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Alectoria (fungus)

Genus of lichens From Wikipedia, the free encyclopedia

Alectoria (fungus)
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Alectoria is a genus of fruticose lichens belonging to the family Parmeliaceae.[1]

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Taxonomy

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The genus Alectoria was circumscribed by the Swedish lichenologist Erik Acharius in 1809.[2] Prior to this, filamentous lichens of similar appearance had been classified within the broad genus Lichen, following the system used by Carl Linnaeus in his Species Plantarum (1753). Linnaeus recognised only three species that are now placed in Alectoria treating them as part of a much larger and undifferentiated group of lichens.[3]

During the late 18th century, botanists such as Georg Franz Hoffmann (1796) began distinguishing filamentous lichens as a separate taxonomic group, though they did not establish a dedicated genus for them.[4] Acharius, a student of Linnaeus and one of the pioneers of lichenology, initially placed species now assigned to Alectoria within Parmelia, grouping them under the section Tricharia in his 1803 work Methodus Lichenum.[3] However, as he continued studying the group, he recognised the need for a separate genus and formally established Alectoria in 1809,[2] distinguishing it from Parmelia based on its slender, branching thallus structure.[5]

Following Acharius, lichenologists continued refining the classification of Alectoria. Elias Magnus Fries (1831) provided a more detailed systematic arrangement of lichens, further solidifying Alectoria as a distinct genus.[6] In the mid-19th century, William Nylander (1860) and James Crombie (1876) contributed to the understanding of Alectoria, using both morphological features and chemical analyses to differentiate it from closely related genera.[7][8] Their work demonstrated that Alectoria species produce unique secondary metabolites, such as usnic acid, which help distinguish them from other lichens in the Parmeliaceae.[3]

Despite these early classifications, Acharius did not formally designate a type species when he established Alectoria. This omission was later addressed by taxonomists in the 20th century. Veli Räsänen (1919) and Gunnar Degelius (1954) refined the genus's taxonomy, clarifying species boundaries and confirming Alectoria sarmentosa as the type species.[9][10] These revisions provided a stable framework for the genus, which remains distinguished by its fruticose (shrub-like), filamentous thallus, lack of cyphellae (small pore-like structures), and its characteristic production of usnic acid and other lichen compounds.[3]

Alectoria was previously placed in the family Alectoriaceae, which was widely accepted as distinct from Parmeliaceae based on differences in reproductive structures such as larger asci, pigmented spores, and distinctive hamathecial characteristics. However, a 1999 molecular phylogenetic study examined the relationship between Alectoriaceae and Parmeliaceae using sequences of nuclear ribosomal DNA. Their analysis included specimens of Alectoria ochroleuca and A. sarmentosa along with various members of the Parmeliaceae. The results showed that Alectoria was derived from within the Parmeliaceae, suggesting the two families should be treated as synonyms. While previous taxonomic work had emphasised differences in ascus structure, spore size, and hamathecial characteristics to justify separating Alectoriaceae, the study concluded that these variations represented extremes within a continuous range of characters found in Parmeliaceae rather than distinct family-level differences. The authors recommended including Alectoria within a broader concept of Parmeliaceae rather than maintaining it in a separate family.[11]

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Description

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Alectoria forms shrub-like (fruticose) growths, which can either stand upright, sprawl along surfaces, or hang down from their substrate. The main body thallus) of these lichens appears in colours ranging from greenish-yellow to brownish-black. Their branches are typically rounded and smooth, though in some cases they may become flattened near their base and where branches meet. One subspecies (Alectoria sarmentosa subsp. vexillifera) is considerably different, having distinctly flattened branches with clear upper and lower surfaces.[12]

A distinctive feature of Alectoria is the presence of white, spindle-shaped structures called pseudocyphellae, which appear as small pores or marks on the surface. These lichens do not produce isidia or soredia, which are specialised propagules for vegetative reproduction. Like most lichens, Alectoria is a partnership between a fungus and an algal partner (photobiont), specifically one from the Trebouxia genus of green algae.[12]

The reproductive structures (apothecia) are rare and appear along the sides of branches. These disc-shaped structures have rims that match the colour of the main body. Inside the apothecia are specialised cells (asci) that produce spores. These thick-walled, club-shaped asci typically contain either two or four spores. The spores themselves are relatively large, single-celled, oval-shaped, and range from colourless to brown, surrounded by a clear outer layer.[12]

The genus also produces small, black, globe-shaped structures called pycnidia that are partially or fully embedded in the thallus. These produce rod-shaped to narrow spindle-shaped asexual reproductive cells called conidia. Chemically, almost all species contain usnic acid, and many produce compounds called orcinol and β-orcinol depsides.[12]

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