Wednesday, August 28, 2013

An unusual conglomeration of wildflowers

I've been staying in Bridgnorth this week. Looking north-east from High Town you can see a bare cliff, called, unimaginatively, High Rock. A walk up clearly beckoned. Sadly the weather was somewhat unkind and quite dull the day I went up, so I've sourced a picture of the view online. I followed an easy route from town (here but without the extra loop as it started raining).

High Rock, Bridgnorth, from High Town looking north east. 
By Pam Brophy on Wikipedia and used under a CC BY-SA 2.0 license.

Wildflowers are excellent geologists. Some are so fussy & sophisticated in their habitat requirements that their presence is a pretty good guide to what lies beneath; soil type and geology. Of course, soil type is not the only factor determining where plants can grow and thrive; other factors, physical (climate, topography), biological (competition, shading, herbivory) and historical (agriculture, quarrying) all have a role to play. Wildflowers with similar ecological needs are found growing together in recognisable assemblages. 

On the walk up to High Rock a first clue to underlying geology was this feeble scrambler Ceratocapnos claviculata, climbing corydalis. It's a delicate, pale flowered climber with tendrils. It prefers acid soils and I've seen it on sandstone. The weather was dank and grey, so it looks paler than usual in my picture.

It even grows happily under bracken, clambering up the stems using its tendrils. There are few plants that relish living under the domination of shady bracken (the photo below take in Sandy, Bedfordshire a few years ago). I admire this tenacious little plant.

Perhaps one day archaeologists will marvel at the skills of the creators of this modern rock art near the top of the rock. Mysterious petroglyphs for our descendants to decipher. The friable Bridgnorth sandstone presents few challenges to those determined to leave their mark. Hmmm.

Personally I prefer to see polypody fern (Polypodium spp) on the rocks and it was indeed frequently encountered growing in deep shade, on exposed rocks, under the dense woodland canopy.

After a rather dull and sometimes steep, walk through the woods, it was a relief to reach the top of High Rock and pause to admire the view. My photos are awful so here is the view.

It was a surprise to see a dainty blue flower growing between the rocks. Sheep's bitJasione montana, is a flower I've previously only seen at Dungeness; a plant of impoverished, dry sandy and cliffs.

It's a lovely pale blue and looks like a small devil's bit scabious (a member of the daisy family Asteraceae). It was also called sheep's scabious. But for all that superficial similarity it's actually a bellflower (Campanulaceae).

Growing adjacent, in shade, with tall stems & dull yellow flowers, was ploughman's spikenard, Inula conzya. This is a robust member of the daisy family. I've only ever seen it on well drained soils on calcareous substrates. In fact, I thought it was a calcareous indicator species, so was perplexed to find it on acidic sandstone. Ploughman's spikenard once had some repute as a efficacious wound herb. An old name for the plant was cinnamon root, and the name Spikenard implies an aromatic quality. It was also called great fleabane; its specific epithet, conyza, being derived from the Greek for 'flea'. The powdered root was used as a flea deterrent.

Further exploration revealed yet another tall daisy nearby, also in shade. Goldenrod, Solidago virgaurea (virg-aurea literally meaning 'rod, 'golden') was yet another pleasing find. I've formerly only found goldenrod (our native goldenrod) on Northern rocky mountain streams and crags. It's a plant of free-draining acidic substrates. A sandstone cliff ledge sounds pretty good then. Goldenrod was another ancient wound herb. Solidago derives from Latin soldare, to make whole.

Common calamint (Clinopodium ascendens) is uncommon in the north and I didn't expect it. It's a plant I see on chalk or limestone grassland. It's listed and recorded as being present on High Rock in 1992, in Lockton & Whild's 2005 Rare Plants of Shropshire (pdf here - see page 43). They describe it as 'a plant of dry, calcareous soils in the south of Britain'.

A few steps further on, another unexpected find; wild liquorice or milk vetch, Astragalus glycyphyllos. This is a fairly uncommon plant that I see infrequently; the last time being down my old road in Sandy. It prefers sandy soils. Wild liquorice is also listed in the Rare Plants of Shropshire (p24) and was last recorded on High Rock in 1991. The seed pods are quite funky, liked clawed hands.

And the naked stems even weirder once the pods have dropped off.

On a sandstone crag it was no surprise, and quite a relief, to see heather, Calluna vulgaris growing nearby.

I thought the plants found up on High Rock were an unusual assemblage and not all typical of acidic grassland on sandstone. It's worth a quick gander at the local geology.

The walk up to High Rock (a Locally Important Geological Site) is essentially walking on rocks formed in the Permian. During this time (250-290 MYA) our island was landlocked in supercontinent Pangaea and positioned roughly where the Sahara is today. So hot, dry, desert. Permian rocks are sandstones; Bridgnorth sandstones.

At the very top of High Rock there were exposures of what looked like a conglomerate, in dramatic contrast to the cross-bedded, finer grained sandstones. Googling revealed it to be Kidderminster Conglomerate laid down during the Lower Triassic (251-247 MYA). It sits uncomformably on top of the sandstones; pebbles and debris dumped, higgledy-piggledy, by a powerful flash flood, like a flood in a wadi. The conglomerate contains Carboniferous limestone, marl & quartzite pebbles, so must have an effect on the flora on High Rock and goes some way towards explaining the presence of plants with varied ecological requirements.

It doesn't look much today, just a rugged lump of rough rock, but the Late Permian/Lower Triassic was a time of catastrophic upheaval on Earth. A massive extinction event wiped out 96% of all plants & animals. The cause is still debated; volcanic, comet, climate change. Life on earth almost died out. It took about 10 million years to recover. A sobering thought during our uncertain times when we treat our environment so causally. Nature is a powerful force.

A quick aside from botany. On the scramble back down form the top of the rock, I stopped to photograph this distinctive little red beetle. It was in deep shade and next to a rotten log. 

It turned out to be a fortuitous snap. (Here is a better photo from Hampshire) This smart little chap is Platycis minutus, a net-winged beetle and Nationally Notable (Nb), more likely to be encountered south of The Wash. My tentative identification was confirmed by Caroline Uff, County Recorder for beetles. It was last recorded over 100 years ago and that record is for Tuckhill (on the way to Stourbridge). Well, I am chuffed. But, do I snap photos of dull looking brown beetles, which could be rarer? No I don't. I admit recording bias towards colourful cuteness.