Immortalised as ‘car-park moss’ by Dr Mark Hill, this denizen of often scruffy places is easily missed by eager bryologists rushing off in search of more appealing habitat. But those prepared to get down on their knees on tracks, gateways and gravelly car parks in the lowlands are likely to find this moss. It’s usually straightforward to recognise it as a Brachythecium but the trick is to separate it from the ubiquitous and very variable B. rutabulum and, to a lesser degree, B. albicans. The first thing to check is the leaf apex – in B. mildeanum it is long and wispy, more so than B. rutabulum. Under the microscope, entire leaf margins confirm it cannot be that species.
B. albicans seems to be increasing inland, and confusingly it can be found in the same places as B. mildeanum. When the plants are trampled, or otherwise prostrate, they can be very similar to little-branched stems of B. mildeanum. Check the alar cells under a compound microscope – you’ll see those of B. mildeanum are rectangular and not much differentiated from cells above. Alar cells of B. albicans are quadrate and form a triangular group that is clearly differentiated from neighbouring cells. Unfortunately both species have leaves with a long wispy tip, so leaf shape doesn’t help much.
B. mildeanum can grow in surprising habitats – arable fields, pool margins and dune slacks to name a few, but it is always restricted to base-rich places.Read the Field Guide account