Wednesday, 6 December 2017

Advent Botany at Bix

Large shuttlecocks of Dryopteris affinis growing toward the bottom of a wooded valley on the Nettlebed Estate
Atlas 2020 recording stops for nothing! The first weekend of December saw local botanists taking up their clipboards and setting out into the mist to record vascular plants around Bix (SU78H) in the Chilterns. There wasn't exactly a throng of us, just myself and an extremely keen companion, but we covered a lot of ground, getting together a list of over 220 taxa. Winter can be surprisingly rewarding if you've never looked for plants outside of what is usually considered 'the season' — one just has to be prepared to identify things vegetatively and from dead stuff ('dead-getatively' I call it). Some of the plants usually considered vernal species, such as Erophila verna (common whitlowgrass) or Ficaria verna (lesser celandine) actually start to reappear in autumn and early winter if you know what to look for (the forked hairs on the tiny leaf rosettes of the former are quite lovely!), so you needn't wait until spring!

The Bix area is similar to much of the rest of the Oxfordshire Chilterns, in that woodlands figure prominently and it is under-recorded. One of the things I find interesting in the Chilterns is the mix of geology, with acid clay-with-flints capping the chalk, allowing calcicolous and calcifugous species to grow right next to one another. The woods also often support particularly interesting assemblages of ferns (who cares about the helleborines!), and would be just the right habitat to re-find Oreopteris limbosperma (lemon-scented fern), not seen in Oxon for many decades. As it was, we didn't find it but spent quite a lot of time examining ferns belonging to the Dryopteris affinis aggregate (scaly male ferns), some of which were impressively enormous.

Dryopteris carthusiana in a Chiltern Beechwood
Although this group of ferns is quite widespread in the county (maybe even under-recorded) nobody has seriously cast a critical eye upon these apomicts and attempted to separate out the distribution of the seggregates. Myself and Oli Pescott have this year both found a number of oddities that look like D. cambrensis (narrow scaly male fern), which has not been recorded in the county before. Some of the plants we found at Bix resembled other possible D. cambrensis I've seen, growing as giant tufts, the fronds with very well-lobed pinnules with more tapered apices than is seen in D. affinis. Specimens were handed to Fred Rumsey at the recent BSBI Annual Exhibition Meeting, so fingers crossed that we'll get the nod to add a new native species to the Oxon list!

We also spent a while puzzling over buckler ferns when we found a thriving colony of D. carthusiana (narrow buckler fern), which is quite frequent in the Chiltern beechwoods. However, D. x deweveri, its hybrid with the common and locally abundant D. dilatata (broad buckler fern) has never been recorded from the county: as I have not seen it either I'm doubly determined to find it, looking for it whenever I encounter both parents together! I collected a few specimens to check the spores at home but don't hold out much hope.

In the afternoon I was left on my own and made the most of this by crawling about under scrub to get a look at abandoned calcareous grassland above the road to Henley. Among the mossy rabbit-grazed turf were many calcicoles, such as Centaurea scabiosa (great knapweed), Knautia arvensis (field scabious), Leontodon hispidus (common hawkbit), Linum catharticum (fairy flax) and Poterium sanguisorba (salad burnet). On anthills in the same grassland was the calcifugous Rumex aectosella (sheep's sorrell) and growing the other side of the road on the banks of the Lambridge Woods were others such as Deschampsia flexuosa (wavy hair-grass), Hypericum pulchrum (slender St John's wort) and Luzula pilosa (hairy woodrush). This juxtaposition of species of differing soil requirement is just the kind of thing that gets ecology nerds like me excited!

The man-made habitats of Bix itself supported the usual suspects, but there were some nice plants. A well-grown specimen of Crataegys persimilis in the hedge by the Henley road was a new county record, and an arable field had the alien grass Ceratachloa carinata (California brome) which I've found a lot this year in similar places. Here we also recorded the threatened arable weed Anthemis cotula (stinking chamomile), and which was still in flower. Altogether an excellent haul for a grey December day. Why not keep recording this winter and see what you can find? I'll be trying my best to organise a New Year Plant Hunt for a few week's time, so maybe see you there.

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