Tiny fern-moss  (Fissidens exiguus)

As the common name suggests, the tiny fern-moss is very small, measuring between 1.5 and 2.5 mm in size (1). Its identification requires detailed microscopic study, and there are doubts as to its species status (3).

This species was originally identified in North America, and was not accepted to occur in Europe until 1953 (3). It is rare in Britain, occurring in the Weald in East Sussex and Kent, with very isolated populations in Somerset, Powys, south Devon, Warwickshire and Cumbria (1). In Europe, this moss has become extinct in Denmark and Germany (2). If tiny fern-moss is found to be a species, its conservation in Great Britain will be of international importance; the 16 known sites in England represent most of the European population (3).

Inhabits sandstone rock close to the water level, and shallow water in streams and rivers (2).

Mosses, hornworts and liverworts form a group of simple plants called bryophytes (4). Bryophytes lack many of the more complex structures of the higher plants, such as a vascular system, and flowers. They do not have roots, instead they have structures called ‘rhizoids' which absorb water and anchor the plant to the substrate. All bryophytes have an interesting life cycle consisting of two main parts, called the gametophyte and sporophyte generations (5). Plants in the gametophyte stage can reproduce sexually. Male organs (antheridia) produce male sex cells, which actually move to the female sex organs (archegonia) (5) through water droplets (6). Fertilisation occurs and a plant develops called a ‘sporophyte', which remains attached to the plant. The sporophyte releases spores from within a capsule; the spores disperse and develop into a new gametophyte stage plant (5).

Although the precise threats facing this species are not fully understood, the following are thought to be factors: eutrophication and other types of water pollution, and decreased shading caused by tree removal (2).

As a UK Biodiversity Action Plan (UK BAP) priority species, the tiny fern-moss has a Species Action Plan, which guides its conservation. This plan aims to maintain all current populations and set up ex-situ populations before 2005 (2). This moss is included in English Nature's Species Recovery Programme, which has part-funded research and survey work in conjunction with Plantlife, the wild plant conservation charity (3). This research has discovered that this moss may not merit species status, and has suggested that taxonomic studies to determine the status of this moss should precede any conservation work (3).

Information authenticated by Plantlife, the wild plant conservation charity:
http://www.plantlife.org.uk