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Description

 Life habit: lichenized, occasionally lichenicolous; Thallus: crustose, adnate, granular, areolate, placodioid or peltate, rarely immersed in the substrate; prothallus: blackish brown, white to whitish gray or not visible; surface: white or various shades of gray, yellow or brown, soredia absent or present, isidia and cephalodia absent; cortex: present (often false and composed partly of dead algal cells), or absent; photobiont: primary one a trebouxioid green alga, secondary one absent; medulla: usually white; Apothecia: immersed, or sessile, constricted at the base or not; disc: variously colored, epruinose or pruinose; margin: usually containing algal cells, generally conspicuous and concolorous with the thallus, in some species inconspicuous, reduced or becoming excluded; amphithecial cortex: present or absent; parathecium: hypothecium and subhymenium: hyaline or pigmented; hymenium: hyaline, strongly amyloid; upper part (epihymenium): usually pigmented, with or without crystals; paraphyses: simple, septate, usually branched apically, thickened or not thickened apically; asci: clavate, Lecanora-type, 8-spored (or in some non-Sonoran species multispored); ascospores: simple, narrowly to broadly ellipsoid, smooth-walled, hyaline; Conidiomata: pycnidial, immersed with hyaline to pale brown walls; conidia: simple, hyaline, bacilliform, filiform or falcate; Secondary metabolites: atranorin or usnic acids or xanthones, and a wide range of depsides, depsidones, terpenoids and aliphatic acids; Geography: cosmopolitan.; Notes: The name Lecanora comes from the Greek lekanon (a small bowl) and ora (form, beauty), in reference to the appearance of the apothecia. Lecanora is characterized by asci of the Lecanora-type, simple hyaline ascospores, and crustose thalli. The apothecial margin usually contains algal cells. It is a heterogeneous assemblage of different groups, several of which deserve generic rank. Lecanora s. str. is characterized by the presence of atranorin and oxalate crystals in the amphithecium. In taxa of Lecanora s. str., presence and size of crystals in the epihymenium and amphithecium and pigments in the epihymenium are important diagnostic features. The amphithecia present in Sonoran species include those with small crystals in the algal-containing and cortical part of the amphithecium or small crystals only in the algal-containing part of the amphithecium (Color plate 30), and large crystals (Color plate 31). The epihymenia in Sonoran species include: (1) those with coarse crystals (soluble in concentrated HNO3 [N]), pigmented or not (if pigmented, pigmentation soluble in K); (2) those lacking crystals, olive green pigmented, (pigmentation altering to green in K); (3) those lacking crystals, red-brown pigmented, (pigmentation insoluble in K); and (4) those with small crystals in the epihmenium (insoluble in N), brownish pigmented, (pigmentation soluble in K). Crystals are best seen in polarized light. Crystals appearing bright in polarized light are denoted as pol+, while those remaining dark are described as pol-. Also included in Lecanora is the subgenus Placodium, a heterogeneous group characterized by rosulate to lobate, squamulose, peltate, or dwarf fruticose thalli, that lack atranorin but have usnic acids and/or xanthones in the upper cortex, and usually lack oxalate crystals in the amphithecium. Important diagnostic features include the growth form and thallus anatomy of this group. In many, but not all Lecanora species the thallus and its associated algae grow around the fungal apothecial structures forming what is designated the amphithecium (e.g., Brodo 1984). In the Zahlbruckner school, which has so extensively influenced lichenology, this amphithecium is often called the thalline exciple. In contrast, 'proper exciple' or 'true exciple' are used to refer to apothecia lacking a thalline part. Mycologists, dealing with non-lichenized fungi, generally use exciple to refer to the outermost hyphae of any apothecium. This designation causes confusion because is not correct for a lecanorine apothecium, where the outermost part is formed by the thallus. An alternative for "lecanorine" apothecia is to designate the fungal part of an apothecium as the parathecium. This avoids the confusion about the correct use of exciple. The terms amphithecium and parathecium have consistently been adopted here, although an alternative would be to simply use "exciple" for the parathecium. 

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© Lichen Unlimited: Arizona State University, Tempe.

Source: Lichen Flora of the Greater Sonoran Desert Region

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