Spiny Heath Lichen

The thalli of Cetraria aculeata form shrubby tufts of up to 1–5 cm height, main branches are from 1 to 4 mm wide, terminal branches up to 1 mm wide, chemical spot tests K and P both negative. The species is found fertile, and seems to propagate mainly by thallus fragmentation. Despite the apparent lack of ascospores, which can be dispersed across long distances, C. aculeata has a very wide distribution. It is frequent in open polar and boreal environments from the maritime Antarctic to the high Arctic. At intermediate latitudes it is mostly found in high mountain ecosystems, as well as its distributional range also extends into forest gaps, woodland and steppe ecosystems, or coastal and riparian sand deposits of the Mediterranean and temperate zones. Although Cetraria aculeata is widespread globally, some isolated tropical mountain populations appear to be at local or national risk of extinction, including those in East Africa and South America. A 2013 review of phylogeographic studies suggested that Cetraria aculeata evolved in the Northern Hemisphere and later spread into the Southern Hemisphere during the Pleistocene. The same review noted that Antarctic populations have very low genetic diversity, consistent with southward colonization followed by little ongoing genetic exchange with northern populations.

Cetraria aculeata is a known host to several lichenicolous fungus species, including Lichenopeltella cetrariicola, Acremonium lichenicola, Clypeococcum cetrariae, Didymocyrtis cladoniicola, Didymocyrtis trassii, Endococcus parmeliarum, Lichenoconium eroden, Eonema pyriforme, Katherinomyces cetrariae, Sphaerellothecium aculeatae, and Taeniolella rolfii. A molecular study found that Cetraria aculeata associates with a single phylogenetic lineage of the green algal species Trebouxia jamesii. Temperate populations consistently contained a distinct photobiont lineage, and the authors suggested that an earlier switch in algal partners may have helped the species colonize both temperate and polar habitats. A later review likewise linked the species' broad environmental range to variation in its algal partners, concluding that photobiont switching probably broadened its ecological niche and was followed by genetic isolation among geographically separated populations. In addition to its fungal and algal partners, Cetraria aculeata harbours characteristic communities of associated Alphaproteobacteria. A study of populations from Antarctica, Iceland, Germany, and Spain found that these communities were dominated by Acetobacteraceae and were less diverse in polar than in temperate populations. …