The invasion history of Elodea canadensis and E. nuttallii (Hydrocharitaceae) in Italy from herbarium accessions, field records and historical literature

Abstract

We analysed the invasion history of two North American macrophytes (Elodea canadensis and E. nuttallii) in Italy, through an accurate census of all available herbarium and field records, dating between 1850 and 2019, and a rich literature collection describing the initial introduction and naturalisation phase that supports the results obtained by the occurrence records. Elodea canadensis arrived in Italy before 1866 and had two invasion phases, between the 1890s and 1920s and between the 1990s and 2000s; E. nuttallii, probably arrived in the 1970s, started invading in 2000 and the invasion is still ongoing. Botanical gardens and fish farming played a crucial role in dispersal and naturalisation of both species. The current invasion range of both species is centred in northern Italy, with scattered occurrences of E. canadensis in central and southern regions. River Po represents a dispersal barrier to the Mediterranean region and a strategic monitoring site to prevent the invasion in the peninsula. The study detects differences in the niches of the two species during the introduction and naturalisation phase and a habitat switch occurred after 1980 in E. canadensis and after 2000 in E. nuttallii, during their expansion phases. For E. canadensis the switch corresponds to the second invasion round. Further research can clarify whether the second invasion round is due to confusion of the recently introduced E. nuttallii with E. canadensis, to a cryptic introduction of a new genotype, to post-introduction evolution, or just to an increased scientific interest in biological invasions.

Ecology of Elodea canadensis Michx. and Elodea nuttallii (Planch.) H. St. John—Insights from National Water Monitoring in Croatia

“…Furthermore, at 5 sampling sites, they were both recorded, but in different years, never accompanying one another. Over the years, E. nuttallii replaced E. canadensis in three reservoirs on the Drava River in Northern Croatia (sites number [33][34][35][36][37][38] and in two canals of the Drava River Basin (sites number 31,32,43,44). Overall, waterweeds were mostly recorded in rivers and canals (90% of records).…”

“…(sites number 31,32,43,44). Overall, waterweeds were mostly recorded in rivers and canals (90% of records).…”

From Dormant Collections to Repositories for the Study of Habitat Changes: The Importance of Herbaria in Modern Life Sciences

“…In this context, the 3500 herbaria that are available worldwide preserve a precious time-stamped tangible record of botanical biodiversity that, at present, consists of more than 400 million specimens (according to a survey of The New York Botanical Garden, https://sweetgum.nybg.org/science/ih/, accessed on 30 October 2023). These collections not only represent a snapshot of both present and past plant biodiversity [8,9], but they also preserve different types of samples (from dried plants and seeds to fungi and algae) collected at different phenological stages. Moreover, several institutions also possess plant materials conserved in liquid solutions that can be used for different molecular analyses [10].…”

“…Lastly, herbaria can be considered unique repositories of phytogeographical data and the most accurate data sources to reconstruct events that occurred in the past. As a consequence, the role of herbaria has widened in recent years, from cataloging the diversity of life to documenting biodiversity changes and tracing spatiotemporal bioinvasion patterns [9,65,66]. Indeed, changes in plant communities are generally well-documented in herbarium collections, especially in the early stage of invasion [9].…”

“…As a consequence, the role of herbaria has widened in recent years, from cataloging the diversity of life to documenting biodiversity changes and tracing spatiotemporal bioinvasion patterns [9,65,66]. Indeed, changes in plant communities are generally well-documented in herbarium collections, especially in the early stage of invasion [9].…”