Optimizing conditions for Nitellopsis obtusa (starry stonewort) growth and bulbil germination in a controlled environment

•In the laboratory N. obtusa germination rate was 87%.•Nitellopsis obtusa bulbil size does not relate to shoot number or size.•Optimal N. obtusa growth was observed in charophyte specific Forsberg’s media II under low intensity metal-halide light. Much attention has focused on understanding the growth of Nitellopsis obtusa [(Desvaux) J. Groves] (starry stonewort) through chemical drivers with limited information on light availability. This is important as, in addition to water chemistry, light availability largely controls the distribution, abundance and growth of macroalgae. Therefore, the purpose of this study was to evaluate optimal cultivation conditions for bulbil germination and N. obtusa growth ex-situ by investigating synthetic media types, light types and light intensities. In general, nutrient concentration, light type and light intensity all directly influenced growth and morphology of N. obtusa, however this relationship was complex and multifaceted. Nitellopsis obtusa grew best in low-light, high-macronutrient conditions but, in general, was capable of growing under all conditions evaluated, though demonstrated considerable morphological differences. The information presented in this study can help guide field studies and determine the role of light in N. obtusa growth and physiology. This study will provide a foundation for optimized culturing conditions for N. obtusa. Controlled environment evaluations will be essential to enhance our understanding of the biology of this now endangered (Eurasia) yet newly invasive (North America) macroalga. Information provided by this work may also provide insight into the development of effective management strategies for N. obtusa in North America.