Monday, 17 April 2017

Weekend highlights

The hybrid violet Viola x scabra showing a mix of hairy and sweet violet traits, notably the hairy petioles and presence of stolons, respectively.
I'd really like the Oxfordshire Botany blog to be a place for local recorders to share their interesting finds and experiences whilst recording. As the recording season is definitely now upon us I therefore thought I'd start with some reflections on my weekend out botanising. Please do let me know if you would like to do a write-up for the blog in future.

One of my main recording objectives for this year is to get the hectad SP42 up to scratch: as one can see on the Atlas 2020 page it is a very under-recorded part of the county. I made a start on that objective this weekend by recording around Tackley in the south-east corner of SP42. Nobody seems to have recorded there since the 1960s, not for the BSBI anyway. The two tetrads that cover most of Tackley (SP42Q and SP42V) have a good mix of habitats, with the village, to the east the River Cherwell, its floodplain and the Oxford canal, a Local Wildlife Site (LWS) in SP42Q and two in SP42V, and large and small woodlands scattered through mixed farmland in the area. Given this diversity of habitats, semi-natural and artificial, I felt the area was a good one to choose as part of my recording of SP42. I mostly focused this weekend on SP42V but the churchyard of St Nicholas' in SP42Q looked enticing and so I recorded there also. Of the local wildlife sites, Tackley Heath (SP42Q) and Crecy Hill are open access, which is useful, and a public right of way passes through part of Northbrook Marsh.

The distribution of wood sorrel in VC 23. Green squares are tetrads with post-2000 records.
Wood sorrel, in Oxfordshire a plant of ancient woodland mostly in more 'upland' areas. It is common where acid clay-with-flints overlies the chalk in the Chilterns area, where it is very under -recorded (map right). Wikimedia Commons
St Nicholas' was a beautiful place, what I wish more churchyards looked like. There was a profusion of goldilocks buttercup (Ranunculus auricomus) in full flower and a few other ancient woodland indicators in some quantity, such as bush vetch (Vicia sepium), dog's mercury (Mercurialis perennis) and wood sorrel (Oxalis acetosella). Remarkably wood sorrel is Near Threatened in England, i.e. not quite endangered but getting there based on recent declines (20-30%). Looking at the records when I got home I was surprised at how little wood sorrel has been recorded in VC 23 recently. This is due to lack of recording in suitable places, but on the face of it the situation of wood sorrel in Oxfordshire looks artificially dire (map right). This illustrates how important it is to keep up with recording: our records contribute toward assessments of national conservation statuses and these depend on spatially and temporarily consistent recording; records are needed of even seemingly widespread species such as wood sorrel, not just our rarest and most obviously threatened plants.

A couple more Near Threatened plants I found on the verges in the village of Tackley - field scabious (Knautia arvensis) and hoary plantain (Plantago media). Again it is quite surprising that these are Near Threatened, and again shows that one oughtn't to be complacent about commoner species. Moving on from Tackley, Crecy Hill at the top of the oolite escarpment overlooking the Cherwell valley was a bit of a disappointment, being very scrubby and quite rank. However, the hairy violets (Viola hirta) were flowering, which brings me to what I would say was my find of the day.

My last post on the blog was about violets, and there I referred to the paucity of Oxfordshire records for the hybrid between the sweet and hairy violets, Viola x scabra. Well, to my surprise I found a hybrid colony in a hedgebank along the track down from Crecy Hill. What drew my attention was its obviously clonal habit and unusually large leaves, quite unlike those of sweet violet in shape. Closer inspection revealed stolons as in sweet violet and hairy petioles, as in hairy violet. However the hairs were a mix of long patent-deflexed hairs as in hairy violet and shorter deflexed hairs as in sweet violet. There were a small number of rather puny flowers, on very long pedicels and with white centers to the corolla, both further hybrid characters; the bract was in the lower half of the pedicel, as in hairy violet. I would hardly have thought to look out for this taxon or felt so confident in identifying it had it not been for the BSBI's excellent new Viola handbook!

Some botanists may regard the identification of hybrids as difficult, esoteric or just pointless. However, I find hybrids fascinating as they confuse our neat taxonomic system that reduces plants to well-defined objects called 'species', adding an extra challenge to recording; hybridisation has also been immensely important in the evolution of plants. I shall therefore always be interested to receive information about possible hybrids in the county. That isn't to say that I will be sufficiently knowledgeable to help in every case where hybridisation is suspected, but the BSBI has plenty of experts who can!

Having taken my time over the violet hybrid I eventually made it down onto the floodplain of the River Cherwell, where squeezed between the escarpment and an expanse of bright green improved grassland in the floodplain is Northbrook Marsh LWS. As this is private land and I am planning to survey the site later in the season I will say no more of the LWS for now.

On Sunday 23rd April there will be the first field meeting of the season that I will be running. The aim of the day is to provide training for botanists interested in recording for Atlas 2020 in the county, as well as to gather some records from an under-recorded area. The meeting will be in Waterend near Stokenchurch (SU79W). Please let me know by email if you would like to attend. See the calendar on the events page for further details of this and future meetings.

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