Morphologically different from all other Ramalina species in Macaronesia (Aptroot & Schumm 2008) and elsewhere in the world. See Aptroot & Schumm (2008) for a key to distinguish this species from othres
Thallus saxicolous, ascending, up to 6 cm high, tufted from a holdfast
2-4 mm diam., sparingly to moderately branched, branching mainly dichotomous but in part irregular. Laciniae solid, 0.2-3(-4)mm wide, subterete to complanate, tapering gradually to blunt apices, linear pseudocyphellae often present near base. Soralia lateral, delimited, oval, with longest axis 0-5—1 mm, producing coarse, c. 200 μm diam. granules and frequently also short branchlets with hook-shaped apices. Cortex 40-50 μm thick. Chondroid tissue welldeveloped, dominating the cross-section of the branch. Medullary tissue and algal cells found between the chondroid strands throughout. Apothecia not seen.
Macaronesian endemic, only known worldwide from Porto Santo Island. Not currently protected. High risk of extinction. Described already in 1990 and never found anywhere else, but always observed by lichenologist visiting the only locality.
Criterion A: does not apply
Criterion B: does not apply because of lack of trend data (otherwise AOO is c. 10 km2 and number of locations would be = 5)
Criterion C: does not apply
Criterion D: <250 m2 is occupied by this species, which is known from a single mountain top. The species fits the criteria of EN under D.
Conclusion: Ramalina erosa is proposed for status EN under criterion D.
Endemic to Porto Santo Island in Macaronesia. Described 1990 (Krogh) and never found somewhere else.
Growing together with other endemic macrolichens, such as Anzia centrifuga, Ramalina confertula, R. jamesii, R. nematodes and R. timdaliana.
The Area of Occupancy of the population is certainly less than 100 square meters. the species occurs on several volcanoes, but only at higher altitude (above 200 m), and is only known from Porto Santo. It occurs scattered between other Ramalina species.
In May 2015, an attempt was made to assess the total number of indiviuals of this species. About 100 individuals were found, on 4 different localities (Aptroot, pers. com.). The species was never present in large groups, but mixed in between other, locally more common Ramalina species. However, only 10% of the suitable habitat could investigated (much of it is on steep rock surfaces).
Population Trend: Stable
On exposed rockface of old volcanoes. Always scattered between other, dominant, Ramalina species.
The risks are trampling by tourists who go of the track and collecting by lichenologists.
The mountain tops should be protected and the visitors should be required to keep to a track.
Tourism to the summit of the Pico de Facho should be strictly regulated, either by forbidding access altogether (which will impossible to control) or rather by opening a small trail and putting an information shield in place alerting the tourist on the unique lichens present, and the harm done to them by trampling.
The species should feature on a leaflet with protected plants.
Krog, H. 1990 New Ramalina species from Porto Santo, Madeira. Lichenologist 22(3): 241-247
Aptroot, A and Schumm, F. 2008 Key to Ramalina species known from Atlantic islands, with two new species from the Azores. Sauteria 15: 21-57.