Calicium adspersum
Calicium adspersum is a species of pin lichen in the family Caliciaceae. It forms grey, granular crusts on bark and dead wood, producing black, pin-like fruiting bodies about 0.6–1 mm tall with a yellowish, powdery coating on the head. It was described by Christiaan Hendrik Persoon in 1798 from material on oak wood, and later authors applied a series of alternative names and rank placements to the same taxon in the early 19th century. The species has an antitropical distribution, occurring in temperate regions of both hemispheres, but is generally uncommon and is especially scarce in North America, where few verified collections are known. A Tasmanian subspecies, C. adspersum subsp. australe, differs in its thinner thallus and smaller, grey spores with oblique ridges. Two other subspecies have been described, including one from the Himalayas of India. Under the microscope the species has spirally ridged ascospores and also produces tiny asexual spores that can germinate and form fungal colonies in laboratory culture. NatureServe ranks the species as globally vulnerable, linking its decline mainly to the loss and fragmentation of old-growth forest habitat and noting that it may be slow to recover because suitable host trees take many decades to develop.
Taxonomy
Calicium adspersum was described by Christiaan Hendrik Persoon in 1798, in his Icones et descriptiones fungorum minus cognitorum. In the original Latin, Persoon characterised it as a gregarious, stalked species with a thick, entirely black fruiting body "sprinkled" with green powder, and reported it as growing on oak wood, where it is associated with a powdery or darkening crust. Persoon also recorded variation in the stalk length, from very short to about 1–2 lines long, and described the cup as black beneath and somewhat funnel-shaped. He wrote that the could be flat or convex and wrinkled, but that it is always dusted with a rather coarse olive-green powder that separates it from similar species; he even speculated about whether this powder is an intrinsic part of the fungus or an external deposit or parasitic growth, concluding that he could not decide.Erik Acharius later interpreted Persoon's species as part of a distinct roscidum entity, first publishing it as Calicium claviculare var. roscidum in 1803, and subsequently recombining the same epithet several times under different species concepts and ranks, including C. hyperellum var. roscidum and f. roscidum, C. lygodes var. roscidum, and C. mutabile var. roscidum. He also raised it to species level as Calicium roscidum in 1816. Samuel Frederick Gray transferred the taxon to Phacotrum in 1821 as Phacotrum hyperellum var. roscidum, and Göran Wahlenberg later returned it to Calicium as C. clavellare var. roscidum. Ludwig Schaerer eventually made the combination Calicium adspersum var. roscidum in 1833. Taken together, these names reflect a long history of shifting circumscriptions and rank around a persistent roscidum morph, even as Persoon's original name, Calicium adspersum, has remained in use for the species.
Description
The thallus of Calicium adspersum is grey and granular in texture. It produces black, pin-like apothecia about 0.6–1 mm tall, typically standing three to five times higher than the width of their stalk. The apothecial head is broadly lens-shaped, with a yellowish on the head and along the margin of the . The stalk is slender, about 0.1–0.3 mm in diameter.Under the microscope, the apothecial stalk is surrounded by a thin, colourless sheath that turns faintly blue in iodine. Microscopically, the asci are club- to cylinder-shaped. The ascospores measure about 13–16 × 5.5–6.5 μm and have spiral ridges on their surface. In standard spot tests, the thallus reacts K+ and Pd+, consistent with the presence of norstictic acid, while the yellow pruina contains vulpinic acid.
The species also produces asexual spores in pycnidia. Vobis reported the conidia as colourless, single-celled and thin-walled, about 2.0–2.2 × 1.2 μm. In laboratory culture on bark-extract agar, the conidia swelled within about a week and later formed germ tubes. After several weeks to months they developed branched hyphae and small mycelial mats, and colonies derived from groups of conidia were maintained for more than a year. These experiments show that the conidia can germinate and produce mycelium under favourable conditions, and may therefore contribute to dispersal of the fungal partner.
Subspecies
described the subspecies Calicium adspersum subsp. australe in 1984 from Tasmanian material. Compared with the nominate subspecies, it is characterized by a very thin, whitish-grey thallus and apothecia 0.3–0.7 mm wide that are raised on glossy black stalks typically 1–2.2 mm tall. The ascospores are smaller and grey, measuring 9.8–12 × 4.7–5.5 μm, and bear conspicuous parallel ridges running obliquely across the spore wall. Chemically it is usually associated with norstictic acid, though substances may be undetectable in some specimens, and the yellow pruina contains vulpinic acid; spot tests are reported to be unreliable.Garima Pant and Dharani Dhar Awasthi described the subspecies Calicium adspersum subsp. himalayense in 1989, from specimens collected in West Bengal, India.
Similar species
Calicium sequoiae is a close relative of Calicium adspersum in phylogenetic analyses using internal transcribed spacer sequences. It can be separated from C. adspersum by a combination of traits reported for C. sequoiae: the stalk tissue is I+ blue, the apothecia develop a prominent white pruina, and the species produces thamnolic acid as its major secondary metabolite. Ecologically it appears tightly associated with old-growth coast redwood, having been collected only on thick, fibrous bark of large Sequoia sempervirens trunks high above the ground in low-elevation redwood forests of north-western California.Habitat and distribution
Calicium adspersum has an antitropical distribution, and is widespread in temperate areas of both hemispheres. In the United Kingdom, where it is rare, it grows on dry, old oak bark. In Switzerland, it has been recorded on oak in the Swiss Plateau and on conifers at high elevations in the northern Prealps. In Tasmania, Calicium adspersum subsp. australe is considered rather uncommon and occurs on dead wood, usually on standing trees, in sclerophyll forest and rainforest. In north-western European Russia, Calicium adspersum has been confirmed from Leningrad Region on Picea bark, and it is otherwise reported from Karelia and widely across Fennoscandia and the Baltic states, where it is associated with southern taiga forests.In North America, it was known from only 11 verified collections in 1999. In a 2003 survey of fungi and lichens of Oregon, Jouko Rikkinen characterized the species as uncommon, occurring on conifer bark in humid low-elevation forests. Other western North American states in its range include Washington and California. In eastern North America, the occurrence of C. adspersum was long uncertain, because several older reports published under the synonym Calicium roscidum were unverified and some herbarium material later proved to be misidentified. Selva confirmed the species from two Maryland specimens collected in 1909 on Acer rubrum, and also reported it from Tennessee on Tsuga canadensis; he also noted a published record from Acadia National Park in Maine.