2.1 | Study species
Peltigera is a cosmopolitan genus of lichen-forming fungi; its
species form large foliose lichens which mainly grow on soil and among
bryophytes (O’Brien et al., 2009). Our study species Peltigera
britannica (Gyelnik) Holtan-Hartwig & Tønsberg is a Holarctic species
which prefers oceanic climates (Martínez et al., 2003). It forms a
tripartite morph with the green alga Coccomyxa sp. and small
amounts of the cyanobacterium Nostoc sp. embedded in granular
structures on the upper side (cephalodia) and a bipartite morph
containing only Nostoc sp. as photosynthetic partner (hereafter
referred to as cyanomorph) (Pardo-De la Hoz et al., 2018;
Holtan-Hartwig, 1993). The two morphs of P. britannica have a
characteristic morphology (Fig. 1): when wet, the tripartite morph is
apple green whereas the cyanomorph is of a bluish-gray color (Goffinet
& Hastings, 1994). The photomorphs grow either as separate individuals
or as a single compound thallus with cyanobacterial and tripartite
sectors (Goward et al., 1995).