Monograph of the Genus Abrothallus (De Notaris and Tulasne emend)
Authors: Lindsay W. Lauder 
Published: April 2021

ABSTRACT
The genus Abrothallus, and especially the species here-after described as A. Smithii, have long been familiar to lichenologists under a variety of designations; but their true structure and place in classification were quite misunderstood until the comparatively recent researches of De Notaris,* in Italy, and Tulasne, † in France. A. oxysporus (infra descript) has generally been regarded as a species of Endocarpon, especially when it bore only young apothecia; while the apothecia of A. Smithii have been denominated cephalodia, and have been variously looked upon as the abortive, monstrous, or accessory apothecia of certain Parmelias, Lecideas, and other lichens, or as parasitic fungi. Sir William Hooker, in his ‘British Flora’ vol. ii, p. 200 (1833), says that P armella saxatilis, and its variety omphulodes, “ are liable to be infested with a parasite, which has been called Endocarpon parasiticum, Ach.” (‘E. Bot.,t.1866.) Onfurfuraceous states of P. saxatilis the Abrothalli are most abundant. In his ‘Flora Scotica’ (part ii, p. 44, 1821), Hooker gives as the characters of this Endocarpon parasiticum (Lichen parasiticus, ‘E. Bot.,’ t. 1866): “Thallus coriaceous, convex, rounded, lobed, copper-coloured, at length rugged, black and shaggy beneath, orifices scattered, sunk, minute, coal-black, at length convex.” This description, in so far as it applies to the apothecia, appears to confound the two species A. Smithii and A. oxysporus; and, in so far as it describes a thallus, it is erroneous, since recent researches have proved the genus Abrothallus to be really athalline. The latter error, however, is rectified in the ‘British Flora,’ p. 159, where it is stated that the “Endocarponparasiticum, Ach., is now universally considered to be a portion of the thallus of Parmelia saxatilis or omphalodes deformed by a parasite.” The view that the Abrothalli are abortive apothecia of certain familiar foliaceous lichens is maintained so lately as 1850 in Schærer’s elaborate ‘Enumeratio critica Lichenum Europæorum,’ (Berne, 1850). He describes the species mentioned by Hooker as End. parasiticum, under the name of Parmelia saxatilis, var.parasitica, in the following terms: “Thallo supra apotheciis abortivis, atris, subpatellæformibus vel hemisphæricis, immarginatis, consito.” His description of the var. abortiva of Parmelia conspersa is precisely similar. Of Parmelia olivacea, var. abortiva, he says, “Thallo supra sphærulis atris (apotheciis abortivis) distincto.” These are characteristic descriptions of A. Smithii, the variety which I have hereafter described as a, ater. To my variety pulverulentus of the same species, he refers, sub nom. Sticta fuliginosa, var. abortiva, when he says: “Thallo supra patellulis superficiaribus, olivaceo-viridi-pulverulentis, immarginatis, distincto.” Schærer’s specific and generic characters have too evidently been founded wholly on external appearances: he himself deplores his deficient microscopical knowledge and skill. But he does not appear to have been aware of—or at least he does not allude to—the researches of De Notaris on the genus Abrothallus, which bear date between the years 1846 and 1849,—prior to the publication of his own ‘Enumeration Of Tulasne’s investigations he could not avail himself, as they were published two years subsequently. By other observers, again, there has been too great a tendency perhaps to take for granted the bold and sweeping assertion of Fries that “Lichenes in aliis parasitici normaliter nulli genuini,’—an assertion whose incorrectness the labours of subsequent observers have sufficiently proved. It has been too much the custom lazily and ignorantly to refer minute, black, point-like or spot-like parasitic lichens to the great family of the Fungi; but I feel assured that many species of Sphæria, Dothidea, Peziza, and other fungi, presently so-called, which are parasitic on the thallus of various familiar lichens will ultimately be found to belong themselves to the ranks of the lichens. I attribute, however, no blame to my predecessors for having erred in regard to the structure and place in classification of these minute organisms. Nay, I do not see how such errors could have been avoided; for the parasitic lichens, to which I refer, could not have been properly studied prior to the introduction of the microscope. I believe it to be too common now-a-days to depreciate the labours of the earlier botanists; but the more we study the minuter Cryptogams the more must we become convinced of the extent, accuracy, and value of their observations. Most of the organisms with which we are now acquainted were noticed and described by them; and we cannot hold them altogether responsible for the misinterpretation of their nature and alliances.