Two Shades of Grey: Effect of Temperature on Seed Germination of the Escaping Ornamental Species Lychnis Coronaria and Stachys Byzantina

Abstract

This paper describes germination and cytological variability in two popular ornamental and potentially invasive species, lamb’s ear Stachys byzantina and rose campion Lychnis coronaria. Both xerophytic species have the potential to invade natural habitats across Europe and create viable naturalised populations, with subsequent impacts on native vegetation. To assess the species’ invasiveness, seeds were collected from naturalised populations and germination rate recorded under different temperature regimes. Flow cytometry, used to record cytological variability, indicated that all populations of both species were cytologically homogeneous. Germination success, a key spreading factor in both species, was significantly influenced by temperature, with final germination of L. coronaria being extremely high at temperatures > 15/10 °C (98.5%) and extremely low at temperatures < 10/5 °C (2.9%). In comparison, final germination in S. byzantina highest at 22/15 °C (55.6%), reducing to 40.3% at 15/10 °C and just 0.3% at temperatures < 10/5 °C. No significant differences in germination rate were observed between escaping and non-escaping populations, though there were differences between particular populations. Our results indicate germination temperature limits between species consistent with sizes of primary distribution and distance between primary and secondary distribution borders. However, the observed germination rates allow for successful generative reproduction of both species over their secondary distribution areas, suggesting that these species are likely to become invasive species of European grasslands soon.