Substratum preference of two species of Xanthoparmelia

• Xanthoparmelia cumberlandia showed preference for the mica schist treatment over the other treatments.
• Xanthoparmelia viriduloumbrina grew significantly better on granodiorite and the malt yeast agar control.
• Ascospores of both species of Xanthoparmelia did not produce germination tubes on the dolostone treatment.
• Photobiont haplotypes of X. viriduloumbrina and X. cumberlandia were most similar to Trebouxia jamesii.
• Photobiont haplotypes did not show evidence of substratum specificity.

The distribution of established saxicolous lichens has been previously studied but substratum preference and elemental composition has been relatively unexplored. The objectives of this study were to compare ascospore germination and growth for two species of Xanthoparmelia using media supplemented with pulverized rock and to explore photobiont selectivity relative to ecological guilds. Mature apothecia from X. cumberlandia and X. viriduloumbrina were subjected to five treatments, which include water agar supplemented with crushed granodiorite, basalt, mica schist, dolostone, and malt yeast agar as the control. The algal actin gene was sequenced and the closest algal matches were retrieved from GenBank and analysed to produce a haplotype network. X. cumberlandia exhibited substratum preference for the mica schist treatment, while X. viriduloumbrina grew better on granodiorite and malt yeast agar relative to dolostone. Ascospore germination for both species failed to progress beyond the initial swelling and protrusion stage on the dolostone treatment. The actin gene sequences for the algae were most similar to those of Trebouxia jamesii. The rock substrates did not correspond with the photobiont haplotypes, which does not support the ecological guild hypothesis. This study provided insights into substratum preference and the suitability of the substratum for algal selection.