In most parts of the country, this is the most likely Fossombronia you will encounter and plants typically bear mature (black) capsules from September well into winter. Like other common monoicous Fossombronia species with purple rhizoids, it’s always necessary to check the ornamentation of mature spores under a high power microscope to confirm its identity. Plants are, however, usually slightly larger than F. wondraczekii, its commonest relative.
What to do when you come across a tantalising Fossombronia which lacks ripe (black) capsules? Green capsules are immature and spore ornamentation will not be fully developed. However, if young capsules are present, Fossombronia species respond well to home cultivation and they will turn black within a few weeks, under the right conditions. All you need to do is keep your plants moist (but not too wet) on soil or kitchen roll, in a well-illuminated place, such as a windowsill or greenhouse and keep checking them. A petri dish can be useful as the lid will help to prevent the plants drying out. If plants don’t already have immature capsules then they may not go on to develop any in cultivation.Read the Field Guide account