Micarea capitata M. Svensson & G. Thor sp. nov

MycoBank No. MB 519054

Thallus crustacea, muscicola. Apothecia multa, 0·10–0·35 mm diametro, atra. Sporae octonae, ellipsoideae, incoloratae, (0–)1-septatae, (7·5–)9–11(–12) × (2·5–)3–4(–4) µm. Micarea hylocomii Poelt & Döbbeler sub similis, sed paraphyses anastomosantes; pigmento hymenio et hypothecio differt.

Typus: Sweden, Härjedalen, Tännäs parish, the E slope of Mt. Ramundberget, above the holiday village of Kvarnbäcken, subalpine deciduous forest, on Hylocomium splendens on boulder, 62°41·654′N, 12°23·662′E (WGS84), alt. 730 m, 2 June 2007, M. Svensson 1004 (UPS—holotypus).

(Fig. 1)

Fig. 1. Micarea capitata (holotype, UPS). A, habitus; B, section (16 µm thick in water) of apothecium, showing the mottled pigmentation of the hypothecium (arrow); unless K is applied and the tissues pushed apart by applying some pressure, individual paraphyses and asci are hardly discernible. Scales: A = 2 mm; B = 60 µm.

Thallus crustose, forming small patches on Hylocomium splendens (Hedw.) Schimp., episubstratal but often very thin and then barely visible, pale grey; hyphae 1·0–1·5 µm diam. Photobiont ‘micareoid’; cells regularly globose, 4–7 µm diam.

Apothecia numerous, scattered, immarginate, convex to hemispherical, constricted at the base, black, (0·10–)0·15–0·25(–0·35) mm diam. Hymenium blue-green in streaks or rarely hyaline, 30–40 µm tall, K−, C−, N± red, I+ blue, K/I+ blue. Epithecium not well delimited, pale to dark blue-green, up to 5 µm tall, K−, C−, N+ red. Asci clavate, 8-spored, 30–35 × 10–12 µm, Micarea-type. Ascospores ellipsoid, straight or slightly curved, rarely guttulate, hyaline, (0–)1-septate, (7·5–)9–11(–12) × (2·5–)3–4(–4) µm (length: = 10·00, SD = 1·17, n = 32; width: = 3·29, SD = 0·52, n = 32). Paraphyses numerous, branched and anastomosing, hyaline, immersed within gel-matrix that does not dissolve in K, 0·8–1·5 µm wide; apices 0·8–2·0 µm wide and sometimes with an indistinct greenish apical cap. Hypothecium mottled blackish green without any red or purple tinge, 40–60 µm tall, K−, C−, N+ red; composed of densely interwoven, anastomosing hyphae, 1–2 µm wide. Excipulum soon reflexed, composed of branched hyaline hyphae, sometimes coated with blackish green pigment, 1·5–2·5 µm wide, K−, C−, N± red.

Pycnidia not observed.

Chemistry. Thallus K−, C−, KC−, Pd−, UV−. No lichen substances detected by HPTLC. Of the insoluble pigments described in Meyer & Printzen (Reference Meyer and Printzen2000), the blue-green pigment in the apothecia is most similar to ‘Cinereorufa-green’, but differs in reacting HNO₃+ red/ K+ dark brown/ HCl+ brown/ K+ dark brown, instead of shifting between blue-green and dark purple.

Etymology. The epithet ‘capitata’ refers to the globose apothecia of the new species.

Ecology and distribution. Micarea capitata is only known from two localities in Härjedalen in north-western Sweden. Both collections were made on the bryophyte Hylocomium splendens on rocks in open forests. The type material was collected on a boulder in a subalpine deciduous forest dominated by Betula pubescens and the second specimen was collected close to a stream in an old-growth Picea abies forest. The species was found on one to three year old shoots of its host. These were usually yellowish (apparently dying), which indicates that the substratum for the species is short-lived. Thus, the species is probably adapted to frequent dispersal and establishment on new Hylocomium splendens shoots. Species with this type of life strategy are rarely restricted to small geographical areas (e.g. Döbbeler Reference Döbbeler1997). We therefore assume the species to be more common and widespread than the current findings indicate, especially since its host is such a ubiquitous species in Fennoscandia. However, we have searched unsuccessfully for M. capitata at several localities in northern Sweden from 2008–2010. Although the habitat requirements of the species are not fully understood, one possible explanation for this might be that its apothecia are most frequent in the spring and hence less likely to be found in the summer and autumn when most of our subsequent searches have taken place. We have also revised all the bryophilous material filed under Micarea in herbarium UPS without finding any additional material of the new species, although it should be noted that almost none of the available collections were collected on Hylocomium splendens.

Notes. Micarea capitata is characterized by its bryophilus habit, small, black apothecia with a constricted base, (0–)1-septate ascospores and the mottled appearance of the hypothecium, which is caused by patchy distribution of pigment (Fig. 1B). This pigment appears very dark even in thin sections. It should also be noted that individual paraphyses and asci are hardly discernible unless K is applied and the tissues pushed apart by applying some pressure.

