Plectocarpon dimorphosporum Etayo, Flakus & Kukwa, 2018

Etayo, Javier, Flakus, Adam & Kukwa, Martin, 2018, Three new lichenicolous species of the genus Plectocarpon (Ascomycota: Lecanographaceae) discovered in the Bolivian Andes, Phytotaxa 357 (4), pp. 275-283 : 276-278

Plectocarpon dimorphosporum Etayo, Flakus & Kukwa sp. nov. MycoBank MB 824895

Diagnosis: Differs from Plectocarpon triebeliae in having two types of mature ascospores (1- and 3-septate), smaller ascomata, and a different host selection ( Ricasolia patinifera ).

Type:— BOLIVIA. DEPT. TARIJA: Prov. Aniceto Arce, Papachacra, 21°41’52”S, 64°29’15”W, 1900 m, Tucumano-Boliviano altimontano forest, on corticolous Ricasolia patinifera , 8 Aug. 2012, M. Kukwa 11075 (holotype UGDA!, isotype LPB!). ( Fig. 1 )

Ascomata stromatic, developing on the upper surface of the host thallus, single, rounded to elliptical, first flattened and immersed in the host thallus, emarginate and covered by the cortex of the host that becomes brownish and fissured, later convex, bursting through the host cortex (with remnants of the cortex on the ascomatal surface forming a star-like pattern) and forming small, basally unconstricted galls, with a residual pseudo-margin consisting of the host thallus, when mature breaking completely the cortex and fully exposed, (0.3–)0.5–1.5(–3.0) mm in diam.; surface rough, obscurely lirellate. Stroma multilocular, 150–350 μm thick; sterile stromatic tissue pigmented, dark brown to black (in part carbonized) in upper parts with granular pigment on the surface and in the hyphal walls (often covered by cortex fragments of the host), K+ olive-black, N+ red-brown, and orange to brown pigment below the loculi, K– (or slightly reddish brown), N+ orange-brown; loculi rounded in section, generally 80–100(–150) μm wide. Hymenium hyaline, I+ blue, changing quickly to red, K/I+ blue, up to 80 μm high. Epihymenium brown. Paraphyses branched, septate, not distinctly swollen at the apices, 2–3 μm thick, in upper parts brown. Asci narrowly clavate, Opegrapha - type, with an apical K/I+ blue ring, 65–80 × 15–19 μm, 4–6-spored (frequently 3- and 1-septate ascospores mixed together in the same ascus). Ascospores hyaline, oblong, either (2–)3-septate, 16–28(–32) × 5–7 μm (n=35) and 1-septate, 10–19(–21) × 4–6 μm (n=36), sometimes slightly constricted at the septa, with a thick gelatinous coat up to 2 μm thick; 1-septate ascospores with upper cell slightly shorter and broader than the lower one; mature ascospores of both types (1- and 3-septate) developing a pale to dark brown, thick granular perispore. Pycnidia not observed.

Host: Plectocarpon dimorphosporum inhabits the thalli of corticolous Ricasolia patinifera . The species obviously does not damage the host (not developing a necrosis), so we can assume it as a biotrophic mycoparasite probably obtaining nutrients from living host hyphae.

Distribution and habitat: So far the new species is known from two localities in the Bolivian Andes, where it grows in montane Tucumano-Boliviano forests. Although the host has been commonly collected in Bolivia and other South American countries (e.g., Kukwa et al. 2014) the new fungus seems to be rare.

Notes: The new species is most similar in habit, stromatic pigments (Atra-brown) and ascospores size to P. triebeliae Diederich & Ertz (in Ertz et al. 2005: 109), so far an extratropical Plectocarpon inhabiting a related host ( Ricasolia quercizans ) and known only from the type locality in North America. The ascomata of P. triebeliae are, however, much larger [up to 3(–5) mm diam.], meanwhile in P. dimorphosporum ascomata are smaller [up to 1.5(– 3.0) mm in diam.]. Ascospores of P. triebeliae are consistently 3-septate, whereas in P. dimorphosporum 3-septate ascospores are produced together (often in the same ascus) with a large number of 1-septate ascospores. Both types of ascospores (1- and 3-septate) produced by P. dimorphosporum seem to be fully mature, and the 1-septate ascospores also becoming brown and strongly verruculose when mature. Although there are several examples of fungi producing dimorphic ascospores within the same ascoma [e.g., Chromocrea spinulosa (Fuckel) Petch ex F.T. Brooks & Mathieson , Mamillisphaeria dimorphospora K.D. Hyde, S.W. Wong & E.B.G. Jones , Weddellomyces tartaricola (Linds.) Alstrup & D. Hawksw. ( Brooks & Mathieson 1950; Alstrup & Haksworth 1990; Hyde et al. 1996)], the phenomenon was not observed before in the genus Plectocarpon (Ertz et al. 2005) . One of the most spectacular examples of dimorphic ascospores among lichenicolous fungi has been reported from Ovicuculispora macrospora Etayo (2010: 111) . This peculiar species is characterized by production in the same ascus of a single macrospore (of size 67–105 × 32–40 μm) together with 2–3 microspores (10–13.5 × 4.5–5 μm). The possession of dimorphic ascospores can possibly increase the dispersal ability of species as mentioned by Hyde et al. (1996), however, in case of P. dimorphosporum there is no evidence supporting such hypothesis so far.

Plectocarpon dimorphosporum should also be compared with P. violaceum Ertz, R.Sant., Diederich & Wedin in Ertz et al. (2005: 116) known from Argentina and Chile, as this species shows a very similar development of ascomata. It can be distinguished by larger stroma (up to 3 mm in diam.) with very particular pigments reacting K+ greyish to bluish green, and K+ violet blue to turquoise, and consistently 3-septate ascospores, which are always constricted at the septa. Additionally the species parasitizes the non-related Nephroma antarcticum (Ertz et al. 2005) .

Additional specimen examined (paratype). BOLIVIA. DEPT. TARIJA: Prov. O’Connor, 26 km from Entre Ríos, near Soledad, 21°39’52”S, 64°07’22”W, 1700 m, Tucumano-Boliviano montano forest, on Ricasolia patinifera on trunk, 11 Aug. 2012, J. Etayo 28785 (LPB!, hb. Etayo!).

Holotype of Plectocarpon triebeliae examined. U.S.A. MINNESOTA, Lake Country, Superior National Forest (9 miles W of Tofte), 47°36’04” N, 91°02’11” W, 1190 ft, Sec. 12 & 13, T 59 N, R 6 W, in mature sugar maple stand with some old yellow birch, on Ricasolia quercizans , 28 July 1999, Wetmore 83138 (M!).

Figures

FIGURE 1. Plectocarpon dimorphosporum (holotype).A, habit of the fungus:A–B, young ascomata with remnants of the cortex forming a star-like pattern; C–D, mature obscurely lirellate ascomata; E–F, cross section through part of stroma; G, mature asci showing amyloid zone above ocular chamber, seen as two dark blue lines (mounted in K/I); H, young asci; I, 1-septate ascospores with the upper cell slightly shorter and broader, and a thick gelatinous coat (two overmature spores on the right have a dark brown granular perispore); J, 3-septate ascospores with a thick gelatinous coat (first ascospore on the right overmature, with a dark brown granular perispore). Scales: A=250 μm, B–D=500 μm, E=100 μm, F=50 μm, G–J=10 μm.