Nash, T.H., Ryan, B.D., Gries, C., Bungartz, F., (eds.) 2007. Lichen Flora of the Greater Sonoran Desert Region. Vol 3.
Life habit: lichenized Thallus: ±white, or with greenish tinge, or sometimes reddish pruinose, not disrupting bark, ±hypophloeodic, effuse, with dark prothalline lines photobiont: trentepohlioid Ascomata: isolated, often strongly elongated, repeatedly branched, with sinuous branches and acute to rounded tips, up to 2 mm long and branches c. 0.12-0.24 mm wide, in section 70-90 µm tall, sessile disc: black, rather narrow and plane, epruinose to whitish pruinose; peripheric hyphal structures: conspicuous, up to 80 µm wide, but occasionally poorly developed, reddish pruinose, in cross section a not crystallized, violet pigment is deposited below this layer; occasionally with large hyaline crystals (10-15 µm in diam., insoluble in K) epihymenium: pale brown, 10-15 µm thick, hyphae often not embedded in gels, 2-3 µm wide hymenium: pale brown, 40-50 µm tall; in cross sections with 1-2 mature asci per section; paraphysoids: indistinct in water, branched and anastomosing, with cells 3-5 x 1 µm; subhymenium: pale brown, 20-25 µm thick; cells: ±round, 2-5 µm in diam., with gelatinized outer walls asci: clavate, 35-42 x 12-19 µm, 8-spored, indistinctly stipitate, lateral endotunica thin ascospores: initially hyaline but soon becoming brown, 4-sepatate (slightly constricted at the septa), septation proceeding downwards from the upper third, ovoid, 18-20 x 6-8 µm, becoming verrucose Chemical reactions: ascomatal gels I+ pale blue, KI+ blue; epihymenial reddish pigments K+ violet and dissolving; asci with KI+ blue elongated (c. lower half of the tholus) ring-structure, apically indistinctly delimited. Substrate ecology: on smooth bark of shrubs and tree, a pioneer species in dry and sun-exposed habitats World distribution: East Africa, Galapagos, and Mexico Sonoran distribution: Baja California and Baja California Sur. Notes: Arthonia speciosa is a characteristic member of the Arthonia cinnabarina group by its asci with a KI+ blue tholus structure and by its ascomata, which can become strongly elongate. Specimens, which do not have fully developed ascomata, can still be identified as A. speciosa due to the constantly found KI+ blue ascus reaction, which is always missing in A. cinnabarina s.l., and the crimson pigments which are found predominantly at the perihymenial margins. However, the pruina are not constantly developed in Arthonia speciosa. Typically, both young and mature ascomata are covered by whitish pruina on the surface and distinct crimson pruina at the edges. Three different reddish compounds have been detected in A. speciosa by TLC. All three pigments occur in different combinations and concentrations. Arthonia speciosa shares two reddish pigments with A. cinnabarina (and A. fallax), i.e. CIN-1 and CIN-4. SPE-1 is hitherto known only from A. speciosa, but is not always present. In old ascomata, the pruina are usually depauperate. Such material was labelled as A. hassleri in US; it has a typically elongated KI+ blue ring structure in the ascus tholi and is included here because of the overall similarities in the morphology of the ascomata. The material was cited by Willey (1890: 41) as '260. A. -' and sent to Nylander under n. 13.