Ikaeria serusiauxii, a new Caloplaca-like lichen from Macaronesia and mainland Portugal, with a lichen checklist for Porto Santo

The new species Ikaeria serusiauxii (Teloschistaceae, lichenized Ascomycetes) is described from the Madeira Archipelago, Canary Islands and continental Portugal. It is a crustose lichen on twigs and branches of trees and shrubs in xerophytic maritime vegetation. Superficially it is similar to Caloplaca cerina and C. haematites, from which it differs by the often black apothecium margin, very thick spore septa, black pycnidium ostioles, and the presence of the pigment Cinereorufa-green instead of Sedifolia-grey. ITS sequences suggest Ikaeria aurantiellina (syn. Caloplaca aegatica) as the closest relative. Added is a preliminary lichen checklist for Porto Santo (Madeira Archipelago, Macaronesia).


Introduction
The Madeira Archipelago, one of the island groups of Macaronesia, is situated in the Atlantic Ocean some 500 km off the shore of NW Africa. Politically it belongs to Portugal. Like the Canary Islands, it has a dry warm climate except where higher mountains cause increased precipitation. During a visit to Porto Santo, the second largest island of the Madeira Archipelago, for a lichen mapping project (Sparrius et al. 2017), an unusual Caloplaca-like, epiphytic lichen showed up frequently on shrubs and trees, which somewhat resembled C. cerina or C. haematites. Morphological and macromolecular analyses showed it to be an undescribed species, which is treated below. Further results of this expedition are presented at https://archive.bgbm.org/sipman/Zschackia/ PortoSanto/genuslist.htm, and a preliminary checklist for Porto Santo is presented below (Table 1).

Material and methods
Specimens were studied with a stereomicroscope and a compound microscope in tap-water mounts. ITS sequences were generated by Alvalab (Spain). The sequences were analysed using https://www.ebi.ac.uk/ Tools/msa/muscle/ with standard settings and http://iqtree. cibiv.univie.ac.at/ (Trifinopoulos et al. 2016) with standard settings and sequence type = DNA (accessed 18 June 2019). Branch support values were obtained with ultrafast bootstrap (Hoang et al. 2018) implemented in IQ-TREE (Nguyen et al. 2015).
Vouchers are deposited in B, BR, M, MADJ and herb. van den Boom.

