Small four-tooth moss (Tetrodontium repandum)
| Kingdom | Plantae |
|---|---|
| Phylum | Bryophyta |
| Class | Polytrichopsida (1) |
| Order | Tetraphidales |
| Family | Tetraphidaceae |
| Genus | Tetrodontium (2) |
| Size | Stem length: up to 2 mm (3) |
Classified as Critically Endangered in Great Britain (3).
Small four-tooth moss is minute (4), 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 (5). 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(5).
The last confirmed records of this species in Great Britain were made in the 1950s, in east Sussex and north-east Yorkshire (3). 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 (3). Elsewhere this moss is rare in central and southern Europe, it also occurs in western North America, Newfoundland, south-east Asia and the Caucasus (3).
Grows underneath moist overhanging gritstone or sandstone rocks (4).
Little is known of the biology of this species. Mosses, hornworts and liverworts form a group of plants called bryophytes (3). 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 (6). 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) (6) through water droplets (7). 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 (6). In Britain this moss is not known to produce sporophytes, instead it spreads by vegetative reproduction(3).
As so little is known about British populations, the threats facing the species are unclear (3).
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 (4).
Information authenticated by Royal Botanic Gardens, Kew:
http://www.rbgkew.org.uk/
- Capsule: in mosses and liverworts, the spore-bearing structure, held aloft on a stalk called a seta. Capsules have a variety of shapes. Most moss capsules have a mouth, which is covered by a lid until the spores become ripe and the lid falls off, revealing a single or double ring of teeth, known as the ‘peristome’. The spores are released and dispersed in the wind. In liverworts the capsules do not have lids; when the spores are ripe the capsule splits into four, releasing the spores.
- Gametophyte: a life cycle stage in plants, which has one set of chromosomes (threads of DNA protein) in the cell nucleus (a condition known as ‘haploid’), which arises from a spore (which is also haploid). Sex cells (gametes) are produced during the gametophyte stage. This is the dominant life-cycle stage in liverworts and mosses.
- Rhizoids: thread-like structures that help to anchor the plant to the substrate, and absorb minerals and water. In liverworts they consist of a single cell, in mosses they are multi-cellular.
- Spores: microscopic particles involved in both dispersal and reproduction. They comprise a single or group of unspecialised cells and do not contain an embryo, as do seeds.
- Sporophyte: the stage of a plant life cycle that produces spores (microscopic particles used in dispersal and reproduction). This stage is diploid (in the cell nucleus there are two sets of chromosomes - threads of DNA protein) and is dominant in ‘higher’ plants such as flowering plants.
- Vascular system: in plants, the system that allows water and nutrients to move around.
- Vegetative reproduction: type of asexual reproduction (reproduction without recombination of genetic material) that results in the propagation of plants using only the vegetative tissues such as leaves or stems. The resulting plant is genetically identical to the original plant. A well-known example of this is the reproduction of strawberry plants from ‘runners’.
- Shaw, A. & Goffinet, B. (2000) Bryophyte Biology. Cambridge University Press, Cambridge.
- Crosby, M. & Magill, R. (1978) A Dictionary of Mosses. Missouri Botanic Gardens.
- Church, J. M., Hodgetts, N. G., Preston, C. D. & Stewart, N. F. (2001) British Red Data Books: mosses and liverworts. Joint Nature Conservancy Committee, Peterborough.
- UK BAP (August 2002): http://www.ukbap.org.uk
- Allaby, M. (1998) The Oxford Dictionary of Plant Sciences. Oxford University Press, Oxford.
- Mosses and Liverworts in Wales (August 2002): http://home.clara.net/adhale/bryos/
- Egerton, H. & Jones, F. (Eds.) (1998) Nature Encyclopedia. Dorling Kindersley, London.