Page 6 - CELESTI-GRAPOW

1124 L. Celesti-Grapow et al.

Table 2. List of the non-native vascular plant species showing the greatest increase in the number of islands where the species was recorded
as regards the previous survey of the same study area (Pretto et al. 2012).
Taxon Family Est + N
Austrocylindropuntia subulata (Muehlenpf.) Backeb. Cactaceae N 10
Erigeron sumatrensis Retz. Asteraceae I 9
Opuntia amyclaea Ten. Cactaceae I 9
Solanum lycopersicum L. Solanaceae C 8
Anredera cordifolia (Ten.) Steenis Basellaceae I 6
Cotyledon orbiculata L. Crassulaceae C 5
Eucalyptus camaldulensis Dehnh. Myrtaceae N 5
Lantana camara L. Verbenaceae N 5
Mirabilis jalapa L. Nyctaginaceae I 5
Pelargonium zonale (L.) L’Hér. Geraniaceae C 5
Pittosporum tobira (Thunb.) W.T.Aiton Pittosporaceae N 5
Symphyotrichum squamatum (Spreng.) G.L.Nesom Asteraceae I 5
Aeonium haworthii Salm-Dyck ex Webb & Berth. Crassulaceae N 4
Carpobrotus edulis (L.) N.E.Br. Aizoaceae I 4
Euphorbia maculata L. Euphorbiaceae I 4
Cyperus alternifolius L. subsp. flabelliformis Kük. Cyperaceae N 4
Iris albicans Lange Iridaceae N 4
Malephora crocea (Jacq.) Schwantes Aizoaceae C 4
Oxalis articulata Savigny Oxalidaceae N 4
Parthenocissus quinquefolia (L.) Planch. Vitaceae N 4
Tropaeolum majus L. Tropaeolaceae N 4
Acacia saligna (Labill.) H.L.Wendl. Fabaceae I 3
Amaranthus hybridus L. Amaranthaceae N 3
Amaranthus retroflexus L. Amaranthaceae I 3
Crassula muscosa L. Crassulaceae C 3
Drosanthemum floribundum (Haw.) Schwantes Aizoaceae N 3
Kalanchoë daigremontiana Raym.-Hamet & H.Perrier Crassulaceae C 3
Opuntia stricta (Haw.) Haw. Cactaceae I 3
Paraserianthes lophantha (Willd.) I. C.Nielsen Fabaceae I 3
Senecio angulatus L.f. Asteraceae I 3
Veronica persica Poir. Plantaginaceae I 3
Zantedeschia aethiopica (L.) Spreng. Araceae I 3
Notes: Est = establishment status in the study area, assigned on the basis of the highest stage in the invasion process documented in any
island. I = invasive, N = naturalized, C = casual (see text for details on the methods). +N = increase in the number of islands compared
with the previous survey.

Firstly, the total number of non-native species (203) the presence of established aliens alone was usually
is markedly higher than that recorded during the recorded (Celesti-Grapow et al. 2009). As a matter
previous survey we conducted in the same study area of fact, the inclusion of casual species in floristic
(49 more species) (Pretto et al. 2012). lists, especially ornamentals that have escaped from
This remarkable difference may partly be ex- cultivation, was often frowned upon. Non-estab-
plained by the greater knowledge of introduced lished species were sporadically included in studies
plants on the islands resulting from extensive cam- that focused on small-scale floristic accounts or on
paigns of field surveys, which have focused specifical- human-made environments, such as urban, agricul-
ly on non-native species and which may have led to tural or artificial systems, but were excluded from
the discovery of populations that had for some time more general flora inventories and from community
escaped detection. Despite being integrated with focused plant sociology research (Blasi et al. 2011), as
herbaria records and unpublished information from well as from works that tended to focus either on the
field work, the previous data-set was based above all conservation of the most endangered native species
on the literature available at the time of the national and habitats, or on the most widespread and noxious
survey of the non-native flora of Italy conducted in invasive species. As a result, the data on the presence
the years 2006–2007 (Celesti-Grapow et al. 2009). It of casuals were biased in favour of the most common
was not within the scope of that project to include all casuals, with several introduced plants in the earliest
non-established species, nor would it have been pos- stages of the naturalization process, which are usually
sible to conduct an exhaustive field survey campaign rare, probably being overlooked (Celesti-Grapow
that covered all the Italian islands within its frame- et al. 2009; Stinca et al. 2015b).
work. An underestimation of the non-native flora in In our study area, in which botanic research has
the botanic literature, particularly as regards casuals, focused on peculiar natural ecosystems that are rich
had already emerged at that time and was ascribed in native endemic species and protected habitats, we
to the traditional approach towards non-native spe- found that this trend was even more evident, with
cies in Italian botanic research, according to which the synanthropic sites in which most non-established