Parmotrema cetratum (Ach.) Hale, 1974
Parmotrema cetratum is recognizable by the absence of vegetative propagules and the production of salazinic acid (medulla K+ yellow → blood red). Some similar species can be distinguished: P. austrocetratum Elix & Johnston is lacinulate, develops schizidia and has filiform conidia up to 25 μm long (holotype CHR!); P. hawaiiensis (H. Magn.) Blanco, Crespo, Divakar, Elix & Lumbsch also bear schizidia, but the conidia are just up to 15 μm long and the lacinules lacking (holotype S!); P. homotomum presents norlobaridone and loxodin (medulla K–, KC+ rose or reddish) and finally P. macrocarpum (Pers.) Hale has just caperatic acid (Fleig 1997).
According to the current literature, P. cetratum shows a wide range of morphological variation, maybe a consequence of too broad species concepts, clearly seen by the long list of synonyms attributed to this species (see Hale & Fletcher 1990).
Galloway (1985) reported several morphological differences between specimens from coastal rocks and from wood or bark inland. Fleig (1997) recognized three distinct groups of species, based on thallus shape. Interestingly, Moon et al. (2001), studying material from Hawaii, also established three groups, adding features from cilia and substrate preferences, and that correspond to Fleig’s groups. These patterns maybe are indicative of specific variation, not just environmental modifications.
[Spielmann & Marcelli 2009]