| Usnea sphacelata | |
|---|---|
 | |
Scientific classification  | |
| Domain: | Eukaryota |
| Kingdom: | Fungi |
| Division: | Ascomycota |
| Class: | Lecanoromycetes |
| Order: | Lecanorales |
| Family: | Parmeliaceae |
| Genus: | Usnea |
| Species: | U. sphacelata |
| Binomial name | |
| Usnea sphacelata R.Br. (1823) | |
| Synonyms [1] | |
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Usnea sphacelata is a species of saxicolous (rock-dwelling), fruticose lichen in the large family Parmeliaceae. It is found in both polar regions of Earth, as well as in southern and northern South America and in New Zealand.
The lichen was formally described as a new species in 1823 by Scottish botanist Robert Brown. The type specimen was collected from Melville Island in the Canadian Arctic Archipelago. [2]
A 2007 study using phylogenetic and morphological analysis of a large number of Antarctic Usnea specimens suggests that Usnea sphacelata comprises at least two genetically distinct groups with no clear differences in morphology. [3]
Usnea sphacelata has a range of distinctive morphological characteristics. Its central axis is relatively thin, accounting for about 20–40% of its structure. Soralia, which are numerous, are typically restricted to the ultimate branches . Minute papillae , which are often pigmented, can be observed on its surface. Fibrils are usually absent from this species. Additionally, its pigmentation is noteworthy; the upper portion is conspicuously variegated, or it can be continuously pigmented towards the tips. This set of features helps to distinguish Usnea sphacelata from other sympatric Antarctic Usnea species, including U. antarctica , U. aurantiaco-atra , U. subantarctica , and U. trachycarpa . [3]
The lichen has a bipolar distribution; that is, it occurs in both the Antarctic and the Arctic. It is also found in southern South America, the northern Andean regions of South America, and the South Island of New Zealand. [3] In the Windmill Islands area of continental Antarctica, Usnea sphacelata tends to grow in drier sun-exposed areas where snow does not tend to persist. Typical lichen associates at this location include Buellia frigida , Buellia soredians , Pseudephebe minuscula , and Umbilicaria decussata . [4] In some regions, the crustose Buellia frigida is often the only species that can become established on smooth, ice-polished rock. Once its thallus is about 2 cm or more in diameter, Pseudephebe minuscula or Usnea sphacelata often start growing near the centre of the thallus. [5]
A 1989 study near Casey Station, Antarctica found that U. sphacelata showed potential for photosynthetic activity even under challenging environmental conditions. The research demonstrated that while humidity levels above 80% were optimal for photosynthesis, the lichen could maintain positive net photosynthesis across various exposures on Antarctic rocks, with its biomass reaching up to 900 grams dry weight per square metre in suitable habitats. [6]
Other research conducted near Casey Station revealed that U. sphacelata exists in two forms: a blackish pigmented light-form found in exposed sites and a yellowish shade-form in sheltered habitats. The species can photosynthesise while covered in snow, even at temperatures below freezing, though its productivity is limited by several factors. The lichen shows signs of photoinhibition (decreased photosynthetic rate) when exposed to light levels above 600 μmol m⁻² s⁻¹ PAR, particularly at lower temperatures, suggesting that it photosynthesises most efficiently during overcast conditions. During the studied austral summer period, the lichen was only physiologically active for about 27% of the time, primarily when moistened by snow, producing approximately 3.44 g carbon per square meter. This productivity is significantly lower than laboratory studies had suggested, highlighting the challenges of survival in the Antarctic environment. [7]
Trebouxia is a unicellular green alga. It is a photosynthetic organism that can exist in almost all habitats found in polar, tropical, and temperate regions. It can either exist in a symbiotic relationship with fungi in the form of lichen or it can survive independently as a free-living organism alone or in colonies. Trebouxia is the most common photobiont in extant lichens. It is a primary producer of marine, freshwater and terrestrial ecosystems. It uses carotenoids and chlorophyll a and b to harvest energy from the sun and provide nutrients to various animals and insects.
Buellia is a genus of mostly lichen-forming fungi in the family Caliciaceae. The fungi are usually part of a crustose lichen. In this case, the lichen species is given the same name as the fungus. But members may also grow as parasites on lichens (lichenicolous). The algae in the lichen is always a member of the genus Trebouxia.
Pseudephebe is a genus of fruticose lichens in the family Parmeliaceae. It contains three species that grow on rocks.
Xanthoparmelia is a genus of foliose lichens in the family Parmeliaceae. This genus of lichen is commonly found in the United States, South America, southern Africa, Europe, Australia, and New Zealand.
The Caliciaceae are a family of mostly lichen-forming fungi belonging to the class Lecanoromycetes in the division Ascomycota. Although the family has had its classification changed several times throughout its taxonomic history, the use of modern molecular phylogenetic methods have helped to establish its current placement in the order Caliciales. Caliciaceae contains 39 genera and about 670 species. The largest genus is Buellia, with around 300 species; there are more than a dozen genera that contain only a single species.
Menegazzia is a genus of lichenized fungi containing roughly 70 accepted species. The group is sometimes referred to as the tree flutes, honeycombed lichens, or hole-punch lichens. The most obvious morphological feature of the genus is the distinctive perforations spread across the upper side of the thallus. This makes the group easy to recognise, even for those not particularly familiar with lichen identification.
