Flora of New Zealand Series

Thallus crustose, orbicular to spreading, areolate, verrucose or continuous, white, yellowish, greenish, ashy-grey or brownish, corticate, cortex of compacted, gelatinised cells, medulla of loose hyphae, lacking a lower cortex, the lower side grading into a black, continuous or radiating prothallus. Photobiont Trebouxia. Apothecia lecideine, black, small, 0.2-0.5(-2) mm diam., circular or angular, disc ± plane, concave or convex in some species, ± between areolae usually on prothallus, disc smooth to minutely roughened or "sooty", black proper margin distinct in young fruits, often excluded with age. Hymenium colourless, greenish to red-brown near epithecium. Epithecium inspersed with black granules. Hypothecium dark brown, 30-55 µm tall. Paraphyses septate, strongly conglutinate, richly branched anastomosing, 1.5-2.5 µm thick, apices globose to clavate, 3-6 µm diam. Asci narrowly clavate to cylindrical 8-spored, rarely (1-)2-6-spored. Ascospores uniseriate or biseriate, 1-septate to ± muriform, colourless, pale brown to brown-black often with a greenish tinge, sometimes halonate with a gelatinous epispore 3-10 µm thick.

Rhizocarpon is a large genus of c. 200 described species included in the family Lecideaceae, widely distributed in all parts of the world but particularly in alpine and polar regions. Species are long-lived, growing on rock, and have been widely used in studies on moraine-dating, a procedure known as lichenometry, [Webber and Andrews Arct. alp. Res. 5: 295-302 (1973)] and used with some success in the Southern Alps of South I. [Burrows and Lucas Nature 216: 467-468 (1967); Burrows and Orwin N.Z. J. Sci. 14: 327-335 (1971)]. European [Runemark Opera Bot. 2 (1): 1-152 (1956); Opera Bot. 2 (2): 1-150 (1956); Feurer Ber. bayer. bot. Ges. 49: 59-135 (1978);], and Arctic [Thomson Nova Hedwigia 14: 421-481 (1967)] populations are monographed but much work is needed on the species in New Zealand. At present yellow species in New Zealand tend to be referred to R. geographicum, and grey species to R. grande, but this is a simplistic view and doubtless many taxa are involved. Both Zahlbruckner [ Denkschr. Akad. Wiss. Wien math.-naturwiss. Kl. 104: 321-322 (1941)], and Dodge [ Rep. B. A. N.Z. Antarctic Res. Exped. Ser. B, 7: 114-119 (1948)] describe species of Rhizocarpon from the New Zealand region, but a detailed study of the group remains an urgent necessity here. Eight species are discussed below.