Summary1. This account presents information on all aspects of the biology of Ambrosia artemisiifolia L. (Common ragweed) that are relevant to understanding its ecology. The main topics are presented within the standard framework of the Biological Flora of the British Isles: distribution, habitat, communities, responses to biotic factors, responses to environment, structure and physiology, phenology, floral and seed characters, herbivores and disease, and history, conservation, impacts and management. *Nomenclature of vascular plants follows Stace (2010) and, for non-British species, Flora Europaea.

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Standardized tools are needed to identify and prioritize the most harmful non-native species (NNS). A plethora of assessment protocols have been developed to evaluate the current and potential impacts of non-native species, but consistency among them has received limited attention. To estimate the consistency across impact assessment protocols, 89 specialists in biological invasions used 11 protocols to screen 57 NNS (2614 assessments). We tested if the consistency in the impact scoring across assessors, quantified as the coefficient of variation (CV), was dependent on the characteristics of the protocol, the taxonomic group and the expertise of the assessor. Mean CV across assessors was 40%, with a maximum of 223%. CV was lower for protocols with a low number of score levels, which demanded high levels of expertise, and when the assessors had greater expertise on the assessed species. The similarity among protocols with respect to the final scores was higher when the protocols considered the same impact types. We conclude that all protocols led to considerable inconsistency among assessors. In order to improve consistency, we highlight the importance of selecting assessors with high expertise, providing clear guidelines and adequate training but also deriving final decisions collaboratively by consensus.

Solanum carolinense is a serious weed from North America that has recently invaded crop fields in Austria and Italy. In this study, a climate suitability analysis using the CLIMEX model was carried out, to assess the potential distribution of S. carolinense in Central Europe, to identify areas at risk of an invasion and to derive an efficient management strategy. In North America, the plant currently occupies almost its full range of suitable climates. In contrast, S. carolinense occurs only rarely as a ruderal plant and weed in several countries of Central Europe. The projections of climatic suitability under current climate reveal considerable scope for further invasion. The land area climatically suitable for S. carolinense is highest in Hungary (100% of the total land area), Poland (83.6%), followed by Slovenia (70.5%), Slovakia (64.5%), Germany (41.5%), Czech Republic (37.0%), Austria (34.9%) and Switzerland (16.6%). Solanum carolinense has a high capacity for spatial dispersal by natural means and different human-mediated pathways. Thus, it is likely that the plant will expand its range and infest cultivated land, particularly around existing naturalised populations. A management strategy is warranted, including early detection and eradication of nascent foci of S. carolinense, to contain the plant to its current restricted distribution and to limit the chances for further spread of this invasive weed to other agricultural areas. The widespread occurrence of this species would have serious consequences for agriculture.

Pueraria lobata (kudzu) is an invasive weed originating from East Asia. Local infestations have been recently observed in Switzerland and northern Italy; however, the potential for P. lobata to spread and to become abundant and damaging in the Alpine countries is not known. The aim of this study was to project the potential distribution of P. lobata under current climate in Switzerland, Austria and Slovenia and parts of northern Italy using the ecoclimatic model CLIMEX. In addition, areas at risk were identified where P. lobata may occur as a strong and aggressive competitor. This was derived from the plants’ distribution and climatic requirements in the south-eastern United States where the heaviest infestations occur. Projections show that 60.84% of the total land area of northern Italy, followed by 47.08% of Slovenia, 21.01% of Austria and only 1.97% of Switzerland are climatically suitable. P. lobata may become a troublesome weed due to very favourable climatic conditions only in some parts of northern Italy and Slovenia. In climatically suitable areas, any occurrence of the plant should be carefully observed. In infested and highly climatically suitable areas, there is a need for strategic management to prevent further spread of P. lobata.