Graphis alba Dantas, Lücking & M. Cáceres, 2017

Dantas, Jaciele De Oliveira, Alves, Elaine Santos, Lücking, Robert & Cáceres, Marcela Eugenia Da Silva, 2017, Three new species of Graphidaceae (lichenized Ascomycota) from the semi-arid region of northeast Brazil, Phytotaxa 331 (2), pp. 289-294 : 290

Graphis alba Dantas, Lücking & M. Cáceres sp. nov. Fig. 1A–C

Mycobank No.: MB 822329

Diagnosis: Differing from Graphis riopiedrensis in the labia featuring a conspicuous white cover and eventually becoming striate.

Type: BRAZIL. SERGIPE: Poço Verde, Fazenda Santa María da Lage ; 10º44’37” S, 38º05’44” W, 390 m; isolated remnant of Caatinga vegetation, on tree bark; 28 January 2015, J. Dantas ( ISE 30803 — holotype) ; ibid., J. Dantas ( ISE 30800 — paratype) .

Etymology: The epithet refers to the white-covered labia.

Description: Thallus corticolous, epiperidermal, up to 5 cm diam., continuous; surface uneven, light cream-colored; prothallus absent but thin black prothallus line sometimes formed when bordering other lichens. Thallus in section 70–120 μm thick, with cartilaginous upper cortex, 5–10 μm thick, irregular photobiont layer, 50–100 μm thick, with large clusters of calcium oxalate crystals above and within the photobiont layer. Photobiont Trentepohlia ; cells rounded to irregular in outline, in irregular groups, yellowish green, 7–12 × 6–10 μm. Ascomata lirelliform, flexuose, partly branched, erumpent, with thick lateral thalline margin, 1.5–3 mm long, 0.3–0.4 mm wide, 0.15–0.2 mm high; disc concealed; labia thick, entire (first generation lirellae) to striate, black beneath but with thick, white cover contrasting with the cream-colored thallus; thalline margin laterally thick, light cream-colored. Excipulum entire (first generation lirellae) to crenulate, laterally carbonized but somewhat converging basally, 50–100 μm wide, black; laterally covered by corticate algiferous thallus including clusters of crystals; hypothecium prosoplectenchymatous, 10–20 μm high, pale yellowish; hymenium 90–110 μm high, colorless, clear; epihymenium olive-grey granulose, granules not soluble in K, 10–20 μm high, olive-brown. Asci fusiform, 80–100 × 20–25 μm. Ascospores 8 per ascus, ellipsoid, (sub-)muriform with 5–7 transverse and 0–2 longitudinal septa per segment, 25–35 × 10–15 μm, 2–3 times as long as wide, colorless, I+ violet-blue. Secondary chemistry: stictic acid (major), constictic acid (minor), thallus and ascomata in section with K+ persistently yellow efflux.

Habitat and distribution: Thus far only known from the state of Sergipe in northeast Brazil, growing on tree bark in an isolated Caatinga remnant.

Characterization and taxonomic relationships: Among species of Graphis with small, muriform ascospores and clear hymenium ( Lücking et al. 2009), Graphis alba is morphologically characterized by the conspicuous, white cover on the lirellae (hence the epithet alba ), contrasting with the surrounding thallus, in combination with the stictic acid chemistry. The labia start out entire but eventually become striate, and the laterally carbonized excipulum converges somewhat basally. Hence, the new species also needs to be compared with other taxa with the same chemistry and small, muriform ascospores having entire or striate labia and a laterally or completely carbonized excipulum. Only four taxa fit these criteria ( Lücking et al. 2009). Among these, G. deserpens Vain. has entire, black labia with lateral thalline margin of the same color as the surrounding thallus, whereas the paleotropical G. fujianensis Z. F. Jia & J. C. Wei features prominent lirellae lacking a thalline margin. Likewise, the paleotropical G. hunanensis (Zahlbr.) M. Nakan. & Kashiw. , with striate labia, has lirellae lacking a thalline margin. Graphis discarpa A. W. Archer agrees with G. alba in the conspicuous white cover of the labia, but the labia are immersed and flush with the surrounding thallus and separated from the latter by a distinct split, and the species produces transversely septate ascospores.

Figures

FIGURE 1. Graphis alba (A, ISE 38000, paratype; B–C, ISE 38003, holotype). A–B. Thallus with lirellae showing conspicuous white labia cover. C. Ascospore. Halegrapha redonographoides (holotype). D–F. Thallus with more or less pseudostromatic lirellae, the reddish portions indicating decomposing norstictic acid; G–H.Asci with ascospores.Thelotrema pachysporoides (I, ISE 38001, paratype; J–L, ISE 38002, holotype). I–K. Thallus with apothecia; L. Ascus with ascospores. Scale in A–B, D–F, I–H = 1 mm, in C, G–H, L = 10 μm.