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.

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-The invasive species Elodea nuttallii was recorded for the fi rst time in the Croatian fl ora in 2006, in the drainage channels of Kopački rit (Baranja). After its establishment, E. nuttallii begins to spread to the eastern and northern part of the drainage channel network from 2006-2009. High water levels are responsible for the linear spreading direction of E. nuttallii, E. nuttallii and E. canadensis show a wide range of morphological variation, which is characteristic of successful invaders. To show morphological variations of two Elodea species, the most impor tant characters indicated in the literature were measured on 24 fresh collected samples from the seven sites in Croatia. In spite of some overlap in leaf length and width between the two Elodea species, the differences of all morphological traits except internode length are statistically signifi cant. In E. nuttallii leaf width, length and internode length show a higher morphological variability as a result of the higher adaptive strategy to environmental parameters. The most reliable morphological characters distinguishing E. nuttallii and E. canadensis are leaf width 0.5 mm below the tip and the angle at the apex. E. nuttallii can be expected to spread to other areas of Croatia.

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