Friday, 13 September 2019

Autumn recording

Rosa sherrardii at Meadow Farm. The main features visible are the forward-pointing sepals and strong straight prickles.

A full press, product of looking at roses at Meadow Farm
With the coming of the season of mellow fruitfulness, I have of late been thinking about all those brightly-coloured berries, drupelets, drupes, haws, hips and pommes in hedgerows and scrubby places. As readers familiar with my interests will anticipate, this has mostly focused on roses, but I have also been scratching my head over hawthorns and having a go at brambles. This blog post is about what I have been finding this autumn.

Roses were the main target for a recording meeting I ran at Meadow Farm Nature Reserve in Blackthorn. The highlight was Rosa sherardii (Sherard's downy-rose), a predominantly northern and western species which has largely disappeared from our area (see map below). Gareth Knass recently found it on the downs in the VC22 part of modern Oxfordshire, but except for the one bush at Meadow Farm I am not aware of any confirmed recent records for VC23. I have only otherwise seen the hybrid with R. canina from VC23 (R. x rothschildii, e.g. at Sydlings Copse). Gareth has taken many wonderful photos of roses — you can see his images of R. sherardii here.

We also found the hybrid between R. canina (common dog-rose) and R. micrantha (small-flowered sweet-briar) (R. x toddiae), which seems to be the first record for VC23 since 1930. There were also R. canina hybrids involving R. obtusifolia and R. tomentosa, which are quite widespread, as well as R. obtusifolia itself, which seems to be a more local plant. Other unusual hedgerow things included a big specimen of Salix cinerea subsp. cinerea, quite an uncommon plant in Oxon.

Oli Pescott and I spent an afternoon looking at roses around Hills Watlington, Pyrton and Shirburn on the Chiltern escarpment, another good area for roses (I blogged a couple of years ago about the rich rose flora at Aston Rowant). One of the most characteristic species is the downland rose R. rubiginosa (sweet-briar), which is quite uncommon as a native plant but is widely planted in hedgerows. With its strong apple smell, big hips with forward-pointing sepals and fiercely-armed stems it is one of the more straightforward species to identify. Oli and I also found a number of bushes at Watlington and Pyrton that at first looked like R. micrantha but that on closer inspection had a few small slender prickles (acicles) toward the ends of the flowering branches and irregularly-sized hips — these were the hybrid with R. rubiginosa. This was only recently found in Oxon, from Sydlings Copse, but these new finds suggest it may be more widespread.

Roses aren't all about hybrids, though they are certainly very common, and Oli and I saw a fine bush of R. tomentosa (harsh downy-rose) at the edge of Shirburn Wood. Recording for Atlas 2020 seems to have shown that this species is more common than previously indicated but that it is largely confined to the Chilterns, downy roses in the rest of the county being hybrids. We also had time to pay homage to the nationally scarce R. agrestis (small-leaved sweet-briar) at Pyrton Hill, which was rediscovered in the county in 2016.

Crataegus x subsphaerica at Watlington Hill (note the forward- directed sepals)
I have written a few times this year about about non-native shrubs that look similar to native species. So far, however, I have not introduced the non-native hawthorns. This was mainly because I hadn't seen many examples in Oxon, but this autumn I have seen quite a lot, and I encourage others to have a look while these things are at their most conspicuous. There are two taxa to look out for, Crataegus rhipidophylla (large-sepalled hawthorn) and its hybrid with C. monogyna which is called C. x subsphaerica and is the more commonly planted taxon (whether we also have the hybrid with C. laevigata I don't know). I have seen bushes of C. x subsphaerica that are pretty old so this taxon is likely to have been with us for a long time — there seems to be a lot of introgression with C. monogyna, which must explain why these things have been over-looked. Some bushes I have found can only have arisen from bird-sown seeds, so it may be widespread and not just confined to planted hedgerows.

As you will have guessed, the conspicuous features are the haws, which are larger than usual and the sepals stick up from the fruit. The haws are often a brighter shade of red than C. monogyna and more square-shaped. If you look at haws of C. monogyna you will see that the sepals are reflexed so that they lie against the haw and the sepals are short triangles with blunt tips — if you see a hawthorn with some haws with erect sepals and the sepals longer than wide and verging on acute, then you are probably looking at C. x subsphaerica. The leaves of this hybrid are similar to C. monogyna, though they are heterophyllous, and one can usually find some leaves that are broader toward the base and have more teeth, features of C. rhipidophylla. True C. rhipidophylla has leaves that look like similar to Sorbus torminalis (wild service tree). The descriptions and keys in the books suggest the differences are subtle but really they are quite striking, so don't be deterred!

The photograph to the right gives a good idea of what to look for. David Broughton has also blogged about hawthorns and has some good images — see here.

Tuesday, 13 August 2019

Atlas recording in Sutton

After a pretty ordinary Atlas recording session a fortnight ago, on Sunday we had a return of luck and the big lists of earlier in the season. Expecting again ordinary countryside around Sutton (SP40D), we were rewarded with over 320 taxa, a list that included many interesting native plants but that of course was boosted significantly by garden escapes and other aliens. As last time, I will single out the native look-alike shrubs in the hope that this will generate more records and demonstrate that these things are ubiquitous (last time we were far away in SP42F). Maybe I should put together a key to these things — if you'd find this useful or interesting then leave a comment below and I might consider it!

If you look in the floras and the literature about native look-alikes, you'll see that there is an alien taxon for just about every native hedgerow and woodland shrub in Oxon, and some, like the dogwoods I blogged about last time, have several. This meeting it was the turn of the guelder roses, a commonly planted hedgerow shrub (entirely inappropriately, the native Viburnum opulus being largely a plant of damp woods) and of which Sell and Murrell describe two non-native forms of the native species and two similar alien species. My practice had been to lazily assume that planted things were at least the native species, if perhaps cultivars, but confronted with strange-looking plants in the Sutton area I had to revisit this assumption. The native guelder rose is an elegant plant with quite thin yellow-green small and neatly toothed leaves — if you see anything with thicker or darker or larger leaves with strange shapes then consider V. sargentii (Asian guleder-rose) and V. trilobum (American guelder-rose). I think we had both on Sunday, new to the county but doubtless overlooked elsewhere. V. trilobum has odd-looking thick-stalked glands on the petioles (I had never even noticed that guelder roses had glands!) and the leaves on the upper parts of branches have the middle lobes longer than wide. V. sargentii is similar to V. opulus with sessile glands and the middle leaf lobes as long as wide or less, but the leaves are thicker and darker and less toothed (some other differences are also described in Stace and Sell and Murrell).

Continuing with aliens, but aliens we botanists are prepared to tolerate and even admire, we also had a good variety of arable weeds. A fallow field sported no fewer than five species of Chenopodium, with the common C. album (fat-hen) and C. polyspermum (many-seeded goosefoot), the less common C. rubrum (red goosefoot) and the quite scarce C. ficifolium (fig-leaved goosefoot) and C. hybridum (maple-leaved goosefoot). We also had Euphorbia exigua (dwarf spurge), both species of Kickia (fluellens) and the fairly rare Polygonum rurivagum (cornfield knotgrass). I wouldn't be surprised if the latter were a little under-recorded — look out for its eye-catching dark pink tepals and narrow leaves (sorry for not taking a photo).

We did quite well for aquatic plants too. A new pond had Potamogeton crispus (curled pondweed) and P. berchtoldii (small pondweed), and the aquatic liverwort Riccia fluitans which I had never seen in Oxon. Other waterbodies turned up Zannichelia palustris (horned pondweed) and four species of Lemna (duckweeds).

