Flora of New Zealand Series

Parmelia arnoldii Du Rietz, Nytt Mag. Naturvid. 62: 80 (1924).

Thallus orbicular to spreading, loosely attached, to 8 cm diam., corticolous. Lobes rather narrow, 3-8 mm wide, margins sinuous, ciliate, with ± numerous, dentate laciniae, 2 mm wide and to 4 mm tall, often crowded centrally. Upper surface pale greenish-grey to dark greenish-brown, smooth, matt, faintly maculate at margins, becoming reticulate-cracked centrally, sorediate. Soralia developed mostly on marginal laciniae, later coalescing into ± extensive abraded patches at lobe tips which become hooded or recurved. Apothecia, isidia, pseudocyphellae and pycnidia absent. Lower surface black, with a broad, brown, naked, marginal zone. Rhizines central, black, simple. Chemistry: Cortex K+ yellow; medulla K-, C-, KC+ pink, Pd-, UV ± bluish-white. atranorin, alectoronic and ?-collatolic acids.

N: Wellington (Pohangina Valley, Pongaroa). Still very much undercollected in New Zealand.

Pantropical

It grows in similar habitats to P. perlatum from which it is distinguished by the marginal laciniae and the UV ± reaction of the medulla.