Lynge B 1928. Lichens from Novaya Zemlya. In Holtedahl O. Report of the Scientific Results of the Norwegian Expedition to Novaya Zemlya 1921. Oslo. 1-299.
Thallus flat, determinate, irregular, 2-3 cm. wide. Crustose grayish-yellow, margin commonly turning a pale colour; moderately thick, +/- rimose-areolate; areolae continous (young areoles subcontinuous only at the margins), large, up to 1-2 mm, subplane, then convex, smooth, not sorediate. Bluish-gray coloured hypothallus distinctly surrounding thallus. Thallus up to 0.6 mm, thick. Photobiont layer ca. 80 µ gonidia bright green. Upper cortex 20-25 µ, granules pale grey, evenly inspersed, so that cortical hyphae difficult to distinguish (scarcely separated).
Apothecia rounded, mature diam. 1 mm., dispersed, numerous, immersed in areolae, subequal in thallus, almost as in Aspicilia. Disc plane not umbonate, black, not pruinose, surrounded by a thin, integral, subpersistent margin. Excipulum black, upper hypothecium dark reddish-greyish-brown. Hymenium tall or very tall: 160-190 (200) µ +/- inspersed, olive-black above. Paraphyses very thin, not or very slightly thickened at the apex, narrowly coherent, indistinct, septate and seemingly branched frequently. Asci 8-spored, 20-25 µ thick. Spores hyaline, then sickly, +/- dark, triseptate for a long time, then one submuralis longitudinal septum, surrounded by a thick halo. Spores moderately small: (16) 19-25 (28) X 9-12 µ.
Pycnidia not seen.
Medulla J, KOH and CaCl2O2 no change, hymenium J persentently blue, KOH olive-green colour not changing.
In MALME’s Conspectus its place would be near Rhizocarpon obscuratum or Rhizocarpon lavatum, but it cannot be confused with either of them. The latter has much larger spores: 35-40 X 13-16 µ, the former species a much darker, brown thallus and a lower hypothecium: 125 µ high.
In VAINIO’s Lich. Pitlekai there is no comparable species.
Its nearest relative is evidently Rhizocarpon amphibium (FR.) TH. FR. That species has another colour: “caesio-cinerascens” (TH. FR. Lich. Scand. pag. 630), “caesio-cinereus” (VAIN. Lich. Fenn. II pag. 306) and very small, generally about 0.5 mm. large areolae, often verrucose or convex. They are so small that they are almost entirely occupied by the apothecia. The apothecia of Rhizocarpon amphibium are not so profoundly immersed: “immerse vel paullum emergentia” (TH. FR. l.c.),
I have so far found my plant (there is only one) specifically distinct from Rhizocarpon amphibium, but a larger Arctic material may modify this view.
At Mt. Syernaia in Matotchkin Shar I collected a Rhizocarpon of the section amphibium. It was infested by a parasite: Phaeospora rimosicola (det. KEISSLER), that had damaged it and made its determination difficult and uncertain.
Its differs from Rhizocarpon amphibium itself by its grayish-yellow colour. All the amphibium-plants, which I have seen, have an ash-grey thallus, not a yellowish, e.g. E. FRIES Lich. Suec. No. 381, TH. M. FRIES Lich. Scand. No. 45, HAVAS Lich. Norv. No. 467 and Lich. Norv. Occid. No. 46.
My plant has a high hymenium, about 150 u and uncoloured, muriform, but few-celled spores: 3 transversal septa, 1 longitudinal septum, 26-29 X 16-19 µ.
It is thinner than Rhizocarpon cinereoflavescens, it has smaller areolae and a very narrow, hardly visible hypothallus. But it is hardly possible to distinguish it specifically from that species.