Invasive plants in the Ponziane islands - Carpobrotus

Invasive plants in the Ponziane islands - Carpobrotus

15 April 2021

Let's start the series of factsheets on invasive plants in the Ponziane islands with Carpobrotus, which is commonly known as Hottentot-fig or ice plant. The local name is capocchia (in Ventotene) or rosemarine (in Ponza).

Carpobrotus is a genus (family Aizoaceae) of plants native to South Africa, that were introduced in the Mediterranean Basin for ornamental purpose since the early 20th century. They are trailing succulent plants, whose leaves have a triangular cross-section. Flowers are large (up to 12-15 cm in diameter), solitary and can be yellow, orange, rose purple or sometimes white. The fruit is fleshy and edible and carries many seeds.

The most common species outside South Africa are Carpobrotus acinaciformis and C. edulis, both listed among the worst 100 invasive species (animals, algae, fungi and plants) in Europe. According to the original descriptions, the main character for the identification was the colour of flowers, yellow in C. edulis and rose purple in C. acinaciformis. However, C. edulis can have purple flowers as well and this character is no longer considered fully reliable. Moreover, the two species tend to produce intercrosses (hybrids), which confuse identification. While taxonomic studies are being carried out, the two species are often considered as a complex.

In Europe flowers develop between February and June and fruits remain on the plant until late autumn, when animals (rabbits, rats, cats) begin to eat them. 

Carpobrotus species may also reproduce vegetatively by the expansion of prostrate stems that develop roots and sprouts or even from pieces of stems and leaves. The high reproductive capability, the dispersal by animals, and the wide ecological adaptability enable Carpobrotus to spread widely and form dense mats.

In Europe, Carpobrotus preferentially grows on rocky and sandy coasts, with many impacts on coastal habitats. These plants tend, indeed, to replace and exclude native species, through direct competition for water and space and indirectly, through the alteration of soil properties (for example they lower moisture level and increase salt content).

In the Mediterranean coastal areas, which are rich in rare and/or endemic species and in habitats of Community interest (under the Habitats Directive 92/43/EEC), the spread of Carpobrotus is especially alarming.

For these reasons, in recent years many projects were aimed at managing and removing such an invasive from the Mediterranean Basin: in Spain, Portugal, France and, in Italy, in Tuscany, Sardinia, Sicily…and the Ponziane, as well! In these islands, Carpobrotus especially threatens the sea cliffs vegetation, which hosts rare or endemic Limonium species.