Argopsis megalospora Th.Fr.
Holotype (fide Lamb loc. cit. p. 450): New Zealand. Campbell I. J. D. Hooker, UPS!
Thallus firmly attached. Pseudopodetia terete or slightly flattened, sparingly to moderately branched forming clumps to 7 cm tall. Surface uniformly corticate, greyish-white or pinkish, matt, smooth, sometimes becoming cracked or wrinkled-verrucose. Phyllocladia rather sparse, short (to 2 mm long), terete, corticate, smooth, simple or sparingly branched. Cephalodia small (to 2 mm diam.) spherical, sessile, brownish-grey, smooth or shallowly wrinkled, sometimes clustered. Apothecia common and often abundant, terminal, large (4-8 mm wide) disc plane, smooth, black or brown-black with a prominent, persistent, pale margin, thalline exciple well developed, pale or flesh-coloured, strongly wrinkled-scabrid. Ascospores 1-2 per ascus, colourless, ellipsoid to cylindrical, irregularly muriform, 50-120 × 30-50 µm. Chemistry: Cortex and phyllocladia K+ yellow; medulla K-, C-, KC-, Pd+ red. Atranorin, argopsin [Bodo and Tholho C. r. hebd. Séanc. Acad. Sci. Paris ser. C, 278: 625-627 (1974); Huneck and Lamb Phytochemistry 14: 1625-1628 (1975)], fumarprotocetraric and perlatolic acids, and an accessory unidentified compound. Lamb ( loc. cit. pp. 449-450) records that populations of A. megalospora contain two distinct chemodemes, one with fumarprotocetraric acid (Pd+ red), and one in which this compound is replaced by psoromic acid (Pd+ orange-yellow). The two chemodemes are anatomically and morphologically indistinguishable and share the same geographical distribution.
A: C: On exposed rock outcrops in subalpine grassland, open shrubland and in fellfield. Not known from Macquarie I., Stewart I., or the mountains of South I.
Endemic
A. megalospora is scarcely likely to be confused with any other lichen in New Zealand except Stereocaulon argus, and in the Auckland Is and Campbell I., the two species are sympatric. The plane, expanded apothecial disc, the massive warted thalline exciple, the plane, smooth pseudopodetial cortex and the scarcity of cephalodia and phyllocladia sufficiently distinguish A. megalospora from S. argus. Further, the large, muriform spores of A. megalospora are characteristic.
