A quick look at Sanionia uncinata will leave you in no doubt at all that it is one of the so-called ‘hook-mosses’, pleurocarps with leaves that are turned to one side to a significant degree at the stem and branch tips if not elsewhere.
This group includes many different species and has a reputation for being difficult. Fortunately, however, S. uncinata, despite being morphologically variable and catholic in habitat preference, is straightforward to pick out from the rest of the hook-mosses.
Look closely at its long, curved stem leaves with a x 20 lens. You’ll see that they are strongly plicate (most obviously when plants are dry). Of potential hook-moss lookalike species, only Palustriella species and the rare Tomentypnum nitens are also strongly plicate, whilst Hamatocaulis vernicosus has weakly plicate leaves. All of the others, as well as Hypnum species, lack plicae.
Habitat can provide some useful clues too. S. uncinata is found in a wide range of habitats, but a plicate-leaved hook-moss in a relatively dry habitat, such as grassland, on rock or on the bark of shrubs and trees can only be this species (or S. orthothecioides, a rare Scottish species). Palustriella spp., T. nitens and H. vernicosus are all species of consistently wet places.Read the Field Guide account