Limestone lovers

Berry Head in South Devon is quickly becoming one of my favourite haunts with its rich botanical landscape and marine wildlife. Last September I blogged about one of its specialities, the White Rock-rose (Helianthemum apenninum), a nationally rare species (see http://nicksnaturenotes.blogspot.co.uk/2011/09/last-white-rock-rose.html). The unusual mix of physical geography and chemistry provided by the Devonian limestone sea cliffs of Berry Head provide conditions for the White Rock-rose shared only by a handful of other sites in the South West. I was visiting it again this weekend with friends and showed off the White Rock-rose amongst other more common plants. Towards the end of the afternoon we wandered up to the remains of the fort in search of summer migrant birds amongst the scrub. Resting my arms on the battlements and enjoying a Whitethroat and possibility of Cirl Buntings, I became curious about a stunted-looking plant which I had almost leant on. Closer inspection revealed what looked like a bonsai version of an umbellifer, a dwarf parsley or carrot plant. My companion with much pleasure eventually identified it as Honewort (Trinia glauca), which is indeed a member of the carrot family and another local limestone specialist. Apparently, in turf closely grazed by rabbits, plants of Honewort grow to no more than a few centimetres tall (BRC, 2012), as was the case with many of the Berry Head plants that we observed.

When I got home I looked at the distribution map on the National Biodiversity Network's Gateway (see http://data.nbn.org.uk/gridMap/gridMap.jsp?allDs=1&srchSpKey=NBNSYS0000003662) and fascinatingly it is found in almost the same isolated areas as the White Rock-rose. These rare fragmented habitats of dry limestone, with short-grazed south facing aspects have created almost identical conditions for such specialists to cling on to their slopes. However their hold is truly precarious, the species being listed as ‘Near Threatened’ (BRC, 2012). The challenge for the Honewort is made more challenging as it is dioecious (having separate male & female plants, requiring cross-pollination) and has poor seed dispersal, most likely reliant on ants (Carvalheiro, et al., 2008).

These two limestone loving species are literally hanging on in Britain, exposed to human disturbance.  This makes it all the more important to value these wonderful wildlife hotspots and for me to take more care where I lean my tired ‘binocular-ed’ arms.

BRC (2012) Online Atlas of the British and Irish flora [online] http://www.brc.ac.uk/plantatlas/index.php?q=plant/trinia-glauca [Accessed 7/5/12]

Carvalheiro, L.G., Barbosa, E.R.M. and Memmott, J.(2008) Pollinator networks, alien species and the conservation of rare plants: Trinia glauca as a case study. Journal of Applied Ecology, 45: 1419–1427

National Biodiversity Network's Gateway  (NBN) (2012) Grid map of records on the Gateway for Honewort (Trinia glauca) [online] http://www.brc.ac.uk/plantatlas/index.php?q=plant/trinia-glauca [Accessed 7/5/12]