Senecio matatini is a recently delineated New Zealand endemic of the Astereceae family with four recognised subspecies. However, the existence of several morphologically deviating populations in limestone environments prompts the question of whether the limestone populations should be recognised as one or more subspecies of S. matatini or if they should be recognised as another one or more distinct species. These taxonomically ambiguous calcicolous plants are only known from small and isolated populations, which are considered to be declining. This further necessitates taxonomic research, as well as obtaining a better understanding of their patterns of genetic connectivity and diversity.

We used genomic data obtained through Genotyping by Sequencing to determine the amount of genetic diversity in populations and the extent of connectivity among populations of six limestone forms of S. matatini - S. aff. matatini “Cape Campbell” , S. aff. matatini “Castle Hill”, S. aff. matatini “Mt Cass” (de Lange et al., 2018; Ornduff, 1960; Rogers et al., 2018), S. aff. matatini “North Dean”, “South Marlborough Limestone” and S. aff. matatini “Tablelands”. We also included representatives of the four currently recognised subspecies of S. matatini in my analyses - S. matatini subsp. basinudus (Ornduff) Courtney, de Lange & Pelser, S. matatini subsp. discoideus (Cheeseman) Courtney, de Lange & Pelser, S. matatini subsp. matatini and S. matatini subsp. toa (C.J.Webb) Courtney, de Lange & Pelser. We used landmark analysis on a subset of this species complex to help resolve some of the patterns of genetic structure. This was to determine how genetically distinct they are to the limestone forms. We aimed of identify limestone populations and forms that have unique genetic variation or are genetically isolated from other populations and forms. We also aimed to determine which and how many taxa to recognize within this taxonomically complex group. We found patterns of genetic structure within the species complex which showed the most support for five distinct genetic clusters with little admixture between the groups. The individual limestone entities hold unique variation further indicative of their genetic isolation. The limestone entities were not all distinct from the subspecies. The population genetic analyses found the limestone entities to hold high levels of genetic variation, however, metrics for some entities were influenced by low sample sizes. Taxonomic recognition for two new subspecies representing limestone entities is recommended. One limestone entity, thought to be unique clustered tightly with one of the subspecies. Other entities largely can be accommodated in the current taxonomic classification of S. matatini, however these may need further study. The results of this study will help inform the formal classification of the S. matatini complex, contribute to an accurate assessment of its conservation status, and facilitate effective conservation management.