Parmotrema cetratum (Ach.) Hale
Parmelia cetrata Ach., Syn. Lich.: 198 (1814).
Thallus large, orbicular to spreading, loosely attached, to 20 cm diam., corticolous and saxicolous. Lobes broad (6-12 mm wide), rounded to subirregular, often laciniate or dissected, margins entire, sinuous, ciliate: Upper surface pale greyish-white (greenish when wet), finely maculate-cracked, in older specimens cracked to margins, soredia and isidia absent. Lower surface black, with a broad, brown, naked marginal zone. Rhizines central, black, dense, simple or squarrosely branched. Apothecia rare, pedicellate, disc brown, to 8 mm diam., consistently perforate in older fruits, margins entire at first becoming deeply lacerate with age, thalline exciple smooth or wrinkled, maculate near margin. Ascospores 13-16 × 6-7 µm. Pycnidia common at lobe margins, punctiform, black. Chemistry: Cortex K+ yellow; medulla K+ yellow → red; C-, KC+ red, Pd+ orange. Salazinic acid and atranorin.
N: Three Kings Is to Pohangina Valley. S: Canterbury (Hawkswood Ra., Banks Peninsula), Otago (Horse Ra., Mt Watkin, Black Head, Dunedin Whare flat). On rock or Metrosideros excelsa bark in coastal habitats north of Auckland where it grows most commonly. Elsewhere it occurs on both native and introduced trees but it is still very much undercollected and poorly understood.
Cosmopolitan
P. cetratum is a rather variable species, appearing to have a northern form found on coastal rocks and a southern form from wood or bark in inland localities. Specimens collected from coastal rocks and cliffs north of Cook Strait (especially from off-shore island groups north of Auckland) have narrower, more folded and laciniate lobes than the southern corticolous forms, and there is also a reduction in marginal cilia, a lack of Apothecia and a more prominent pattern of maculation with the algal-free zones being markedly white, shining and slightly raised enclosing the darker, algal-rich areas in minute, shallow faveolae. In young specimens the surface of the cortex is smooth and continuous and reticulate cracking is not often seen. In southern collections, fine reticulate-cracking occurs even in young lobes and the upper cortex is matt and not shining and not faveolate; Apothecia are ± common and marginal cilia are frequent and obvious. Thallus lobes also tend to be more closely appressed, larger and more rounded than in the northern coastal form.
