Salix aegaea Cambria, C. Brullo, Giusso, Sciandr., Siracusa & Brullo, 2020

Cambria, Salvatore, Brullo, Cristian, Galdo, Gianpietro Giusso Del, Sciandrello, Saverio, Siracusa, Giuseppe & Brullo, Salvatore, 2020, Salix aegaea (Salicaceae), a new species from island of Ikaria (Greece), Phytotaxa 447 (2), pp. 127-136 : 130-135

Salix aegaea Cambria, C. Brullo, Giusso, Sciandr., Siracusa & Brullo sp. nov. ( Fig. 1 )

Type: GREECE. Ikaria Island , Raches , Chalaris river near the Pezi plateau, 740 m, 37° 33’41.87”N 26° 2’53.66”E, 24 March 2018, S. Cambria s.n. (holotype, CAT; isotypes, CAT) .

Salice kaptara affinis, sed distincta ramis vetustioribus cortice glabrescentibus, vibicibus brevioribus, gemmis majoribus, lamina foliorum oblanceolata, apice acuto, inferne viridi-glaucescenti, subglabra, 9–12 nervata, petiolo longiori, stipulis auriculatis, majoribus, breviter dentatis margine, pedunculo amentibus breviori, bracteis ovato-spathulatis, rotundato-undulatis margine, quasi omnino nigriscentibus superne et breviter albidis base, bis longioribus quam ovari pedunculo, stylo glabro, filamentis staminorum longioribus.

Shrub or small tree 4–8 m tall, with bark of old branchlets brown-greyish, glabrous, provided with short longitudinal ridges in the wood under the bark, 5–10 mm long. Previous year branchlets subglabrous to minutely tomentose. Buds 5–12 mm long, ovate, flattened, greenish-ivory, reddening, minutely pubescent. Stipules 7.5–10 × 4.3–6 mm, auriculate, shortly toothed. Petioles 4–14 mm long, minutely tomentose. Leaf blade 30–100 × 12–28 mm, oblanceolate, cuneate at the base, acute at the apex, provided with 9–12 (13) pairs of secondary nerves, green and glabrous adaxially, green-glaucous and subglabrous abaxially, smooth-undulate at the margin, sometimes obscurely denticulate. Female catkins 21–27 mm long, with villous peduncle, 3–7 mm long, leafy (with few leaflets); male catkins 20–26 × 9–11 mm, cylindrical–ellipsoid, usually erect, with peduncle 1–2 mm long. Floral bracts 1.9–2.5 × 0.9–1.2 mm, obovate-spathulate, rounded-undulate at the margin, long hairy, almost all blackish above and briefly whitish below, twice longer than the peduncle of the ovary. Female nectary 0.4–0.6 × 0.4–0.6 mm, subrounded to obovate; male nectary 0.5–0.7 × 0.4–0.5 mm, similar to the female, sometimes retuse. Ovary 2.5–3.5 mm long, ovoid-pyriform, hairy, with peduncle 1–1.4 mm long; style single, glabrous, 0.2–0.3 mm long; stigmas yellow, bifid, each bipartite, 0.3–0.4 mm long. Stamens 2, with filaments 7.0– 7.5 mm long, white, free, pilose at the base; anthers 1–1.1 mm long, ellipsoid, yellow. Capsule 8–9 mm long, hairy, with carpophore 2.3–2.5 mm long. Seed not seen.

Leaf micro-morphology:― As emphasized by several authors ( Mariani Colombo et al. 1982, Paiero et al. 1984, 1985, 1992, Martini & Paiero 1988, Cameron et al 2002, Tomaszewski 2004, Szafranek et al, 2008, Zieliński & Tomaszewski 2008, Brullo et al. 2015, Cambria et al. 2019), the structure of the leaf epicuticular waxes provides relevant information as support to taxonomic treatment of the genus Salix . Usually, under scanning electron microscopy ( SEM) the two surfaces of the leaf show remarkable differences in the ornamentations, since the abaxial surface is covered by conicoids, consisting of terminal fused wax filaments, while the adaxial one has a layer of a more or less homogeneous wax film. As concerns S. aegaea , its leaves are covered in the abaxial surface by quite spaced conicoids ( Fig. 2 A 1,2), instead the adaxial one is characterized by a dense layer of irregular vermiform ridges ( Fig. 2 B 1,2). Besides, the two sides of the leaf are usually glabrous or sometimes with scattered hairs only in the midrib, which are flat and inserted on a small hollow covered by a smooth layer of wax ( Fig. 2 A 3,4; B 3,4).

Etymology:―The specific epithet refers to latin “ Aegaeum ” sea of East Mediterranean, where Ikaria island is localized.

Phenology:―It is a deciduous tree, flowering and fruiting in early spring (March to April).

Habitat and distribution:− Salix aegaea currently occurs in the western part of Ikaria, island located in the Central-East Aegean area near the Turkish coast. It grows on wet soils, usually flooded for short periods, along the banks of Chalaris river, at 730–750 m of altitude, in Pezi plateau ( Fig. 3 ). The substrate is represented by raches granitoids dating back to Miocene, covered in the depressions by Quaternary alluvium ( Laurent et al. 2015, Rabillard et al. 2018). This willow is a member of riparian woodland characterized by Platanus orientalis Linnaeus (1753: 999) , Salix alba Linnaeus (1753: 1021) . Rubus sanctus Schreber (1766: 15) , Pyrus spinosa Forskål (1775: 211) , Hedera helix Linnaeus (1753: 202) , etc. ( Fig. 4 ).

