This is black sedge (Carex nigra), also known as common sedge. It grows along the Lambrok tributary either in the shallow water or on the bank and there is a bed of it in the woods just past the wooden bridge.
We think there must be a spring there because the ground is always waterlogged, making it perfect for black sedge, which likes to keep its feet wet. It’s a new species for our list and seems very well established for something we haven’t noticed before. Sedges are flowering plants but because they are wind pollinated they have no need for showy and colourful petals to attract pollinators or the attention of a passing Friend of the park.
Sedges have developed other features instead. Their long-stemmed flowers develop right at the top of the plant above the leaves, and have very light pollen which can be easily blown away by the wind; they have feathery, prominent stigmas to catch wind-blown pollen.
Most sedges are herbaceous perennials. At the end of the growing season, they die right down but all summer they have been storing energy, as starches, in adapted underground stems called rhizomes. In the spring, when the temperature rises, the plant will use this store of energy to begin its re-growth.
The rhizomes enable sedges to reproduce vegetatively as well as sexually. When the plant finds an ideal environment like the marshy patch in the woods, the rhizomes spread away from the original plant in all directions and new growth can begin at any node.
Next time you walk along the footpath between the two ponds on the Lambrok tributary, look into the woods near the little wooden bridge; beyond the cow parsley there is a bed of black sedge.
Another new species growing by the Lambrok tributary: