| TAXON: | Cladonia portentosa (Dufour) Coem. (1865) |
| RECENT SYNONYMS: | Cladonia azorica Ahti (1961) |
| FAMILY: | Cladoniaceae |
| GROWTH FORM: | Secondary thallus fruticose, heteromerous (podetiate); primary thallus crustose, heteromerous (squamulose) |
| SUBSTRATES: | Mineral soil, peat |
| PHOTOBIONT: | Asterochloris alga |
| REPRODUCTION: | Pycnidia |
| ASCUS: | – |
| SPORES: | Conidia curved |
| NOTABLE FEATURES: | Podetia ecorticate, hollow, richly and mainly trichotomously branching in all directions, often interweaving to form small thickets; axils between branches often perforate; primary thallus evanescent |
| CHEMICAL TESTS: | Thallus KC± pale yellow, Pd± red, UV+ light blue (perlatolic acid, ±usnic acid, ±fumarprotocetraric acid) |
| HABITAT: | Heathlands, moorlands, stabilised dunes; sometimes woodland (leaning or fallen tree trunks) |
| DISTRIBUTION: | Widespread and common in Britain, though less common in Midlands due to past industrial pollution |
| CONSERVATION STATUS: | Least Concern |
| LICHENICOLOUS FUNGI: | Abrothallus cladoniae, Cercidospora cladoniicola, Cryptodiscus cladoniicola, Niesslia cladoniicola |
| IDENTIFICATION DIFFICULTY: | Green 1: Field identification possible |
| CONFUSION SPECIES: | Cladonia ciliata, C. mediterranea |
FIELD NOTES
Cladonia portentosa is one of the three most common ‘reindeer lichens’ in Britain, alongside C. furcata and C. rangiformis. It tends to grow in little cream-coloured thickets on heaths, moors or dunes where vascular plants haven’t been able to take over. And there’s a foolproof test you can use to tell when you’ve encountered it.
C. portentosa is one of only two reindeer lichens in Britain to produce perlatolic acid. This substance causes the lichen to fluoresce a striking ice-blue in ultraviolet light. If you can create sufficient shade with a jacket, hat or bag, you can use your UV torch to pick out C. portentosa even from among a tangle of multiple reindeer-lichen species.
The other British reindeer lichen that produces perlatolic acid is C. mediterranea. Not only does it fluoresce ice-blue, it also looks very much like C. portentosa. But it’s exceedingly rare, and unless you find yourself in a couple of very specific locations in Cornwall where it grows, you can fully discount it.
Apart from perlatolic acid, which is reliably present, C. portentosa is chemically variable. It may produce fumarprotocetraric acid, in which case it reacts Pd+ orange-red. It may also produce usnic acid, in which case it reacts KC+ pale yellow. But it might not produce either substance, so the UV-test is probably the only test useful to conduct on this lichen.
It’s worth mentioning that you don’t need a UV torch to identify C. portentosa in the field, thanks to its fairly distinctive appearance. Like C. ciliata, its pale podetia lack a cortex, and they have a felted texture. But unlike C. ciliata, which branches dichotomously and exhibits a ‘nap’ or directional bend, C. portentosa branches mainly trichotomously in all directions, somewhat like a head of broccoli. It also tends to develop a hole in the axil or ‘crook’ between its branches.
It would be harder to confuse C. portentosa with its common cousins C. furcata and C. rangiformis. Not only do they branch dichotomously, but their podetia also have a cortex and tend to be mottled or brownish in colour.
LAB NOTES
Cladonia portentosa can normally be identified without microscopy.
SPECIMENS
Cladonia portentosa : England : VC25 East Suffolk : TM4468 : September 2024 : On mineral soil
Cladonia portentosa : Scotland : VC98 Argyll : NR8393 : August 2024 : On mineral soil
Cladonia portentosa : Scotand : VC101 Kintyre : NR6974 : August 2024 : On mineral soil
Cladonia portentosa : Scotland : VC101 Kintyre : NR7372 : August 2024 : In soil pocket on siliceous boulder
Cladonia portentosa : Scotland : VC101 Kintyre : NR7372 : August 2023 : In soil pocket on siliceous boulder
Cladonia portentosa : Scotland : VC101 Kintyre : NR6974 : August 2023 : On moss on siliceous boulder
