Small Four Tooth Moss

Little is known of the biology of this species. Mosses, hornworts and liverworts form a group of plants called bryophytes (2). 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 (4). Plants that are in the gametophyte stage can reproduce sexually. Male organs (antheridia) produce male sex cells or gametes called antherozoids, which actually move to the female sex organs (archegonia) (4) through water droplets (5). 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 (4). In Britain this moss is not known to produce sporophytes, instead it spreads by vegetative reproduction (2).

A Species Action Plan has been produced for this moss under the UK Biodiversity Action Plan (UK BAP). This plan aims to maintain any populations that may persist in Britain (3).

Small four-tooth moss is minute (3), and is so called as the capsule (the spore-bearing structure which is held aloft on a stalk or 'seta') has four teeth fringing the mouth, which are covered by a 'lid' until the spores become ripe and the lid falls off (6). The teeth absorb moisture from the air, and changes in humidity cause changes in the length of the teeth, causing the capsule to move as a result; this helps with the dispersal of the spores (6).

Grows underneath moist overhanging gritstone or sandstone rocks (3).

The last confirmed records of this species in Great Britain were made in the 1950s, in east Sussex and north-east Yorkshire (2). The moss has not been recorded since then, but it is very small and difficult to find, so it may persist at these sites but have been overlooked (2). Elsewhere this moss is rare in central and southern Europe, it also occurs in western North America, Newfoundland, south-east Asia and the Caucasus (2).

Classified as Critically Endangered in Great Britain (2).

As so little is known about British populations, the threats facing the species are unclear (2).

Plants with numerous flagelliform shoots, these 2-5 mm with 3-ranked, tightly appressed linear to lanceolate leaves at the base of the stem. Thallose protonematal flaps ovate-lanceolate, without a distinct mucronate point, margins ± dentate, less than 0.5 mm. Leaves with costa absent. Spores about 16 µm.

Tetraphis repanda Funck in J. Sturm et al., Deutschl. Fl. 2(17): plate 4. 1819; T. brownianum var. repandum (Funck) Limpricht

Tetrodontium repandum, the small four-tooth moss, is a moss in the family Tetraphidaceae. It is one of only two recognized species in the genus Tetrodontium, and is native to subalpine regions of the Northern Hemisphere. It has been reported from Alaska, British Columbia, Washington state, Japan, and Europe.