Parmelia

Parmelia sulcata, copyright James Lindsey.

Belongs within: Parmeliaceae.

Parmelia is a cosmopolitan genus of foliose lichens, light-coloured above and black below with the lower surface anchored to the substrate by rhizenes, and often with squarish ends to the thallus lobes.

Learning to like lichen
Published 9 December 2010
The lichen Parmelia saxatilis. The red cups at the top of the photo are the lichen’s fruiting bodies (apothecia) that produce fungal spores. Photo from here.

We all know what lichens are. They’re the standard example of a mutualistic association that we were all presented with in high school, an association of fungus and unicellular alga allowing both to survive long-term in situations that would normally be fatal for them both. More than 15,000 species of lichen have been described—or, rather, species of lichenised fungi, as names applied to lichens technically apply to the fungal member of the association (only a relatively small number of algae form lichen associations). Though these species can all be attributed to the Ascomycetes among the main fungal subdivisions*, they do not form a single clade within the asomycetes. Instead, it appears that the lichen lifestyle has been gained and/or lost on numerous occasions.

*Lichen-like associations are sometimes formed by other fungi such as Basidiomycetes but they lack the integrity of the ascomycetous examples. Lab workers have even been able to induce lichen-like associations between unicellular algae and colonial or hyphal bacteria such as myxobacteria and streptomycetes (Ahmadjian 1965).

Parmelia is a genus of foliose lichens which is found worldwide but has its highest diversity in Asia (Molina et al. 2004). Well over 1000 species have been assigned to the genus over the years but many (though not all) recent authors have tended towards a much more restricted circumscription of about forty species. True Parmelia, in this sense, is distinguished from other genera in the lichen family Parmeliaceae by its linear pseudocyphellae (pore-like structures in the upper-surface of the lichen’s cortex) and its particularly small spores and conidia (conidia are reproductive structures like spores but produced asexually rather than sexually) (Elix 1993). ITS rDNA phylogeny is mostly consistent with many of the proposed segregate genera, including the restricted Parmelia, though it provides little information on their higher relationships (Crespo & Cubero 1998).

Another view of Parmelia saxatilis. As well as the spore-producing apothecium, this photo also shows numerous isidia, the small finger-like protrusions covering the thallus. Containing both fungal and algal cells, the isidia can break off to form new lichens. Photo by Stephen Sharnoff.

Parmelia achieves its highest diversity in temperate or boreal regions. The type species, P. saxatilis, is one of the world’s most widespread lichen species, found in both the Arctic and the Antarctic, as well as cooler localities in between (Molina et al. 2004). Lichens can reproduce in one of two ways: small pieces of the thallus containing both algal cells and fungal hyphae may break off to grow directly into a new thallus elsewhere, or the lichen can release spores and/or conidia in the manner of other fungi. A germinating lichen spore will grow extremely slowly: even in laboratory cultures on agar, some lichen fungi will only reach a diameter of 1 mm within the course of a year when grown without algal symbionts (Ahmadjian 1965). Formation of the lichen association is dependent on the fungus randomly coming into contact with an alga, and growing lichen fungi will form exploratory hyphae around anything (even grains of sand) that they touch that might turn out to be an alga (Ahmadjian 1960). The low variety of algal species occuring in lichens appears to be dependent not on any direct attraction of the alga for the fungus, but on the alga’s ability to resist digestion by the fungus’ hyphae. Lichens are famed for their slow growth even after an association is established, and may increase in diameter by only a millimetre a year*, but the limiting factor is probably not so much their inherent growth abilities as that their favoured environments such as exposed on rocks may only allow growth for a minute part of the year.

*If you’re thinking that that doesn’t sound any greater than the rate for symbiont-less fungi that I cited above, remember that the latter rate applies to growth in the laboratory under theoretically optimal conditions; growth in the natural environment would be much, much slower.

Systematics of Parmelia
Parmelia Ach. 1803 (nom. cons.) (see below for synonymy)KC01
|--*P. saxatilis (L.) Ach. 1803 [incl. P. saxatilis var. laevis]G94
|--P. afrorevoluta Krog & Swinscow 1979KC01, G94 (see below for synonymy)
|--P. austrosinensis Zahlbr. in Handel-Mazzetti 1930KC01, G94 [=Parmotrema austrosinense (Zahlbr.) Hale 1974G94]
|--P. caperata (see below for synonymy)G94
|--P. crowii Elix 1993G94
|--P. cunninghamii Cromb. 1876 [incl. P. brownii Dodge 1970]G94
|--P. encaustaF33
|--P. erumpens Kurok. 1969 [=P. tenuirima f. corallina Müll.Arg. 1883]G94
|--P. glomelliferaF33
|--P. intestiniformisC74
|--P. isidiotylaF33
|--P. mussooriensisBB05
|--P. norcrambidiocarpa Hale 1987G94
|--P. omphalodesE99
| |--P. o. var. omphalodesE99
| `--P. o. var. discordansE99
|--P. protosignifera Elix & Johnst. 1988G94
|--P. protosulcata Hale 1982G94
|--P. pseudotenuirima Gyeln. 1931 (see below for synonymy)G94
|--P. queenslandensis Hale 1987G94
|--P. salcrambidiocarpa Hale 1987G94
|--P. signifera Nyl. 1888 [=P. saxatilis var. signifera (Nyl.) Müll.Arg. 1892]G94
|--P. stellarisH04
|--P. stygiaC74
| |--P. s. var. stygiaC74
| `--P. s. var. septentrionalisC74
|--P. subcoerulea Wilson 1889 (n. d.)G94
|--P. sulcata Taylor 1836G94
|--P. tenuirima Hook.f. & Taylor 1844 (see below for synonymy)G94
| |--P. t. f. tenuirimaG94
| `--P. t. f. multifida Wilson 1893 (n. d.)G94
`--P. testacea Stirt. 1878 (see below for synonymy)G94

