Caloplaca molariformis Frolov, Vondrák, Nadyeina & Khodos. | MYCO-LICH

Caloplaca molariformis Frolov, Vondrák, Nadyeina & Khodos.

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Thallus epilithic, ochre, white-grey to dark grey, usually with white pruinose spots, forming irregular spots to several cm wide; of tightly arranged, angular to rounded, more or less flat areoles or somewhat umbilicate squamules, (044–)070–095–126 (–205) mm diam. [100; 10; 035]. Marginal areoles sometimes bigger than areoles in the centre. Several small, tightly arranged areoles may merge to form larger units, but on the contrary, large areoles are sometimes divided into smaller subareoles due to secondary crevices. Thickness of the thallus, together with brown (probably necrotic) lower medulla (02–)06–12–22(–50) mm [30; 3; 10]; thickness of the thallus without lowermost brown part (01–)03–04–05(–09) mm [30; 3; 02]. The brown lower medulla usually distinct, up to 125 times thicker than the rest of the thallus. Colourless medulla also present, (50–)140–235–330(–550) mm thick [26; 3; 145]; cells hardly observable due to presence of extracellular crystals insoluble in KOH and only partly dissolved and recrystallized into needles in H2SO4. Algal cells arranged in vertical stacks, (30–) 67–91–129(–250) wide [47; 6; 44], and (100–)223–263–334(–550) mm high [47; 6; 112]. Algal cells globose, (80–)126–137–
145(–220) mm diam. [30; 3; 32]. Cortex above the algal stacks absent or indistinct, alveolate cortex present, up to c. 15–30 mm thick; upper fungal cells in algal stacks grey, containing Sedifolia-grey. Fungal stacks (measured with epinecral layer) (13–)45–86–120(–270) wide [46; 6; 55] and (75–)180–322–505(–750) mm high [46; 6; 165]; formed by vertically oriented palisade prosoplectenchyma; size of cells in the middle part of stacks (45–)94–119–133(–180) (30–)37–43–48(65) mm [30; 3; 39 & 09]. In lower part of stacks, cells longer and narrower; in uppermost part, cells almost isodiametric, c. 4–7 mm diam. Epinecral layer above fungal stacks usually well-developed, (5–)20–95–200(–350) mm thick [81; 9; 72]; dead cells (colourless in cotton blue) recognizable in the lower part. Boundary between epinecral layer and upper cells of the fungal stack sometimes indistinct, but recognizable after KOH treatment as a sordid grey-violet line caused by traces of the Sedifolia-grey in uppermost fungal stack cells. Epinecral layer often forms distinct ridges on thallus surface above fungal stacks, because it is absent from surface of algal stacks (Fig. 7C). Epinecral ridges best developed in samples from deserts of Western Kazakhstan, but less distinct in samples from Slovakia and Ukraine. Fungal stacks sometimes reaching medulla at the bottom and the boundary between the stacks and medulla recognized by the crystals abundant in medulla but absent from stacks. Margins of areoles and squamules and the lower surface of squamules usually with cortex, up to c. 20 mm thick, of isodiametric cells, c. 4–7 mm diam. Vegetative diaspores are blastidia (always present) or rarely soredia; sometimes diaspores poorly developed, present only on few areoles. Blastidia simple, more or less globose, (30–)54–67–89(–150) mm diam. [52; 6; 25], dark grey, present on the margin and upper surface of areoles and squamules; detached blastidia occasionally cover the whole surface. Blastidia sometimes with appearance of consoredia, with internal soredia-like structures. Extracellular crystals soluble in KOH and Sedifolia-grey pigment present in outer fungal cells of blastidia. Soralia rarely observed, on the upper surface between epinecral ridges; soredia c. 25–40 mm diam. White pruina always present, better developed between epinecral ridges. Prothallus indistinct or absent. Thallus frequently affected by brown hyphomycetes resembling species of Intralichen. Apothecia (033–)042–055–072(–132) mm diam. [100; 10; 015], zeorine or rarely almost lecanorine; mature apothecia sessile, usually not abundant on thallus, sometimes absent. Richly fertile populations known only from Slovakia and Ukraine. Disc brown to black, not pruinose, sometimes cracked; true exciple concolourous with the disc, occasionally white pruinose; thalline exciple concolourous with the thallus, with white pruina. Hymenium (63–)91–102–109(–175) mm high [30; 3; 23], colourless, often with very small (<1 mm) extracellular oil drops, sometimes strongly inspersed with extracellular oil drops up to c. 2 mm diam., sometimes not inspersed; without crystals. Epihymenium brown, grey or grey-brown. Hypothecium colourless, underlain by the algal layer, usually with extracellular oil drops, without extracellular crystals; with a central conical extension downward, (75–) 153–174–185 (–275) mm high [30; 3; 48]; formed of thin-walled cells variable in shape. Exciple c. 10–160 mm wide. True exciple (10–) 18–35–54(–93) mm wide [30; 3; 22], and thalline exciple (0–)18–24–27(–68) mm wide [30; 3; 20]. Upper part of the true exciple grey-brown, brown-grey or grey, of thin-walled cells (40–)62–66–73(–100) (20–)34–45–52(–80) mm [100; 10; 11 & 11]. Lower part colourless, of palisade prosoplectenchyma of thin-walled cells (60–) 77–82–87(–115)  (20–)24–28–33(–50) mm [30; 3; 13 & 08]. Thalline exciple sometimes with cortex in its upper part, c. 8–20 mm thick; cortex changing into alveolate cortex in the lower part of thalline exciple. Cells of the cortex spherical, c. 35–70 mm diam., often hardly observed due to extracellular crystals insoluble in KOH. Paraphyses (15–)21–23–28(–35) mm wide [100; 10; 04] in lower part, but widening gradually to (30–)35–44–55(–65) mm [100; 10; 08] in upper part; rarely branched and anastomosed; the uppermost cell of paraphyses usually dead and deformed. Asci clavate, (40–)58–64–69(–85)  (12–)17–20–21(–28) mm [30; 3; 1 & 10]. Ascospores polarilocular, (120–)143–162–183(–230)  (50–) 64–77–91(105) mm [70; 8; 23 & 13]; septa (20–)26–30–33(–40) mm wide [70; 8; 05]. Ascospore length/breadth ratio: (140–)198–212–227(–286) [70; 8; 032]; septum width/ascospore length ratio: (011–) 017–019–022(–030) [70; 8; 004]. Ascospores with well-developed septa often absent. Pycnidia rare, c. 140–190 mm wide, mainly with a single chamber, present on the upper thallus surface, but also on the lower surface of squamules; superficially hardly distinguishable. Old pycnidial chambers sometimes filled by crystals insoluble in KOH. Conidiophores of spherical or triangular, more or less isodiametric cells. Conidia narrowly to broadly ellipsoid, 25–45  15–20 mm
[14; 2; 02 & 05]. Chemistry. Spot tests: thallus Ke violet (sometimes not observable or observable only in spots with blastidia and soredia), apothecia K--, thallus and apothecia C--, P--, UV--. Epihymenium, uppermost true exciple, uppermost fungal cells in thallus and vegetative diaspores contain Sedifolia-grey (grey or invisible in water, K+ sordid violet). The reaction above fungal stacks usually weaker than above algal stacks. Strongest reaction in superficial hyphae of vegetative diaspores. True exciple non-amyloid (I--); hymenium and hypothecium amyloid (I+). No substances revealed by HPLC (apothecia and thallus of an isotype were investigated).

