Parmotrema robustum
≡Parmelia robusta Degel., Göteborgs Kungl. Vetensk.- och Vitterh- Samhälles Handl. sjätte följden, ser. B, 1 (7): 33 (1941).
Description : Thallus loosely adnate, membranaceous, 10–20 cm diam. Lobes rounded, 10–15 mm wide, margins entire, ciliate; cilia sparse, 0.5–1.5 mm long, best seen in lobe axils. Upper surface grey to greenish grey, smooth, matt, faintly white-maculate (×10 lens) at margins, becoming reticulate-cracked centrally, sorediate, without isidia. Soralia marginal, short, linear on small, incised marginal laciniae, the sorediate laciniae becoming convolute. Soredia white, granular. Lower surface black, with a wide, smooth, naked, pale-brown, marginal zone, rhizinate centrally. Rhizines sparse, simple, black. Apothecia and pycnidia not seen.
Chemistry : Cortex K+ yellow; medulla K+ dingy yellow→dirty brown, C−, P+ orange-red; containing atranorin, chloroatranorin, protocetraric acid (major) with or without unidentified fatty acids.
N: Known also from the Atlantic coast of Europe from Portugal to Ireland, from Macaronesia, Taiwan, Thailand, Papua New Guinea, E Australia and New Caledonia (Østhagen & Krog 1976; Elix 1994p; Louwhoff & Elix 1999, 2002b; Kurokawa & Lai 2001; Wolseley et al. 2002; McCarthy 2003c, 2006).
Pantropical
Illustrations : Elix (1994p: 157, fig. 56A); Louwhoff & Elix (1999: 109, fig. 60).
Parmotrema robustum is characterised by: the corticolous habit; the loosely adnate, membranaceous thallus; broad lobes with sparse cilia; marginal soralia on short, incised laciniae; and protocetraric acid in the medulla.
