Oxfordshire: Oxford Centre & Port Meadow

223 July 2012
Length: All day                A good town centre map is adequate for this walk

We began in the High Street, going south along the narrow lanes going to the old roads of Blue Boar Street, Bear Lane and Merton Street.  The old college walls along these were explored in our walk of 12 April and most of the species recorded then were still evident.  In addition to that list we saw Oxford ragwort Senecio squalidus, polypody Polypodium vulgare, maidenhair spleenwort Asplenium trichomanes, red valerian Centranthus ruber, Canadian fleabane Conyza canadensis, bristly oxtongue Picris echioides, nipplewort Lapsana communis, buckshorn plantain Plantago coronopus and Welsh poppy Meconopsis cambrica.  A hawkweed was also frequent, with sticky glandular hairs and few stem-leaves, which we identified as Hieracium amplexicaule or “sticky hawkweed”. 

Hieracium amplexicaule

Leaf-mines on many of these were caused by the agromyzid fly Chromatomyia atricornis (actually a combination of two species that are difficult to separate).  At the base of some walls there was also fern-grass Catapodium rigidum and ratstail fescue Vulpia myuros. 

Fern-grass

The pavements were also enlivened by the miniature exotic “palm-trees” of common liverwort Marchantia polymorpha ssp ruderalis.

Common liverwort

We returned to the High Street and went east to the Botanic Garden.  Opposite Magdalen College, Rose Lane travels along the side of the gardens.  The Hieracium scotostictum (leaves dark-splodged like maculatum but with no or only one stem-leaf) that we had seen here only in leaf before was now in flower and seed, while the rue-leaved saxifrage was very brown indeed.  They were now joined by purple toadflax Linaria purpurea and, on the wall-top, by flattened meadow-grass Poa compressa.

          We then revisited the gardens, which always have something of interest throughout the year, and not always deliberately planted. 

Oxford Botanic Garden

We noticed the Mediterranean rue Ruta graveolens was a popular nectaring plant among the bees, and might be a good addition to a garden, although if touched in sunlight it is prone to cause blisters.  Nearby a small tree of Sargent’s rowan Sorbus sargentiana contained a large bunch of berried mistletoe Viscum album unusually at eye-level, very convenient for a closer look than one can usually get. 

Mistletoe on Sargent’s rowan

We revisited the true service tree mentioned in our April blog and now it was fruiting quite prolifically, although these fruits, like miniature pears (hence its other name of “Whitty pear”), were as yet still green. 

True service with green fruit

It was also now in leaf so that one could see the great similarity to our native rowan, which makes the tree difficult to spot in the wild if (as is usually the case) it is not fruiting.

True service leaves

Two exotic broomrapes have been recorded from the gardens, one parasitic on barberry and the other on butterbur (see the “Flora of Oxfordshire” by John Killick, Roy Perry and Stan Woodell), but we could not find either of those host plants growing there today.  There was plenty of ivy broomrape Orobanche hederae.

Ivy broomrape

There were also a few intriguing spikes of broomrape on a plant of sea-holly Eryngium maritimum, which seemed to match those of the distinct yellowish variety of common broomrape Orobanche minor that is found on the same plant at Sandwich Bay in Kent (which has in the past been wrongly identified with the Mediterranean Orobanche amethystea, a parasite of Eryngium species!). 

Broomrape on sea holly

It is possible that the gardens obtained their plants of sea-holly from Kent and thus unwittingly introduced the broomrape with them, although some argue that common broomrape assumes different forms according to its host, whose chemical make-up may affect colouring and form of its parasites.  Ivy broomrape has itself often been considered as just a form of common broomrape rather than a separate species.

          A less welcome accident in the gardens is small balsam Impatiens parviflora, plants of which were noticeable in many different beds.  Its explosive seed-pods make it good at spreading itself and once present is difficult to eradicate.  We have noticed that it is an increasing problem in many native woodlands.

