Italy’s alien flora grows: new records and rising invasive species mapped

A new instalment of Italy’s long-running inventory of alien vascular plants has added dozens of records, confirmations and status changes to the country’s floristic map. Published in the journal Italian Botanist in December 2022, the fourteenth set of notulae to the Italian alien vascular flora documents new records for Italy as a whole and for individual administrative regions, along with confirmations of previously uncertain occurrences and formal changes in the naturalization status of established species. As in earlier contributions, the work is built on herbarium-verified specimens, most of them deposited in the FI Herbarium of the Museum of Natural History in Florence, and each entry carries precise locality data, elevation, date of collection and the names of the botanists responsible for the finding.

The contribution compiles floristic records submitted by specialists across the country, following a well-defined protocol. New records are submitted electronically to the FI Herbarium in Florence, together with the corresponding specimen or its scan or photograph, while texts concerning nomenclatural novelties, exclusions and confirmations are handled through a separate editorial channel. Each individual note is limited to 1,000 characters including spaces, a constraint that keeps the entries terse but densely informative. Nomenclatural, status and distribution updates and corrections to the national baseline, together with updates summarised in the Portal to the Flora of Italy, are provided in a supplementary file accompanying the paper.

Several of the new records are additions to the national list itself. In Lombardia, the crossvine relative Bignonia capreolata, a species native to south-eastern North America, was collected in May 2022 on a wasteland margin in the piazza d’Armi area of Milan; a single sterile individual was found, and the record is treated as a casual alien new for the flora of Italy. In the same region, Hertia cheirifolia, a composite native to Algeria and Tunisia that has been traded as a floricultural plant in Bergamo for several decades, was found in February 2022 growing spontaneously on a north-west-facing wall in the Upper City, where attempts at cultivation in flowerbeds of the Lower City have been less successful than the spontaneous wall population.

Calabria contributed two further national additions, both recorded in the Parco della Biodiversità Mediterranea in Catanzaro. Cenchrus clandestinus, a grass native to the humid highlands of central and eastern Africa that has been introduced as pasture and ornamental grass to temperate and subtropical regions of America and Australia, was found in March 2022 emerging from a cement retaining wall fed by a water leak; it had been used to create a small lawn in a nearby area and usually reproduces vegetatively by rhizomes. Earlier in the year, in February 2022, the same park yielded Chloris gayana on an uncultivated grassy slope; the few observed individuals were uprooted in order to prevent a future colonisation.

Sardegna produced perhaps the most biogeographically striking national novelty. In June 2022, Fatoua villosa, an annual mulberry relative native to East Asia, the Pacific islands and Australia and previously reported for Europe only in Corsica, was gathered in marginal areas near greenhouses and nurseries at Santa Margherita di Pula in the province of Cagliari; only a few individuals were observed. Elsewhere, Abruzzo gained two national additions: Phlox caespitosa, identified following standard regional treatments and observed spontaneously along a roadside near L’Aquila from 2019 onwards, and Sarcococca confusa, a shade-tolerant ornamental shrub widely grown in cultivation, of which some young plants were found in street planters in Teramo in November 2021.

Many other records fill gaps at the regional level. Abies nordmanniana, the Caucasian fir, was recorded for the first time in Trentino-Alto Adige from a woodland clearing in a thermophilous downy oak forest in the Adige Valley near Trento; herbarium specimens from valley-bottom sites testify to its long use in afforestation and support its limited spread, and the species is also cultivated as a Christmas tree in Val Sugana and sometimes planted in gardens. Acacia dealbata entered the flora of Umbria with adult individuals along a provincial road near Orvieto, originating from seeds of nearby trees, with a substantial spread of individuals at different growth stages observed along the roadside. Amaranthus viridis was new for Molise, Anethum graveolens for Puglia, Eschscholzia californica subsp. californica for Basilicata, and Magnolia grandiflora and Melia azedarach for Lombardia, each represented by casual occurrences documented with herbarium material.

Island and southern regions also gained new entries. Sardegna received Achillea filipendulina, found as a group of four flowering individuals on a riverbank at Capoterra and probably originating from seeds of nearby plants, together with Lepidium virginicum subsp. virginicum, recorded as naturalized in the fixed dunes at Porto Pollo in the north-east of the island and also observed on the eastern coast, Oenothera speciosa in pastures near houses at Masainas, and Lobelia erinus in wall and pavement cracks in the village of Villanovaforru. In Campania, the recently described hybrid Mesembryanthemum × vascosilvae, widely cultivated throughout Italy as ground cover and nowadays more frequent in cultivation than its parent Mesembryanthemum cordifolium, was recorded as a casual alien nothospecies new for Campania on the island of Gallo Lungo in the Li Galli archipelago off Positano, where it has escaped from mass plantings along paths.

