Ampliotrema cocosense

Ampliotrema cocosense has a grey-olive-yellow thallus with a verrucose texture and a dense paraplectenchymatous cortex. The photobiont layer and/or medulla contain clusters of calcium oxalate crystals. The apothecia are sessile and rounded, measuring 1–2 mm in diameter, with a brown-black disc that is partially covered by a 0.3–0.6 mm wide pore. The disc also exhibits a yellow-to-orange pruina. The margin is entire, fused, and yellowish-white, covered by a thalline layer. The species lacks a columella and periphysoids. The hymenium has a height of 150–200 μm and is inspersed with apically branched paraphyses. The ascospores are 80–100 by 17–22 μm in size, oblong, colourless, and I+ (violet-blue) when treated with iodine (indicating an amyloid reaction). They are richly muriform with thick septa and rounded lumina. The secondary chemistry of this species includes protocetraric and virensic acids along with structurally related compounds, and the thallus (medulla) has C−, K−, and P+ (orange-red) reactions to standard chemical spot tests. The lichen is most closely related to A. lepadinoides, which has similarly sized ascospores, but much narrower with transverse septa only. …

Ampliotrema cocosense is known from a single, well-developed collection found in the lower montane rainforest of Cocos Island. The island's lichen diversity is not well-documented, particularly for non-foliicolous (leaf-dwelling) species. The discovery of this new species indicates that Cocos Island may harbour a unique lichen biota for certain groups of lichens. Most of the island's lichen flora represents pantropical species, with A. cocosense as the sole endemic representative.

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