Sporopodium


Sporopodium is a genus of lichen-forming fungi in the family Pilocarpaceae. Most Sporopodium species grow on living leaves in tropical forests worldwide, though some also occur on twigs or bark. The genus is known for producing, small hood-like outgrowths that produce conidia and help the lichen disperse to new surfaces. Species in the genus produce a wide variety of chemical compounds, including yellow and orange pigments that can help identify individual species. The genus was established in 1851 with the description of a first species from tropical leaves collected in French Guiana.

Taxonomy

Camille Montagne established Sporopodium in 1851 when he described the foliicolous species Sporopodium leprieurii from leathery tropical leaves in French Guiana. The genus was defined by three features: apothecia without a ; a vesiculose ; and an unusual spore development in which a single, many-celled spore becomes exposed on a long stalk as the breaks down. The thallus was described as very thin, green-glaucous, and granular, with small, dark apothecia whose margin becomes indistinct with age. The asci were described as club-shaped and apparently lacking paraphyses, with each ascus producing a single spore that becomes stalked and pale olive at maturity. The thallus was compared with Fée's Echinoplaca, but the fruiting structures were treated as distinct.
In modern classifications, Sporopodium is placed in an expanded Pilocarpaceae that brings together several mainly leaf-dwelling lineages. Vězda reinstated Pilocarpaceae to accommodate genera such as Byssoloma, Fellhanera and Byssolecania. Later treatments expanded the family to include the -bearing taxa previously placed in Ectolechiaceae, with Sporopodium among the central genera. Later DNA-based analyses of mitochondrial small-subunit rDNA supported this expanded circumscription and suggested that Micareaceae is part of the same larger clade. Relationships among the included genera, however, remain uncertain.

Description

Sporopodium forms a continuous, relatively thick thallus that is pale in colour and dull in texture. The surface is often finely powdery and, in some species, has scattered small warts. The apothecia are in form and vary from pale to dark in colour. Their —the rim tissue surrounding the —is and may contain crystals or be crystal-free. The paraphyses are richly branched and anastomosing. The asci are surrounded by a gelatinous sheath that stains blue with iodine. They have a distinctly blue-staining with a broad at the top. Each ascus usually contains a single ascospore, although one species has eight spores per ascus. Small algal cells are sometimes embedded in the .
The are pale and usually the same colour as the thallus; in species with yellow apothecia or margins, the campylidia are also distinctly yellow. Structurally, each campylidium forms a small hood over a cavity where conidia develop; the opening leads onto a small platform that is partly covered by a lobe. The conidia are ellipsoid to broadly club-shaped and are usually non-septate ; one species has 1-septate conidia. In some species, algal cells occur within the conidiogenous layer, as well as in the epithecium.

Chemistry

Chemical analyses show that Sporopodium species produce a broad range of secondary metabolites. Reported compounds include many xanthones, as well as depsides and depsidones such as pannarin and atranorin. Some species also contain zeorin and pigments related to vulpinic acid, and some contain usnic and isousnic acid. In Sporopodium isidiatum, HPLC and HPTLC analyses detected 2,7-dichlorolichexanthone and zeorin as major substances, with several additional compounds in smaller amounts. This particular pair of major substances was not reported from the other species compared.

Habitat and distribution

Most Sporopodium species grow on living leaves, but many also occur on twigs, and a small number are known only from bark. The genus is largely pantropical in distribution, with species reported from multiple tropical regions worldwide. Some species appear widespread across the tropics, while others are confined to particular regions.

Species