From greenhouse to the wildlife: global invasion patterns of Kalanchoe ×houghtonii (Crassulaceae)

Abstract

The invasive alien species are currently considered one of the main threats to global biodiversity, with ornamental horticulture being the major introduction pathway of alien plants. One of the most rapidly expanding invasive plants in recent times is Kalanchoe x houghtonii (Crassulaceae), an artificial hybrid created in the 1930s in the United States, by experimental crossings between two species endemic to Madagascar, K. daigremontiana and K. tubiflora. Soon, thanks to its large colonizing capacity and to its extended ornamental use, this nothospecies escaped from cultivation and quickly spread in many parts of the world. Its actual range is not well known because of the lack of a formal description until recent times (2006), and its strong morphological resemblance with one of its parentals (K. daigremontiana). The study delimits for the first time the present distribution area of K. x houghtonii at global scale by gathering and validating all the occurrences and to track its colonization history. Although it did not reach a global distribution until the 2000s, K. x houghtonii now can be found in all continents except Antarctica. In the Mediterranean Basin, the species was detected at late 1990s, and at present it is behaving as an aggressive invader. In some areas, such as the eastern part of the Iberian Peninsula, it is a very common species in urban and peri-urban habitats. Its potential distribution, estimated with MaxEnt modelling, is mainly centered in Mediterranean-climate and subtropical regions, from 20º to 40º of both northern and southern latitudes. Unexpectedly, niche models suggest a considerable reduction of its range at worldwide scale (of up to one-third compared to the present) concomitant to a poleward migration for the year 2070, which might be related with the Crassulaceaean Acid Metabolism (CAM) of K. x houghtonii.