Cladonia chlorophaea sens. lat.

22 March 2025

TAXON:	Cladonia chlorophaea sens. lat.
RECENT SYNONYMS:	–
FAMILY:	Cladoniaceae
GROWTH FORM:	Secondary thallus fruticose, heteromerous (podetiate); primary thallus crustose, heteromerous (squamulose)
SUBSTRATES:	Mineral soil, including among and on moss; decaying wood and timber (C. grayi sens. lat. typically on more acid substrates)
PHOTOBIONT:	Asterochloris alga
REPRODUCTION:	Pycnidia; apothecia frequent; sometimes sorediate
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:	Basal squamules small, often inconspicuous, sometimes erect or incised; podetia green-gray, or sometimes brownish (particularly C. grayi sens. lat.); podetia surface corticate below, becoming granular above as though dusted in caster sugar, sometimes partly sorediate (particularly C. chlorophaea sens. str.); exposed medulla white, or pink-brown (particularly C. grayi sens. lat.); scyphus wider than stalk, gradually tapered, often proliferating from rim, granular or partly sorediate within; apothecia and pycnidia brown, on scyphus rim, sometimes stalked.
CHEMICAL TESTS:	Pd+ orange-red, but otherwise varies by cryptic species: see table in lab notes
HABITAT:	Heathland, grassland and moorland (particularly C. grayi sens. lat.); woodland
DISTRIBUTION:	Common and widespread in Britain
CONSERVATION STATUS:	Least Concern
LICHENICOLOUS FUNGI:	Arthrorhaphis aeruginosa, Epicladonia sandstedei, E. stenospora, Heterocephalacria bachmannii, Lichenoconium pyxidatae
IDENTIFICATION DIFFICULTY:	Green 1: Field identification possible
CONFUSION SPECIES:	Cladonia cyathomorpha, C. fimbriata, C. humilis, C. pocillum, C. pyxidata

FIELD NOTES

Cladonia chlorophaea sens. lat. was once thought to be a single species, and indeed one of the most common ‘pixie-cup’ Cladonia in Britain. Today, it’s understood to be a group of at least six cryptic species. The precise distribution of each of these species isn’t fully clear, because they’re extremely difficult to distinguish except by advanced techniques such as thin-layer chromatography or DNA sequencing.

Fortunately, it’s not too difficult to recognise C. chlorophaea in the broad sense. For its part, the British Lichen Society also accepts C. chlorophaea sens. lat. as a pragmatic recording category. You should always use it unless you’re an experienced recorder.

If you do have that experience, and you’d like to try to analyse your specimen further, see the lab notes below. Otherwise, read on for help distinguishing C. chlorophaea sens. lat. from other common ‘pixie-cup’ Cladonia species.

The best method is to examine the surface of the podetia closely. They tend to be corticate or squamulose at the base, but covered in corticate granules further up, including within the cup. The texture of these corticate granules is rather fine, recalling caster sugar.

By contrast, the podetia of other ‘pixie-cups’ you might expect to encounter have different surface textures. C. pocillum, C. pyxidata and C. cyathomorpha also produce corticate granules, but they’re comparatively coarse, recalling granulated sugar rather than caster sugar. Likewise, though C. chlorophaea sens. lat. might become sorediate in part, its podetia aren’t fully farinose-sorediate, like those of C. fimbriata or most specimens of C. humilis.

C. chlorophaea sens. lat. differs from other ‘pixie-cups’ in additional ways as well. If you’re unsure of the surface texture of the podetia of your specimen, you might also note that:

C. cyathomorpha tends to have large basal squamules with ‘veined’ or ‘grooved’ undersides
C. fimbriata tends to have abruptly widening scyphi, making the podetia look a bit like golf-tees
C. humilis tends to have conspicuously short podetia, and it can react K+ yellow from atranorin
C. pocillum tends to have well-developed, horizontally spreading basal squamules
C. pyxidata tends to have more obvious, rounded and erect basal squamules

It might seem daunting to try to separate all these similar species by observing surface texture and other tiny characteristics. But as with most Cladonia, once you know what you’re looking for, it becomes easier to spot.

LAB NOTES

Cladonia chlorophaea sens. lat. can normally be identified without microscopy. But if you’re an experienced recorder, you might like to try narrowing down your specimen to one of the cryptic species in the group: C. chlorophaea sens. str. on the one hand, or one of the ‘C. grayi sens. lat.’ subgroup on the other, which includes C. asahinae, C. cryptochlorophaea, C. grayi, C. merochlorophaea and C. novochlorophaea.

If so, you’ll need to conduct a series of careful chemical and ultraviolet tests. Some of these tests are fleeting, some unreliable, and some are just hard to observe in the field. You’ll want to collect a sample for analysis under controlled conditions.

As a first step in your analysis, you should note the following features:

If the podetia of your specimen are more greenish, and if the exposed medulla is white, you may have C. chlorophaea sens. str.
If the podetia of your specimen are more brownish, and if the exposed medulla is pink-brown, you may have one of the ‘C. grayi sens. lat.’ species

As shown in the table below, testing your specimen will involve the full range of basic lichenological reagents, plus ultraviolet light.

Taxon	C	K	KC	Pd	UV
C. asahinae	–	–	–	+ red	–
C. chlorophaea sens. str.	–	–	–	+ red	–
C. crypto-chlorophaea	± yellow	+ yellow turning red	+ wine-red (fleeting)	+ orange-red	+ pale yellow
C. grayi	–	–	–	± red	+ mauve-white
C. mero-chlorophaea	± red	–	+ wine-red (fleeting)	± orange-red	+ faint blue
C. novo-chlorophaea	± red	–	–	± orange-red	± white

When conducting your tests, you might find it helpful to section at least part of your specimen into small bits that you can organise on a spotting plate. A white ceramic spotting plate can also furnish a helpful background against which to see the colour reactions.

As you can see from the table above, some of the cryptic species in the C. chlorophaea sens. lat. group have the same or very similar spot-test reactions. Note also that some of the reactions aren’t always reliable. Ultimately, it may simply prove impossible to identify your specimen to cryptic species. And even if you think you’ve reached a positive conclusion, you must seek confirmation from an expert before you submit your record.

As ever with lichens, you might have to be satisfied with ‘perhaps this’ or ‘maybe that’!

SPECIMENS

Cladonia chlorophaea sens. lat. : England : VC28 West Norfolk : TF9428 : October 2024 : On well-rotted tree-stump