Salix nebrodensis C.Brullo, Brullo, Cambria & Giusso, 2015

Brullo, Cristian, Brullo, Salvatore, Cambria, Salvatore & Galdo, Gianpietro Giusso Del, 2015, Salix nebrodensis (Salicaceae), a new species from Sicily, Phytotaxa 218 (3), pp. 268-278 : 269-274

Salix nebrodensis C.Brullo, Brullo, Cambria & Giusso sp. nov. ( Figs.1 , 2 )

Salice apennina affinis, sed distincta ramis vetustioribus cortice brunneo-rubescenti, vibicibus absentibus, gemmis 5–10 mm longis, lamina foliorum elliptico-oblanceolata, majore, 11–17-nervata, bracteis oblanceolatis, nigriscentibus et viridibus base, 2, 8 mm longis, rotundatis apice, florum foeminorum nectario 0,40–0,45 × 0,30–0,35 mm, ovario 1,8–1,9 mm longo, pedunculo 0,9–1,1 mm longo, stilo unico, 0,2–0,3 mm longo, florum masculinorum nectario 0,70–0,80 × 0,40–0,45 mm, filamentis staminorum 3,2–3,5 mm longis, capsula 6 mm longa.

Type:― ITALY. Sicily: Nebrodi, sponde dei corsi d’acqua dei versanti sopra il pianoro di Contr. Pantana, presso Pizzo della Battaglia , a circa 900–1000 m di quota, 19 April 1988, S. Brullo & P. Minissale s.n. (holotype, CAT!; isotypes, CAT!) .

Shrub 3–5 m high, many-stemmed. One year old branchlets densely grey-tomentose; oldest (2–3 years) branchlets with bark reddish-brown, glabrous to lightly pubescent, rugose, bare wood without longitudinal ridges. Buds ovate, flattened, reddish-brown, glabrescent, 5–10 mm long. Stipules semicordate, denticulate. Petioles grey-tomentose, 5–20 mm long. Leaf blade elliptic-oblanceolate, cuneate at the base, acuminate to obtuse at the apex, 32–80(–100) mm long, (12–)20–32(–45) mm wide, provided with 11–17 pairs of secondary nerves, above green, glabrous with pubescent midrib, below opaque, glaucous, glabrous to sparsely pubescent, pilose along the nerves, denticulate at the margin. Catkins female 30–50 mm long, with villous peduncle, 5–10 mm long, leafy (2–3 leaflets); male ones 13–20 × 8–11 mm, cylindrical, erect to curved, with peduncle 0–0.2 mm long. Floral bracts oblanceolate, rounded at apex, long hairy, 2–2.8 × 0.5–0.7 mm, almost entirely blackish, greenish at the base. Nectary in female flowers 0.40–0.45 × 0.30–0.35 mm, subrectangular, throttled near the apex, solitary, slightly retuse; nectary in male flowers similar, but larger (0.70–0.80 × 0.40–0.45 mm). Ovary 1.8–1.9 mm long, ovoid-pyriform, with short and appressed hairs, with peduncle 0.9–1.1 mm long; styles connate, 0.2–0.3 mm long; stigmas yellow, bifid, each bipartite. Stamens 2, with filaments white, free, pilose at the base, 3.2–4.5 mm long; anthers ovate, yellow, 0.7–0.8 mm long. Capsule 6 mm long, hairy, with loculi divaricate-curved at the dehiscence, with carpophore 1–1.1 mm long. Seed olive-green, ellipsoid, 1.2–1.3 mm long, with stipe cylindrical, 0.3 mm long.

