Tiny Fern Moss

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).

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).

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).

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

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).

Classified as Near Threatened in Great Britain (2), and receives general protection under Schedule 8 of the Wildlife and Countryside Act 1981 (1). It is classified as Rare in Europe (3).

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).

Fissidens exiguus SuU. Mem. Am. Acad
II. 3: 60. 1846.
Fissidens viridulus var. Lylei Wils. Bryol. Brit. 304. 1855. Fissidens incurvus var. exiguus Aust. Musci App. 19. 1870. Fissidens pusillus var. Lylei Braithw. Brit. Moss-Fl. 1: 68. 1881.
Plants very small, 1-2 mm. high; leaves 3-6 pairs, the upper reaching 1 mm. in length, the perichaetial a little longer, narrowly oblong-lanceolate, acute to roundedobtuse, smooth, the margin entire or rarely slightly irregular near apex, usually only the vaginant laminae of the perichaetial leaves bordered, the costa usually vanishing 2-3 cells below apex; upper median leaf-cells 8-15 m in longest dimension, irregularly roimded-hexagonal ; dioicous; seta 2-4 mm. long, pale; capsule erect and symmetric or somewhat inclined, the urn reaching 0.6 mm. long, the exothecial cells oblong, strongly collenchymatous ; operculum long-conic to short-rostrate, about two-thirds the length of the urn ; divisions of peristome-teeth spirally thickened and very strongly papillose; spores 15-20 ju in diameter, mature in summer.
Type locawTy: Near Columbus, Ohio.
Distribution: On stones in moist shaded places; King Oscar Land, southeastern Canada and northern United States east of the Rockies, south to North Carolina and southern Missotiri {Drew) ; Honduras {Wilson 4); Puerto Rico (with long narrow perichaetial leaves, Steere); Bermuda (£. G.
Britton 322) .
Iivi^usTRATiONS : Mem. Am. Acad. II. 3: pi. 2, B; SuU. Ic. Muse. pi. 23; Jennings, Mosses W. Pa.
pi. 11.