A very slender, thread-like pleurocarp closely appressed to a stone in a dry, dark, sheltered place – what could it be? If it hasn’t got a narrow, drawn out leaf (possessed by small forms of Amblystegium serpens, also the rarer Serpoleskea confervoides, Platydictya jungermannioides and Conardia compacta) then Heterocladium flaccidum is likely.
H. flaccidum is very similar to the common, larger H. heteropterum but is far more likely to be present in basic habitats. It is the only one of the two that is found on hard limestone, for example.
Did you know that the name Heterocladium alludes to the dimorphic stem and branch leaves of this genus? While this is a reasonably obvious character in the more robust Heterocladium species, this feature is not easy to see in H. flaccidum.Read the Field Guide account