Owing to its small size, the species is easily overlooked. In the field, it can be detected as a slight discolouring of Hylocomium splendens, but this is likely to be missed if not actively searched for. Examined under the hand-lens, it bears some resemblance to Arthonia muscigena Th. Fr., which may grow on bryophytes in a similar fashion. It might also be somewhat similar to various non-lichenized fungi, which are often present on dying bryophytes in boreal forests in Sweden. Coppins (Reference Coppins1983) divided Micarea into 11 infrageneric groups, some of which have received support from later molecular studies [e.g. the Micarea sylvicola group and the Micarea peliocarpa group (Andersen & Ekman Reference Andersen and Ekman2005); the Micarea prasina group (Czarnota & Guzow-Krzemińska Reference Czarnota and Guzow-Krzemińska2010)], while other groups still remain unclear. Micarea capitata is not easily accommodated in any of these groups because of its atypical apothecial pigment; however, it is possible that it is related to species in the ‘Group H’ of Coppins (Reference Coppins1983), a group which contains other species with minute, black apothecia, 0–1 septate ascospores and a thin thallus without lichen substances.

In Fennoscandia, most lichen species overgrowing bryophytes grow on dead specimens of their hosts and although adequate data are missing for many species, they generally seem to exhibit low host specificity. A few of these species might eventually prove to be host specific (e.g. some of the species growing on Andreaea spp. in alpine situations), but many of them also grow on other substrata. The only well-documented bryophilous lichen in Fennoscandia is Puttea margaritella (Hulting) S. Stenroos & Huhtinen, which grows exclusively on the liverwort Ptilidium pulcherrimum (G. Web.) Hampe, where it is viewed as a necrotrophic parasite or a colonizer of damaged parts of its host (Stenroos et al. Reference Stenroos, Huhtinen, Lesonen, Palice and Printzen2009). Although the available data on M. capitata are insufficient for any firm conclusion, its presence on seemingly still living specimens of its host suggests a parasitic life strategy similar to that of P. margaritella.

Among lichenized species, M. capitata is probably most likely to be confused with M. hylocomii Poelt & Döbbeler, a rarely collected species which has only been reported from the Alps and Norway (Poelt & Döbbeler Reference Poelt and Döbbeler1975; Poelt & Buschart Reference Poelt and Buschart1978). Although superficially similar in habit and pigmentation, this species is clearly different from M. capitata in having smaller (0·05–0·15 mm) ± adnate apothecia without a clearly constricted base and simple or rarely sparingly branched paraphyses, which have apices (–3 µm diam.) with a dark brown or a black pigment hood (Poelt & Döbbeler Reference Poelt and Döbbeler1975). The ascospores of M. hylocomii (holotype, GZU!) were originally given as 2 µm wide; our own measurements range between 1·5–3 µm, which is on average thinner than the ascospores of M. capitata, although there is an overlap. Further, the blue-green apothecial pigment in M. hylocomii, although also reacting K− and N+ red, seems different from the one found in M. capitata, since it dissolves rapidly in C (M. Svensson & G. Thor, personal observations). Overall, the position of M. hylocomii in Micarea is doubtful (Poelt & Döbbeler Reference Poelt and Döbbeler1975; Coppins Reference Coppins1983).

Micarea botryoides (Nyl.) Coppins is similar to M. capitata in having apothecia that are constricted at the base and in the size and septation of the ascospores, but differs in having a reddish brown hypothecium, two types of paraphyses and numerous stalked pycnidia (Coppins Reference Coppins1983). Micarea melaena (Nyl.) Hedl. has apothecia of similar shape and although this species is chiefly corticolous or lignicolous, it might occasionally grow on bryophytes. It differs from M. capitata in having a hypothecium that usually has a dark purple pigment, reacting K+ green, larger (12–21 × 4–5·5 µm), mostly three-septate ascospores and a better developed thallus, reacting C+ red due to presence of gyrophoric acid (Coppins Reference Coppins1983; Czarnota Reference Czarnota2007). Micarea prasinella (Jatta) I. M. Lamb may also grow on bryophytes and likewise has predominately 1-septate ascospores and black apothecia that are clearly constricted at the base, but differs in having more distinctly stalked apothecia, a purple-brown, K+ purple or K+ green pigment in the apothecia and a better developed thallus that contains gyrophoric acid (Coppins Reference Coppins, Smith, Aptroot, Coppins, Fletcher, Gilbert, James and Wolseley2009). The bryophilous M. turfosa (A. Massal.) Du Rietz differs in having a black thallus, a mottled reddish brown hypothecium and larger (10–25 × 3·5–5 µm) ascospores (Coppins Reference Coppins1983). A species that may be found growing over bryophytes in subalpine habitats similar to the one M. capitata was found in, is Helocarpon crassipes Th. Fr., which, however, has a more well-developed thallus, a much more developed excipulum and contains a purple-brown pigment in the apothecia (Coppins Reference Coppins1983).

Additional specimen examined. Sweden: Härjedalen: Tännäs parish, 900 m SSE of Svalåvallen, by stream in old-growth mixed coniferous forest, 62°37·161′N, 12°25·193′E (WGS84), alt. 700 m, on Hylocomium splendens on vertical side of boulder, 4 vi 2007, G. Thor 21842 (UPS).