Dr M is potty about Pottiales, partly because it can be a tricky group to deal with, partly because it is a common and widespread group of acrocarps so it is an important order of mosses and partly just because Pottiales is such a great name!
The leaves of Pottiales are variable, in some genera they are tongue-shaped, sometimes with an excurrent nerve/hair point (in Tortula etc), in other genera leaves are ovate or lanceolate (Barbula, Didymodon etc).
If present, the capsule is erect, oval, oblong or sub-cylindrical with sometimes twisted/contorted peristome teeth (Tortula etc). This twisted (but never bitter!) character can be seen with a lens if the capsules are at the right (i.e. mature) stage of development, unripe capsules will not reveal their peristomes to anyone!
Around 800 species world wide. growing on the ground, walls, rocks and tree trunks.
Tortula muralis – This little moss forms neat cushions on walls and similar habitats, extremely common and often associated with Grimmia pulvinata (see Grimmiales post). Tortula muralis is easily recognised by the erect cylindrical capsule (always abundant) and tongue-shaped leaves with white hair points – leaf plus hair point 3-4 mm long. A microscope reveals the recurved leaf margins and the smooth hair point – the related Syntrichia species have rough hair points.
Syntrichia ruralis – Sometimes grows with Tortula muralis but this is a more robust plant, forming irregular cushions, bright golden-green above and reddish brown below. Like Tortula muralis the leaves are recurved but the hair point is rough with small spines – leaf and hair point about 5-6 mm long.
Barbula convoluta – One of the commonest small acrocarps of bare ground and wall tops where it may grow in extensive dense vivid yellow-green mats. The leaves are tiny – less than 1.5 mm long – and there is a blunt leaf tip with short protruding tip. The nerve is NOT excurrent (as it is in the related Barbula unguiculata). There are many other genera of small green acrocarps in similar disturbed ground habitats – check out the delightful names – Pseudocrossidium and Didymodon, for example!.
The featured image at the top of this post shows one of Dr M’s students going potty about Pottiales growing on an ant hill at the Aston Rowant NNR! Wherever there are little green acrocarps there are pretty sure to be Pottiales!