Stereocaulon argus Hook.f. & Taylor
S. argodes Nyl., C. r. hebd. Séanc. Acad. Sci. Paris 83: 87 (1876).
Lectotype: New Zealand. Campbell I. J.D. Hooker, FH.
Thallus large, robust, 4-7(-10) cm tall, branching ± dichotomous at base becoming sympodial towards apices. Pseudopodetia very firmly attached by a well-developed holdfast, basal or primary branches stout, 1.5-3(-5) mm wide, often decorticate, smooth, to strongly vertically furrowed and cracked, upper parts of branches mostly corticate although the cortex may extend to the base of pseudopodetia. Phyllocladia sparse, corticate, with smooth, white, shining tips, simple, terete, gnarled, finger-like at first and often ± restricted to the base of pseudopodetia, becoming flattened, coralloid-branched at maturity (to 7 mm long) and often ridged and cracked, at the apices of pseudopodetia phyllocladia are smaller and nodular, rounded or flattened. Cephalodia developed on large pseudopodetia, small, globose (1.5-)2-5 mm diam., sessile or very shortly stalked, greyish-white, surface smooth, matt, never areolate or maculate. Apothecia terminal, large (to 5 mm diam.), disc brownish-purple to black, plane in immature fruits and then with a conspicuous pale margin, becoming convex and immarginate at maturity. Hypothecium 75 µm tall, colourless to pale brownish. Asci clavate, 6-8-spored. Ascospores colourless to pale yellowish, 3-7 -septate, 30-50 × 4-6 µm. Chemistry: Atranorin and perlatolic acid.
C: A: M: Ant: On open windswept grasslands of the subantarctic islands on rock outcrops.
Austral
S. argus may be confused with Argopsis megalospora, as the two species are often sympatric and have a similar geographical distribution and habitat preference. S. argus may also be mistaken for some forms of S. ramulosum. However, the cortex of the pseudopodetia, and the structure of the phyllocladia and cephalodia distinguish S. argus (the chemistry of the two species is similar), and when fertile the fruits of the two species are readily separable.
