''Usnea articulata'', commonly known as the string-of-sausage lichen, is a pale greenish-grey, densely branched

lichen A lichen ( , ) is a composite organism that arises from algae or cyanobacteria living among filaments of multiple fungi species in a mutualistic relationship.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 (plural: 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. Many of these organisms wer ...

(vegetative tissue) of this

fruticose A fruticose lichen is a form of lichen fungi that is characterized by a coral-like shrubby or bushy growth structure. It is formed from a symbiotic relationship of a photobiont such as green algae or less commonly cyanobacteria and one, two or mor ...

(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 contamination of air due to the presence of substances in the atmosphere that are harmful to the health of humans and other living beings, or cause damage to the climate or to materials. There are many different types ...

, 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 toxic gas responsible for the odor of burnt matches. It is released naturally by volcanic activ ...

; 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 was the transition to new manufacturing processes in Great Britain, continental Europe, and the United States, that occurred during the period from around 1760 to about 1820–1840. This transition included going f ...

. 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 ( cy, Cymru ) is a Countries of the United Kingdom, country that is part of the United Kingdom. It is bordered by England to the Wales–England border, east, the Irish Sea to the north and west, the Celtic Sea to the south west and the ...

, particularly

Pembrokeshire Pembrokeshire ( ; cy, Sir Benfro ) is a Local government in Wales#Principal areas, county in the South West Wales, south-west of Wales. It is bordered by Carmarthenshire to the east, Ceredigion to the northeast, and the rest by sea. The count ...

. 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, fl ...

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 Mutualism describes the ecological interaction between two or more species where each species has a net benefit. Mutualism is a common type of ecological interaction. Prominent examples include most vascular plants engaged in mutualistic intera ...

between an

alga Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mi ...

and a

fungus A fungus ( : fungi or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and molds, as well as the more familiar mushrooms. These organisms are classified as a kingdom, separately from th ...

; in this instance the alga is a green alga, but not '' Trentepohlia''. Reproduction in this species is mainly by fragmentation of the thallus, with an apparent absence of

spore In biology, a spore is a unit of sexual or asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the life cycles of many plants, algae, f ...

production limiting its ability to recolonise parts of its range where it has been

extirpated Local extinction, also known as extirpation, refers to a species (or other taxon) of plant or animal that ceases to exist in a chosen geographic area of study, though it still exists elsewhere. Local extinctions are contrasted with global extinct ...

References

{{Taxonbar, from=Q10711209 articulata Lichen species Lichens described in 1753 Lichens of Africa Lichens of Europe Taxa named by Carl Linnaeus