Nomina nuda: Parmelia neohollandica Nyl. 1886G94
Parmelia pubescens Wilson 1890G94

Parmelia Ach. 1803 (nom. cons.) [incl. Aspidelia Stirt. 1900, Lichen L. 1753 (nom. rej.), Parmeliomyces Thomas ex Cif. & Tomas. 1953]KC01

Parmelia afrorevoluta Krog & Swinscow 1979KC01, G94 [=Hypotrachyna afrorevoluta (Krog & Swinscow) Krog & Swinscow 1987G94, Parmelinopsis afrorevoluta (Krog & Swinscow) Elix & Hale 1987G94]

Parmelia caperata [incl. P. caperata var. sorediosa Wilson 1889 (n. n.) nec P. ochroleuca f. sorediosa Müll.Arg. 1883 nec P. mundata f. sorediosa]G94

Parmelia pseudotenuirima Gyeln. 1931 [=P. tenuirima f. isidiosa Müll.Arg. 1896 nec P. limbata f. isidiosa Müll.Arg. 1887 nec P. conspersa var. stenophylla f. isidiosa Müll.Arg. 1892 nec P. virens f. isidiosa Müll.Arg. 1892]G94

Parmelia tenuirima Hook.f. & Taylor 1844 [incl. Aspidelia beckettii Stirt. 1900 (nom. inv.), P. tenuirima var. coralloidea Wilson 1887 (n. n.) nec P. hypoleuca var. coralloidea Müll.Arg. 1887 nec P. borreri var. coralloidea, P. tenuirima var. platyna Zahlbr. 1941, P. tenuiscypha Taylor 1847]G94

Parmelia testacea Stirt. 1878 [incl. P. tenuirima var. erimis Nyl. 1885, P. erimis (Nyl.) Hillmann 1939, P. signifera f. pallidior Zahlbr. 1941, P. rudior Nyl. 1888]G94

*Type species of generic name indicated

References

Ahmadjian, V. 1960. The lichen association. Bryologist 63 (4): 250–254.

Ahmadjian, V. 1965. Lichens. Annual Review of Microbiology 19: 1–20.

[BB05] Banik, D., & P. Bujarbarua. 2005. Lichens on Agapetes D. Don ex G. Don (Ericaceae) in India. Bulletin of the Botanical Survey of India 47: 59–62.

[C74] Coineau, Y. 1974. Éléments pour une monographie morphologique, écologique et biologique des Caeculidae (Acariens). Mémoires du Muséum National d’Histoire Naturelle, nouvelle série, Série A, Zoologie 81: 1–299, 24 pls.

Crespo, A., & O. F. Cubero. 1998. A molecular approach to the circumscription and evaluation of some genera segregated from Parmelia s. lat. Lichenologist 30 (4-5): 369–380.

Elix, J. A. 1993. Progress in the generic delimitation of Parmelia sensu lato Lichens (Ascomycotina: Parmeliaceae) and a synoptic key to the Parmeliaceae. Bryologist 96 (3): 359–383.

[E99] Eriksson, O. E. (ed.) 1999. Notes on ascomycete systematics. Nos 2440–2755. Myconet 2: 1–41.

[F33] Frey, E. 1933. Cladoniaceae (unter Ausschluss der Gattung Cladonia), Umbilicariaceae. In: Die Flechten (Dr. L. Rabenhorst’s Kryptogamenflora von Deutschland, Österreich und der Schweiz vol. 9 sect. 4 pt 1. Akademische Verlagsgesellschaft M. B. H.: Leipzig (reprinted 1971. Johnson Reprint Corporation: New York).

[G94] Grgurinovic, C. (ed.) 1994. Flora of Australia vol. 55. Lichens—Lecanorales 2, Parmeliaceae. Australian Biological Resources Study: Canberra.

[H04] Haeckel, E. 1899–1904. Kunstformen der Natur. Bibliographisches Institut: Leipzig und Wien.

[KC01] Kirk, P. M., P. F. Cannon, J. C. David & J. A. Stalpers. 2001. Ainsworth & Bisby’s Dictionary of the Fungi 9th ed. CAB International: Wallingford (UK).

Molina, M. del C., A. Crespo, O. Blanco, H. T. Lumbsch & D. L. Hawksworth. 2004. Phylogenetic relationships and species concepts in Parmelia s. str. (Parmeliaceae) inferred from nuclear ITS rDNA and β-tubulin sequences. Lichenologist 36 (1): 37–54.

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