| TAXON: | Cladonia glauca Flörke (1828) |
| RECENT SYNONYMS: | – |
| FAMILY: | Cladoniaceae |
| GROWTH FORM: | Secondary thallus fruticose, heteromerous (podetiate); primary thallus crustose, heteromerous (squamulose) |
| SUBSTRATES: | Rotting wood, particularly tree-stumps; exposed peat |
| PHOTOBIONT: | Asterochloris alga |
| REPRODUCTION: | Pycnidia; apothecia very rare |
| 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 grey-green, pointed and with brown apical pycnidia, but sometimes branched towards tips, and more rarely with narrow scyphi; upper part farinose sorediate; middle part sometimes with thin longitudinal fissure; basal part usually densely squamulose; squamules small, incised, with white undersides |
| CHEMICAL TESTS: | Medulla typically UV+ white but otherwise negative (squamatic acid); or K+ yellow to orange, Pd+ yellow and UV- (thamnolic acid) |
| HABITAT: | Woodland; heathland; moorland |
| DISTRIBUTION: | Widespread but scattered; locally common in Scotland |
| CONSERVATION STATUS: | Least Concern |
| LICHENICOLOUS FUNGI: | Heterocephalacria bachmannii |
| IDENTIFICATION DIFFICULTY: | Amber 3: Field identification may not be possible |
| CONFUSION SPECIES: | Cladonia macilenta, C. rei, C. subulata |
FIELD NOTES
Cladonia glauca is an uncommon ‘heath-tail’ Cladonia found across Britain, particularly on old, rotting tree-stumps or exposed peat. It’s perhaps commoner than we think, as it’s fairly easily confused with other ‘heath-tail’ species, and it may be under-recorded. If you find a ‘heath-tail’ on a tree-stump that looks something like the lichen in the specimen gallery below, it might be worth taking care to determine whether you have C. glauca.
You should first check whether the pycnidia at the tips of the podetia are brown or red. If the latter, or if red apothecia are present, then your lichen certainly isn’t C. glauca, and you might consider C. macilenta instead. The podetia of C. macilenta also usually lack the abundant squamules that tend to characterise C. glauca, as well as the thin, longitudinal fissure that you can also sometimes find with C. glauca.
If the pycnidia are brown, your next step is to test with Pd. If your lichen is Pd+ orange-red or rust-red from fumarprotocetraric acid, then it’s certainly not C. glauca, and you might consider C. subulata instead. C. subulata can resemble C. glauca perhaps even more closely than C. macilenta does, though its podetia tend to sport squamules less often, and a thin, longitudinal fissure more often.
But if the pycnidia are brown, and your lichen also tests Pd- or Pd+ yellow, then you have C. glauca. In England, there’s also a slight chance you might have the rare C. rei. But C. rei tends to test Pd+ yellow turning orange slowly if not Pd-, to be green-brown rather than grey-green, to have granular rather than farinose soredia in some cases, and to grow on mineral soil rather than tree-stumps or peat.
So far, so good. But what if you’re unsure of the colour of the pycnidia, or if you can’t find any? Your task has become much harder. C. glauca and C. macilenta can otherwise resemble each other too closely to distinguish conclusively from appearance alone.
Unhappily, chemical tests can’t help. C. glauca can sometimes produce thamnolic acid like C. macilenta usually does, in which case its medulla also tests K+ yellow to orange and Pd+ yellow. And C. macilenta can sometimes lack thamnolic acid like C. glauca usually does, in which case its medulla also tests K- and Pd-.
In this situation, the sensible decision is to move on and try to find better-developed material. If you can’t find any, or if you’re obliged to analyse the material before you, see the lab notes below for further advice.
LAB NOTES
It may not be possible to identify Cladonia glauca in the field. It might also not be desirable, if your find would be the first record for C. glauca in the area. In either case, and assuming you’ve followed the advice in the field notes above, it’s likely that the main confusion species that you need to rule out is C. macilenta.
Collect a small sample of your suspected C. glauca for examination at your bench. Never collect the whole lichen! Ensure that your sample is dry before you begin your analysis, as the necessary chemical and UV-tests won’t produce sufficiently clear results from wet material.
Examine your sample under the stereomicroscope. You might find red pycnidia at the tips of the podetia that you somehow overlooked in the field. If you find any, you can confidently conclude you don’t have C. glauca, and that you probably do have C. macilenta.
You might also find thin, longitudinal fissures in the podetia that you overlooked in the field. If you find them, you can conclude that you have either C. glauca or C. subulata. You can then apply a Pd-test as per the field notes above to determine the species to which your lichen belongs.
If you’re still unsure, or if you need conclusive evidence for a first record, then test three different spots on the medulla of your sample with K, Pd and UV. If you find that these spots are:
- K-, Pd- and UV+ pale blue, your lichen is C. macilenta (with barbatic but not thamnolic acid)
- K-, Pd- and UV+ white, your lichen is C. glauca (with squamatic acid)
However, if you find that these spots are K+ yellow to orange, Pd+ yellow and UV-, then:
- Your lichen is probably C. macilenta (with thamnolic and barbatic acid)…
- …or your lichen is possibly C. glauca (with thamnolic acid)
In that case, it’s probably best to abandon your analysis in the hope of finding better-developed material on another occasion. If the morphological characters described in the field notes above were clear enough, you probably wouldn’t have reached this late stage of analysis!
When conducting your UV test, bear in mind that the lichen and its backdrop can reflect some of the UV light, which both your eyes and your digital camera sensor will interpret as blue or mauve. This reflected UV light can mask the true UV+ white fluorescence of the squamatic-acid chemotype of C. glauca. Even under controlled conditions, it can be difficult to distinguish between UV reflectance and UV fluorescence.
To ‘reduce’ UV reflectance, photograph a UV test with a good camera in RAW mode, adjust the white-balance in post-production by ‘warming’ to at least 8000-10000K, and shift the tint sharply to purple. The resulting image will more clearly show any true UV fluorescence, despite being somewhat artificial. The UV-test image below has been digitally developed in this manner.
SPECIMENS
Cladonia glauca : England : VC28 West Norfolk : TF9428 : October 2024 : On well-rotted tree-stump : First record for hectad
