The effect of local latitudinal variations on the phenology and morphological development of garden lupine (Lupinus polyphyllus)

The garden lupine (Lupinus polyphyllus) is an invasive species that threatens biodiversity by altering ecosystems and outcompete native plant species. The phenological and morphological patterns of invasive plants are often influenced by climatic factors, which affect their spread and establishment. This study aimed to investigate how local latitudinal variations in Värmland, Sweden, influence the growth and development of L. polyphyllus, with the hypothesis that lower latitudes promote increased growth and earlier phenological events due to more favorable climatic conditions. The study was conducted at ten sites distributed between the regions of Karlstad and Brattfors along a 34 km north-south gradient. Canopy height, flowering, and seed maturation were recorded throughout one growing season and analyzed using two-way ANOVA and regression models. The results showed significantly greater canopy height in Karlstad (37.10 ± 1.94 cm) compared to Brattfors (33.42 ± 1.89 cm), with a general increase over the season. First flowering occurred in Karlstad on day 160 (9 June), while Brattfors reached the same stage on average eight days later, on day 168 (17 June). Seed maturation was observed in Karlstad on day 195 (14 July) and in Brattfors on day 203 (22 July). The findings demonstrate that small-scale latitudinal variations influence the phenology of L. polyphyllus, which has important implications for management strategies. Control measures should be adapted to regional differences in developmental patterns to effectively limit the species' spread.