The Marsh Gentian (Gentiana pneumonanthe) is a rare plant in Britain, though can be locally frequent in ideal conditions on damp acid heathland. The main focus of the 5 September meeting of the Sussex Botanical Recording Society was to survey the known populations on Ashdown Forest and (ideally) find new ones.
This striking blue flower has been recorded on the forest since at least 1835, and some populations here had thousands of plants in the 1950s. However, with the reduction in grazing over the forest, Purple Moor-grass (Molinia caerulea) tends to take over and the Gentian has certainly declined.
Ruth Eastwood led the field meeting, focussing primarily on one main site which is still grazed to some extent. The plants don’t like very wet places, but they need damp locations, often associated with Cross-leaved Heath (Erica tetralix) and Dwarf Gorse (Ulex minor).
The first patch of suitable habitat didn’t result in any finds, despite it being a location where Gentians have been found in the past. However, some of the boggy pools did provide some interest too, including what was almost certainly the Raft Spider (Dolomedes fimbriatus).
Finally, on a part of the heath gently falling away to a boggy place we found our first Gentians. Only some 10cm or so tall, the spikes tended to have one, or occasionally two or more, flowers, though because it was cloudy none were fully open. Several groups were found and recorded, though only numbered maybe 40 or 50 plants, one of which was being visited by what we believe is the larva of the Broom Moth (Melanchra pisi).
After lunch we located another of the known spots for the Gentians, though it is now much overgrown, with Molinia dominating, and encroached heavily by Bracken and Gorse (Ulex europaeus). In the small patch of shorter vegetation a tiny handful of Gentians was just about managing to cling on.
There were a few other nice finds in the area too, including Saw-wort (Serratula tinctoria), Bog Bush-crickets (Metrioptera brachyptera) and the rather striking Wasp Spider (Argiope bruennichi). I also got a decent close look at the parasitic Dodder (Cuscuta epithymum) for the first time. Interestingly, there are still tetrads on the forest in which it hasn’t been recorded.
So, on balance, it was nice to see that the Gentians are still growing locally, though they are certainly in decline, and are one of many species on the forest that clearly require local grazing for their continued survival.
 Rich, Tim et al. Flora of Ashdown Forest. 1996. Sussex Botanical Recording Society. Available from: http://www.bsbi.org.uk/Flora_of_Ashdown_Forest.pdf