Stomatal Structure in Symphyotrichum Nees Species as an Additional Index of Invasiveness

Abstract—The study was aimed on a comparison of morphometric traits of the stomatal apparatus in cultivated Symphyotrichum Nees species to evaluate the adaptive capacity of these alien taxa. The study included eleven Symphyotrichum species from the collection of the Botanical Garden of Padua (Italy): S. novi-belgii, S. novae-angliae, S. ciliolatum, S. laeve, S. lateriflorum, S. puniceum, S. × salignum, S. × versicolor, S. chilense, S. cordifolium, and S. tradescantii. For these species, original data on 21 quantitative morphometric characteristics of the stomatal apparatus are presented. The species were divided into three groups according to the index of relative transpiration area (RTA). High RTA values (12–14%) were observed in S. novae-angliae, S. novi-belgii, and S. × salignum; medium RTA values (3–7%) were typical of S. lateriflorum, S. ciliolatum, S. laeve, S. × versicolor, and S. puniceum; finally, low RTA values (0.2–2.0%) were revealed in S. chilense, S. cordifolium, and S. tradescantii. As in the previous study of the genus Solidago, a positive correlation was observed between the RTA and the invasiveness of alien species. A hypothesis was proposed that a high RTA value indicates a greater adaptability of alien species and, along with other traits, can be used to predict the further expansion of their secondary range and possibility of their transformation into invasive species.