About Baeomyces heteromorphus Nyl. ex C.Bab. & Mitt.
Baeomyces heteromorphus Nyl. ex C.Bab. & Mitt. is a species of lichen that forms wide, expansive patches which can exceed 50 cm in width, and has a diverse, intricate structure. This lichen has a crustose thallus (the main body of the lichen) with a texture that ranges from smooth, to verruculose (wart-like), to areolate-subsquamulose (cracked to slightly scaly). Its colour ranges from pale greyish white to greenish grey, and it often turns pale pinkish grey when stored. The thallus is relatively thick, reaching up to approximately 700 μm, and spreads without a defined boundary because it lacks a prothallus (the initial growth phase of lichens). Baeomyces heteromorphus does not produce soredia or isidia, the common asexual reproductive structures found in many lichens. Instead, it occasionally develops schizidia (fragmented pieces of the thallus), but these are typically only observed in damaged specimens. The apothecia (fruiting bodies) of this lichen are small, measuring 0.1 to 3 mm in diameter. They can be round, slightly raised (subsessile), or more frequently distinctly stalked; they appear either singly or in clustered formations that resemble branches or racemes. The stalks of these apothecia can grow up to 7 mm tall, may be smooth or have longitudinal grooves, and sometimes have gnarled sections near the base from thalline (lichen) tissue. The colour of the apothecial disc ranges from pale greyish pink to reddish brown, and its shape shifts from persistently concave to flat, or even wavy to convex as the apothecium ages. The surrounding proper exciple (rim) is paler than the disc and may become less visible in older apothecia. Internally, the hypothecium (the bottom layer beneath the hymenium in apothecia) ranges from clear to pale yellowish, and is underlain by a thick layer of loosely interwoven fungal filaments. The hymenium, the fertile, spore-bearing layer, is clear and is topped by a yellow-brown layer that dissolves in potassium hydroxide (K). The asci, spore-containing structures, measure 70–95 by 5–8 μm, while the paraphyses, sterile filaments between the asci, are 1.5–2 μm thick. Ascospores, the reproductive spores, vary in size from (7–)8.5 to 13(–15) by 3 to 5 μm. Pycnidia, asexual reproductive structures, have not been observed in this species. Chemically, Baeomyces heteromorphus contains norstictic and connorstictic acids, with occasional traces of other compounds. Standard spot testing gives distinct results: the thallus turns yellow-red when treated with potassium hydroxide (K+), shows no change with calcium hypochlorite (KC−) and bleach (C−), turns orange with para-phenylenediamine (P+), and shows no fluorescence under ultraviolet light (UV−). Baeomyces heteromorphus has a broad geographical range, and grows on a variety of substrates including soil, peat, stones, and wood. It occurs particularly in high rainfall regions and locally moist microhabitats, and can be found from lowland areas to alpine elevations. This species contributes to ecological succession, and is often among the first organisms to colonise and stabilise newly exposed earth, such as areas disturbed by road construction, along pathways, or around the root mounds of upturned stumps. It is commonly found across mainland Australia and New Zealand. On Tasmania's Mount Wellington, it occurs in three vegetation zones: woodlands with mixed Eucalyptus coccifera and Eucalyptus urnigera stands; wet sclerophyll forests dominated by Eucalyptus delegatensis; and wet sclerophyll forests dominated by Eucalyptus obliqua. Baeomyces heteromorphus also occurs in New Guinea, Fiji, and Kaikōura Island, and extends into the subantarctic region, with documented populations on Macquarie Island.
