Category Archives: Vascular plants

Fly Orchids in the Avon Gorge

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Fly Orchid (Ophrys insectifera) is in flower currently in the Avon Gorge. To see the most accessible plants, head north on the towpath on the west side of the gorge, to an area of rock falls about half a mile north of the Suspension Bridge. I counted 10 plants in flower today by the fence at the bottom of the rocky slopes (see map & photo below). Here they grow in the open, in limestone grassland, but at other sites Fly Orchids occur in woodland.

Fly Orchid is a scarce plant around Bristol. The Avon Gorge is the only site in close proximity to the city: the location I visited on the North Somerset side is the most well-known, although Fly Orchid has also been found occasionally on the Bristol side. Elsewhere in the region, there is a cluster of sites in the Avon valley southeast of Bath, including Browns Folly and Avoncliff. There are several other sites farther south and east of here into Wiltshire and east Somerset, including Cleaves Wood near Wellow, Morgans Hill near Devizes, and a grassy bank on the north side of the A303 near Wincanton. Elsewhere in Somerset, Fly Orchid is only found on cliffs near Blue Anchor. Its stronghold is in the Cotswolds, with around 10 sites in the Stroud area and others southeast of Cheltenham. Although it formerly occurred in the Wye Valley, it is now extinct there.

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Pollination is carried out by male digger wasps of the genus Argogorytes, which are attracted to the flowers by a pheromone; they mistake the flower for a female digger wasp and attempt to mate with it. In doing so, the orchid’s pollen sacs attach to the wasp, and are then transported to the next orchid the wasp visits. The Avon Gorge Fly Orchids are of particular note, as in the past, this process went a little awry and hybridisation occurred with Bee Orchid (Ophrys apifera): when these hybrids were first discovered here, in 1968, they were new to science. Hybrids are not known from the Avon Gorge currently, but they are present at the Wincanton site. Hybridisation has also occurred in Kent with Early Spider Orchid (Ophrys sphegodes).

Lanceolate Spleenwort in Oldbury Court woods

The fern in the photo below is Lanceolate Spleenwort (Asplenium obovatum), a scarce species which is mainly found in coastal locations in southwest England and Wales, but which has a small population in the woods on the Oldbury Court estate (a location sometimes also referred to as “Glen Frome”), where it was first found in 1835.

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There are several features which enable Lanceolate Spleenwort to be told apart from its more common relative Black Spleenwort (Asplenium adiantum-nigrum). To make this easier to follow, I need to introduce a few bits of fern terminology. The stipe of a fern is the main stalk of a fern frond. In most fern species, the frond is divided up: the main segments are called pinnae, and the lobes on each pinna are called pinnules.

Lanceolate Spleenwort has an elongated oval or oblong frond, with the pinnae nearest the base usually shorter than the ones further along, and these are often bent back towards the base of the plant (you can see this on some of the fronds in the photo if you look carefully). By contrast, in Black Spleenwort, these lowest pinnae are usually the longest, giving the frond a triangular shape. On Black Spleenwort the stipe is also usually much longer than on Lanceolate Spleenwort. I’ve included a photo of Black Spleenwort below, taken at a nearby location, and both of these features are obvious. There are other differences visible when you examine the fern close-up: the sori (spore-bearing bodies) on the underside of the leaf of Lanceolate Spleenwort are found only around the edges of the pinnules, whereas in Black Spleenwort they spread in a fan shape from the vein in the centre of the pinnule. Black Spleenwort gets its name from its solidly black stipe, whereas Lanceolate Spleenwort’s stipe is a green colour above, with a dark brown stripe below,

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Lanceolate Spleenwort grows in sheltered fissures and crevices on acidic rocks, although in the warmer far southwest, it is also found on hedgebanks in lanes. The largest British populations are on sea cliffs in Devon, Cornwall and northwest Wales. The Oldbury Court site is the easternmost extant site in Britain for this species, and is isolated from other populations of Lanceolate Spleenwort by many tens of miles. In southwest England it is not found again until Exmoor, and in south Wales, not until the Gower peninsula, although there are old records from Beachley near Chepstow. Its northernmost locations, in Cumbria and southwest Scotland, are also very isolated. Globally its range extends south through France, Spain and Portugal to the Canary Islands, Madeira and the Azores, a distribution-type that is shared by a number of other fern species. Black Spleenwort is nowhere near as fussy, liking all rock types (loads of it grows on the limestone in the Avon Gorge, for example); I have even found it on walls in the city centre, near the Bristol Royal Infirmary and Old Market.

Here is the location of the plant I photographed (and a photo of the outcrop on which it was growing). If you want to visit it yourself, take care as it is on a steep muddy slope, high above the river. The best approach is to head up the zigzag footpath from the weir, and then take a right turn when you reach some railings. However, there are lots of similar-looking outcrops in the valley, from Eastville Park northeast to Winterbourne and it wouldn’t surprise me if some of these had their own mini-populations of Lanceolate Spleenwort too.

