Technical Description:
Usnea longissima is pale greenish or silvery-yellowish-green, fruticose and pendulous; main branches are cylindric, up to 3 meters or more in length and very rarely dividing, with numerous dense, short perpendicular side branches and fibrils of about equal length (3-40 mm). The cortex is smooth but disintegrating on the main stems, leaving rough patches of white medulla over the pinkish-to-brownish central cord. The unexposed central cord beneath the cortex is white (when exposed with a razor blade), but frequently turns pinkish or reddish brown in decorticate main branches. Papillae are lacking. Soredia or isidia occasionally form on the side branches (Brodo et al. 2001; McCune 2005, McCune & Geiser 1997). Apothecia are extremely rare; when present, they are disk-shaped, 1-3 (5) mm across, terminal on the ends of side branches, with numerous fibrils extending from the thalline margin (Keon 2002).

Chemistry
Central cord I+B. Cortex and medulla K-, C-, KC- PD- (with various combinations of evernic, diffractaic, barbatic, and 4-O-demethylbarbatic acids; sometimes with usnic acid only), rarely K+Y-O, PD+O (salacinic acid)(McCune 2005).