| TAXON: | Illosporiopsis christiansenii (B.L. Brady & D. Hawksw.) D. Hawksw. (2001) |
| RECENT SYNONYMS: | Hobsonia christiansenii B.L. Brady & D. Hawksw. (1986) |
| FAMILY: | Hypocreaceae |
| GROWTH FORM: | Mould |
| SUBSTRATES: | Lichen thalli |
| PHOTOBIONT: | – |
| REPRODUCTION: | Sporodochia (cirrhi) |
| ASCUS: | – |
| SPORES: | Conidia helicoid, multi-septate, filamentous, 17–30 x 11–20 µm |
| NOTABLE FEATURES: | Bright-pink, spongy, globular masses of conidia on lichen thalli, or on bark where host has been killed; swells when wet |
| CHEMICAL TESTS: | – |
| HABITAT: | Wherever suitable hosts found |
| DISTRIBUTION: | Apparently common and widespread in Britain, but categorised as ‘nationally scarce’ due to under-recording |
| CONSERVATION STATUS: | Least Concern |
| HOST LICHENS: | Candelaria concolor, Candelariella xanthostigma, Hypogymnia physodes, Melanohalea exasperatula, Parmelia sulcata, Phaeophyscia orbicularis, Physcia adscendens, P. aipolia, P. caesia, P. dubia, P. leptalea, P. stellaris, P. tenella, Physconia distorta, Scoliciosporum chlorococcum, S. umbrinum, Xanthoria parietina |
| IDENTIFICATION DIFFICULTY: | Green 2: Field identification possible with care |
| CONFUSION SPECIES: | Erythricium aurantiacum, Marchandiomyces corallinus |
FIELD NOTES
Illosporiopsis christiansenii has a defensible claim to be the most recognisable lichenicolous fungus in Britain. Its fairly large, bright-pink spore-bodies stand out, and they’re almost unmistakeable. A parasite of a range of lichens common in Britain, especially Physcia species, I. christiansenii is probably also common, even if its ‘nationally scarce’ status suggests otherwise. Like all lichenicolous fungi, it’s under-recorded.
I. christiansenii is a type of mould. It grows in and on the host lichen, feeding from it, degrading it, and eventually killing it. The infected lichen tissue becomes bleached and necrotic, but the mould itself is visible to the naked eye only when it produces its characteristic ‘cirrhi’: spongy, pink masses of conidia or asexual spores.
Like other fungi, I. christiansenii seems to prefer autumn and winter for reproduction, possibly because wetter weather helps to disperse its conidia. Its cirrhi swell with water, and deepen in colour, so you can find them relatively easily by examining likely hosts on damp days. You can also find its cirrhi on bark very near infected lichens. But it seems likely that the mould is subsisting on dead lichen remains, rather than on the bark itself.
If you’re unfamiliar with I. christiansenii, you might confuse it with one or two other colourful fungi that tend to parasitise some of the same lichens:
- Erythricium aurantiacum produces small, pale-orange spheres or ‘bulbils’ on bleached and necrotic lichen tissue. But not only do they differ in colour from the pink cirrhi of I. christiansenii, they’re composed of packed hyphal cells, not spores. They’re also typically smaller and more numerous than the relatively large cirrhi of I. christiansenii, and they don’t swell when wet.
- Marchandiomyces corallinus produces small pastel or coral red bulbils on its lichen hosts. But though their colour is similar to the pink of I. christiansenii, they’re again composed of hyphal cells and not spores. They’re also once again smaller and more numerous, and they don’t swell when wet.
So if you’ve found sizeable, bright-pink ‘blobs’ on a lichen, especially a Physcia, you’ve probably found I. christiansenii. If unsure, test with a gentle drop of water to see if they swell when wet. If for whatever reason you’re still unsure, take a sample to see if the ‘blobs’ are made up of spores or hyphal cells. In that case, see lab notes below.
LAB NOTES
Illosporiopsis christiansenii can normally be identified without microscopy. However, it’s interesting to observe its helically coiled conidia, as shown in the specimen galleries below. Simply squash a tiny bit of cirrhus on a slide in water or iodine. The spores are distinctive and diagnostic.
SPECIMENS
Illosporiopsis christiansenii : England : VC27 East Norfolk : TG0738 : October 2024 : On Physcia tenella on Cystius twig : First record for hectad
Illosporiopsis christiansenii : England : VC25 East Suffolk : TM3389 : July 2024 : On Physcia adscendens on Malus twig
Illosporiopsis christiansenii : England : VC25 East Suffolk : TM3389 : April 2023 : On Physcia adscendens on Tilia twig : First record for hectad
