Drosera rotundifolia
The headwaters of the River Marlais (a tributary of the Cothi) run through the valley. The valley bottom has a series of mires merging into areas of wet heathy pasture dominated by purple moor-grass ("Molinia caerulea") and rich in sedges. In the very wet, flushed mire areas there is an abundance of bog-mosses ("Sphagnum" spp.) with other localized plants such as marsh St John's-wort ("Hypericum elodes"), round-leaved sundew ("Drosera rotundifolia"), common butterwort ("Pinguicula vulgaris"), and bog pondweed ("Potamogeton polygonifolius").