New Records of Lichens and Lichenicolous Fungi from La Gomera (Canary Islands, Spain), Including the New Species: Usnea boomiana P. Clerc

Abstract Van Den Boom, P. P. G., P. Clerc & D. Ertz (2015). New records of lichens and lichenicolous fungi from La Gomera (Canary Islands, Spain), including the new species: Usnea boomiana P. Clerc. Candollea 70: 165–177. In English, English abstract. DOI: http://dx.doi.org/10.15553/c2015v702a1 Lichens and lichenicolous fungi are very diverse in the Canary Islands but the flora is still poorly known despite numerous recent publications. For this reason, two field trips were undertaken in 2011 in order to study the lichen flora of La Gomera (western Canary Islands). About 1000 specimens were collected in the different habitats of the island. In addition, c. 200 specimens collected in 1986, and c. 60 specimens from the Oslo herbarium (O) were studied. As a result, an annotated list of 107 newly recorded lichens and lichenicolous fungi from La Gomera is presented. Terricolous, saxicolous, as well as corticolous species are included. Further notes are given for 17 taxa that are new for the Canary Islands. Hypotrachyna meyeri (Zahlbr.) Streim. is new to Macaronesia. In addition, one species is newly described in the genus Usnea Dill. ex Adans., Usnea boomiana P. Clerc characterized notably by large and convex soralia and by the presence of caperatic acid in the medulla.


Introduction
La Gomera is, after El Hierro, the smallest of the seven main islands of the Canary Islands, with an area of about 378 km² (Fig. 1) (Pitard & Proust, 1908). This mid-Atlantic island has a volcanic origin and a circular shape of about 24 km in diameter. The central plateau with a gentle relief and the highest point of the island (1487 m) is surrounded by deeply eroded valleys and ravines. It is densely covered with some of the best preserved laurel forests of the Canary Islands, i.e. by evergreen forests dominated by species of Lauraceae. They are included in the protected Garajonay National Park that covers 40 km² and is recognized as a World Natural Heritage by UNESCO. Lichens and lichenicolous fungi recorded from the island are compiled in Hernandez-Padron & Pérez-Vargas (2010)'s checklist. Those results were mainly based on previous studies by Etayo (1996Etayo ( , 1998  In the aim of completing our knowledge of the lichens and lichenicolous fungi flora for La Gomera, the authors gathered c. 1200 specimens for the present study. Specimens were collected all over the island, from coastal areas to the highest laurisilva forests up to elevations of c. 1400 m. During a one-week fieldtrip to La Gomera by two of the authors: Pieter van den Boom (PvdB) in summer 2011 and Damien Ertz (DE) in spring 2011, altogether c. 1000 collections of lichens and lichenicolous fungi were gathered. About 200 specimens were also previously collected by Philippe Clerc (PhC) in 1986. 675 species were already known from La Gomera, the study of our material revealed 107 additional new taxa for the island (Table 1), raising the total number to 782. Detailed comments are provided for the 17 taxa newly recognized taxa for the Canary Islands. A new species of Usnea Dill. ex Adans., U. boomiana P. Clerc has been found and is here described as new. A further detailed study of the genus Usnea on La Gomera was done by PhC, based on our specimens with the addition of c. 60 specimens deposited at O. The taxonomy of many groups are still in a state of flux, therefore several of our specimens are still unidentified so far, and are thus not included in this study. Our study highlights the importance of conserving natural habitats such as the laurel forests and rock outcrops, since they are very diverse in rare lichen species.

Material and methods
About 1260 specimens of lichens and lichenicolous fungi were investigated with a light-microscope or binocular microscope. About 65 of these specimens were also studied by TLC according to Culberson & Ammann (1979) or Orange et al. (2001). Anatomical measurements of the cortex, medulla and central axis (%C/%M/%A) in the genus Usnea were established according the method given in Clerc (1987). The checklists of Hernández-Padrón & Pérez-Vargas (2010), Hafellner (2002Hafellner ( , 2005Hafellner ( , 2008 and the recent papers mentioned in the introduction were consulted for comparison. Voucher specimens studied are deposited in Bruxelles (BR) for DE (Ertz), in the private herbarium of PvdB (Boom) and in G for PhC (P. Clerc). Localities of material examined are presented in Appendix 1 by collectors for PvdB and DE and by herbaria for G and O for the remaining collectors (including PhC) in a numbering order. Substrate abbreviations are as follow:  Table 1 presents the 107 taxa newly recorded from La Gomera and further includes 17 taxa newly recorded from the Canary Islands. This raises the total of taxa of lichens and lichenicolous fungi known from La Gomera to 782.