Status changes form the second major strand of the contribution, and several species were reclassified as invasive. Acacia pycnantha, long used for afforestation and reforestation in Sardegna, was moved from naturalized to invasive, showing invasive behaviour similar to that of Acacia saligna in several inland areas up to roughly 500 metres elevation and at a few coastal sites, including the edges of a pine plantation. In Lazio, Broussonetia papyrifera was found at several sites around Ferentino in Frosinone, where it colonises ruderal areas and abandoned fields and even forms dense thickets, prompting its reclassification from naturalized to invasive. The same promotion was applied to Ligustrum lucidum in Lazio, where rapid colonisation from seeds has been observed in recent years at several sites in the Rome metropolitan area, particularly along the river Tevere, on monuments and in archaeological sites.

In Toscana, Parthenocissus inserta was elevated from casual to invasive after many plants were found covering a large area on the ancient city wall of Pisa, with further plants along the railway tracks towards Florence and a revised herbarium specimen from the Migliarino-San Rossore-Massaciuccoli Regional Park dating to 2018; the authors note that most regional data previously attributed to Parthenocissus quinquefolia may in fact refer to P. inserta. Other species moved in the opposite, still-serious direction from casual to naturalized: Hydrangea macrophylla in Veneto, where a population discovered in 2008 near Sedico was confirmed by surveys up to July 2022 and joined by two further populations, with the species regularly producing abundant flowers and sustaining itself; Paspalum dasypleurum and the bamboo Phyllostachys viridis in Lombardia, the latter with crop residues expanding widely in small woods in Milan and Bergamo; Quercus palustris at the former Piazza d’Armi in Milan; Platycladus orientalis on the walls of the Spanish Fort in L’Aquila, where abundant sexually reproducing individuals were found; Solanum carolinense in Lazio, first recorded in Rome in 2015 as casual and now well established at new sites in Frosinone province; and Trigonella foenum-graecum and Yucca gloriosa in Sardegna, the latter forming a dense clonal population near the Rio Mannu estuary at Porto Torres with further populations on coastal dunes.

Among the status changes, one carries an unusually direct human-health dimension. Toxicodendron radicans subsp. radicans, commonly known as poison ivy, was reclassified from casual to naturalized for the flora of Italy on the basis of a population at Impruneta in the province of Florence, found in June 2022 in mesophilous woodland and humid rocky habitats on serpentinite. In Italy the species had been reported as casual only in Trentino-Alto Adige, based on two old records from 1893 and 1930, so the Tuscan population is the only recent record for the country and the first reported as naturalized. The authors recommend special attention to this species, which in North America causes serious allergic contact dermatitis in millions of people every year. The contribution also records confirmations, including Honorius nutans in Toscana, last reported there in 1908 and now refound as a small population of twenty mature individuals, Tulipa gesneriana subsp. gesneriana in an olive grove near Florence, Wisteria sinensis confirmed as naturalized in Piemonte, and the casual nothotaxon Triticum × requienii nothosubsp. requienii new for Toscana within the therophytic communities of the clay Biancane gullies at Asciano.

Subject of Research: New records, confirmations and status changes of alien vascular plant species in Italian regions

Article Title: Notulae to the Italian alien vascular flora: 14

Article References: Galasso, G., Domina, G., Andreatta, S., Argenti, C., Astuti, G., Bacaro, G., Bacchetta, G., Bagella, S., Banfi, E., Barberis, D., Bartolucci, F., Bernardo, L., Bonari, G., Brundu, G., Buccomino, G., Calvia, G., Cancellieri, L., Capuano, A., Celesti-Grapow, L., … Lastrucci, L. (2022). Notulae to the Italian alien vascular flora: 14. Italian Botanist, 14, 99-118. https://doi.org/10.3897/italianbotanist.14.97758

Image Credits: AI Generated

DOI: 10.3897/italianbotanist.14.97758

Keywords: alien flora, Italy, invasive species, naturalization, floristic records, herbarium specimens, Sardegna, Lombardia, Lazio, Toscana, poison ivy, status change