There are a number of aquatic Ranunculus species commonly found in rivers. In chalk streams, like the River Chess, the two species most often encountered are stream water crowfoot (R. penicillatus) and brook water crowfoot (R. peltatus). Brook water crowfoot is a characteristic plant of winterbourne stretches of chalk streams, where flow is only present from spring to summer. Brook water crowfoot is specially adapted to live in these ephemeral reaches where they are able to tolerate long dry periods thanks to their rootball which can resist dry conditions. In contrast, stream water crowfoot is found only in permanently flowing sections where it is an important species in helping to maintain classic chalk stream habitat that is essential for many other species to survive. Stream water crowfoot grows from early spring, reaching its peak in May-June, when its white flowers can be seen in profusion. After flowering, stream water crowfoot begins to die off as flows decline, allowing watercress to become the dominant plant species in the channel.
The presence of water crowfoot in the channel is very important in helping to maintain water levels and a clear gravel bed, which is essential for many species' survival, including trout and mayfly, such as the yellow may dun. Many invertebrates and fish use water crowfoot as a sanctuary and as a source of food. A common problem in chalk streams is over-zealous weed cutting, where it is perceived that water crowfoot is choking the channel. See the habitat loss page for more information.
Lythrum salicaria flowers in spikes from June to August and is abundant in the wet margins of the Chess. This beautiful plant flourishes in areas where bankside is allowed to grow, rather than in overly-manicured areas. A native perennial, Purple loosestrife is a substantial and striking plant.
This tall plant, Eupatorium cannabinum, grows along the banks of the Chess. Its small, pink flowers are attractive to a variety of insect life, including butterflies, moths and bees. Hemp agrimony flowers between July and September.
Myosotis scorpioides is a beautiful plant with small, delicate sky blue flowers with yellow centres. It is a low-growing, marginal plant that flowers all through the summer.
Sparganium erectum is an emergent plant, meaning that it grows out of the water. The highly distinctive, spiky flowers are produced on branches off the stem. This is the most common of the four bur-reed species found in the UK. Plants will flower from July to September, with the fruits ripening in early winter. Unbranched bur-reed provides a habitat for wildfowl roosting, nesting and feeding. It has also been found to provide nesting material for water voles on the Chess.