Results
The results section is divided in two parts: the first one focuses on the genus Usnea with U. boomiana described as new and a second one provides notes on the new records for the Canary Islands. All new records for La Gomera are provided in Table 1 with their respective distribution among the other islands of the Canary Archipelago. Vahliella atlantica P. M. Jørg. is known from the Canary Islands but its accurate distribution is unknown (Perez-Vargas et al., 2014).
Etymology. -The new species is named after Pieter van den Boom, who collected the type specimen and did a lot of fieldwork on all the Canary Islands since 15 years. Variability. -The constriction of the lateral branches at attachment points might vary from almost not constricted to distinctly constricted, but some branches are always ± constricted (numerous branches should be checked). The papillae might be almost invisible (indistinct) to well developed. Soralia might have few to numerous isidiomorphs.
Taxonomic notes. -Usnea boomiana is a small species that is morphologically and anatomically closely related to U. cornuta Körb. It differs from the latter species by its large and convex soralia as well by its particular chemistry (U. cornuta has mainly salazinic acid or compounds belonging in the stictic acid group, ± lobaric acid or protocetraric acid in the medulla). Other short and shrubby species with large soralia are U. esperantiana P. Clerc, U. fragilescens Lynge, U. glabrata (Ach.) Vain., U. glabrescens (Vain.) Räsänen, U. lapponica Vain., U. macaronesica P. Clerc and U. substerilis Motyka. Usnea esperantiana has a K+ red medulla (salazinic acid), soralia that are not convex but flat and no isidiomorphs at all. Usnea fragilescens has more regularly shaped and circular soralia that are not confluent, more distinctly constricted lateral branches at point of attachment and compounds belonging to the stictic acid group in the medulla. Usnea glabrata has strongly constricted lateral branches at point of attachment and a very lax medulla with protocetraric or barbatic acids. Usnea glabrescens has a conspicuously blackened basis, a thicker and mat cortex, a compact thin medulla, lateral branches that are never constricted at point of attachment and a different chemistry (norstictic ± salazinic ± diffractaic acids, stictic acid group ± diffractaic acid). Usnea lapponica has deeply excavate soralia without isidiomorphs, lateral branches that  are never constricted at point of attachment, a mat cortex and salazinic or psoromic acids in the medulla. Usnea macaronesica has deeply excavate soralia, strongly constricted lateral branches at point of attachment, a thin and smooth cortex, a broader and very lax medulla with stictic and/or barbatic acids. Usnea substerilis has lateral branches that are never constricted at point of attachment, a mat cortex, papillae that are larger and more conspicuous and salazinic and/or barbatic acids in the medulla. Finally, studies of most of the types of North and South American species to find an already published name for this taxon were unsuccessfull.

Usnea fragilescens Lynge
Notes. -This taxon was mentioned for the first time for the Canary Islands by Tavares (1952) under the name U. mollis Stirt., a synonym of U. fragilescens (Clerc, 1987). This indication was then taken up again by Champion & Sanchez Pinto (1978), Hafellner (1995) and Hernández Padrón & Pérez-Vargas (2010), "collected on Tenerife". Usnea cornuta Körb. (= U. inflata (Duby) Motyka) a frequent and variable species was not mentioned for the Canary Islands in the report of Tavares (1952). There is thus a high probability that the species reported as U. mollis by Tavares (1952) was in fact U. cornuta. So the report in this paper of U. fragilescens on La Gomera is the first credible mention of this species for the Canary Islands. One of the specimen (Hernàndez & Pérez 56615) out of the two collected by Hernàndez & Perez on La Gomera corresponds well to the description of U. fragilescens given by Clerc (1987)

Usnea subflammea P. Clerc
Notes. -Described from the Azores (Clerc, 2006), with a paratype collected on Tenerife, this species has been later found to occur in the low montane forests of South America (Truong et al., 2013).

Usnea wasmuthii Räsänen
Notes. -In the Canary Islands, this species was known from La Palma. It occurs on Tenerife as well. Details on this taxon are given in Clerc (2011). Both specimens collected on La Gomera have salazinic and barbatic acids in the medulla.

Verrucaria muralis Ach.
Notes. -This species has often been found on mortar of a wall, but it is easily overlooked. In Macaronesia it was only known from the Azores (Gabriel, 2008