I can't touch on aquatic plants without announcing Judy Webb's excellent pondweed find last year, and which I visited last week because I couldn't quite believe it. I shall deliberately not reveal the exact location of the site, but it would be hard to believe that just about any location in Oxfordshire would be suitable for Potamogeton polygonifolius (bog pondweed) these days. A plant of acid waterbodies and wetlands, it was known once-upon-a-time from Shotover Hill and a small number of other sites with the acid geology that is rare in the county, but had not been seen for decades. Yet there it was, growing in a former limestone quarry with plants of mineral-rich wetlands, like Schoenoplectus tabernaemontanii (grey clubrush) and the moss Campylium stellatum. The national pondweed referee Chris Preston was sensibly circumspect in not confirming the identification from my photographs, but I am happy to announce it now and possibly be proven wrong!

All of the above shows how dynamic our flora is, perhaps a theme of many of my posts on this blog. With people constantly disturbing and changing the environment and many plants good at dispersal and able to take advantage of this (naturally or because we find them attractive or otherwise useful), it is important and fascinating to record these changes and underscores the value of projects like Atlas 2020. So, please keep those records coming!

Tuesday, 30 July 2019

Recording at Glympton

A highlight of the BSBI ASM, Polygala amarella (dwarf milkwort)
It has been over a month since I last blogged and amazingly that was the last time I organised a meeting and did any serious recording in Oxfordshire! I have been botanizing, of course, with a highlight being the BSBI's Annual Summer Meeting which you can read about on the News and Views blog, including posts from yours truly. It might not have contributed to Atlas 2020 in Oxfordshire but it was awfully fun and will have made a big difference to Mid-West Yorkshire which needs records more than we do!

Anyway, this last Sunday I finally managed to find some time in the diary for a recording meeting, and I met up with three other locals at Kiddington. Just in time I had been reminded by Sally Abbey that her recording group had already been there this season, so rather than repeat their work we recorded a tetrad to the east of Kiddington, taking in the lanes, farmland and woodland of Glympton (SP42G). It was a fairly ordinary square without the many lovely highlights of previous meetings this season, but we hit the target of 200 taxa that makes me feel like it was worth going out. A few odd things were found, mostly plants that are likely under-recorded.

One such was the hybrid bindweed Calystegia sepium x silvatica (=C. x lucana), which I am not sure I have ever noticed before. Apparently it is a variable hybrid, but our plants had large flowers like C. silvatica (large bindweed) but with the bracts below the flowers only slightly overlapping and not pouched (as they would be in C. silvatica), and the leaves small, intermediate in shape between C. sepium (hedge bindweed) and C. silvatica (the latter has a broad sinus with a truncate base, the former a narrow sinus with an acute base, as illustrated in Polland and Clement). Another odd plant was Bromus commutatus var. pubens, which looks all the world like the usual meadow brome (var. commutatus) but has shortly pubescent spikelets. As I have described in previous posts, B. commutatus is likely a common cereal weed in Oxon but is significantly under-recorded, probably because botanists think of it as a plant of meadows.

Finally, something must be said about the hedges in the Glympton area, as they were the worst I have seen in Oxon for in-filling and re-planting with alien shrubs sourced from nurseries that should know better. Mile upon mile was full of non-native dogwood and spindle and questionable field maple and hawthorn, presumably on land belonging to the same estate. The dogwood which was the main component of many hedges was a great beast with enormous leaves — I think it was Cornus koenigii (Asian dogwood), a first for the county, rather than the more usual C. sanguinea subsp. australis from south-east Europe and which also often has large leaves. It'd be marvelous if other recorders could be mindful of alien shrubs in hedges and send me records. Planting these shrubs for housing, roads and other developments as well as countryside hedges has become very common and could come to affect our native scrub vegetation, so we need the records to understand potential future change. To encourage records, here's a key to Cornus taken from Sell and Murrell Volume 3.

1. Hairs on underside of leaves mostly curved upwards and basifixed * 2
1. Hairs on underside of leaves mostly adpressed and medifixed ** 3
2. Leaves 4-9 x 2-6cm C. sanguinea subsp. sanguinea
2. Leaves 5-13 x 2.5-7.0cm C. koenigii
3. Leaves with 2–4 pairs of veins; drupes black C. sanguinea subsp. australis
3. Leaves with 4–7 pairs of veins; drupes white or bluish *** 4
4. Twigs bright yellow or bright red in autumn and winter 5
4. Twigs becoming dark brownish-red in autumn 6
5. Twigs becoming bright yellow in autumn and winter C. alba var. flaviramea
5. Twigs becoming bright red in autumn and winter C. alba var. sibirica
6. Plant not stoloniferous; leaves 5–15 × 3–10 cm C. alba var. alba
6. Plant stoloniferous; leaves 4–9 × 2.5–6.0 cm C. sericea

* Bend the top of the leaf over your finger and hold it up to the light - you will see the hairs sticking up. Under a lens the hairs look like they have one arm, or if there appear to be two it is two hairs arising from the same point rather than a single medifixed hair.
** Bend the top of the leaf over your finger and hold it up to the light - you will see no or few hairs. Under a lens the hairs look like they have two arms, with both mostly pressed against the leaf.
*** The two remaining species look very different from the previous three and populations are usually very obviously of horticulutral origin, e.g. landscape plantings, garden rubbish. C. sericea can be invasive of damp woodland.

Thursday, 20 June 2019

Rousham and Oxford Canal

Equisetum x litorale with the tall wide stems of E. fluviatile and whorled filiform branches of E. arvense. O.L. Pescott.
Another haul of excellent records from this weekend, when we were out botanising again in the north of the county. This time we returned to the Cherwell valley and Oxford canal in SP42, where a few meetings were held back in 2017. We met at the church on the Rousham estate, the plan being to quickly look round the churchyard and then head east to fill in a blank square (SP42W) along the canal. However, having parked in a silly place and been confronted by the farm manager, we were very kindly invited to some unplanned botanising of private parts of the estate — how could we resist? Although in the opposite direction and a different tetrad to that planned, it turned up some good wetland plants, including
Dactylorhiza praetermissa
(southern marsh-orchid) and the diminutive pondweeds
Potamogeton pusillus
(small pondweed) and
Zannichellia palustris
(horned pondweed). We also found the hybrid horsetail
Equisetum arvense x fluviatile (=E. x litorale)
(shore horsetail), which as far as I know hasn't been recorded in the county since 1982.

Having bumped up the tetrad records from Rousham (SP42S) and nearby (SP42R), we marched off to Lower Heyford to pick up the canal. Passing through the station (SP42X) we came upon an acquaintance from a previous meeting in the Cherwell valley, another hybrid, the dock
Rumex conglomeratus x obtusifolius (=R. x abortivus)
. The dense widely branched leafy infloresence was eye-catching and the tepals were intermediate in shape. Not a beautiful plant, but attractive in a Rumex sort of way. Surely under-recorded, this is one to look out along our river floodplains.
The Oxford Canal was productive for a range of common wetland plants. Although churned up by boats, the vegetation is less eutrophic than most of our rivers, with plants such as
Carex paniculata
(greater tussock sedge) common along the canal. Wet woodland and damp grassland by the canal provided more
C. pseudocyperus
(cypress sedge) and hundreds of
Dactylorhiza fuchsii
(common spotted-orchid). We had more hybrids, with the willow
Salix caprea x viminalis (=S. x smithiana)
and the woundwort
Stachys x ambigua
. Great to find the latter again this season after we had it at South Newington in May — with very few recent records could it be under-recorded?

The highlight from the canal was
Potamogeton lucens
(shining pondweed), growing in quite a large colony with the much commoner
P. pectinatus
(fennel-leaved pondweed). Always exciting to find a good Potamogeton and catch a glimmer of the former glory of our waterways. Thanks to Oli (pictured left) for being well-equipped with homemade grapnel.

By the end of the meeting I think all our legs were feeling tired, having walked back and forth through five tetrads. With our efforts divided we didn't get the impressive tetrad totals of previous meetings but we gathered over 500 records. Having seen more than 330 taxa the plants were certainly worth the mileage.