          On our last exploration of Oxford in April we looked unsuccessfully for ladder brake Pteris vittata on the outside walls of the greenhouses.  This time we did find a very young specimen among the maidenhair fern Adiantum capillus-veneris on one of the walls. 

Ladder brake on greenhouse wall

Nearby was a lot of mind-your-own-business and, in the cultivated borders, a delicate lilac sorrel with distinctive narrowly-bilobed leaflets was coming up everywhere.  We identified this later as Oxalis livida, using the useful Pacific Bulb Society website.  It comes from South Africa.

Mind-your-own-business on greenhouse wall

Oxalis livida

The River Cherwell comes close to the greenhouses and on the stone banks sticky hawkweed was again in evidence.  There was also much hawkweed on the garden walls, but too high to reach to identify, but certainly Hieracium amplexicaule has been recorded from those walls.

Sticky hawkweed by the Cherwell (with maidenhair spleenwort)

As usual we could not resist another look inside the glasshouses to see what was in flower.  This included an epiphytic orchid Encyclia fragrans from Brazil, apparently the most abundant orchid in the central Amazon. 

Encyclia fragrans

Even more impressive, however, were the hanging bunches of the incredible turquoise flowers of the jade vine Strongylodon macrobotrys from the Phillipines.  The garden’s website was excited about the flowering of this vine, which it does not do every year.  The vine stretches across the whole roof of the Lily House and it is difficult to believe the flower spikes are not artificial plastic ones, so unusual is the colour in nature.

Jade vine

We finally visited the tropical pool with various water-plants, like the spectacular Victoria lily and Nymphaea mexicana water-lilies.

Tropical water-plants

Leaving the garden we backtracked a little to go north on Longwall Street by the side of Magdalen College.  Although this street is indeed bordered by a long wall, the latter is immaculately cleaned and bears no plants at all.  However, it is the direct route to StCross Church, where the old lower churchyard is maintained by volunteers as a wildflower reserve.  We found them there today repairing a wall at the bottom.  There are meadow and hedgerow cranesbills Geranium pratense and G. pyrenaicum to be found here, yellow rattle Rhinanthus minor, and, at the far SE corner, several large clumps of deadly nightshade Atropa belladonna, perhaps appropriate to a graveyard. 

Meadow cranesbill, StCross Cemetery

Deadly nightshade, StCross Cemetery

The flowery long grass attracted many butterflies.  By the entrance gate (which is just before the new cemetery) we found creeping bellflower Campanula rapunculoides, a garden escape.

          We retraced our steps a short way to Holywell Street going off to the west.  We followed this across Parks Road, which at one time was noted for such an abundance of escaped Inchnadamph rampion Phyteuma scheuchzeri on its walls that it gained the local name of “Oxford rampion”.  Unfortunately a session of over-exuberant wall-cleaning in 1993 completely wiped out the colony.  A single plant had also been seen near the Martyr’s Memorial at St Giles, to which we eventually came, but, not unsurprisingly, this was no longer to be found.  From here we continued west along Beaumont Street.  The Ashmolean Museum along here has a rooftop restaurant and provided a respite for lunch on a very warm day.

          Continuing along Beaumont Street to the end we turned south and then west along Hythe Bridge Street.  This crosses both the Oxford Canal and a branch of the Thames, and a footpath descends to the towpath along the narrow length of land separating the two.  Near the bridge were common skullcap Scutellaria galericulata and gypsywort Lycopus europaeus growing on walls beside the water.  Banks of the river had the expected plants like meadowsweet Filipendula ulmaria, purple loosestrife Lythrum salicaria, water dock Rumex hydrolapathum, water figwort Scrophularia auriculata and hemp agrimony Eupatorium cannabinum, but the path side soon became dominated by the miniature gardens that always seem to be planted where barges moor. 

