''Usnea articulata'', commonly known as the string-of-sausage lichen,
[ is a pale greenish-grey, densely branched ]lichen
A lichen ( , ) is a hybrid colony (biology), colony of algae or cyanobacteria living symbiotically among hypha, filaments of multiple fungus species, along with yeasts and bacteria embedded in the cortex or "skin", in a mutualism (biology), m ...
with a prostrate or pendant
A pendant is a loose-hanging piece of jewellery, generally attached by a small loop to a necklace, which may be known as a "pendant necklace". A pendant earring is an earring with a piece hanging down. Its name stems from the Latin word ...
growth form. It grows on bark, on branches and twigs, and is often unattached to a branch and merely draped over it. It grows up to in length.
Description
The thallus
Thallus (: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. A thallus usually names the entir ...
(vegetative tissue) of this fruticose
A fruticose lichen is a form of lichen fungi that is characterized by a coral-like shrubby or bushy lichen growth forms, growth structure. It is formed from a symbiotic relationship of a photobiont such as green algae or less commonly cyanobacteri ...
(bush-like) lichen is densely branched, and forms tangled masses of stems which are prostrate or pendulous. The branches are smooth and somewhat knobbly or spiny, and a greenish-grey colour. The larger stems become articulated, dividing into inflated, sausage-like segments. The lichen is not blackish at the base and sometimes becomes detached, continuing to grow while draped over its support.
Distribution and habitat
This lichen is very sensitive to air pollution
Air pollution is the presence of substances in the Atmosphere of Earth, air that are harmful to humans, other living beings or the environment. Pollutants can be Gas, gases like Ground-level ozone, ozone or nitrogen oxides or small particles li ...
, especially from sulphur dioxide
Sulfur dioxide (IUPAC-recommended spelling) or sulphur dioxide (traditional Commonwealth English) is the chemical compound with the formula . It is a colorless gas with a pungent smell that is responsible for the odor of burnt matches. It is r ...
; it has a widespread but sparse distribution in mainland Europe, but has become extinct in many areas, surviving best in Brittany.[ It occurs on various Mediterranean and Atlantic islands and is present in Saudi Arabia, and the mountainous regions of East Africa and North Africa. In the British Isles, it used to be widespread but disappeared from many areas during the ]Industrial Revolution
The Industrial Revolution, sometimes divided into the First Industrial Revolution and Second Industrial Revolution, was a transitional period of the global economy toward more widespread, efficient and stable manufacturing processes, succee ...
. It is reasonably common in southwestern England, from the New Forest
The New Forest is one of the largest remaining tracts of unenclosed pasture land, heathland and forest in Southern England, covering southwest Hampshire and southeast Wiltshire. It was proclaimed a royal forest by William the Conqueror, featu ...
westwards, and is known from scattered locations in Wales
Wales ( ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by the Irish Sea to the north and west, England to the England–Wales border, east, the Bristol Channel to the south, and the Celtic ...
, particularly Pembrokeshire
Pembrokeshire ( ; ) is a Principal areas of Wales, county in the South West Wales, south-west of Wales. It is bordered by Carmarthenshire to the east, Ceredigion to the northeast, and otherwise by the sea. Haverfordwest is the largest town and ...
. It is rare in southern and western Ireland.[
Sometimes this lichen grows on the ground, in the slacks among ]sand dunes
A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, flat ...
growing over rough vegetation. More often it is arboreal, often high in the canopy or in hedgerows, and not attached to anything, but draped over twigs and branches. Here it is difficult to spot from below and its presence may only become apparent should fragments of the lichen fall to the ground during storms or after snowfall.[
]
Ecology
Like all lichens, this species involves a mutual relationship between an alga
Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, suc ...
and a fungus
A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
; in this instance the alga is a green alga, but not '' Trentepohlia''. Reproduction in this species is mainly by fragmentation of the thallus,spore
In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...
production limiting its ability to recolonise parts of its range where it has been extirpated
Local extinction, also extirpation, is the termination of a species (or other taxon) in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinctions.
Local extinctions mark a chan ...
.[
]
See also
* List of ''Usnea'' species
References
{{Taxonbar, from=Q10711209
articulata
Lichen species
Lichens described in 1753
Lichens of Africa
Lichens of Europe
Taxa named by Carl Linnaeus