The hypothesis of an ancient introduction, i.e. archaeophyte origin, is one of the most challenging questions in phylogeography. Arundo donax (Poaceae) is currently considered to be one of the worst invasive species globally, but it has also been widely utilzed by man across Eurasia for millennia. Despite a lack of phylogenetic data, recent literature has often speculated on its introduction to the Mediterranean region. This study tests the hypothesis of its ancient introduction from Asia to the Mediterranean by using plastid DNA sequencing and morphometric analysis on 127 herbarium specimens collected across sub-tropical Eurasia. In addition, a bioclimatic species distribution model calibrated on 1221 Mediterranean localities was used to identify similar ecological niches in Asia. Despite analysis of several plastid DNA hypervariable sites and the identification of 13 haplotypes, A. donax was represented by a single haplotype from the Mediterranean to the Middle East. This haplotype is shared with invasive samples worldwide, and its nearest phylogenetic relatives are located in the Middle East. Morphometric data characterized this invasive clone by a robust morphotype distinguishable from all other Asian samples. The ecological niche modelling designated the southern Caspian Sea, southern Iran and the Indus Valley as the most suitable regions of origin in Asia for the invasive clone of A. donax. Using an integrative approach, an ancient dispersion of this robust, polyploid and non-fruiting clone is hypothesized from the Middle East to the west, leading to its invasion throughout the Mediterranean Basin.

Arundo donax L. (Poaceae) is considered to be one of the worst invasive plants in the world, and here, we present a synthesis of all aspects of its biology, ecology and management that are relevant to understanding its invasive behaviour. This report presents information on the taxonomy, morphology, distribution, history of introduction and spread, ecology, responses to abiotic and biotic factors, biology, negative impacts, management and uses within the framework of a series of Botany Letters on Monographs on invasive plants in Europe. Arundo donax (giant reed) originated in subtropical Asia and is invasive in other warm regions worldwide, especially in degraded riparian areas. Introduced for use in agriculture, erosion control and construction in the Mediterranean European region since ancient times, it has become naturalized in several freshwater habitats and in disturbed areas. In its introduced range, A. donax shows strong genetic uniformity and no seed production. This situation is reversed in Asia, where this taxon is fertile and morphologically and genetically polymorphic. This perennial grass combines rhizomatous clonal growth with a tolerance to a wide variety of ecological conditions, such as high salinity levels and long droughts. This tall reed can increase the risk of fire, alter the natural drainage of channels and invade very sensitive habitats, posing a serious threat to riparian habitats and freshwater ecosystems. Effective methods to control A. donax are tarps on a cleared giant reed field to completely cover the affected zone, rhizome removal using a modified backhoe bucket adapted to separate soil from the rhizomes, and herbicide application on leaves. The combined technique of herbicide treatment plus stem-cutting can be included in management programmes, and this technique needs to be monitored over the long term to assess its success and to ensure native species colonization and ecosystem recovery. Regarding biological control, A. donax is host to different insect species that have been released to control it in parts of its non-native range (North America) with some success. However, these different methods of control should continue to be studied, evaluating the risks posed to the environment and the control level achieved. In this context, scientific, political and administrative efforts as well as environmental education are effective assets to address the management of this invasive species.

Failure of seed production in the genus Arundo L. (Poaceae) is often attributed to polyploidy. This study tested the impact of two ploidy levels ( 2n  = 12 and 18 x ) on the fertility of four Mediterranean Arundo. Viable pollen was screened from its production to its germination, and seed occurrence was monitored in admixture or isolated conditions. In addition, insights on restructuration of polyploid genomes were analysed using molecular cytogenetics. Our results show that high ploidy levels do not automatically induce failure of sexual reproduction . The two ploidy levels are able to produce viable pollen and seed set depending on species and cultural conditions. The sterility of A. micrantha ( 2n = 12 x ) and A. donax ( 2n  = 18 x ) is due to the early failures of gametogenesis steps. For 18 x cytotypes of A. donaciformis and A. plinii , seed absence for isolated genotype vs. seed production in admixed culture support their auto-incompatibility.