Thallus erect or decumbent, occasionally forming tufts by branching from the base or along the decumbent podetia, cylindrical, the tips pointed, white or cream white; in the herbarium becoming pinkish and staining paper brown on long standing; smooth, seldom with short lateral pointed branches, very variable in size, usually 1 -2 mm broad but reaching 8 mm broad and 12 cm tall.

Reactions: UV—, K+ yellow, P+ orange to red.

Contents: thamnolic acid.

This species grows on many types of tundras, from bare, open gravels and frost boils to rich moist, mossy thickets among the willows and heaths. It is circumpolar, arctic-alpine, the studies by Sato demonstrating clearly that it is more abundant than T. subuliformis in collections from the southward and into the southern hemisphere. Even in the northern hemisphere the collections showed increasing proportions of T. vermicularis over T. subuliformis as Sato studied the populations which had been collected. In North America and Greenland its range appears to be more restricted than that of t. subuliformis, neither ranging as far north nor as far south as the latter. The extent of range of the Thamnolia species as bipolar and in such widely disjunct spots as New Guinea, New Zealand, Australia, and the Andes of South America is difficult to account for in the light of the apparent lack of easily dispersed diaspores. The comment of Sato (1965) that it occurs only on nonvolcanic mountains and dead volcanoes, never on resting or active volcanoes, suggests that dispersal is of great antiquity and not currently occurring.