Rippon Glacier is a small glacier located in Kemp Land, East Antarctica. It is close east of Seaton Glacier, flowing southward into Edward VIII Ice Shelf.
The wildlife of Antarctica are extremophiles, having adapted to the dryness, low temperatures, and high exposure common in Antarctica. The extreme weather of the interior contrasts to the relatively mild conditions on the Antarctic Peninsula and the subantarctic islands, which have warmer temperatures and more liquid water. Much of the ocean around the mainland is covered by sea ice. The oceans themselves are a more stable environment for life, both in the water column and on the seabed.
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 more mycobionts. Fruticose lichens are not a monophyletic and holophyletic lineage, but are a form encountered in many classes. Fruticose lichens have a complex vegetation structure, and are characterized by an ascending, bushy or pendulous appearance. As with other lichens, many fruticose lichens can endure high degrees of desiccation. They grow slowly and often occur in habitats such as on tree barks, on rock surfaces and on soils in the Arctic and mountain regions.
Crustose lichens are lichens that form a crust which strongly adheres to the substrate, making separation from the substrate impossible without destruction. The basic structure of crustose lichens consists of a cortex layer, an algal layer, and a medulla. The upper cortex layer is differentiated and is usually pigmented. The algal layer lies beneath the cortex. The medulla fastens the lichen to the substrate and is made up of fungal hyphae. The surface of crustose lichens is characterized by branching cracks that periodically close in response to climatic variations such as alternate wetting and drying regimes.
Lichens are symbiotic organisms made up of multiple species: a fungus, one or more photobionts and sometimes a yeast. They are regularly grouped by their external appearance – a characteristic known as their growth form. This form, which is based on the appearance of vegetative part of the lichen, varies depending on the species and the environmental conditions it faces. Those who study lichens (lichenologists) have described a dozen of these forms: areolate, byssoid, calicioid, cladoniform, crustose, filamentous, foliose, fruticose, gelatinous, leprose, placoidioid and squamulose. Traditionally, crustose (flat), foliose (leafy) and fruticose (shrubby) are considered to be the three main forms. In addition to these more formalised, traditional growth types, there are a handful of informal types named for their resemblance to the lichens of specific genera. These include alectorioid, catapyrenioid, cetrarioid, hypogymnioid, parmelioid and usneoid.
Pseudephebe pubescens, also known as 'fine rock wool', is a temperate alpine lichen. It is a member of the genus Pseudephebe, a lichen group characterized by dense mats of brown to near-black "hairs".
Amundsenia austrocontinentalis is a species of saxicolous (rock-dwelling), crustose lichen in the family Teloschistaceae, and the type species of genus Amundsenia. Found in Antarctica, it was formally described as a new species in 2014 by Isaac Garrido-Benavent, Ulrik Søchting, Sergio Pérez-Ortega, and Rod Seppelt. The type specimen was collected by the last author from Mule Peninsula, where it was found growing on small stones in glacial till. The species epithet austrocontinentalis refers to its distribution in continental Antarctica.
Peltigera hydrophila is a species of foliose lichen in the family Peltigeraceae. First described in 2020, it distinguishes itself through a distinct, hairless thallus that turns deep blue-violet when it becomes wet. Found primarily in the Magallanes Region of Chile, this small leafy lichen clings closely to mosses and other substrates. Distinctive features include the always-present reddish-brown to dark brown apothecia and the Peltigera-type ascospores that contain three internal partitions, or septa. Despite sharing a habitat with similar species like P. aubertii and P. frigida, P. hydrophila sets itself apart through its unique thallus surface texture and colour. This semi-aquatic lichen primarily thrives in humid forests, shrubby and herbaceous vegetation in southern Chile, particularly near waterfalls, streams, and other wet environments.
Buellia frigida is a species of saxicolous (rock-dwelling), crustose lichen in the family Caliciaceae. It was first described from samples collected from the British National Antarctic Expedition of 1901–1904. It is endemic to maritime and continental Antarctica, where it is common and widespread, at altitudes up to about 2,000 m (6,600 ft). The characteristic appearance of this lichen features shades of grey and black divided into small polygonal patterns. The crusts can generally grow up to 7 cm in diameter, although neighbouring individuals may coalesce to form larger crusts. One of the defining characteristics of the lichen is a textured surface with deep cracks, creating the appearance of radiating lobes. These lobes, bordered by shallower fissures, give the lichen a distinctive appearance and textured surface.
Charcotiana is a single-species genus in the family Teloschistaceae. It contains the species Charcotiana antarctica, a crustose lichen found in Antarctica.
Usnea pallidocarpa is a species of saxicolous (rock-dwelling) beard lichen in the family Parmeliaceae. It is known from Argentina.
Buellia aethalea is a species of lichen that belongs to the family Caliciaceae. It is commonly known as darkened button lichen, and Buellie noircie in French. The lichen's familiar nickname is inspired by the appearance of its surface, adorned with small black spots reminiscent of buttons.
Umbilicaria torrefacta is a species of saxicolous (rock-dwelling), foliose lichen in the family Umbilicariaceae. It is an arctic-alpine species with a circumpolar distribution and is widely distributed within the Holarctic realm, specifically within the Palearctic and Neoarctic biogeographical regions. Characteristic features of Umbilicaria torrefacta include the lace-like fringe in its lobes and the plates on the underside of the thallus. One common name, punctured rock-tripe, refers to the distinctive sieve-like perforations on the thallus margins.