Knowledge of species distribution is an integrative tool between systematics and ecology and therefore indispensable for the evaluation of biodiversity. The distribution data for species is also essential for estimating their extinction risk and classification into threat categories (Litterski & Otte Reference Litterski and Otte2002).

The genus Usnea Adans. is a cosmopolitan and very species-rich lichen genus. It currently comprises c. 300–600 species according to different authors (Kirk et al. Reference Kirk, Cannon, David and Stalpers2001; Wirtz et al. Reference Wirtz, Printzen, Sancho and Lumbsch2006). According to Clerc (Reference Clerc1998, Reference Clerc2004) between 700–800 taxon names have been published in this genus, but probably c. 50% of them will have to be reduce to synonymy in the future. On the African continent there are c. 140 species (Feuerer Reference Feuerer2009), of which 40 are present in the Canary Islands (Hafellner Reference Hafellner1995, Reference Hafellner1999, Reference Litterski and Otte2002, Reference Hafellner2005; Hernández Padrón Reference Hernández Padrón, Izquierdo, Martín, Zurita and Arechavaleta2004), although this number may eventually be reduced to 20 (Clerc Reference Clerc2006).

In recent years, several treatments of Usnea, either taxonomic or phylogenetic have tried to reduce confusion in this genus (Clerc Reference Clerc1998, Reference Hernández Padrón, Izquierdo, Martín, Zurita and Arechavaleta2004, Reference Clerc2006, Reference Clerc, Nash, Gries and Bungartz2007; Herrera-Campos et al. Reference Herrera-Campos, Clerc and Nash1998; Halonen et al. Reference Halonen, Clerc, Goward, Brodo and Wulff1998; Halonen Reference Halonen2000; Fos & Clerc Reference Fos and Clerc2000; Articus et al. Reference Articus, Mattsson, Tibell, Grube and Wedin2002; Wirtz et al. Reference Wirtz, Printzen, Sancho and Lumbsch2006; Torra & Randlane Reference Torra and Randlane2007). Even so, the genus is still insufficiently known (Articus et al. Reference Articus, Mattsson, Tibell, Grube and Wedin2002) in many regions even in Europe (Torra & Randlane Reference Torra and Randlane2007) and tropical and subtropical areas.

During recent studies of the lichen flora of the Canary Islands by the first author, and in connection with the revision of the genus Usnea in the Iberian Peninsula being carried out by the last two authors, some Usnea specimens have been found in some localities in “La Caldera de Taburiente” National Park, La Palma, Canary Islands. Among different species, we have found some interesting specimens determined as Usnea chaetophora Stirt. To our knowledge, these specimens represent the first record from Africa and Macaronesia and are the most southern reports known. In addition, a new chemotype of this species has been identified.

Morphology of the lichen specimens was examined using a Leica ZOOM 2000. Chemical constituents were identified by thin-layer chromatography using solvent systems A, B and C (Culberson Reference Culberson1972; Culberson et al. Reference Culberson, Culberson and Johnson1981; Culberson & Johnson Reference Culberson and Johnson1982; Elix & Ernst-Russell Reference Elix and Ernst-Russell1993). Authentic samples of Usnea chaetophora (identified by P. Clerc and deposited in the personal herbarium of J. Etayo) were checked.

Usnea chaetophora Stirt.,

Scott. Naturalist nov. ser. 1: 76 (1883).

(Fig. 1)

Fig. 1.

Usnea chaetophora TFC Lich: 7024. A, habit; B, base; C, soralia; D, segments with annular cracks. Scales: A = 2 cm; B = 1mm; C & D = 0·5 mm.

Thallus pendulous, more than 15 cm in length, distinguished by the numerous and smooth branches and large number of segments with annular cracks, base distinctly blackened. Papillae and fibrils sparse and irregularly distributed. Soralia mainly punctiform and without isidiomorphs, slightly tuberculate. Cortex moderately thick and medulla dense and white.

Two chemotypes have previously been recognized: chemotype I, with usnic and salazinic acids (K+ yellow to red and Pd+ yellow to orange), and chemotype II, with usnic acid only (K− and Pd−) (Halonen et al. Reference Halonen, Clerc, Goward, Brodo and Wulff1998; Torra & Randlane Reference Torra and Randlane2007). We found only chemotype I among the specimens collected but discovered a new chemotype (III) with usnic and salazinic acids and barbatic acid as accessory substance.

Fig. 2.

World distribution of Usnea chaetophora (• records extracted from the bibliography; ▴ new records). One dot may represent several localities.

Table 1.

Main differences between Usnea chaetophora and related species.

According to Halonen et al. (Reference Halonen, Clerc, Goward, Brodo and Wulff1998) and Halonen (Reference Halonen2000), this is a coastal species, or with distinct coastal tendencies. In fact, all their collections from British Columbia are at, or close to, sea level. However, in Europe it seems that it can grow inland (Torra &Randlane Reference Torra and Randlane2007). Our collection was at 1600 m alt., although we bear in mind the size of La Palma island is only 708 km².

Worldwide, this species is sparsely distributed in the Northern Hemisphere (Fig. 2). In addition to the new records from the Canary Islands, Usnea chaetophora is known from a few localities in Europe where it seems to be rare (James et al. Reference James, Clerc, Purvis, Purvis, Coppins, Hawksworth, James and Moore1992; Halonen et al. Reference Halonen, Clerc, Goward, Brodo and Wulff1998; Torra & Randlane, Reference Torra and Randlane2007), including Turkey (Aslan et al. Reference Aslan, Aptroot and Yazici2002). Nevertheless, the reports from Nordland are very doubtful (Bjerke et al. Reference Bjerke, Elvebakk and Elverland2006). In North America it seems to be restricted to the Pacific Coast of Canada and the NW of USA, but the extent of the North American distribution is poorly known (Halonen et al. Reference Halonen, Clerc, Goward, Brodo and Wulff1998).

U. chaetophora is close to U. filipendula Stirt. s. lat. This species also has salazinic acid as the main secondary compound but is distinguished by the abundance of branches, fibrils and papillae. Furthermore, it has abundant and tall isidia on soralia (Halonen et al. Reference Halonen, Clerc, Goward, Brodo and Wulff1998; Azami et al. Reference Azami, Seriñá and Arroyo2004).

Usnea chaetophora may also resemble other pendulous species for example U. articulata (L.) Hoffm., U. barbata (L.) Weber & F. H. Wigg., U. schadenbergiana Göpp. & Stein, or U. trichodea Ach., all of them present in the Canary Islands. Usnea articulata has conspicuous annulations that are very swollen (James et al. Reference James, Clerc, Purvis, Purvis, Coppins, Hawksworth, James and Moore1992). In many cases, the density of the medulla is a good character to distinguish U. barbata and U. chaetophora (Torra & Randlane Reference Torra and Randlane2007). Usnea schadenbergiana and U. trichodea do not contain salazinic acid, and the first has a different morphology and the latter has a brown central axis (Halonen et al. Reference Halonen, Clerc, Goward, Brodo and Wulff1998) (Table 1).

The status of U. chaetophora is not clear and some authors have pointed out the need for a critical revision, not only of this species (James et al. Reference James, Clerc, Purvis, Purvis, Coppins, Hawksworth, James and Moore1992) but of the whole pendulous species group (Halonen Reference Halonen2000).

Selected specimens examined. Spain: Canary Islands: La Palma, “El Bejenado”, Caldera de TaburienteNational Park, UTM: 219450/317695, 1600 m alt., on Pinus canariensis, 2000, C. Hernández & P.L. Pérez de Paz TFC Lich: 2775 (chemotype III), 7024 (chemotype I).