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Thalli of the endemic epiphytic New Zealand red seaweed Pyrophyllon subtumens are known to contain a high level of xylose and a notable amount of arabinose but the extracted polysaccharide has not been characterised. The linkage/substitution of individual sugars within the water-soluble polysaccharide extract and various derivatives were determined by chemical and spectroscopic methods. No 3-linked sugars nor any d -galactose were found, which excluded agar-, carrageenan- or mixed 3-linked/4-linked β- d -xylan-type polysaccharides found in many other red macroalgae. Instead, the polysaccharide backbone contained predominantly 4-linked β- d -xylopyranosyl, 4-linked 3,6-anhydro- l -galactopyranosyl and 4-linked l -galactopyranosyl units. Some of each type of sugar were sulfated at various positions. Some xylosyl units were substituted at the 2- or 3-position with l -arabinosyl units. The polysaccharide is complex and likely contains a range of structures. However, partial sequencing was successfully used to recover and identify a novel disaccharide 4- O - d -xylopyranosyl-3,6-anhdydro- l -galactopyranose, which indicates a unique →4)-β- d -Xyl p -(1 → 4)-3,6-anhydro- l -Gal p -(1 → repeat unit in the polysaccharide. [Display omitted] [ABSTRACT FROM AUTHOR]