Astrochapsa martinicensis Ertz & Borgato, 2018

Borgato, Luca & Ertz, Damien, 2018, A new species of Astrochapsa (Graphidaceae) from Martinique, with a world-wide key to the species, Phytotaxa 371 (2), pp. 102-110 : 106-107

Astrochapsa martinicensis Ertz & Borgato spec. nov. ( Fig. 2 )

Mycobank #827625

Differing from all other species of Astrochapsa by the combination of an ecorticate, whitish-grey thallus, the ascospores with 5 to 7 transversal septa, of (12.5–)14–24(–29) × (4.5–)5–6.5(–7) μm, and by the chemistry (unidentified terpenoid as main substance).

Type: — MARTINIQUE. Presqu’île de la Caravelle, La Trinité, Pointe Rouge, 14°45’31”N, 60°56’00”W, 35 m elev., forêt sèche littorale secondaire, sur gros tronc, 29 September 2013, D. Ertz 18483 (holotype BR!).

Thallus corticolous, crustose, largely epiphloeodal, whitish-grey, matt, without compact surface, c. 50–125(–170) μm thick; cortex indistinct; medulla lacking calcium oxalate crystals; vegetative propagules and conidiomata absent; prothallus not seen. Photobiont trentepohlioid, with rounded, ellipsoid to slightly rectangular cells, 6.5–13 × 6.5–9.5 μm. Ascomata immersed-erumpent, chroodiscoid, rounded to slightly irregular, 0.4–0.6 mm diam.; ascomatal margin prominent, white to very pale yellow, white-pruinose, of ±triangular, fragile, upright to little recurved lobules of up to 250 μm tall; hymenial disc exposed, flesh-coloured, white-pruinose.

Excipulum pale yellowish, c. 10–20 μm wide. Hymenium not inspersed, 75–90 μm high, I–, KI–; epihymenium unpigmented to pale yellowish, 7–12 μm thick. Hypothecium hyaline to light yellowish, 10–25 μm thick. Paraphyses unbranched, except sometimes at the tips, c. 2 μm wide; tips slightly thickened, adspersed with fine greyish granules. Periphysoids present, ±perpendicular to the hymenium. Asci cylindrical, with tholus (2.8 μm wide), 60–80 × 9–16 μm, I–, KI–. Ascospores hyaline, oblong to ellipsoid-fusiform or fusiform with one distinctly tapering end, 6–8/ascus, (4–)5–7(–9)-euseptate to slightly subdistoseptate, (12.5–)14–[18.1]–24(–29) × (4.5–)5–[5.9]–6.5(–7) μm (n=50); lumina ±rectangular, but ±triangular at the ascospores’ ends; gelatinous sheath indistinct.

Secondary chemistry: —Thallus and ascomata C–, K–, Pd–, UV –. TLC (solvent G): unknown terpenoid (Rf = 66) and traces of four unidentified substances (one UV pink before heating, Rf=46; one UV pink-grey after heating, Rf=51; two UV pinkish after heating, Rf=70 and 80).

Etymology: —The specific epithet refers to the type location ( Martinique).

Distribution and ecology: —Dry littoral secondary forest (35 m elev.). Collected from a big trunk of a living tree. Only known from the type locality.

Remarks: —By its ecorticate thallus and transversely septate small ascospores, the new species is similar to Astrochapsa amazonica , A. graphidioides and A. sipmanii . A. amazonica differs from the new species by a black apothecial disc, 3(–4)-septate, smaller (10–12 × 3.5–4 μm) ascospores ( Kalb 2009). A. graphidioides differs from the new species by larger ascomata (0.5–2.5 mm diam.) and much smaller ascospores (9–11 × 3–4 μm) ( Kalb 2009). A. sipmanii differs from the new species by an olive-brown thallus, thickly white pruinose apothecial disc resembling soralia and smaller ascospores (12–15 × 3–4 μm) ( Weerakoon et al. 2015). The ascospores of A. martinicensis (at least the tapering-ones) are very similar to those of A. verruculosa , A. lobata and A. fusca . However, A. verruculosa has stictic acid ( Papong et al. 2014) and the other two have olive-green and olive-brown corticate thalli ( Lücking 2014, 2015). In addition, A. lobata has narrower ascospores and apothecia becoming lobate when mature ( Lücking 2015). Pseudochapsa kalbii (Frisch) Parnmen, Lücking & Lumbsch (2012: 10) is also similar to the new species but differs by submuriform ascospores and the absence of lichen compounds (Frisch 2006). A. martinicensis is also similar to Chapsa farinosa Lücking & Sipman in Sipman et al. (2012: 37), but this species has larger ascospores (20–30 × 4–6 μm) and calcium oxalate crystals clusters in the thallus. Chapsa cinchonara (Fée) A. Frisch (2006: 96) differs from A. martinicensis by larger (0.5–0.8 mm broad and up to 2.3 mm long), elongated ascomata and more septate (6–12-septa) ascospores with a persistent halo (Frisch 2006).

Figures

FIGURE 2. Astrochapsa martinicensis (holotype). A Thallus with ascomata. B–C Ascomata. D Ascospores in water. Scale bars: a=500 μm, b–c=250 μm, d=5 μm (Photos D. Ertz).