Salix × marchettii M. Merli & F. Mart.

Merli, Marco & Martini, Fabrizio, 2017, Salix × marchettii (Salicaceae), a new nothospecies from the Apuan Alps (Northern Tuscany, Central Italy), Candollea 72 (2), pp. 339-343 : 340-341

Salix × marchettii M. Merli & F. Mart. , nothospec. nova ( Fig. 1 , 2 ).

Typus: ITALY. Reg. Tuscany: Prov. Massa-Carrara, Apuan Alps , NW slope of M. Pelato along the road from Pian della Fioba to the M. Pelato tunnel, 1010 m, 15.V.2016, M. Merli s.n. (holo-: FI! ; iso-: G!, herb. Merli!, ROV!).

Salix ×marchettii shows intermediate characters between S. crataegifolia and S. eleagnos subsp. eleagnos , but differs from both by the young twigs’ indumentum (mixed silky and tomentose trichomes), the presence in the same specimen of both elliptic-oblong or oblanceolate-oblong ( S. crataegifolia ) and narrowly oblanceolate ( S. eleagnos subsp. eleagnos ) leaves.

Shrub (40-)60-120(-140) cm tall, twigs ascending or procumbent, with dark grey to blackish bark; young twigs with blackish indumentum with mixed, silky and tomentose trichomes, becoming glabrous or nearly so at maturity. Leaves elliptic-oblong or oblanceolate-oblong to narrowly oblanceolate, (3.5-)4-8(-9.5) cm, 3-6 times as long as wide, with flat to weakly revolute and toothed margin, with teeth thickened in the distal half; upper side tomentose in young leaves, finally glabrous; lower side silky in young leaves, later only next to the midrib or glabrous. Lateral veins (9-)17-25 pairs, reticulate and weakly prominent only beneath. Petiole 3-8.5 mm long. Stipules absent or minute, triangular. Male catkins cylindrical, arcuate-pendant, 1.5-3(4) cm long, about 0.5 cm in diameter; female catkins initially arcuate-pendant, then suberect, 1.5- 3(4) cm long, 0.5-0.8 cm large; pedicel up to 1 cm long. Floral bracts elliptic-rounded, apex truncate, brown-reddish. Male and female flowers with 1 nectary. Filaments connate for at least half their length, glabrous. Capsule 3.5-4 mm, glabrous, usually sterile; pedicel short.

Phenology. ‒ Catkins appear with the leaves in May-June.

Etymology. ‒ The new hybrid is dedicated to Prof. Dino Marchetti (Massa), researcher and expert on the flora of the Apuan Alps.

Notes. – The diacritical characters which distinguish S. × marchettii from its parents are summarized in Table 1 . In S. × marchettii the young twig indumentum shows mixed trichomes, silky (typical of S. crataegifolia ) and matted (tomentose), characteristic of S. eleagnos ( Fig. 2A ). Size and shape of the leaf, elliptic-oblong or oblanceolate-oblong to narrowly oblanceolate, are also intermediate between those of the parents, as well as the margin, which may vary from flat ( S. crataegifolia ) to weakly revolute ( S. eleagnos subsp. eleagnos ) in the same specimen. Also the number of lateral veins, which varies between (9-)17 and 25 pairs, is intermediate between those of the parents, but in S. × marchettii the veins appear prominent only below, as in S. eleagnos . The silky indumentum of the lower leaf blade and petiole recalls mainly S. crataegifolia and, as in the latter, is very dense in immature leaves. This indumentum persists on leaves when mature only on the midrib or is completely deciduous. The leaf petiole is usually more developed than in S. eleagnos . The heritage of S. eleagnos appears better defined in male catkins, whose sizes are intermediate between those of the parents, but the filaments are connate, as in S. eleagnos , for at least half their length or more ( Fig. 2B ). The development of female catkins recalls, in form and posture, that of S. crataegifolia , but, in the observations so far, the capsules were sterile. The floral bracts are similar in shape to those of S. crataegifolia , usually completely brownish, at first silky then glabrous or nearly so.

Salix eleagnos belongs to the central-southeastern European chorotype ( JALAS & SUOMINEN, 1976). Its intraspecific variability is restricted to two subspecies, S. subsp. eleagnos and S. subsp. angustifolia (Cariot & St. - Lag.) Rech. f., based on leaf morphology (shape, ratio length/width and type of leaf margin). The nominal subspecies seems by far the most dominant one in Italy ( PIGNATTI, 1982; MARTINI & PAIERO, 1988).

Salix crataegifolia , described by BERTOLONI (1813), represents one of the most interesting willow species in Europe. The arcuate-pendant posture of the catkins, always observable in the males while in the females noticeable only until flowering, represents an ancestral character. Moreover, the morphology of the vascular bundles of the leaves, the small size of the pollen grains and low chromosome number are typical characters of this palaeoendemic species, phytogeographically isolated ( BECHI et al., 1996; GARBARI et al., 2007) and with a limited individual variability. For these same reasons SKVORTSOV (1999) hypothesizes a link between several species of the Chinese Himalaya ( S. sikkimensis Anderss., S. daltoniana Anderss. ) and S. ernesti C.K. Schneider from Sichuan. Salix crataegifolia is a steno-endemic chasmophyte of the Apuan Alps, with a distribution area of only 261.6 km 2, which has convinced ROMA-MARZIO et al. (2015) to propose its inclusion among the “Near Threatened” [NT] species. Considering the above discussed features and the absence of other hybrid forms with S. crataegifolia as a parent, the discovery of S. × marchettii has generated considerable surprise. Hence, among all Salix hybrids, S. × marchettii represents a unique case because it is the result of a cross with S. crataegifolia and therefore an endemic nothospecies of the Apuan Alps. From an ecological point of view, it behaves as a genuine gravel species like S. eleagnos , while S. crataegifolia prefers rocks (limestone and metamorphic) and is rarely growing on gravels ( ROMA-MARZIO et al., 2015). Salix × marchettii is known so far from a single population on the northwestern slope of M. Pelato, where, however, it is fairly widespread on the road side gravel and on the underlying rocky slope, together with S. crataegifolia (abundant), S. eleagnos subsp. eleagnos and S. apennina (more rare), S. purpurea and S. caprea (both occasional). According to the local distribution of the two parents as reported by FERRARINI & MARCHETTI (1994) and ROMA-MARZIO et al. (2015), it can be hypothesized that S. × marchettii could be sought with success at least where the parents are most common: for instance, in the Lunigiana area of the Apuan Alps (province of Massa-Carrara) and in the upper and middle valley of the river Serchio (Prov. Lucca). Finally, the discovery of S. × marchettii sheds new light on the capacity of hybridization of S. crataegifolia and careful research could well lead to the identification of new hybrid forms, i.e. with S. caprea and S. purpurea .

Figures

Fig. 1. – Salix ×marchettii M. Merli & F. Mart. A. Male specimen. B. Female specimen.

Fig. 2. – Salix ×marchettii M. Merli & F. Mart. A. Mixed indumentum on young twig: silky and matted hairs. B. Connate filaments.