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Autumn Ladies-tresses on Bristol Downs

There are a few flowering plants that wait till the end of the summer before flowering, and Autumn Ladies-tresses (Spiranthes spiralis) is one of them, never flowering before August and continuing well into September. This is probably the least conspicuous of the orchids which are found in the Bristol area, typically only reaching about ten centimetres tall. The photos below show the way in which the tiny flowers spiral around the stem, a feature reflected in its scientific name.

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I visited the colony on Bristol Downs today, and counted at least 87 plants – although among these were many which weren’t in full flower yet, which I only noticed when I was on my knees next to plants which were in flower, so as I will have no doubt missed other similar individuals, I’m confident the total population here is well into three figures.

Here’s the location: right next to the circular road which runs around the Downs.

Autumn Ladies-tresses is a plant of very nutrient-poor limestone and chalk grassland. In most locations, sheep do the work of keeping the habitat conditions right; on the Downs, in the absence of sheep, the grassland has to be managed by mowing and raking off the cuttings. On the side of the colony closest to the road, the soil has been badly eroded by runners; fences have been erected to encourage people off of this part of the site, in the hope that it will regenerate.

The Downs as a whole are a bit of a curate’s egg botanically, even if you discount the areas which are formally set aside for sports. Although it is certainly the largest area of limestone grassland around Bristol until you reach the Mendips and Cotswolds, that doesn’t necessarily mean it’s good-quality limestone grassland throughout. Some areas are good – I found a few Harebells (Campanula rotundifolia) growing in another spot today, for example – and the stone workings on the southeast side have some botanical interest, as does the area around the observatory. However, other parts are quite species-poor. With the right management to reduce the nutrient levels, though, the Downs could certainly become a lot richer, and complement their neighbour the Avon Gorge.

Two scarce riverbank plants

Earlier this month, I took a walk along the River Avon from Conham to Hanham. to check out some of the scarce plants which occur locally in riverbank habitats. The highlight was this Greater Dodder (Cuscuta europaea), a parasite of the Common Nettle (Urtica dioica): the upright green stems are those of the nettle, and the red stems twining around them belong to the dodder.

This is a nationally scarce plant, found in only a handful of areas in southern and central  England. Locally, it occurs in two areas. It is found along the River Avon from Bristol upstream to Bath, and again to the east of Bath into western parts of Wiltshire; its other stronghold is along the River Severn (mainly around Gloucester but with an outlying site near Frampton-on-Severn).

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The closely-related Common Dodder (Cuscuta epithymum) also occurs in our area, and is also a scarce plant, despite its name. It is found in heathland and dry grassland and parasitises among other things, species of gorse, heather and thyme. It has smaller flowers, although to be certain of the identity of a dodder specimen, a flower has to be dissected under a microscope, to look at tiny features such as the shape of the minute scales at the base of the inner surface of the flower and the relative length of the sex organs.

Here’s the area where I found the plant photographed above:

Also present in good numbers throughout this section of the Avon was Small Teasel (Dipsacus pilosus), the scarce relative of the ubiquitous Common Teasel (Dipsacus fullonum). In and around Bristol, it is found on the River Avon between Bristol to Bath, on the River Frome in northeast Bristol, on the River Chew, and scattered other localities, often in or on the edge of woodland.

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Green-flowered Helleborines

Ashton Court, a walled estate just to the west of Bristol is famous for hosting the Bristol International Balloon Fiesta, but it has a botanical claim to fame too: the only accessible Green-flowered Helleborines (Epipactis phyllanthes) in the Bristol area grow here, in a dark wooded part of the estate called Clarken Combe, just a short hop over the wall from a layby on the B3128. I paid the site a very quick visit last weekend and was surprised to find many more plants than I’ve seen here previously, although all were still in bud. This weekend, however, several were flowering: mostly each plant had just a single stem, but one plant had a cluster of nine: here is a photo, and a close-up of some of the individual flowers.

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These plants have an interesting history. Originally found in 1985, they were thought to be Narrow-lipped Helleborines (Epipactis leptochila), a scarce species of limestone beechwoods. They were listed as this species in the Flora of the Bristol Region, published in 2000, and this identification remained unchallenged until fairly recently. I paid the site a visit in late summer 2011, not really knowing any more than to look in the woodlands at Clarken Combe, I narrowed my search by looking under beech trees, and eventually found three helleborine plants, but they were past flowering, so I visited again in 2012 with Martyn Hall, who took some photos. Still none the wiser as to the plants’ true identity, I posted these to the orchid thread at Birdforum. Midlands-based orchid expert Sean Cole posted a reply, asking whether I was sure the plants were Narrow-lipped Helleborines, as they looked to him more like Green-flowered. That afternoon, Richard Mielcarek and I went back to Clarken Combe, gave the plants a very close look, and confirmed that, just as Sean thought, they were Green-flowered Helleborines.

Part of the reason for the confusion is that back in the 1980s, knowledge about the variability of the Epipactis helleborines, and which identification features are most reliable, was still developing: nevertheless, the plants had been visited by many knowledgeable botanists since, and so it’s surprising that it took so long for them to be re-identified.

