Ephemeral mosses

I found some small ephemeral bryophytes on a reservoir bank on the weekend. The options were: Pseudephemerum, Ephemerum, Archidium and Pleuridium. I found the key to separate these not that great so have put a few notes here. Pleuridium stands out from the others by having a wide base to the leaf sharply narrowing to a mostly long needle like leaf. Archidium should have non fertile shoots with short sharply pointed leaves, quite distinctive when familiar with. This leaves separating Pseudephmerum and Ephemerum. Pseudephemerum has costate and untoothed leaves whereas the most common Ephemerum (minutissimum) has dentate leaves with no costa. Some of the more uncommon Ephemerum are costate and without maginal teeth. Perhaps only E.recurvifolium with its oblique apiculus of the capsule can be done in the field. Separating the rest may depend on the amount of magnification you have as these plants are tiny. Ephemerum sessile for example can be separated from P.nitidum by spore size; 20-32µm in P.nitidum and 60-80µm in E.sessile. The leaves look longer and thinner on E.sessile compared to P.nitidum so I suspect familiarity with these groups could be useful in the field.

Pseudephemerum nitidum

Ephemerum minutissimum showing the dentate leaf