Salvinia molesta found in two localities in Italy
Salvinia molesta (Salviniaceae – EPPO Alert List) originates from South America and is invasive in a large number of places (Africa, India, USA, Australia, etc.). So far, no occurrences of the plant were known in the EPPO region. However, S. molesta has recently been detected in Italy.
In 2000 near Pisa
Salvinia molesta was found in 2000 near Pisa (Toscana) in the Fosso del-Acqua calda, a slow flowing artificial canal 2.5 m wide. This canal is fed from a thermal source maintaining water temperature between 16°C and 27°C in summer. The species is omnipresent in summer months and is not seen during winter time, due both to cold temperatures of the water (minimum of 4°C in January), and management by dredging of the canals. S. molesta has been observed covering 350 m long of the canal, and mats were 7.5 cm deep. It has been observed that the species can double its biomass in a week in its optimal conditions. The species has also been observed totally covering the surface of adjacent canals. Portions of the plant that seemed dead contained live buds that can regenerate under favourable conditions. It was considered that approximately 80 tonnes of the plant were invading these canals.
It is suggested that the species had escaped from a garden or was discarded from an aquarium. Additionally, it was observed that S. molesta displaced the native Salvinia natans which is listed in the Italian red list, and is already suffering from the disappearance of its habitats due to intense urbanization.
In 2003 near Rome
In 2003, S. molesta was observed in the Pozzo del Merro lake (Cornicolani Mountains, Lazio, near Rome), the deepest flooded sinkhole in the world (392 m of water depth). This lake is part of a protected area, the “Riserva Naturale Macchia di Gattaceca e Macchia del Barco”. There, the situation is similar to the one encountered in the Fosso del aqua calda, with water having a constant temperature of 15°C with the rising of geothermic waters. In the pozzo del Meero, S. molesta covered the whole lake in 3 months according to the following chronology:
- 31st of July 2003: S. molesta was not observed;
- 21st of August 2003: first record of S. molesta, covering about the half of the lake;
- 7th September 2003: it covered more than ¾ of the surface of the lake;
- 1st October 2003: it covered about 95% of the lake;
- 2nd November 2003: it entirely covered the lake.
S. molesta displaced the indigenous fern Lemna minor. The pyralid moth Cataclysta lemmata (Lepidoptera: Pyralidae), a polyphagous caterpillar, was observed feeding on S. molesta, but the presence of this insect was not sufficient to prevent its rapid expansion. It is unknown how S. molesta arrived at this lake. It is hypothesized that S. molesta was carried voluntarily or involuntarily by human activities, or discarded with firefighting.
In 2008, the species has not been removed and still covers the entire lake. The species regresses during winter, but the carpet that it forms is so thick that other plants such as Carex pendulma and Epilobium parviflorum grow on it. The mats impede the passage of light, leading to changes in the chemical composition of the water. So far, studies on the fauna of the lake have shown that newts, frogs and invertebrates and vertebrates are still abundant.
General remarks about the plant
The plant is known to die if exposed at temperatures lower than -3°C or higher than 43°C for more than 2 hours. The optimum temperature for growth is 30°C, and growth occurs between 10°C and 40°C. S. molesta is considered to be an hybrid between S. biloba and S. herzogii, originating from the botanical garden of Rio de Janeiro. Studies confirmed that the populations found near Pisa are sterile. In the Pisa location, cariological studies have identified that the plant is pentaploid with 2n=45.
Garbari F, Giovannini A, Marchetti D (2000) [Salvinia molesta D.S. Mitchell (Salviniaceae) new for the Flora of Italy]. Arch. Geobot. 6(1): 73-78 (in Italian).
Giardini M (2008) [The Pozzo del Merro sinkhole (Monti Cornicolani, Roma) five years after Salvinia molesta D. S. Mitchell infestation]. In Le specie alloctone in Italia: censimenti, invasività e piani di azione. Memorie della Società Italiana di Scienze Naturali e del Museo Civico di Storia aturale di Milano. Vol. XXXVI (1), 63 (in Italian).
Giardini M (2003) [Note on the biology, ecology and control of Salvinia molesta D. S. Mitchell (Salviniaceae), invasive species for the Latium]. Rivista di idrobiologia vol. XLII (1-3), 263-282 (in Italian).
Giardini M (2004) [Salvinia molesta D.S. Mitchell (Salviniaceae): second record for Itlay (Latium) and considerations on the control of this invasive species]. Webbia 59(2), 457-467 (in Italian).
Palozzi R (2007) [The Pozzo del Merro sinkhole: immersion with Jim Bowden and Stefano Makula]. Sottacqua, anno 1, n°5, luglio 2007 (in Italian). http://www.sottacqua.info/05_07/05_07_r03_primo_piano_palozzi.htm