Barge moorings

The vegetation then became dominated by garden plants like the hybrid Druce’s cranesbill Geranium x oxonianum (whose specific name apparently refers to Oxford) and its parents, pencilled and French cranesbill G. endressii and G. versicolor, along with that increasingly frequent escape fox and cubs Pilosella aurantiaca, and native wall barley Hordeum murinum.   

Pencilled cranesbill

House holly-fern Cyrtonium falcatum was also established, although it could hardly be judged as really wild.  A bridge at Isis Lock had rustyback fern Ceterach officinarum growing on it in plenty.  In the water here we saw the conspicuous red fins of roach Rutilus rutilus.

          We left the path at the Walton Well Road bridge and took the road west over the railway line, after which we took a footpath on the right going north between a stream and the railway, passing common valerian Valeriana officinalis, water-plantain Alisma plantago-aquatica and false fox-sedge Carex otrubae.  This path eventually runs into a track running west into Port Meadow.  On steps going up to this track we saw knotted hedge-parsley Torilis nodosa, a scarce plant in Oxfordshire.  As we entered Port Meadow, common land divided among many owners in the old tradition, the ground became very marshy.  Tubular water-dropwort Oenanthe fistulosa was everywhere, despite having become generally uncommon with the disappearance of most of the old water-meadows. 

Tubular water-dropwort

Its frequency may have been enhanced this year by the persistent rain from April to late July, which had made Port Meadow much damper than usual.  In fact a large area was still flooded around the very low prominence known as Round Hill, as it would be generally only in the winter months. 

Port Meadow flooded

This frustrated our plans to search for the very rare creeping marshwort Apium repens at its only remaining site, as we remembered having found it close to Round Hill in damp hollows, now under a foot of water.  We hope that this summer inundation does not damage its chances of survival – perhaps it may even help it spread by making the meadow wetter, despite the fact that this year it will have had no chance to flower and seed.  It has to be carefully distinguished from dwarf forms of fool’s watercress Apium nodiflorum, which is common here, by observing the rarer plant’s multiple lower bracts, longer stalks to the flower-heads, broader fruits and rooting at every node.

Creeping marshwort taken in a previous year

(we were hoping to get a better picture this time!)

While we could not search for the marshwort, we could at least observe large flocks of little egrets, grey-lag geese and black-headed gulls enjoying the water and obviously finding plenty on which to feed.  Also abundant were dragonflies, particularly black-tailed skimmers. 

Black-tailed skimmer

As far as we could search the very marshy ground we did find celery-leaved buttercup Ranunculus sceleratus, water forgetmenotMyosotis scorpioides, creeping yellow-cress Rorippa sylvestris and amphibious bistort Persicaria amphibia.

Creeping yellow-cress

Amphibious bistort

We had to abandon our plans to search the Meadow further and returned to the south end and the bridge over the Thames or Isis that runs along the meadow’s west side (chicory Cichorium intybus growing here) and walk north along the bank to Godstow.  It was pleasing to see a great crested grebe here, but the path-sides and the river banks are heavily grazed and used by people, so there were no interesting plants along the way.

Barges in Thames and flooded Port Meadow beyond

Thames near Godstow

This made it a tedious mile and a quarter to get to the ruins of the old nunnery at Godstow.  The target plant here was birthwort Aristolochia clematitis, a medicinal plant grown by the nuns, who presumably, going by its name, acted as midwives for surrounding villages.  The plant survived here in good numbers from medieval times until at least the 1990s, when we found it in plenty in 1994 along a ditch travelling west from the nunnery.  Unfortunately this area is now heavily grazed and the site where we had seen the plant was overgrown with shrubs.  We could not find a single specimen, a sad reflection of our times when such rarities can be so neglected and allowed to disappear in just a few years after centuries of survival.  This made the walk back even more tedious!  There is now little point in making the trek to Godstow (the remains of the nunnery in themselves being very plain) and the walk can best be finished at Port Meadow, from where there are many ways back east over the canal to Oxford.