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Usnea is a genus of fruticose lichens in the large family Parmeliaceae. The genus, which currently contains roughly 130 species, was established by Michel Adanson in 1763. Species in the genus grow like leafless mini- shrubs or tassels anchored on bark or twigs.
Its undifferentiated thallus is an irregular mix of fungal hyphae and scattered photobiont cells, lacking a cortex or any definable layers. [6] [47] Morphologically, it is the simplest growth form. [48] The cell walls of leprose lichens contain chemical compounds which make them hydrophobic, and thus largely water repellent. However, the lack ...
A podetium (plural podetia) is a lichenized stem-like structure of an apothecium rising from the primary body of the thallus. [4] Since it is part of the reproductive tissue, it is not considered part of the thallus. [4] The podetium may be branched, and sometimes cup-like. It usually bears the pycnidia or apothecia or both.
The thallus is different from those of either the fungus or alga growing separately. The fungus surrounds the algal cells, often enclosing them within complex fungal tissues unique to lichen associations. In many species the fungus penetrates the algal cell wall, forming penetration pegs or haustoria similar to those produced by pathogenic fungi.
The Parmeliaceae is a large and diverse family of Lecanoromycetes.With over 2700 species [2] in 71 genera, it is the largest family of lichen-forming fungi.The most speciose genera in the family are the well-known groups: Xanthoparmelia (822 species), Usnea (355 species), Parmotrema (255 species), and Hypotrachyna (262 species).
Usnea filipendula – one of about 20,000 described species of lichen. The following outline provides an overview of and topical guide to lichens.. Lichen – composite organism made up of multiple species – a fungal partner, one or more photosynthetic partners, which can be either green algae or cyanobacteria, and, in at least 52 genera of lichens, a yeast. [1]
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.
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. [1] The epidermal layer provides a barrier to infection from environmental pathogens [2] and regulates the amount of water released from the body into the atmosphere through transepidermal water loss.