Usnea boomiana P. Clerc, 2015

van den Boom, Pieter P. G., Clerc, Philippe & Ertz, Damien, 2015, New records of lichens and lichenicolous fungi from La Gomera (Canary Islands, Spain), including the new species: Usnea boomiana P. Clerc, Candollea 70 (2), pp. 165-177 : 167-172

Usnea boomiana P. Clerc , spec. nova ( Fig. 2 ).

MycoBank No.: MB 807125

Typus: SPAIN. Canary Islands. El Hierro: SSE of Frontera , near mountain top, S or road HI-1, N and W side of Montana de la Fuente , along trail in “fayal brezal” forest, 27°44.15’N 17°59.50’W, 1300 m, on Erica sp. , 31.III.2009, P. van den Boom & B. van den Boom 42838 (holo-: G [ G00262105 ]!; iso-: hb. PvdB!), %C/%M/%A: 7/33/19. Chemistry: usnic and caperatic acids.

Thallus shrubby, to 5 cm long; lateral branches very slightly to distinctly narrowed at attachment point; mature soralia as large or even broader than branch’s diameter, convex with numerous isidiomorphs; cortex shiny and thin; medulla dense and thick containing caperatic acid.

Thallus shrubby, short, 3-5 cm long, greyish green; branching anisotomic- to isotomic-dichotomous; trunk short, 1-4 mm long, with a short (1 mm) but distinct jet-black pigmented zone in the basal part. Main branches 0.9 to 1.3 mm large, irregular to fusiform with larger diameter not close to the basal part, usually inconspicuously segmented. Lateral branches very slightly to distinctly narrowed at point of attachment, sometimes fusiform; apices thin with few ramifications; segments terete and cylindrical to slightly fusiform. Foveoles and transverse furrows absent. Pseudocyphellae and maculae absent; papillae numerous, regularly disposed, indistinct to short verrucous. Tubercles absent. Fibrils short (1-3 mm), few, irregularly disposed. Fibercles few. Soralia developing on the cortex “ad initio”, ± circular when young, of ± irregular shape, as large or even broader than branch’s diameter when mature, flat to distinctly convex and efflorescent, often becoming confluent especially towards the tips. Isidiomorphs usually numerous on young and mature soralia; cortex shiny, moderately thin, (6-)7% (-9); medulla thick, dense to lax, (25.5-)30%(-33); axis thin (19-) 25%(-36). Ascomata and conidiomata not observed.

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.

Chemistry. – K-, C-, KC-, P-. Usnic and caperatic acids.

Habitat and distribution. – Usnea boomiana grows on shrubs and trees of Erica sp. in “fayal brezal” forests or at the edge of laurisilva at around 1300 m of altitude. This species is so far known only from the Canary Islands of La Gomera and El Hierro.

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.

Paratypi.– SPAIN. Canary Islands. El Hierro: Frontera , El Golfo , Izique , on Erica arborea in Fayal-Brezal, 1200 m, 1.X.1986, P. Clerc G262107 ( G) ; ibid. loc., P. Clerc G262108 ( G) ; SSE of Frontera, Montana de la Fuente , on Erica in Fayal-Brezal , 1300 m, 31.III.2009, Boom 42773 (hb. PvdB) ; ibid. loc., Boom 42771 (hb. PvdB) . La Gomera: Garajonaj N. P. , NE of Igualero , on Erica arborea at the edge of laurisilva, 1350 m, 5. IX. 2011, Boom 46370 (hb. PvdB) ; ibid. loc., Boom 46371 (hb. PvdB) ; Alajero, Lomo de la Mulata , on Erica arborea and Pinus sp. in pine plantations, 1320-1340 m, 23-25.IX.1986, P. Clerc G262113 ( G) ; ibid. loc., P. Clerc G262116 ( G) ; ibid. loc., P. Clerc G262117 ( G) ; ibid. loc., P. Clerc G262118 ( G) ; Hermigua, Bosque El Cedro , on Castanea sativa in agricultural landscape, 850-900 m, 5.X.1986, P. Clerc G262110 ( G) ; Hermigua, Las Mimbreras , on Laurus sp. in laurisilva, 1000 m, 27.IX.1986, P. Clerc G262109 ( G) ; Hermigua, Cabezo Alto , on Erica arborea on windy ridgeline, 900-1000 m, 27.IX.1986, P. Clerc G262111 ( G) ; Vallehermoso, Montana de la Zarza , on Ilex and Erica arborea in Fayal-Brezal, 900 m, 26.IX.1986, P. Clerc G262106 ( G) ; ibid. loc., P. Clerc G262112 ( G) ; Valle Grand Rey, Las Cabecillas , on Erica arborea in Fayal-Brezal, 1080 m, 23.IX.1986, P. Clerc G262114 ; ibid. loc., P. Clerc G262115 ( G).

Figures

Fig. 2. – Usnea boomiana P. Clerc. A. Basal part with blackish pigmentation; B. Main branches; C. Main branch with slightly constricted lateral branches at ramification points; D. Young soralia with isidiomorphs; E. Mature soralia without isidiomorphs; F. Mature soralia a few isidiomorphs; G. Overmature soralia with numerous isidiomorphs; H. Transversal section of a main branch; I. Small verrucous papillae on the cortex. [A-B: P. van den Boom & B. van den Boom 42838, G; C-E, H: P. Clerc G262116, G; F-G: P. Clerc G262111, G]