| TAXON: | Graphis scripta (L.) Ach. (1809) sens. str. |
| RECENT SYNONYMS: | – |
| FAMILY: | Graphidaceae |
| GROWTH FORM: | Crustose, heteromerous |
| SUBSTRATES: | Smooth bark |
| PHOTOBIONT: | Trentepohlia alga |
| REPRODUCTION: | Apothecia, pycnidia |
| ASCUS: | Clavate to subcylindrical; apex Graphis-type; (6-)8-spored |
| SPORES: | Ascospores fusiform, 5-13-septate, 20-63 × 5-12 µm, lumina elliptical or lentiform; conidia cylindrical to ellipsoidal |
| NOTABLE FEATURES: | Thallus white, smooth, thin, uneven; apothecia lirellate, black, long, branching, appearing like cryptic writing; discs black, slit-like, closed, epruinose; proper exciple not furrowed; thalline margin very narrow (<0.1 mm) |
| CHEMICAL TESTS: | – |
| HABITAT: | In shaded situations on wide variety of trees; also pioneer species on new bark |
| DISTRIBUTION: | Widespread in Britain, but mainly confined to ancient woodland in central England |
| CONSERVATION STATUS: | Least Concern |
| LICHENICOLOUS FUNGI: | Arthonia graphidicola, Stigmidium microspilum, Taeniolella punctata |
| IDENTIFICATION DIFFICULTY: | Green 2: Field identification possible with care |
| CONFUSION SPECIES: | Other Graphis species |
FIELD NOTES
Graphis scripta was once thought to be a fairly straightforward lichen to identify. Its long and branching lirellate apothecia, strongly reminiscent of cryptic writing, are unmistakeable. And it was easy to differentiate from likely alternatives with similar apothecia: G. elegans with K+ yellow turning red reaction and furrowed proper exciple, and G. inustuloides with broad, white thalline margin.
However, it’s now recognised that what was once called G. scripta is in fact four different cryptic species: G. betulina, G. persoonii, G. pulverulenta and G. scripta sens. str. This particular entry is about the last of them, which you might think of as ‘proper’ G. scripta. Data are deficient, but it seems that G. scripta sens. str. is one of the most common of the four, alongside G. pulverulenta.
Fortunately, it’s possible to distinguish these four species in the field, presuming conditions are right and you take some extra care. But if your specimen is too young and underdeveloped, or if it’s too damp for certain diagnostic features of the apothecia to be clearly visible, you won’t be able to identify it reliably. In that case, see under ‘Lab notes’ below.
Assuming you have a well-developed and dry specimen, you must first be sure it’s a candidate for G. scripta sens. lat. Examine a few of its apothecia with a hand-lens: the apothecial disc or slit should be rather narrow or closed. The ‘labia’ or proper exciples should also be generally smooth rather than furrowed, ruling out G. elegans and related species. If you’re unsure about that, test with K to ensure your specimen doesn’t react K+ yellow turning red from norstictic acid.
Once you’re convinced that your specimen meets these criteria, you’ll need to examine the apothecia more closely. Check that there’s no broad, white thalline margin (>0.1 mm) bordering the black proper exciple, ruling out G. betulina and G. inustuloides. Check also that the apothecial disc or slit is fairly tightly closed, and that wherever it’s visible it’s neither reddish brown in hue, ruling out G. persoonii, nor dusted with a whitish or greyish pruina, ruling out G. pulverulenta.
If your specimen passes these tests, you can conclude it’s G. scripta sens. str. If you’re still unsure, then either move on to a more suitable specimen, or see under ‘Lab notes’ below.
LAB NOTES
Graphis scripta sens. str. can normally be identified without microscopy. However, not all specimens are suitable for field identification. Young specimens may not have developed enough, and damp specimens are problematic because pruina or other fine features might not be clearly visible. In such cases, try first to find a more suitable specimen.
However, should you be obliged to work with a specimen unsuitable for identification in the field, you’ll have to collect some of the thallus for inspection at your bench. Once your specimen dries, you can examine it for the diagnostic features of G. scripta sens. str. as described above under ‘Field notes’. Microscopic examination of ascospores shouldn’t be required.
Indeed, the ascospores of the four cryptic species formerly included within G. scripta sens. lat. are only very subtly different. Those of G. scripta sens. str. are generally longer, and they’re the only ascospores that might exceed 56 µm in length. In most cases, though, microscopic examination can only add evidence to support external morphological analysis.
You can improve your chances of finding ascospores in lirellate lichens such as G. scripta sens. str. by first moistening the apothecium, and then running a fine dissecting needle down the length of the slit to extract the hymenium.
SPECIMENS
Graphis scripta sens. str. : Scotland : VC101 Kintyre : NR7890 : August 2024 : On Sorbus trunk
Graphis scripta sens. str. : Scotland : VC101 Kintyre : NR7890 : August 2023 : On Ilex trunk
