Rewriting the evolutionary history of the lichen genus Sticta (Ascomycota: Peltigeraceae subfam. Lobarioideae) in the Hawaiian islands

Abstract

Hawaiian lichen species have been thought to be widespread, with low endemism. Nine species of the genus Sticta (Peltigeraceae subfamily Lobarioideae) have previously been reported for Hawaii, all supposedly cosmopolitan or Pantropical or widespread in the Paleotropics except for the putative endemic S. plumbicolor. This study is the first one employing a molecular phylogenetic approach to Hawaiian Sticta, elucidating the relationships of these conspicuous and ecologically important macrolichens. We sequenced the ITS fungal barcoding locus and used a maximum likelihood approach to reconstruct phylogenetic relationships of Hawaiian Sticta from a large dataset of more than 200 species. Thirteen species were identified among Hawaiian Sticta, four more than previously recorded. Of these, seven are new to science and putatively endemic to Hawaii. Only four previously reported species were confirmed: S. fuliginosa, S. limbata, S. plumbicolor and S. tomentosa. Together with S. plumbicolor and S. scabrosa subsp. hawaiiensis (described elsewhere), putative endemism in Hawaiian Sticta is estimated at 69%. The 13 species correspond to nine or ten colonization events, predominantly from the Australasian realm. Thus, the evolutionary history of Sticta lichens in the Hawaiian archipelago is very different from what has been assumed, and matches that of other organisms in many aspects. The seven new species, all with cyanobacterial photobionts, are Sticta acyphellata, a small, stipitate Sticta with isidia and lacking cyphellae; S. antoniana, a mid-sized Sticta with abundant marginal lobules, apothecia, and a thick, grey-brown lower tomentum ending abruptly to leave a bare marginal zone; S. emmanueliana, a small, shortly stipitate Sticta forming small lobes with marginal isidia and black cilia; S. flynnii, a small, shortly stipitate Sticta with largely unbranched thallus with marginal isidia and a veined underside producing large, irregular cyphellae; S. hawaiiensis, a small Sticta with a suborbicular thallus with laminal isidia, conspicuous white cilia, and papillae on the membrane of the cyphellae; S. smithii, a small, stipitate Sticta with marginal, flattened isidia and small cyphellae; and S. waikamoi, a small to mid-sized Sticta with a much-branched thallus with slightly canaliculate lobes and marginal, dark isidia, and a thick, dark brown lower tomentum with strongly contrasting whitish cyphellae.