Aggregatorygma triseptatum
Aggregatorygma triseptatum is a species of lichen in the family Graphidaceae. First described in 2014 from collections near Porto Velho in Rondônia, it forms pale gray-green patches on tree bark with distinctive star-shaped clusters of narrow fruiting bodies. The species is characterized by extremely small spores with three cross-walls and two unidentified secondary metabolites. It grows in the shaded understory of undisturbed Amazon rainforest and has since been recorded in several Brazilian states.
Taxonomy
Aggregatorygma triseptatum was introduced as a new genus and species by Marcela Cáceres, André Aptroot, and Robert Lücking in a survey of Graphidaceae from Rondônia. The holotype was collected on March 15, 2012 on tree bark in primary rainforest at Fazenda São Francisco, about north of Porto Velho at an elevation of. The original emphasized the combination of aggregated, branched and extremely small, 3-septate ascospores. Sequence accessions from the type corroborated that the taxon did not cluster with existing graphidoid genera.In form, the species can resemble some Diorygma, but it differs in its distinctive clustering of lirellae, the consistently tiny, 3-septate spores, and its chemistry. The authors therefore placed it in Aggregatorygma rather than expanding Diorygma.
Description
The bark-dwelling thallus of Aggregatorygma triseptatum forms pale, gray-green patches with a very finely dusty surface; a thin white border may be present. In section it lacks a true, and consists of a of green Trentepohlia algae over a thin, crystal-rich medulla.Fruiting bodies are the key macroscopic feature: narrow, elongated apothecia occur in small, star-shaped clusters, mostly immersed in the thallus with only thin lips visible; each slit is typically 1–3 mm long. The lips often carry a light, powdery bloom. In section, the apothecial wall is pale and thin; the spore-bearing layer is clear and about 50–60 μm tall. The ascospores, which number eight per ascus, are hyaline, ellipsoid, and tiny with three cross walls; they show a violet-blue iodine staining reaction, indicating amyloidy.
Standard spot tests on thin sections are negative, but TLC in solvent C shows two unidentified compounds as light gray-brown spots at about Rf 25 and Rf 40.