Polysaccharides of foliose thalli of Pseudocyphellaria clathrata (De Not.) Malme, a fungus lichenized with a green photobiont, were extracted and chemically characterized. The thalli were successively extracted with water and 2% aqueous KOH, at 100°C. After neutralization, the solution was subjected to freeze-thawing and Fehling treatment of the supernatant precipitated a structurally complex galactoglucomannan (GGM) that was identical to a similar fraction obtained from Pseudocyphellaria aurata (Ach.) Vainio, a fungus lichenized by the green alga Dictyochloropsis symbiotica. Isolated from the supernatant of the Fehling precipitation, was an arabinogalactomannoglucan (AGMG) that contained arabinose, galactose, mannose, and glucose in a 12:34:40:14 molar ratio. Methylation analysis showed 18 different structures, the principal being nonreducing galactofuranosyl end-units (25%) with the main chain composed by (1→3)-linked β-glucopyranosyl units, as seen by controlled Smith degradation.