Cololejeunea minutissima Minute Pouncewort

Individual plants of this hyperoceanic leafy liverwort are minute, like some other members of Lejeunaceae, but the dull green colonies made up of clusters of irregularly branched thalli can be seen easily. The tiny leaves are almost circular and differ in shape to the more oval leaves of Microlejeunea ulicina. It is also autoicous and is frequently found with 5-pointed perianths, almost like a minute Phillip's screwdriver head. It is epiphytic on a wide variety of hardwood trees, particularly willow, and is also found occasionally on conifers and Heather (Calluna vulgaris). In The Student's Handbook of British Hepatics (1912), Symers Macvicar described this species as very rare. Nearly 80 years later, Tony Smith also decribed it as rare in The Liverworts of Britain & Ireland (1990) and it was not even listed by Roy Perry in Flora of Glamorgan (1994). But since 1990 it has undergone a spectacular range expansion, particularly in the south and west of Britain and Ireland and it is now a common and widespread epiphyte in south and west Wales. It is widespread and locally abundant in West Glamorgan in both lowland and upland locations and it is now the most common hyperoceanic species in the county. The extent of this rapid range expansion could be compared with that of Colura calyptrifolia, but Cololejeunea minutissima is much more common as an epiphyte in lowland habitats outside the coniferised zones of West Glamorgan where it may be exhibiting a striking and significant response to climate change and cleaner air like many other epiphytes.