Rhizoplaca
Rhizoplaca Zopf, 1905
| Common name | Rock-posies | |
|---|---|---|
| Field Characters | Crustose, areolate, squamulose or leaf-like, pale chlorolichens. Thalli to 3 cm across, typically thick, unbranched, either attached broadly (crustose to areaolate), with a central holdfast (umbilicate), attached along one edge (squamulose) or unattached (vagrant). Upper cortex creamy grey to pale yellow, slightly shiny. Lower cortex typically present (absent in crustose species), varying from smooth and grey to black to cracked, exposing chalky or cartilaginous medulla. Lacking rhizines. Vegetative propagules absent, apothecia common. Apothecia may be laminal or marginal, and the color of the disc is an important feature to separate some species, varhing from greenish grey to salmon pink. | |
| Similar species & genera |
Lecanora, Protoparmeliopsis: taxonomists have repeatedly broken down and reassembled genera traditionally separated by their growth form. Some crustose and areaolate species have been shuffled repeatedly. Here we retain a slightly older concept of Rhizoplaca in alignment with NatureServe. | |
| Ecology | Saxicolous or vagrant. Common in the grasslands and mountains, rare in the parkland and shield regions of Alberta. | |
| Chemistry | Cortices C–, K–, KC+ yellow, PD– (usnic acid), rarely lacking usnic acid and then KC-. Medullary chemistry variable. | |
| Molecular support |
Poor. Rhizoplaca as originally delimited is polyphyletic (Arup and Grube 2000; Zhao et al. 2016). Rhizoplaca peltata is currently considered part of Parmeliopsis. The remaining three species are known to include multiple, monophyletic clades, an example of cryptic diversity (Leavitt et al. 2013; Szczepańska et al. 2020). Until we have sequenced local material, these species concepts are adopted in the broad sense. | |
| Links |
Species recorded in Alberta: 4
- R. chrysoleuca (Sm.) Zopf Syns.: Lecanora chrysoleuca, L. rubina (ABMI, ACIMS)
- R. melanophthalma (DC.) Leuckert & Poelt Syn.: Lecanora melanophthalma (ABMI, ACIMS)
- R. peltata (Ramond) Leuckert & Poelt. The most current accepted name is Protoparmeliopsis peltata Syn.: Lecanora peltata (ACIMS)
- R. subdiscrepans (Nyl.) R. Sant. (ABMI, ACIMS)
DICHOTOMOUS KEY
1a. Lower surface with white cracks creating a net-like pattern; medulla chalky in texture; apothecia brown and embedded in thallus when young; usually on calcareous rocks (in Alberta in mountains)…..R. peltata
1b. Lower cortex with at most radial cracks but typically continuous; medulla cartilaginous; apothecia various…..2
2a. Apothecia orange to tan…..3
2b. Apothecia olive-black to olive to tan…..R. melanophthalma
3a. Thallus of crowded, stalked lobes, appearing almost crustose with swollen lobes…..R. subdiscrepans
3b. Thallus umbilicate, often lumpy and irregular but not crustose; lower cortex often blackening at margin and slightly visible from above, creating a striking contrast with the yellow to whitish upper cortex; common especially on siliceous rock in the mountains and grasslands…..R. chrysoleuca
Resources
Arup, U. & M. Grube. 2000. Is Rhizoplaca (Lecanorales, lichenized Ascomycota) a monophyletic genus? Canadian Journal of Botany 78: 318-327.
Brodo, I. M. 1986. A new lobate species of the lichen genus Lecanora (Ascomycotina, Lecanoraceae). Mycotaxon, 26: 309–317.
Keuler, R. 2023. Assessing the role of hybridization in the evolution of two common lineages of lichen-forming fungi. PhD Dissertation, Brigham Young University. 94 pp.
Leavitt S., F. Fernández-Mendoza, S. Pérez-Ortega, M. Sohrabi, P. Divakar, T. Lumbsch, L. St. Clair. 2013. DNA barcode identification of lichen-forming fungal species in the Rhizoplaca melanophthalma species-complex (Lecanorales, Lecanoraceae), including five new species. MycoKeys 7: 1-22. https://doi.org/10.3897/mycokeys.7.4508
McCune, B. 1987. Distribution of chemotypes of Rhizoplaca in North America. The Bryologist 90: 6-14.
McCune, B. & R. Rosentreter. 2007. Biotic soil crust lichens of the Columbia Basin. Monographs in North American Lichenology 1: 1-205.
Ryan, B. D. & T. H. Nash III. 1997. Placodioid taxa of Lecanoraceae sensu Zahlbr. (lichenized Ascomycotina) in North America: taxa excluded from Lecanora subgen. Placodium. Nova Hedwigia 64: 393–420.
Szczepańska K., J. Urbaniak & L. Śliwa. 2020. Taxonomic recognition of some species-level lineages circumscribed in nominal Rhizoplaca subdiscrepans s. lat. (Lecanoraceae, Ascomycota) PeerJ 8:e9555 https://doi.org/10.7717/peerj.9555
Zhao X., S. D. Leavitt, Z. T. Zhao, L. L. Zhang, U. Arup, M. Grube, S. Pérez-Ortega, C. Printzen, L. Śliwa, E. Kraichak, P. K. Divakar, A. Crespo & H. T. Lumbsch. 2016. Towards a revised generic classification of lecanoroid lichens (Lecanoraceae, Ascomycota) based on molecular, morphological and chemical evidence. Fungal Diversity 78: 293-304.