Results and discussion
For complete documentation of the new species, ITS sequences were generated. These gave a preliminary view of the affinities of the new species. A BLAST search in Genbank in 2017 gave the surprising result that the closest relatives were in the genus Lecidea. A repeated BLAST search in 2019 suggested an affinity with the genus Ikaeria, which was published meanwhile by Kondratyuk et al. (2017). It comprises the single species Ikaeria aurantiellina, based on samples from Tenerife, Canary Islands. The genus was found to belong to the subfamily Teloschistoideae as sister to the genus Yoshimuria, and not to the Caloplacoideae or Xanthorioideae where most crustose 'Caloplaca' species in Europe and the Mediterranean belong.
Following these suggestions, a comparison of the new species with putative relatives was made. ITS sequences, mostly downloaded from Genbank, were aligned with Megalospora, Brigantiaea    as potential relatives, with the genus Ikaeria, and with selected representatives of the three main groups of Teloschistaceae, the subfamilies Xanthorioideae, Caloplacoideae and Teloschistoideae (Arup et al. 2013).
The resulting tree ( Fig. 1) shows that the new species is clearly distinct from C. cerina and C. haematites, and that it has Ikaeria aurantiellina as the closest relative. Therefore the new species is included in the genus Ikaeria.
From Porto Santo, where the new species was recognized first, few lichen species have been reported so far. Krog & Østhagen (1980) and Krog (1990) reported Ramalina species, and Haugan (1992) a species of Anzia. These authors discovered remarkable lichen endemism on the island. Short lists of additional species were published by Follmann (1990), Carvalho et al. (2008) and Sparrius et al. (2017). Some recent monographers included material from the island, in particular Timdal (1992) on Toninia. The presented checklist (Table 1) is based mainly on the more easily recognizable lichen species observed during our mapping fieldwork. An attempt was made to study some groups in more detail, but the example of Ikaeria serusiauxii showed that a full evaluation requires more effort than we can invest currently. Therefore we are using the opportunity to publish all data collected so far in a checklist, including information on whether TLC was done, and we release all newly generated ITS sequences, including for groups for which no conclusive taxonomy is settled yet. Sipman, MycoBank MB 833026
Chemistry. Not tested by TLC; the black parts of the apothecia, the pycnidium ostiole and the prothallus contain dark olive-green pigment in the outer locules of the cortex, in K turning more greenish but persistent (Cinereorufa-green); the epithecium turning violet in K, releasing clouds of fine violet crystals (indet. anthraquinones); thallus and apothecium margin lack anthraquinones (K-).
Etymology. Named after Emmanuel Sérusiaux, our esteemed companion on expeditions in Papua New Guinea, who contributed significantly to the exploration of the lichen diversity of Macaronesia.
Distribution and ecology. The species is known from Macaronesia (Madeira Archipelago and Canary Islands) and from mainland Portugal (Algarve, Estremadura). Here it is found on twigs and branches of trees and shrubs in open, rather xerophytic vegetation, e.g. on Euphorbia piscatoria, but also on introduced Cupressus and Pinus. On Porto Santo it is fairly common at 350-400 m a.s.l. From the Madeira Island, so far two records are available, from 500-575 m a.s.l. The localities in mainland Portugal are close to the seashore.
Notes. Caloplaca cerina is the most likely species to be confused with Ikaeria serusiauxii, as it shares an anthraquinone-free, pale thallus, anthraquinone-free apothecium margins and yellow to orange-colored discs (Šoun et al. 2011). However, I. serusiauxii differs clearly from C. cerina s.l. by the black pycnidium ostioles, the presence of the pigment Cinereorufa-green, and the thick ascospore septa 8-12 μm wide instead of 5-8 μm (Fletcher & Laundon 2009). Another rather similar species in the Mediterranean, Caloplaca haematites, has, like C. cerina, an anthraquinone-free thallus, anthraquinone-free apothecium margins and often orange-coloured discs, but in full light the thallus is very dark, almost black, due to a different, grey, K+ violet pigment (Sedifolia-grey), and the discs are reddish; only in shade are the thallus greenish grey and the discs orange. Thus, I. serusiauxii is clearly distinct in full light by the thallus-and apothecium color, and by the presence of Cinereorufa-green, while Follmann (1990)  recognition of the shade forms relies on the black pycnidium ostioles and thick septa. The tropical species C. leptozona may be closer to I. serusiauxii because it shares the black pycnidia, but that species is saxicolous, its discs turn black, and its spores have shorter septa about half as thick as spore length. Unfortunately, no ITS sequence of this species was available in Genbank. The only other Ikaeria species, I. aurantiellina, shares the black pycnidia and thick spore septa (spores 12-14 × 7-8 μm, septa ~6-8 μm thick, ratio of septum width/ spore length 0.5-0.67), and can be distinguished easily by the 'biatorine' apothecia (Giralt et al. 1992). However, a closer look shows that the apothecia of the two species are anatomically indistinguishable except for the somewhat shorter ascospores in I. aurantiellina. Externally there is a difference in apothecium margin color. In I. aurantiellina the margin is deep yellow to orange, slightly paler at the disc, reflecting the constant presence of anthraquinones. This gives it a biatorine appearance, but anatomically the margin contains numerous algae. In I. serusiauxii the margin is greenish grey, with more or less black pigment, and it lacks anthraquinones. This gives the apothecia a lecanorine appearance, especially when the black pigment is scarce.
The synonymy of I. aurantiellina (as Caloplaca aurantiellina) with C. aegatica was first suggested by Boom & Etayo (2006), who admitted that the original description of C. aurantiellina is fairly different. Apparently they did not study any type material, so the synonymy may need revision. Kondratyuk et al. (2017) mentioned two genera closely related to Ikaeria or having a similar basal root: Yoshimuria and Fominiella. The first genus is included in Figure 1, where it shows up in the Caloplacoideae. Thus it seems unrelated to our new Ikaeria species. The second contains two species: F. skii and F. tenerifensis. The ITS sequence of F. skii shows an affinity with the genus Athallia, as Kondratyuk et al. (2017) admit. In our Figure 1 the species is positioned accordingly and shows no close relation with Ikaeria. For the second species, F. tenerifensis, no ITS sequence is available. The description and illustration of F. tenerifensis suggest that it differs from I. serusiauxii by the absence of black pigment in the prothallus, apothecium margins and pycnidium ostioles, and by the shorter ascospore septa, about half of spore length. The illustration presented in Kondratyuk et al. (2018, p. 179, Fig. 20) also suggests a different species.