This habitat is of interest right through the year and has the advantage of being easy to examine from the bank or tow-path. It is from April, however that it becomes more interesting. Here and there in the more open places, you will find dense clusters of pale pink flowers growing directly out of the bare ground. These belong to Butterbur, a plant related to Dandelions and Daisies. As summer approaches, the flowering stalks elongate, and it is only then that the leaves appear, looking like some kind of giant rhubarb, and casting shaows so dark that little except nettle can grow beneath. Butterbur is most often found on the banks of rivers that are prone to flooding, thriving in places where alluvial, nutrient-rich silt has been washed down and deposited.
On sunny days in May, you will spot a whit butterfly with vivid patches of orange on its wings, flying from flower to flower. This is the male Orange Tip Butterfly. Once you find one you will see many others in the same area, but the females which lack the orange markings will be less obvious. Both sexes have an attractive pattern of green and white markings on the underwings. If you let the butterflies settle you will see this quite clearly. The females spend a good deal of time landing on the flowerheads of Cuckoo Flower or Lady’s Smock a plant about a foot high with four pale pink or white flowers, each with four petals. She may well be laying her eggs on the flowers because this plant is the principal food for the caterpillars of this particular species. The eggs can be seen adhering to the stalks of the individual flowers and are yellow in colour when first laid.
As the tiny caterpillars within the eggs develop, the egg itself darkens. Later in the season you may find the caterpillars feeding on the leaves.
As you move along the banks, you will occasionally come upon large colonies of Yellow Flag or Yellow Iris. This is a close relation of our garden Irises but the flowers do not last as well. If you look at the strong flat leaves you may notice that large numbers of snails are congregating on their surfaces. These are snails of the genus Succinea, a group which contains species that are, strictly speaking, neither land nor water snails. These seem to spend all their time well out of the water, but never venture too far away from aquatic habitats.
In some places you may notice a large yellow-flowered plant with five petals, looking a little like a buttercup, but with roundish undivided leaves. It is, indeed a relation of the buttercup and is called Marsh Marigold or King Cup, and can often be found in marshy fields. If you are out walking in mid-summer you will find that the petals have fallen and the plant is now producing large numbers of strange pointed fruits.
Other plants to look out fot in this habitat are Reed-Mace (sometime called bulrush), with its huge cigar-shaped heads, Meadow-Sweet which has dense sprays of fragrant small cream-coloured flowers, and two plants with magenta-pink flowers, Purple Loosestrife and Hairy Willow Herb. The Willow-Herb looks like a giant version of our garden weed Willow Herbs, but as its name suggests it is covered with a coating of soft down. All these plants are tall-growing species with the exception of the Marsh Marigold and are not perturbed by occasional fluctuations in the water level. Some indeed, especially the Willow-Herb can grow in apparently unsuitable ground, because their strong rooting system can get down to water that may be some distance underground.