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.

Broughton Casttle

The first meeting of June and the fifth of the season was held last weekend at Broughton Castle near Banbury. This site had been recorded previously for Atlas 2020 but we had special permission to botanise the whole park and therefore hoped to refind some of the plants historically recorded but not seen since 2000.

I had particularly hoped that we might find some of the nice aquatic plants that had been recorded from the Castle Moat. As it turned out the moat was a brown soup with very few macrophytes, an unpleasant appearance completed by floating dead freshwater mussels. The Sor Brook was no better, sporting also the invasive non-native aquatic plant

Egeria densa

, the first reported sighting of this plant in Oxon for 35 years. Tributaries of the Sor Brook had some other infamous beasties, with

Fallopia sachalinensis

(giant knotweed) and its giant handkerchief-like leaves and

Heracleum mantegazzianum

(giant hogweed). On a positive, we did find quite a lot of

Ranunculus fluitans

(river watercrowfoot), which was good to see.

Elsewhere in the park plant diversity was quite limited. There was a decent stand of calcareous grassland with plants like

Cirsium acaule

(dwarf thistle),

Koeleria macrantha

(crested hair-grass) and

Helianthemum nummularium

(common rock-rose), but these had all been recorded previously. In all we managed to find about 250 taxa, bumping up the tetrad total to 338 from 252. Not the enormous haul of records of previous meetings, but eminently respectable and goes to show that even in well-recorded tetrads there is always more to find.

Interesting things have been turning up elsewhere in the county this spring. I was contacted independently by Frank Hunt and Andrew Lack after they both found a new population of

Scandix pecten-veneris

(shepherd's-needle) near Sandhills, north-east of Oxford. Frank also found a new population of

Montia fontana

(blinks), surprisingly at the well-botanised North Leigh Common. This time of year always produces some sore heads when the marsh orchids come out, and surveying a meadow in the VC 22 part of modern Oxfordshire Judy Webb and I found what with the help of BSBI Dactylorhiza referee Ian Denholm we determined as a swarm of

D. maculata

(heath spotted orchid),

D. praetermissa

(southern marsh orchid) and their hybrid D. x hallii. The latter was new to VC 22 and the modern county.

Botanising less obviously delightful places for Atlas 2020 near Adderbury, I found

Viola tricolor

(wild pansy) and, along the Oxford Canal,

Lepidium heterophyllum

(Smith's pepperwort). According to the Flora of Oxfordshire the latter has not been seen in the vice county since 1983! Not far away was possible Galium parisiense (wall bedstraw), but I want to check the fruits to be sure. This has not been seen in Oxon before, but was recently found new to Northants (VC 32), in the VC 32 part of Banbury and elsewhere.

The excellent Oxfordshire's Threatened Plants published last year reported that the small annual

Minuartia hybrida

(fine-leaved sandwort) had gone the way of many such plants and was extinct in Oxon. Fortunately not so, as the population known historically from the old chalk pit in Chinnor is still there, found by Paul Stanley back in 2013 and also seen by Oli Pescott, David Roy and myself while recording around Chinnor. The old pit has many other interesting plants, so do go and see this little delight while it is still out.