Conservation status:― Currently, Salix aegaea is an exclusive plant of a submountain area of the Ikara Island (east central part of the Aegean sea), where it is represented by a well circumscribed population, growing along a small temporary water courses. The riparian vegetation characterized by this new species of Salix develops for just over one kilometre along a siliceous plateau. On the whole, it is well structured and rich floristically for the occurrence of several hygrophilous species, represented mainly by tall and old trees. In particular, S. aegaea is here quite widespread and well developed with several hundred individuals, which for the moment does not seem seriously threatened. However, since it is a single population located near an area subject to a certain anthropogenic pressure, represented mainly by crop activities, as well as by road and remediation works, such as the nearby artificial basin created by a small dam, which could alter the delicate water balance of this territory.

The growth of Salix site falls within a special protected area (Birds Directive), corresponding to “Nisos Ikaria (Notiodytiko Tmima) (GR4120005)”. Moreover, the species is almost on the borders of the special area of conservation “Ikaria - Fournoi Kai Paraktia Zoni” (GR4120004), according to the Habitats Directive.An extension of this area could be proposed, to include the Salix -community in the Nature 2000 network, in order to better preserve the species and above all ensuring the conservation of its singular natural habitat.

Basing on our field observation, this species is represented by less than 1000 individuals, arranged along a narrow temporary stream characterized by siliceous substrata. Due to its limited area and low number of individuals, Salix aegaea should be classified, according to the IUCN protocol ( IUCN 2017), as “Vulnerable” VU (D1).

Taxonomic relationships:― Within the extremely large and variable genus Salix , currently represented by about 500 species ( Fang 1987, Maassoumi 2009, Argus 2010), S. aegaea seems morphologically closely related to the group of S. apennina . According to literature data ( Skvortsov 1965, Martini & Paiero 1988, Brullo et al. 2001b, 2015, Cambria et al. 2019), it includes some endemic species distributed in the Mediterranean area, such as S. apennina s. str. from Italy and Corsica, S. tyrrhenica Brullo, Scelsi & Spampinato (2001b: 46) from South Italy, S. anatolica Zieliński & Tomaszewski (2008:386) from Turkey, S. nebrodensis C. Brullo, Brullo, Cambria & Giusso (2015: 289) from Sicily and S, kaptarae from Crete. On the basis of the taxonomic treatment proposed by Skvortsov (1999), these species can be ascribed to the sect. Nigricantes Kerner (1860: 235) as already emphasized by Cambria et al. (2019). In particular, they share some significant morphological feature regarding the shape of the leaves, inflorescences and mainly of the flowers, such as more or less lanceolate leaves, which are usually denticulate at the margin, glabrous or subglabrous above and sparsely pubescent to tomentose below, elongated catkins with leafy and hairy petiole, densely hairy ovary and capsule, staminal filaments hairy at the base and floral bracts partially blackish. In spite of these remarkable morphological affinities, they differ very well from each other as can be easily deduced from the comparative table ( Table 1). Other relevant diagnostic characters can be observed in the micro-features of leaf epicuticular waxes.

Taxonomically, S. aegaea seems to have close relationships mainly with S. kaptarae , occurring always in the Aegean area and recently described from Crete by Cambria et al. (2019). However the two species, although they share several vegetative and reproductive characteristics, show significant diagnostic features that allow differentiating them to specific rank. In particular. S. kaptarae stands out well from S. aegaea in having old branchlets pubescent, with longer wood ridges, buds 4–6 mm long, leaves oblong-lanceolate to lanceolate, obute to apiculate at the apex, tomentose in abaxial surface, denticulate at the margin, 12–20 nerved, stipules semicordate, very smaller (2–3,6 mm long), long dentate, leaf petiole max. 7 mm long, floral bracts ovate to oblong, acute, blackish only in the upper part, slightly longer than ovary petiole, style hairy, staminal filaments 5–5.5 mm long. As concerns the structures of the leaf epicuticular waxes and kind of indumentum, S. aegaea shows instead greater affinity with S. tyrrenica . According to Brullo et al. (2015), the latter shows in the adaxial surface the same micro-features, represented by vermiform and densely intricate ridges, as well as the scattered and scarce hairs localized only on the ribs, are also typically flat and undulated. Within of the S. apennina group, both these micro-morphological characteristics occur exclusively in the aforesaid species.

In particular, S. aegaea for its rarity and morphological peculiarities can be considered a geographical vicariant, originating from an ancient isolation of its population from the others of this group.

Additional specimen examined (paratypes):― GREECE. Ikaria Island, Raches, Chalaris river near the Pezi plateau, 740 m, 37°33’41.87”N 26° 2’53.66”E, 3 October 2019, S. Brullo & S. Cambria s.n. (CAT).

For the identification of the species belonging to Salix apennina group, an analytical key is provided:

Figures

FIGURE 1. Diagnostic features of Salix aegaea. A. Sterile branch. B. Wood ridges. C. Branch with male catkins. D. Branch with female catkins. E. Stipules. F. Leaf lower surface. G. Female flowers. H. Male flowers. I. Floral bract. J. Capsule. K. Illustrations by S. Brullo based on living materials coming from the type locality (CAT!).

FIGURE 2. SEM micrographs of the leaf blade of Salix aegaea. A. Abaxial surface. B. Adaxial surface. 1. Surface at low magnification (×200). 2. Structures at high magnification (×1500). 3. Hairs (x 50), 4. Hair inserction (×500) from type material (CAT!).

FIGURE 3. Geographical distribution of Salix aegaea based on herbarium material (red dots).

FIGURE 4. Phenological features of Salix aegaea. A. Natural habitat with Platanus orientalis and Salix alba. B. Habit of S. aegaea. C. and D. Detail of leaves. E Male inflorescences. F. Female inflorescences (Photos by S. Cambria).