Green-flowered Helleborine occurs in several varieties (forms of characteristic appearance caused by small genetic differences). The Clarken Combe flowers open quite widely, seem to have a clear distinction between the ‘cup’ (hypochile) and the ‘lip’ (epichile) and in some, the lip is bent back under the cup, whereas in others it is not, and then appears quite long and pointy. As I understand it, this points to them being of the variety known as ‘vectensis’, but I’d be interested in views from others with more knowledge of this subject. The pointy lower lip and the fact that the flowers open widely may be one of the reasons why the plants were originally thought to be Narrow-lipped Helleborines. However, the hypochile of Narrow-lipped Helleborine is filled with a sticky dark purplish liquid, not present in the Ashton Court plants, and the lip of Narrow-lipped is even longer and thinner. There are several other features visible with a hand-lens, which Richard and I checked last year to satisfy ourselves that our re-identification was correct.

In a local context, Green-flowered is only marginally less rare than Narrow-lipped. Narrow-lipped’s nearest population is in the woodlands at the top of Cheddar Gorge; Green-flowered occurred in the past on the towpath below Leigh Woods, but has not been seen here for many years, and only occurs at one other site, a private garden near Stowey. Further north, on the Cotswolds, both species have strong populations, and Green-flowered also occurs at several sites in Wiltshire. Nationally, Narrow-lipped is the scarcer of the two, and its populations are in decline, whereas Green-flowered is if anything on the increase.

Here is a map showing the location of the plants. If you visit, please take great care where you put your feet, as some of the plants are quite small. There are differing views among botanists about the levels of secrecy that should surround locations of scarce plants, and in particular orchids. One orchid site on the edge of Bristol suffered from theft of a very rare species this year, so concerns are very valid. Fortunately, I don’t have to make the decision over the Ashton Court plants, as Bristol City Council have publicised them for many years as one of the features of the site (albeit unwittingly as the wrong species).

Upright Spurge in the Wye Valley

Yesterday I paid a visit to Ravensnest Wood in the Wye Valley, to see one of the rarest plants found in this area, Upright Spurge (Euphorbia serratula). As a native species, Upright Spurge is found in Britain only in an area centred on the Wye Valley and the Forest of Dean. It is also naturalised in scattered locations, mainly in southern England. Although a rare plant in Britain, globally, it is found eastwards to central Asia.

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Upright Spurge’s habitat is woodland on limestone, but not the dense dark parts: instead, it is found in the open, and does best on disturbed ground. Newly created forestry tracks and clearings are where it does best, particularly if limestone chippings are laid. Ravensnest wood held 500 plants in 1997, presumably when the access track there was very new. Yesterday I counted a much more modest 17 plants: along much of the track, grassland had become established, crowding the spurge out, and it was only present in areas where there was still very sparse vegetation. Here is a map of the location:

According to Sell and Murrell’s Flora of Great Britain and Ireland, the most authoritative reference work on Britain’s flowering plants, Upright Spurge occurs in only about 24 British localities. The densest concentration is around Tintern and so, predictably, it has acquired the local name “Tintern Spurge”. Other locations in the Wye Valley are spread throughout a 10km-long stretch from about Wynd Cliff in the south to around Whitebrook in the north. In the Forest of Dean, its main concentration is just to the west and north of Lydney. Much further east, it grows in Highnam Woods, just west of Gloucester. West of the Wye Valley, it occurs in Chepstow Park Wood and in Coed Wen Wood, east of Newport (note that the Grid Reference in Trevor Evans’ Flora of Monmouthshire for this last site is incorrect).

Seeds of Upright Spurge can lay dormant in the soil for years, possibly decades, and so if a site becomes overgrown, fresh disturbance can boost the population. At Highnam Woods, the RPSB does just that, using a rotavator, and so the population there is likely to be secure. At other sites, Upright Spurge has declined or even vanished, but could no doubt be encouraged to flower again if similar techniques were applied. How about it, Gwent and Gloucestershire Wildlife Trusts?

Lamplighters Marsh

Last week, I visited one of my favourite Bristol plant sites, Lamplighters Marsh. This is the strip of land between the Avonmouth railway line and the River Avon, from the M5 Avon bridge southeast to the former Lamplighters pub. It’s got a mix of habitats: lots of scrub and tall herb, one of Bristol’s few reedbeds, and areas of sparse vegetation (and the tidal Avon, a interesting site in its own right, is right next door). Here are a few photos of the site:

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Among the star plants here are a large population of Viper’s Bugloss (Echium vulgare) and a small population of Moth Mullein (Verbascum blattaria), both scarce plants in the Bristol area. Viper’s Bugloss occurs in a variety of habitat types in Britain: chalk and limestone grassland, at the coast in sand dunes, on shingle or cliffs, and in disturbed open ground such as that found in disused quarries or railway lines. Although Lamplighters Marsh could be described as coastal, the habitat here is more like the last of these, and in the Bristol area, it is not really a coastal plant, although in some parts of Britain it is exactly that. My visit was on a sunny evening and many bumblebees were visiting the plants.

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Moth Mullein is an introduced plant. It is distinctive among the mulleins in having large flowers, and not being densely hairy or downy like many mullein species. It occurs in both white-flowered and yellow-flowered forms.  It has been recorded at several other sites in Bristol, but is very scarce away from the city.

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