Leaf micro-morphology:―Based on literature ( Mariani Colombo et al. 1982, Paiero et al. 1984, 1985, 1992, Martini & Paiero 1988, Cameron et al. 2002, Tomaszewski 2004, Szafranek et al. 2008), the structure of leaf epicuticular waxes plays an important role as additional character for the identification of a given taxon. In fact, it shows a remarkable morphological variability within the Salix species and represents a conservative and stable character having relevant taxonomic implications. The micro-features of the leaf surfaces put in evidence relevant differences between the adaxial and abaxial surface of the leaf blade. In particular, very peculiar wax structures (named “conicoids”) occur on the abaxial surface, consisting of terminally fused wax filaments ( Tomaszewski 2004, Szafranek et al. 2008), with different shape and size in all the surveyed taxa. In contrast, the adaxial surface is usually covered by a more homogeneous wax film, never structured in conicoids. As concerns Salix nebrodensis , the leaves are characterized by large and dense conicoids in the abaxial surface, interspersed by narrow and smooth spaces ( Fig. 3A 1 ), while contorted and loose trichomes mainly occur along the midrib and secondary nerves ( Fig. 3A 2 ). On the contrary, the adaxial surface is covered by a more or less homogeneous and undulate wax layer, sprinkled with minute scales and ridges ( Fig. 3A3 ). Salix tyrrhenica shows many considerable differences in the wax layer structure in respect to S. nebrodensis . In fact, the abaxial surface of the leaf is characterized by smaller and very scattered conicoids, interspersed by large and ridged spaces ( Fig. 3B 1 ), while undulate and loose trichomes mainly occur along the midrib and secondary nerves ( Fig. 3B 2 ). The adaxial surface is very peculiar being almost uniformly covered by vermiform and densely intricate waxy ridges ( Fig. 3B3 ). As concerns S. apennina , the leaf micro-features were investigated by Martini & Paiero (1988) and resulted well diversified from those of S. nebrodensis . Actually, the conicoids of the abaxial surface are more developed and large, while the adaxial surface is covered by a densely papillose waxy layer.

Etymology:―From “ Nebros ”, Latin name of the Nebrodi mountain area located in north-eastern Sicily.

Phenology:―Deciduous plant, flowering and fruiting in spring (April to May).

Habitat and distribution:― Salix nebrodensis grows on damp soils, along some mountain streams of the Nebrodi range (NE Sicily), at an elevation of 800–1500 m a.s.l. ( Fig. 4 ). The species is linked to siliceous substrata, chiefly represented by schist and gneiss, geologically belonging to the Numidian flysch. Usually, it is a member of riparian thickets characterized by other hygrophilous trees, such as Salix pedicellata Desfontaines (1799: 362) , Sambucus nigra Linnaeus (1753: 269) and Fraxinus angustifolia Vahl (1804: 52) .

Conservation status:― Salix nebrodensis occurs in some mountain streams, where it forms few-numbered and very localized populations in the Nebrodi Regional Park, a wide protected area of northern Sicily. Therefore, the species at issue seems to be not threatened, but being a strictly hygrophilous species and ecologically very specialized, threatened by the alteration of the environmental conditions of the growing sites. According to the IUCN protocol ( IUCN 2014), this species is here classified as Vulnerable: VU B2ab(iii).

Taxonomic relationships:―Based on the descriptions available ( Skvortsov 1965, Martini & Paiero 1988), the new species appears morphologically related to S. apennina . The latter species, according to Skvortsov (1999), belongs to the Sect. Nigricantes Kerner (1860: 235). In particular, S. apennina mainly occurs in several localities of the Italian peninsula ( Skvortsov 1965, Pignatti 1982), but it is also quoted for Sicily ( Jalas & Suominen 1973, Martini & Paiero 1988, Skvortsov 1999, Giardina et al. 2007). More recently, it was recorded from Corsica ( Jeanmonod 2000) and Switzerland, limitedly to a very small stand in the Canton Ticino ( Büchler 1988, Falcinelli & Moraldi 2002, Aeschimann et al. 2004). As concerns the occurrence of S. apennina on Mt. Etna (Sicily), the above mentioned authors do not quote any herbarium specimen and, therefore, its presence on the island has to be considered as very doubtful. Both species share some important morphological features, as the glabrous or subglabrous bark of old branchlets, the grey-tomentose bark of annotinous branchlets, the bright leaf blade, green above and opaque below, waxy, glaucous, pilose along the nerves below, denticulate at the margins, the flowers showing a single nectary, the hairy ovary, the 2 staminal filaments, free and pubescent at the base, the capsule usually hairy. As concerns their morphological differences ( Table 1), S. apennina is well distinct from S. nebrodensis in having the bark of old branchlets grey, with occurrence of ridges on the wood under the bark, buds 2–3.5 mm long, leaf blade obovate to oblanceolate, 25–80 × 10–32 mm, with 7–10 pairs of nerves, male catkins 15–30 × 10–14 mm, with peduncle up to 8 mm long, female catkins up to 70 mm long, with peduncle up to 15 mm long, floral bracts oblong to obovate, 1–2 mm long, brown and blackish upward, with apex obtuse, nectary 0.4–0.6 mm long, ovary 2.5 mm long, with peduncle 0.5 mm long, style bifid 0.5–0.9 mm, staminal filaments 5–6 mm long, capsule 6.5–8 mm long, with carpophore 1–3 mm long ( Martini & Paiero 1988: “tav. 15”). Other differences concern their ecological requirements, since S. apennina is also found at lower altitudes (300–1600 m a.s.l.), where it occurs on marshes, lakes and also along the streams on various substrata. Besides, Salix nebrodensis is related also to Salix tyrrhenica , endemic to southern Calabria ( Italy), localized to some narrow streams close the sea. Morphologically, the latter differs from S. nebrodensis in several significant diacritic features, such as the occurrence of scattered and short ridges on the wood under the bark, leaf blade ovate to oblong-lanceolate, (60–)80–120(–140) × (32–)35–50(–80) mm, with 8–10 pairs of nerves and petiole 4–7 mm long, male and female catkins 24–40 mm long, floral bracts elliptical-lanceolate (2.5–3.2 × 0.7–0.9 mm), acute, blackish in the upper half and whitish in the lower one, female nectary 0.6–0.8 mm long, male one 0.8–1 mm long, ovary 2.5–3 mm long, with peduncle 2.5 mm long, style 0.3–0.5 mm long, staminal filaments 4.5–5 mm long, anthers 1–1.1 mm, capsule 8–8.5 mm long, with peduncle 1.6–2 mm, seed 1.6 mm long, with stipe 0.4–0.5 mm long ( Fig. 5 ). In conclusion, Salix nebrodensis based on its chorology may be considered a geographical vicariant respect with the two related species, probably arisen for geographical isolation ( Fig. 6 ).

