When growing in a seepage on a crag in the uplands, R. aquaticum is in classic habitat. Its name suggests it is an aquatic species but in fact it rarely grows in rivers or other places where it may be submerged.
It has a particular look in the field, usually forming flattish, dark green, densely packed pendent patches on vertical or sloping rock. Its stiff-looking leaves are narrowly obtuse and have no trace of a hair-point. Look closely at the leaf base and you’ll see that the nerve is often red-tinged.
Its leaf shape most resembles R. obtusum (form without hair-points) although that species is olive-green to yellow, and shuns the kind of wet places favoured by R. aquaticum. The growth form of the two species is also different – R. aquaticum is little-branched whereas R. obtusum often has numerous short stubby branches.Read the Field Guide account