Cladonia furcata

10 December 2024

TAXON:	Cladonia furcata (Huds.) Baumg. (1790)
RECENT SYNONYMS:	Cladonia furcata subsp. subrangiformis (Sandst.) Abbayes (1938)
FAMILY:	Cladoniaceae
GROWTH FORM:	Secondary thallus fruticose, heteromerous (podetiate); primary thallus crustose, heteromerous (squamulose)
SUBSTRATES:	Mineral soil, including calcareous soil (particularly C. furcata subsp. subrangiformis); mossy basic rocks
PHOTOBIONT:	Asterochloris alga
REPRODUCTION:	Pycnidia; apothecia occasional
ASCUS:	If present, elongate-clavate; apex thickened, with K/I+ blue tholus and deep-blue gelatinous outer sheath; 8 spores
SPORES:	Conidia curved; ascospores if present ellipsoid
NOTABLE FEATURES:	Podetia tall, corticate, hollow, dichotomously and usually narrowly branching; cortex smooth, brown or mottled green and white; apothecia if present brown; primary thallus evanescent, but some squamules with white, ecorticate undersides may remain on basal parts of podetia C. furcata subsp. subrangiformis: podetia thick, supine, worm-like, with perpendicular branching from main stem; cortex rough, warty, darker
CHEMICAL TESTS:	Thallus K± dingy or rarely ‘clean’ yellow, Pd+ red (fumarprotocetraric acid, ±atranorin) C. furcata subsp. subrangiformis: thallus K+ yellow, Pd+ red, K/UV+ yellow (atranorin, fumarprotocetraric acid)
HABITAT:	Grasslands, calcareous turf (particularly C. furcata subsp. subrangiformis), heathlands, dunes, lawns, mossy rocks in woodlands
DISTRIBUTION:	Widespread and common in Britain
CONSERVATION STATUS:	Least Concern
LICHENICOLOUS FUNGI:	Bachmanniomyces punctum, Cercidospora cladoniicola, Epicladonia sandstedei, Epicladonia simplex, Heterocephalacria bachmannii, Lichenoconium erodens, Lichenosticta alcicornaria
IDENTIFICATION DIFFICULTY:	Green 1: Field identification possible Green 2: Field identification possible with care (C. furcata subsp. subrangiformis)
CONFUSION SPECIES:	Cladonia rangiformis

FIELD NOTES

Cladonia furcata is one of the three most common species of ‘reindeer lichen’ in Britain, alongside C. portentosa and C. rangiformis. You’ll most often encounter it on more-or-less acidic soil in grasslands, heathlands and stabilised dunes. Its name is apt, as its tall, forked podetia are distinctive.

All the same, you might confuse C. furcata with C. rangiformis at first glance. The podetia of both species branch dichotomously, they’re both hollow, and they both have a smooth cortex. Yet they can be told apart fairly readily.

Relative to C. rangiformis, C. furcata tends to be taller and more gracile in overall appearance. Its ‘gracefulness’ is due in large part to the way it branches: less richly than C. rangiformis, and at generally narrower angles. And though the primary, squamulose thallus of both species disappears as they mature and produce podetia, persistent squamules sometimes cling to the basal parts of the podetia of C. furcata.

It’s sometimes said that C. furcata tends to the brownish, while C. rangiformis displays a characteristic green-and-white mottling resembling giraffe spots or crazy paving. But while the mottling of C. rangiformis is more obvious, and the species is rarely if ever brown, C. furcata can sometimes look quite pale, and it can also show distinct mottling. You shouldn’t rely on colour alone, but only in conjunction with form as described above.

Both C. furcata and C. rangiformis are chemically variable. Spot-tests can only add weight to an identification you’ve reached by examining form and colour. That said, in Britain C. furcata doesn’t normally react K+ yellow from atranorin, and it always reacts Pd+ red from fumarprotocetraric acid.

By contrast, C. rangiformis always reacts K+ yellow, and only occasionally Pd+ red. Don’t mistake a K+ dingy or brownish yellow reaction, which sometimes results from fumarprotocetratic acid, with a ‘clean’ K+ yellow reaction from atranorin. C. rangiformis will always show the latter, but C. furcata will often show the former.

If you’re unsure, shine a UV torch on your spot-test. Atranorin always gives a K/UV(dry)+ bright yellow signal, while fumarprotocetraric acid never does. Both K/UV(dry) results, positive and negative, are shown in the galleries below.

Now, the notes above hold true for most of the C. furcata specimens you’ll encounter. However, you might find a special ‘morph’ of C. furcata, particularly on calcareous ground. This morph is called C. furcata subsp. subrangiformis, though in truth it’s more a forma than a subspecies, as recent research suggests there’s no genetic distinction involved. Nevertheless, it’s recorded separately in Britain for ecological reasons (note the two BLS numbers above).

As its name suggests, C. furcata subsp. subrangiformis looks more like C. rangiformis than ‘ordinary’ C. furcata, and it more usually tests K+ yellow from atranorin. Yet it’s still quite distinct from C. rangiformis in form. It tends to be low, supine and worm-like, with a robust but creeping main stem from which branches diverge nearly at right angles. It also has a rougher cortex, often with small, burst spots on the main stem.

LAB NOTES

Cladonia furcata can normally be identified without microscopy.

SPECIMENS

Cladonia furcata subsp. furcata : England : VC25 East Suffolk : TM4468 : September 2024 : On mineral soil