in June was a feast of locally rare plants, mostly those of the acid soils that are so uncommon in Oxfordshire. The ponds in the old clay pits on the common have been restored over the last few years, involving the clearance of trees as well as the introduction of plant species. The thread-like aquatic fern Pilularia globulifera (pillwort) once grew not far away at Peppard and was one such introduction, while Carex echinata (star sedge) and Hypericum elodes (marsh St John's wort) though not previously known from the Oxfordshire Chilterns are characteristic of acid, nutrient-poor ponds, growing particularly with Sphagnum moss, as is still to be found naturally at Nettlebed. Other acid species we saw included an abundance of Juncus bulbosus (bulbous rush) and Lythrum portula (water purslane) in the ponds, and Calluna vulgaris (heather) in the small area of heathland remaining on the common, as well as the locally rare sedges C. binervis (green-ribbed sedge) and Carex demissa (common yellow sedge). I was grateful to have had Sally Rankin along to show us around: we probably wouldn't have seen any of these plants if I had been leading! The unusual heathland was complemented nicely by a walk around the nearby beech woods, a classic Chilterns habitat, where we saw a classic Chilterns orchid Epipactis purpurata (violet helleborine).