Cladonia callosa


Cladonia callosa

Delise ex Harm. (1907)
Cladonia fragilissima
Conservation Status
LC NS (Key)
BLS Number
Taxon Photo
General Description

A small Cladonia, of banks and open ground in heathland and moorland and post industrial sites, mostly occurring as sterile mats of basal squamules with brown to grey-green upper surfaces and bright white tomentose undersides, but occasionally supporting small distinctive branched podetia. Has a distinctive UV fluorescence.


Predominantly occurring as sterile mats of small, 1-5mm long squamules, usually a warm shade of brown, bronze-green or, in the shade, grey-green. The undersides are distinctive, being bright white and tomentose. The podetia are infrequent and small, to 1.5cm high. These are grey-green and areolate, with a white cortex showing through, forming a mosaic. Older podetia can be more decorticate and blackened at the base. The podetia are typically branched at one point, essentially formed by proliferating branches from the rim of a small perforated cup. Apothecia brown and found in terminal clusters at apex of the podetia.  

Reactions: thallus C–, K–, KC–, Pd–, UV+ strongly blue-violet; parma violet colour (grayanic acid).

An easily over looked Cladonia when sterile, but can be identified by the combination of negative spot tests, the very bright UV fluorescence and the tomentose white underside. It is most similar to sterile Cladonia crispata, which also has brown squamules, with negative spot tests and a bright but whiter UV fluorescence. The key difference is the tomentose underside of Cladonia callosa; the undersides of Cladonia crispata squamules are also bright white but are smooth. Larger groups of squamules may be reminiscent of small morphs of Cladonia strepsilis, but this is is C+ emerald green (strepsilin). When the small branched podetia are present the species is very distinctive.

The UV fluorescence is so bright that the species can be detected by scanning likely heathland banks and path sides with a UV lamp on overcast days.


On very acid humus rich soils, ranging from well drained to sometimes waterlogged, typically where recently disturbed, but also on long established open patches in low productivity lowland wet heaths. Found on banks and path edges in lowland heaths and also rarely in acidic post industrial sites. In the uplands mainly found on the edges of peat haggs and on thin soils over rocks.

It appears to be quite a mobile species, being occasionally found in quarries and post industrial sites at some distance from more stable habitats.

Distribution Map
Key to map date classes

Likely to be very under recorded and probably widespread in the uplands.  Recent intensive surveying in the New Forest heaths found it to a widespread and characteristic species of lichen rich heathland here, but it appears to now be very rare in the lowlands beyond the New Forest. Sampling in the uplands in Britain and Ireland suggests it is still widespread here and is to be looked for anywhere with disturbed exposed humus or peat.

Worldwide it appears to be a western European endemic, found from Norway to France.  Britain is likely to support a large proportion of the world population.

Threats & Status

A little known species but one than appears to be dependant on regular disturbance regimes and the maintenance of openness in heathland habitats.  The species is frequent on the still traditionally managed New Forest, which suggests it would once have been frequent in many other lowland heathlands. Sampling suggests that it is now very rare now beyond the New Forest in the lowlands in lightly or unmanaged heaths but frequent and very over looked in the uplands.  However, a survey of Ashdown Forest in 2020, indicated that, as a pioneer species, it can respond rapidly to grazing restoration and quickly become frequent. Probably much less threatened in the uplands but could decline with abandonment of tradition moorland management.

Britain: Notable. If as widespread as sampling suggests, then the British population will be of international importance, so potentially an International Responsibility species.

Wales: Data Deficient


Ahti, T. & Stenros (2013) Cladonia.  In:  Nordic Lichen Flora, Volume 5 Cladoniaceae (ed. T. Ahti, S. Stenros & R. Moberg) 8-86.  Uppsala:  University of Uppsala.

Aptroot, A., van Herk, K. & Sparrius, L. (2011) Korstmossen van Duin, Heide en Stuifzand.  Bryologische en Lichenologische Werkgroep van de KNNV

James, P. W. (2009) Cladonia P. Browne (1756).  In:  The Lichens of Britain and Ireland (C. W. Smith, A. Aptroot, B. J. Coppins, A. Fletcher, O. L. Gilbert, P.W. James & P. A.  Wolseley, eds): 309 – 338. London:  British Lichen Society.

Sanderson, N. A. (2017) The New Forest Heathland Lichen Survey 2011 – 2015.  A report by Botanical Survey & Assessment to Natural England, Forest Enterprise & The National Trust. Link

Text by Neil A Sanderson, based on James (2009)

Lichenicolous Fungi
Arthrorhaphis aeruginosa R. Sant. & Tønsberg