Thompson, J., 1984. American Arctic Lichens: The Macrolichens.
Thallus fruticose, prostrate, rigid except at the apices, to 10 cm long; branching aniso-tomic dichotomous at the base, isotomic dicho-tomous toward the apices, rather sparse, the main branches weakly to strongly compressed, the sides ridged or striated or foveolated, greenish yellow to yellow, the apices of same color or becoming black.
Apothecia not seen.
Reactions: cortex K—, KC+ yellow, C—, P —; medulla K—, KC— or KC+ red, P-.
Contents: usnic acid with accessory atranorin in the cortex, and accessory alecto-ronic acid in the medulla. Hawksworth (1972) reports also possibly squamatic acid and a-col-latolic acid in the medulla in some.
Growing in open, more or less windswept gravelly areas and on old frost boils, sometimes mixed in heath vegetation, this species shares the same chemistry and variability of chemistry as A. sarmentosa with which many lichenologists classify it, e.g., Brodo & Hawksworth (1977). It does occur farther north and in more exposed ecological conditions as well as being decumbent instead of pendent on trees as in A. sarmentosa. Ahti and Hawksworth (1974) mention finding intermediates on Newfoundland and in Europe, but that these two populations seem to be quite different over most of North America. Possibly these are ecads instead of species but in view of the differing habits and ranges I have taken the course of retaining them as separate species until experimentation decides this question. The range of A. vexillifera is circumpolar arctic-alpine with the North American range extending south to Newfoundland, Alberta, and Washington. Its close relative, A. sarmentosa, is confined to the boreal forest.