Wednesday, 30 August 2017

Little Milton Square Bash

Alien grasses sown for game, Ecinochloa crus-gali, Panicum milliaceum and Zea mays
It is some time since I posted on here, which is a shame, but the season (work) had the better of me for a while. However, this weekend I managed to get out again with local botanists and gather some much needed records. For those of you who might have missed my botanical waffle, here's an account of what we got up to.

Now that SP42 is looking better recorded I thought I'd turn my attention to another under-recorded area, roughly the Oxfordshire part of the Thame catchment, from a few miles south of Oxford east to Thame and pretty much all the way to the foot of the Chilterns. As it is mostly arable land with very few nature reserves or similar sites one can appreciate why it might not appeal, but it still needs doing. A few botanists have been working on it, but it is a large area and there isn't much time before the end of the recording period for Atlas 2020. Wanting to contribute to this effort, therefore, six of us met at Little Milton where we were very kindly treated to tea and freshly baked cake by resident botanist Liz Powell. The tetrad (SP60A) has had some recording already so I had hoped to make it toward Stadhampton (SU69E) in order to cover new ground. Hardly surprisingly we didn't get that far, but we added a lot to the tetrad total for Little Milton, getting it up to 288 taxa. Of course there were a host of the usual garden escapes but the total also includes some more unusual and interesting plants.

The first species of interest were along the A329, where we had Torilis nodosa (knotted hedge parsley), a characteristic plant of dry, well-mown verges, and Lactuca virosa (great lettuce). The latter is a colonist of roads that is still relatively uncommon in Oxfordshire but that is everywhere if one botanises further south or east. Botanising late in the summer we were also able to identify damsons (Prunus domestica subsp. institia) rather than having to leave bushes unsatisfactorily as wild plum (P. domestica).

There were other planted shrubs and trees around Little Milton, including a few weird-looking 'native' hedgerow species. Acer campestre var. leiocarpum (or subsp. leiocarpum) is a big-leaved version of the native field maple (var. campestre) that has more prominent leaf lobes and glabrous samaras (the winged fruits also known as 'keys') — the infraspecific taxonomy of field maples is nicely set out in Sell and Murell's flora, volume 3. Growing nearby was a big-leaved hazel, which could have been any of Corylus avelana var. grandis, C. maxima or C. avellana x maxima but squirrels had pinched all the nuts so we couldn't tell.

Heading out into arable country didn't look promising, so we were thankful to the local pheasant shoot for their headlands sown for the game. There were several alien grasses one finds in such places, the commonest being Echinochloa crus-gali (cockle-bur), but also a lot of Ceratochloa carinata (California brome). These unsprayed strips are often valuable for arable weeds, and here we found Erysimum cheiranthoides (treacle mustard), a much-declined and red-listed species. Eventually we made it to the River Thame, adding some variety to our list, with Berula erecta (lesser water-parsnhip) and Mentha arvensis (corn mint). Both have only a scattering of post-2000 records. There was also an impressive crack willow pollard with no fewer than four other woody plants growing from its crown, including Rosa canina x obtusifolia (=R. x dumetorum). This is one of the commonest roses around where I live: as this was my first time botanising in this part of the county it was interesting to see its (known) range expand.

Also interesting in terms of verifying findings from my local patch was the presence of Bromus commutatus (meadow brome), which I find as a common weed of cereals. Traditionally thought of as a species of unimproved alluvial meadows it is an often abundant weed, usually as a much more robust-looking thing than in meadows and frequently and confusingly having hairy lemmas (B. commutatus var. pubens). This alternative habitat for this annual grass does not seem to be reflected in the county's records: most named localities are from meadows. Please look out for it in cereal crops, where it may also occur with the similar and potentially increasing Bromus secalius (rye brome).

Hypericum x desetangsii nothosubsp. desetangsii with the rounded sepals and black-streaked petals of H. maculatum.
I cannot close without a mention of des Etang's St John's wort (Hypericum x desetangsii), the fertile hybrid between the common or perforate St John's wort (H. perforatum) and what is with us the scarce imperforate St John's wort (H. maculatum). I first learnt about this plant on the chalk in Cambridgeshire but since then I have only ever seen it on wasteground, including here at Little Milton, growing by a farm track. It has three post-2000 records including this one, and only four pre-2000 records.

This is of a similar stature to H. maculatum, and from a distance looks quite like it with its broad leaves. However, the leaves have an irregular scattering of translucent glands (as in H. perforatum) and the stem is weakly four-angled (as in H. maculatum). The main character to examine is the sepals, which although perhaps apiculate like H. perforatum are mostly abruptly rounded at the tip as in H. maculatum. The shape of the sepals might vary across the plant, but examine several and you may also find a few with two or three rough teeth either side of the apex. This is indicative of H. m. subsp. obtusiusculum, the hybrid with which is the nominate nothosubspecies. The hybrid with subsp. maculatum, called nothosubsp. carinthiacum, is very rare and not known from VC 23.

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