Chrysothrix bergeri (Ascomycota: Arthoniales: Chrysothricaceae), a new lichen species from the southeastern United States, the Caribbean, and Bermuda

A crustose lichen species new to science – previously characterized in the literature but unnamed – is formally described. This new species, Chrysothrix bergeri sp. nov., ranges from the southeastern United States southwards to the Caribbean islands (Bahamas and Cuba) and eastwards to Bermuda. It is most easily confused with C. xanthina, from which it differs in both chemistry and ascospore shape. Bilimbia aurata and Bilimbia stevensoni are both confirmed as synonyms of C. xanthina. A lectotype is selected for Bilimbia aurata. Solvent E is recommended for the chromatographic separation of leprapinic and pinastric acids – two lichen secondary products critical for diagnosing certain species of Chrysothrix, including C. bergeri.


Introduction
Active revision of Bermuda's lichen flora over the past 12 years has resulted in multiple new species and combinations Berger & Aptroot 2008;Berger & LaGreca 2014;Berger et al. 2016). While doing field work in the archipelago in 2004, Franz Berger collected an unknown species of Chrysothrix along the Bermuda Railway Trail in Southampton Parish. Additional field work, as well as herbarium work, produced other Bermudian specimens of this taxon. A review of the literature pointed towards a widespread, yet undescribed, species ('Chrysothrix sp.') discussed in detail by Harris and Ladd (2008) from the southeastern United States and Caribbean islands. The new species is distinguishable from similar species in these regions by its possession of smaller granules and/or it consistent production of calycin as its major secondary product. The present paper contributes further to our knowledge of the lichen diversity of both North America and the Neotropics with a formal description of this new species.
Etymology. Named in honor of medical doctor Franz Berger (Kopfing, Austria), a prolific collector of neotropical lichens and lichenicolous fungi, and the first person to recognize this new taxon in Bermuda. Dr. Berger has contributed enormously to our understanding of not only Bermuda's lichens, but the lichens of many other North Atlantic island groups (the Azores, Canary Islands, and Madeira) as well.
Ecology and distribution. This species is known primarily from hardwood trees and shrubs -mostly Quercus spp. (Harris & Ladd 2008), but also from others, e.g., Casuarina equisetifolia, Prunus caroliniana, and Suriana maritima. Two specimens were collected from dead Juniperus bermudiana wood (Berger 22365, DUKE and LaGreca 2510, BM); one from the bark of a live J. bermudiana (Hervey s.n., FH); two from dead Pinus bark (Ladd 14600, hb. Ladd; Harris 43313, NY); and one from Taxodium (Evans 88, FH). The species ranges from the southeastern United States, southwards to the Caribbean islands (Bahamas and Cuba), and eastwards to Bermuda (Fig. 3) Remarks. The new species can be distinguished from all other Chrysothrix species in the areas that it occurs by its (a) small granule size; (b) ascospores with no medial constrictions, and sometimes with one pointed end; and (c) consistent production of calycin as its major secondary product, sometimes together with leprapinic acid (major) and pinastric acid (minor or trace).
In the Coastal Plain of the southeastern United Stateswhere most specimens have been collected -Chrysothrix bergeri can be most easily confused with C. xanthina (BM!, lectotype selected by Laundon 1981: 110), a common lichen also found on hardwood bark (Lendemer et al. 2016;Lendemer & Noell 2018) that has granules the same size and color as C. bergeri. The two can be separated, however, by TLC. C. bergeri always produces calycin, whereas C. xanthina produces pinastric acid only. In addition, unlike C. xanthina, the ascospores of C. bergeri have no medial constrictions, and are sometimes pointed at one end (although these characters are of limited use, since C. bergeri is usually sterile). Chrysothrix xanthina was resurrected from synonymy with C. candelaris by Kalb (2001) by virtue of its smaller granules and different chemistry (calycin in C. candelaris s.str. versus pinastric acid in C. xanthina). Over the intervening 20 years, there has been disagreement on the size of the granules produced by C. candelaris s.str. According to Kalb (2001) and Fletcher and Purvis (2009), the granules of C. candelaris s.str. are large, ranging from 75-200 µm and from 10-300 µm, respectively; but Harris and Ladd (2008) and Olszewska et al. (2014) recorded granules between 50-75 µm and 20-50 µm (but most 30-40 µm), respectively. Tønsberg (1992) reported even smaller granules for this species from Norway [(6-)12-25(-30) μm]. As Kukwa and Knudsen (2011) rightly point out, these discrepancies indicate that further study of material from throughout the geographic range of C. candelaris s.str. is needed to ascertain whether it is one morphologically and perhaps also chemically (see Olszewska et al. 2014) variable species occurring in Europe or a complex of poorly understood taxa. By contrast, the reported granule sizes for both C. xanthina and C. bergeri are more consistent, ranging between 20 and 50 µm (e.g., Kalb 2001;Harris & Ladd 2008;Kukwa & Knudsen 2011). As Kukwa and Knudsen (2011) noted, the unusually large granule sizes (20-80 μm) reported for Australian C. xanthina by Elix and Kantvilas (2007) were probably due to the measurement of granule aggregations, rather than true granules. Differences in reported granule sizes for both species could also be due to dry-mounting the granules (e.g., Harris & Ladd 2008) vs. mounting in water (e.g., Kalb 2001;Olszewska et al. 2014). All of this suggests it is impossible to confidently key out all specimens of Chrysothrix based on granule size alone, however, any attempts to use this character should include careful measurement of the largest (single) granules.
TLC, on the other hand, reveals a major difference between Chrysothrix candelaris s.str. (sensu Kalb 2001) and C. xanthina. The former species always produces large amounts of calycin, sometimes with pinastric acid in minor or trace amounts, while the latter produces pinastric acid only (Kalb 2001). Like C. candelaris s.str., C. bergeri produces calycin as its major substance, but, as noted above, most specimens of C. bergeri can be differentiated from C. candelaris s.str. by their production of minor amounts of leprapinic acid.
In any case, Chrysothrix candelaris s.str. is a strictly European species (Kukwa & Knudsen 2011;Olszewska et al. 2014) with modern workers agreeing that all North American specimens of 'C. candelaris' are referable to other species -mostly C. xanthina (Harris & Ladd 2008;Kukwa & Knudsen 2011), and to a lesser extent, C. bergeri (this paper). There is also some indication that C. xanthina and C. bergeri typically occur in warmer climes and more disturbed habitats than C. candelaris s.str. Interesting discussions of these ecological preferences (for C. candelaris s.str. vs. C. xanthina) are presented by both Kalb (2001) and Olszewska et al. (2014), but their observations require more rigorous verification.
Because of the numerous, complicated synonyms that exist for Chrysothrix candelaris (Laundon 1981), Harris and Ladd (2008) cautiously refrained from formally describing the taxon named here as C. bergeri. A literature search, however, revealed that the type specimens of all    Laundon's (1981) synonyms for C. candelaris are Old World in origin. It is, therefore, highly unlikely that any of those synonyms represent previous names for C. bergeri, a New World species. If future monographers of Chrysothrix are able to demonstrate that one of those synonyms is conspecific with C. bergeri, then C. bergeri may itself be relegated to synonymy. Until that time, however, this common lichen needs a name, so that it can be included in regional species checklists and floras.
Another similar southeastern Chrysothrix species whose range overlaps that of C. bergeri is C. insulizans (Harris & Ladd 2008). Although the two species cannot easily be separated on the basis of chemistry (C. insulizans produces calycin plus leprapinic acid), C. insulizans is usually quite different morphologically, its thalli consisting of separate, soralium-like patches. In addition, in areas where the two species co-occur, C. insulizans almost always grows on rocks. As mentioned in Harris and Ladd (2008), the corticolous specimens of C. insulizans -only three of which (Shchepanek 29A, CANL; Wetmore 65307, NY; and Harris 47176, NY) have been collected within the geographic range of C. bergeri -merit closer inspection, as they probably represent another distinct species (or, perhaps, multiple species).
In Bermuda, Chrysothrix bergeri is the only species of Chrysothrix present. The first modern Bermudian specimen of this species, collected in 2004 by Franz Berger on Casuarina equisetifolia (Berger 19580, DUKE), was the most luxuriant, well-developed material of this species so far examined. Initially, it was my first choice for the holotype. Unfortunately, it is sterile, so I was obligated to instead choose the only known fertile specimen (Hioram 5777, NY), which was collected from Cuba.
It should be noted here that leprapinic and pinastric acids are nearly impossible to tell apart on TLC plates using the standard solvents A, B', and C, which prompted solicitation of a second opinion on the chemistry of Chrysothrix bergeri from Jack Elix. Upon learning of the easy separation of leprapinic and pinastric acids in Solvent E from Jack, I subsequently re-ran all specimens of C. bergeri in solvent E. The fact that Harris and Ladd (2008) did not run solvent E casts some doubt on their observations regarding Chrysothrix species identification in eastern and central North America. Their discernment of the species named here as C. bergeri, however, is not problematic since, according to a comparative table of the Chrysothrix species they treat (Table 1, p. 30, Harris & Ladd 2008), no morphologically similar, lignicolous/ corticolous Chrysothrix species in the southeastern USA are also chemically similar -except for the three corticolous specimens of C. insulizans mentioned above. These three specimens (i.e. Shchepanek 29A, CANL; Wetmore 65307, NY; and Harris 47176, NY) need to be checked to ascertain if they are, in fact, C. bergeri.
In future studies of the genus Chrysothrix, it is highly recommended that solvent E (Elix & Crook 1992) be used in addition to the standard three-solvent system for TLC of lichen secondary products. It is also recommended that workers continue to survey herbarium specimens of 'C. candelaris' from North America and the Caribbean with TLC, in the hopes of better understanding the geographic distributions of C. bergeri, C. xanthina and similar species.
In addition to the specimens cited above, one specimen (Harris 41773, NY), collected from a fencepost, possesses a chemistry similar to that of C. candelaris: calycin (major) and possibly pinastric acid (minor), plus many longwave-UV-fluorescent substances (probably from the bark), but no leprapinic acid. Its granules, however, are 31-43.5 μm wide, which fits within the range of C. bergeri.
The chemistries of comparative material of C. candelaris, C. insulizans and C. xanthina (listed below) examined for this paper were mostly, but not entirely, determined by me using solvents A, B' and C. Those specimens cited below whose chemistry was determined by other workers are denoted with a cross ( †), together with the name of the person (or persons) who performed the chemical analysis.