Diagnostic Characteristics
The whitish upper surface, black non-rhizinate lower surface, and hollow lobes identify this species as a Hypogymnia. Few other species of Hypogymnia share H. heterophylla's long, narrow, laterally branched lobes, dark brown medullary cavity, and lack of soredia. Among similar species: 1) H. duplicata and 2) H. imshaugii have a white medullary cavity; 3) H. enteromorpha and 4) H. apinnata have broader lobes (averaging to 2.5 - 5 mm wide) with more or less knobby swellings; and 5) H. inactiva is almost exclusively fork-branched. Some specimens of the last species do, however, intergrade morphologically with H. heterophylla, and must then be distinguished by their PD- medullary reaction (versus PD+ red in H. heterophylla) (Goward, 1996).
Habitat
Common on conifers along the Pacific coast, especially Pinus contorta (in Canada). It is found in rather exposed seaside situations, usually within approximately 1 km of the open ocean. It occupies the driest subzones of the Coastal Western Hemlock Zone, in a region of rainshadow-induced mediterranean climate.