Morphological and micro-morphological comparative study of Genista etnensis populations.

In the framework of the studies carried out on the genus Genista L. (Fabaceae) in the Mediterranean area, the populations currently attributed to Genista etnensis (Raf.) DC. have been investigated. Our investigations are based on taxonomical, karyological, molecular, phylogenetic, lhytogeographical data. This species, originally described from Mt. Etna (Sicily) by Rafinesque (1814) as Spartium etnensis, was later attributed by De Candolle (1825) to the genus Genista. Other authors, such as Presl (1845), included it into another genus, named Drymospartum,while Spach (1845) separated this species from the genus Genista, referring it to Dendrospartum. Basing on literature, this species is often reported as described by Bivona Bernardi (1814), but in the protologue he quotes Rafinesque as author of this species, mentioning also the bibliographic data. As concerns its taxonomical position, G. aetnensis was included by Valsecchi (1993) within G. sect. Aureospartum belonging to the subgen. Spartocarpus Spach. This is also supported by the molecular analyses carried out by De Castro et al. (2002) and Pardo et al. (2004), where the surveyed populations of G. etnensis are falling in a distinct subclade of the Genista clade. Therefore, despite its phylogenetic isolation and several autapomorphies, G. etnensis cannot be recognized as an independent genus, as already observed by De Castro et al. (2002). Also from the karyological viewpoint,the G. etnensis populations show an unusual chromosome complement (2n = 52) for genus Genista (Forrissier 1973, Cusma Velari et al. 2011). Genista etnensis occurs in Sicily (exclusively on Mt. Etna), Sardinia (Mt. Limbara, Monti di Alà, Supramontes, Golfo di Orosei, Gennargentu, Sette Fratelli, Monte Lattias, Is Cannoneris), Corsica (in three stands). Besides, it has been introduced into Campania (southern Italy), where it now occurs as an invasive alien in Ischia island, the Sorrentine Peninsula and especially on the Vesuvius. According to Agostini (1959), the population of the latter locality originated from introduced plants after the eruption of 1906. In-depth morphological investigations focused on the flowers and pods of living specimens allowed to highlight that the populations occurring in these territories are well differentiated, especially in the shape and size of the floral pieces, pods and seeds. In particular, the size of the flowers of the Sicilian populations is very similar to the Sardinian ones, but they differ in their shape. The Corsican populations are characterised by very small flowers,while the Vesuvian populations show flowers much bigger than the others. Calyces are clearly differentiated for their size, but also for the shape of the dorsal and ventral lips. In particular, teeth of the ventral lip are very small in the Sicilian populations, while they are more developed in the other populations, especially in the Sardinian ones. Anthers are longer in the Sicilian and Vesuvian populations, while they are much shorter in the Cyrno-Sardinian ones. Furthermore, pods and seeds coming from the Vesuvius are bigger than the others; those from Sicily are slightly smaller, while those from Sardinia and Corsica show a definitely smaller size. Finally, pod color of the Sicilian populations is usually blackish, while in the others it is always pale brown. Computerised image analysis on germplasm confirms this differentiation. Significant differences were also observed in the micro-sculptures of the seed testa of the investigated populations. Besides, Rizzi Longo & Feoli Chiapella (1994) emphasized that the Sicilian and Sardinian populations show relevant differences in the micro-morphology of pollen grains. Presl (1845), while examining the Sardinian populations of G. etnensis, had previously observed many morphological differences with the Sicilian ones, and he described them as Drymospartum sardum (= Genista etnensis Moris, non DC.). A similar opinion was expressed by Walpers (1848), who coined the name Dendrospartum sardoum Spach nom. nud., considering G. etnensis Moris as its synonym. As for the taxonomic treatment of the populations of G. etnensis s.l., further detailed phylogenetic and taxonomic investigations are needed for clarifying this issue.