When the 26 August meeting of the Sussex Botanical Recording Society was planned, I’m sure most people would have anticipated being able to spend a nice sunny day on the Levels studying aquatic plants. However, in reality the most noticeable aquatic component of the field meeting was that falling from on high, sometimes in a cycle of pouring and stopping in quick succession.
I was fairly soaked just while waiting in the car park at Chilley Farm, and Plan B quickly rolled into action. The walk leader, Jane Birch, lives nearby, so we de-camped to her kitchen for the morning with various bagfuls of vegetation to pour over.
Jane has been surveying the ditches of Pevensey Levels for several years and showed us several of the less common aquatic species, which we may not have seen before. Keying out the Potamogeton species is certainly challenging, and there was much debate and discussion over particular samples; one particular example proved very stubborn, even with a huge heap of different books, and will have to be sent off for further study.
Still, the large and striking Potamogeton lucens (Shining Pondweed) was relatively easy to key out, especially after Jane had told us what it was, and the rather rare Potamogeton acutifolius (Sharp-leaved Pondweed) was also distinctive, with its abruptly tapering leaves and flat stem.
Another first for me was being shown a stonewort, in this case Chara vulgaris (Common Stonewort), which is one of the freshwater green algae in the division Charophyta. These are taxonomically-interesting plants, being separate from the green seaweeds and also from the mosses and liverworts and other terrestrial plants. They are in the process of major taxonomic revision, and the groupings (and names) may well look somewhat different in a few years. Like many of the group, Chara vulgaris had an odd odour.
After lunch the rain had eased off a bit so we were keen to get out into the field so returned to Chilley Farm and walked across the fields, where we saw some Trifolium fragiferum (Strawberry Clover), which was another one that was new for me.
On reaching the drainage ditches there was a good array of plants to see, as well as hundreds of the micro-moth Cataclysta lemnata (Small China-mark). We also had the opportunity to compare Oenanthe aquatica (Fine-leaved Water-dropwort), Oenanthe fistulosa (Tubular Water-dropwort), and Oenanthe lachenalii (Parsley Water-dropwort). Other species included Mentha aquatica (Water Mint), Ranunculus sceleratus (Celery-leaved Buttercup), and the smallest flowering plant in the world, Wolffia arrhiza (Rootless Duckweed). The grapnels pulled out more Potamogeton acutifolius allowing us to see it fresh from its normal habitat, and we could also see some Hottonia palustris (Featherfoil) in the shallow water on the edges of some ditches.
Finally a couple of non-natives were less welcome: Hydrocotyle ranunculoides (Floating Pennywort) and Crassula helmsii (New Zealand Pygmyweed), though mercifully the latter didn’t seem to be completely taking over.