Additional specimens examined (paratypes):― ITALY. Sicily: Nebrodi, Abbeveratoio sotto Pizzo Nido , 26 June 1990, S. Brullo, G. Spampinato & P. Minissale s.n. ( CAT!) ; Nebrodi, Bosco di Caronia , 15 October 1997, S. Brullo & R. Guarino s.n. ( CAT!) ; Nebrodi, sponde dei corsi d’acqua presso Portella dell’Obolo, a quota 1400–1500 m, 22 May 1997, S. Brullo, R. Guarino & G. Siracusa s.n. ( CAT!) ; Nebrodi, valle del fiume Caronia, a quota di 900–1000 m, 7 November 1991, S. Brullo s.n. ( CAT!) ; Nebrodi, sponde di corsi d’acqua di Pizzo Luminaria, a quota 1000–1200 m, 15 October 1997, S. Brullo & R. Guarino s.n. ( CAT!) .

Figures

FIGURE 1. Diagnostic features of Salix nebrodensis. A. Sterile branch. B. Branch with male catkins. C. Branch with female catkins. D. Stipules. E. Leaf upper surface. F. Leaf lower surface. G. Male flowers. H. Female flowers. I. Closed capsule. J. Open capsule. K. Style and stigma. L. Seed. Illustrations by S. Brullo based on living materials coming from the type locality preserved in CAT.

FIGURE 2. Holotype of Salix nebrodensis (CAT).

FIGURE 3. SEM micrographs of the leaf blade of Salix nebrodensis (A) and S. tyrrhenica (B). 1. Abaxial surface. 2. Indumentum of the abaxial surface. 3. Adaxial surface, from type material preserved in CAT.

FIGURE 4. Geographical distribution of Salix nebrodensis based on herbarium material (red dots). In green, the Natural Regional Park of Nebrodi is highlighted.

FIGURE 5. Diagnostic features of Salix tyrrhenica. A. Sterile branch. B. Branch with male catkins. C. Branch with female catkins. D. Stipules. E. Leaf upper surface. F. Leaf lower surface. G. Male flower. H. Female flower. I. Closed capsule. J. Open capsule. K. Style and stigma. L. Seed. Illustrations by S. Brullo based on living materials coming from the type locality (Torrente Mancusi, Favazzina) and preserved in CAT.

FIGURE 6. Geographical distribution of Salix apennina (grey area), S. tyrrhenica (stars) and S. nebrodensis (dots). The distribution of S. apennina is derived from Martini & Paiero (1988), Jeanmonod (2000), and Aeschimann et al. (2004).