Thatch moss, as its name implies, is sometimes found on old thatched roofs. In the semi-natural state, it is found on the decaying bases of rush and grass tussocks, occasionally on rabbit droppings, and very rarely, on trees. It forms dull-green patches. The tiny leaves are spear-shaped with reproductive structures called gemmae at the tips. These disperse and aid the spread of the moss, and no other British moss has these gemmae on the tip of its leaves.
Mosses are among the lower order of plants, which includes liverworts and hornworts. They are very different from the higher plants in that they do not have true leaves, that is, leaves furnished with ribs and pores. Neither do they possess roots, but mosses do have structures called rhizoids which anchor the moss to the surface on which it grows. Mosses usually reproduce by spores, but also spread by budding off small clusters of cells and by fragmentation.
This moss is distributed widely over Europe but is known to be rare everywhere. In Britain, it used to be found on thatched roofs across much of southern England. Today, it is restricted to three sites on thatch in Wiltshire, Dorset and West Sussex, with a recent discovery in Somerset. It is also found in four semi-natural locations on grass tussocks in Norfolk, Suffolk, Hertfordshire and Greater London.
Thatch moss has suffered through changes in thatching methods. Thatched roofs are much less common than in the past and thatch is replaced more frequently as owners are more affluent and can afford to do so. This does not allow the moss to form colonies, and the re-roofing process destroys those that do get established. The zinc-coated wire, used to prevent bird damage, may also be toxic to the moss.In its semi-natural habitats, thatch moss suffers from drought conditions, and the encroachment of scrub.
Thatch moss is listed in the UK Biodiversity Action Plans (UKBAPs), and included in English Nature's Species Recovery Programme (SRP). Its status is still precarious, and it is important to preserve the existing populations of the moss.
Several of the semi-natural sites are managed as nature reserves, and scrub control is being carried out to maintain the right conditions for the moss. Surveys are being conducted to find new populations. Thatch moss was found recently on the thatched roofs of the National Trust's estate at Honeychurch in Somerset, and they are taking steps to conserve it. It may prove possible to alter modern thatching methods so they are more thatch moss friendly. Advice is being provided to owners of thatched properties on which the moss grows to ensure it is preserved when any re-roofing takes place.
The UK Biodiversity Action Plan for this species is available at UK BAP.
In bryophytes, a structure involved in vegetative reproduction, a 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'. In vascular plants, gemmae are modified organs of the parent plant that can allow vegetative reproduction.
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.
Site/ habitat altered by human influence or management, which has taken on a natural aspect owing to the length of time over which the influences have persisted.
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.
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