Etymology. Areoles and squamules of the lichen thallus often resemble molars of herbivores.

Similar taxa. The thallus anatomy, with tissues in stacks, is very rare within the Pyrenodesmia subgroup of Caloplaca. It is present in one known species only, Caloplaca albovariegata (B. de Lesd.) Wetmore, which is very similar to C. molariformis but has no vegetative diaspores (Wetmore 1994; lectotype in UPS seen). This species was described from North America, but similar morphotypes are known in continental Eurasia (our observations). Zhou et al. (2012) reported a taxon with tissues in stacks from China and named it C. albovariegata, but it has a thallus surface without ridges derived from the epinecral layer and it does not resemble C. molariformis. Other similar taxa are Caloplaca albopustulata Khodos. & S.Y. Kondr. (with pustules and schisidia), C. bullata (Mu¨ ll. Arg.) Zahlbr. (bullate thallus without vegetative diaspores), C. concreticola (with soralia) and C. transcaspica (Nyl.) Zahlbr. (without vegetative diaspores), but all these taxa have thallus tissues arranged in horizontal layers, not in stacks. They also do not have specific ridges derived from the epinecral layer. (Type specimens and other comparative material studied by the authors.) Phylogeny. In the ITS phylogeny (Fig. 5), Caloplaca molariformis is placed in the C. variabilis group, closely related to C. albopustulata.

Distribution and ecology. Caloplaca molariformis is mainly distributed in steppes and deserts of Iran, Kazakhstan, continental Turkey and southern Russia, at altitudes of 50– 2100 m. Two isolated localities are also known from the steppe or forest-steppe, in eastern Ukraine and southern Slovakia. The species occurs in sunny habitats on soft limestone, chalk, calcareous sandstone or tuffs with evident content of lime (always reacting with HCl). Co-occurring lichen taxa include Acarospora spp., Aspicilia spp., Caloplaca concreticola, C. crenulatella s. lat., C. decipiens, C. flavocitrina, C. soralifera, C. sororicida, C. teicholyta, C. tominii, C. transcaspica s. lat., C. xerica, Candelariella aurella, Lecanora muralis s. lat., Lemmopsis arnoldiana, Lichinella sp., Verrucariaceae spp. (e.g. Staurothele frustulenta, Verrucaria macrostoma, V. nigrescens agg.).

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