A genomic study reconstructs for the first time the evolutionary history of this Mediterranean ornamental plant and identifies the gene responsible for the colour change
Genomic (right) and floral (left) characteristics of Lobularia maritima.
Flower colour is one of the traits that most captivates us in ornamental plants. Yet behind these colours there are often evolutionary and genetic histories that remain unknown. Until recently, this was the case of sweet alyssum (Lobularia maritima), a plant widely found in the wild but also common in gardens and balconies, displaying white, pink or violet flowers.
Now, a study led by Sichuan University (China) and the Botanical Institute of Barcelona (IBB, CSIC-CMCNB) has reconstructed for the first time the domestication history of this species. The results, published in Horticulture Research, reveal that all current cultivars derive from a single domestication event that took place in Tunisia slightly more than five thousand years ago. There is also another surprising finding: violet-flowered varieties, so common today, did not appear until approximately seven hundred years ago.
An origin in North Africa more than five millennia ago
Sweet alyssum is native to the Mediterranean basin and, in the wild, bears white flowers. To understand how and when it became the diverse ornamental plant we know today, the research team generated a high-quality reference genome and analysed 84 samples, both wild and cultivated, from different locations in the western Mediterranean.
Genomic analyses show that all cultivated varieties form a single lineage related to wild populations from Tunisia. This indicates that domestication occurred in this North African region during the Middle Neolithic, in a context where agricultural societies were already managing and selecting plants of interest.
From white to violet: a medieval innovation
Following this initial domestication, the plant spread and diversified under human influence. However, the most visible change —the emergence of purple flowers— is much more recent. Using demographic models and genetic comparisons between white and violet varieties, researchers estimate that the latter originated around 700 years ago. This period coincides with the development of particularly sophisticated horticulture in al-Andalus and North Africa during the Middle Ages, which may have favoured the selection and dissemination of this new colour.
The genetic basis of this change is a variant of the PAP1 gene, a key regulator of anthocyanin synthesis —the pigments responsible for red, purple and blue hues. All analysed wild populations retain the version associated with white flowers, whereas the variant linked to violet colour is found only in cultivated plants. Functional experiments show that this new gene version activates the pigment biosynthetic pathway more strongly, explaining the accumulation of anthocyanins and the colour shift.
Genetic findings may inform local conservation policies
Furthermore, as explained by Jordi López-Pujol, co-leader of the study, the genetic results may also have implications for local conservation policies: populations of Lobularia maritima subsp. columbretensis —a taxon exclusive to the Columbretes Islands and included in the Spanish Red List— are genetically very close to nearby populations of L. maritima subsp. maritima, thus questioning the need to maintain separate protection status for this taxon (currently listed as a “monitored flora species” in Valencian regional protection catalogues).
The study, Domestication history and genetic changes for the newly evolved flower color in the ornamental plant Lobularia maritima (Brassicaceae), is available here.