Naturalization of the Ornamental Plant Crocus tommasinianus Herb. (Iridaceae) in Forest Ecosystems: A Case Study from Poland

Highlights: Though not highly invasive, bulb and corm ornamental plants can escape cultivation and naturalize in new areas. Studying their naturalization is key to understanding their ecological impact and managing biodiversity. Objectives: This study aimed to document the first naturalization case of Crocus tommasinianus Herb. in Poland and assess the morphological variability of the naturalized population under different environmental conditions. Another objective was to identify diagnostic features in seed testa ornamentation to distinguish C. tommasinianus from related species (C. vernus (L.) Hill. and C. scepusiensis (Rehmann et Wol.) Borbás ex Kulcz.). Methods: The morphometric studies were performed within four subpopulations of C. tommasinianus differing in environmental conditions, determined with Ellenberg indices. Multivariate tests, ANOVA, and post-hoc tests were used to determine the morphometric diversity of specimens and to relate them to environmental factors. Seed micro-ornamentation was examined using a scanning electron microscope. Results: Light and temperature were negatively correlated, while moisture, soil pH, and nitrogen were positively correlated with many morphological traits. Plants spreading into forest ecosystems exhibited better-developed features (larger leaves and flowers) than those in former cultivation sites, indicating higher survival potential. The seed coat is papillate, with distinct differences in the shape, size, and secondary sculpture of the papillae compared to C. vernus and C. scepusiensis. Given that floristic studies often occur during the fruiting period of crocuses, testa ornamentation is crucial for identifying the studied species. Conclusions: The observed naturalization of C. tommasinianus demonstrates the high morphological plasticity of plants, which makes them capable of colonizing new areas, including forest habitats.