Rhizocarpon geographicum subsp. geographicum
Common name
Map lichen
Synonyms
Lichen geographicus, Rhizocarpon geographicum var. neozelandicum, Rhizocarpon geographicum var. knightii, Rhizocarpon neozelandicum
Family
Rhizocarpaceae
Flora category
Lichen – Native
Endemic taxon
No
Endemic genus
No
Endemic family
No
Structural class
Lichens - Crustose
Current conservation status
2018 | Not Threatened | Qualifiers: SO
Brief description
Characterised by the saxicolous habit; the bright greenish yellow, areolate thallus dispersed on a black prothallus, that is also often well-developed at margins; subimmersed to sessile black apothecia, on or between areolae; a red-brown to olive green-brown epithecium (K+ purplish red); a colourless to pale-greenish or -brownish hymenium; a dark-brown hypothecium; 8-spored asci; and dark greenish brown to black, muriform (6–24 cells in optical section) ascospores, (20–)22–40(–46) × 10–20(–22) μm and rhizocarpic and psoromic acids in the medulla.
Distribution
North Island: Northland (Kawerua, Bay of Islands, Urupukupuka Island, Chicken Island, Great Barrier Island, Goat Island), Auckland (Karekare, Piha, Rangitoto Island), South Auckland (Mt Tarawera, Mt Maunganui, Kaimanawa Ranges), Wellington (Ruapehu, Tararua Mts). South Island: Nelson (Cobb Valley, Mt Arthur), Marlborough (Mt Stokes, Chetwode Is), Canterbury (Arthur’s Pass, Sebastopol, Mt Cook), Otago (Central Otago mountains, Maungatua, Flagstaff, Dunedin), Southland (Fiordland, West Dome, Takitimu Mts, Lumsden, Hokonui Hills). Stewart Island: (Mt Anglem, Mt Allen). Auckland Islands. Campbell Island: (Beeman Hill).
Cosmopolitan. Known also from Great Britain, Europe, Scandinavia, the Artic, Morocco, Tunisia, Turkey, the Ukraine, Asia, North America, South America, Marion I, Bouvetøya, South Georgia, South Shetland Is, South Orkney Is, Antarctica, and Australia,
Habitat
A very widespread species, on maritime to high-alpine rocks, and on gravel chippings in bitumen and on walls, bridge cappings and gravestones in cemeteries in lowland and urban habitats.
Detailed description
Thallus crustose, orbicular to irregularly spreading or in coalescing patches, to 20 cm diam., prothallus black, often conspicuous at margins and between areolae. Areolae contiguous to dispersed, to 2 mm diam., rarely rounded, ± angular, flat to convex, bright yellow to greenish-yellow, smooth, dull or glossy. Apothecia to 1.5 mm diam., between areolae, rounded to angular, flat, matt, rarely subconvex, margins thin, distinct or disappearing. Hypothecium dense, brown-black 100-300 µm tall. Hymenium 100-180 µm tall colourless or faint brownish. Asci 100-150 × 20-30 µm containing 8 spores. Ascospores muriform with few to many septa 20-40 × 10-22 µm.
Chemistry: Thallus K−, C− or ±red, Pd− or ±orange-yellow; containing rhizocarpic acid and either psoromic or barbatic acids and sometimes ±gyrophoric acid.
Similar taxa
Rhizocarpon geographicum subsp. arcticum has a whitish yellow to white thallus, rather than the bright greenish yellow thallus of R. geographicum subsp. geographicum.
Substrate
Saxicolous
Attribution
Fact sheet prepared by Melissa Hutchison (31 December 2021). Brief description, Distribution, Habitat, and Features sections copied from Galloway (1985, 2007).
References and further reading
Galloway D.J. 1985: Flora of New Zealand: Lichens. Wellington: PD Hasselberg, Government Printer. 662 pp.
Galloway D.J. 2007: Flora of New Zealand: Lichens, including lichen-forming and lichenicolous fungi. 2nd edition. Lincoln, Manaaki Whenua Press. 2261 pp.