Lichen growth forms
gross morphological classification
Lichens are symbiotic colonies composed of multiple species: a fungus, one or more photobionts (an alga and/or a cyanobacteria) and sometimes a yeast. They are regularly grouped by their external appearance – a characteristic known as their growth form. Based on the appearance of vegetative part of the lichen (its thallus), this form 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, placodioid 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.
Context
Lichens are composite organisms made up of multiple species: a fungal partner, one or more photosynthetic partners (also known as photobionts), and sometimes a yeast. It is a symbiotic relationship, to which each partner contributes. In most cases, the fungal partner provides the structure in which the various partners live; this structure helps to protect the photobiont from environmental pressures.
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This entry incorporates text from “Lichen growth forms” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.