How is flower diversity produced? Insights from Asarum

Examining the similarities and differences in plants species spread across proximal but separated landmasses can give interesting insights into plant evolution and the evolution of the organisms they interact with. Asarum (commonly known as wild ginger) is a genus of plants with over 100 different species found in Asia, Europe and North America. Half of this species diversity is however crowded into just 10% of the landmass across which Asarum species can be found, specifically around Japan and Taiwan. A group of Asarum species known as Heterotropa are found particularly around the Japanese islands, and like other Asarum species have highly diverse flower structures. In a new paper in Annals of Botany, Okuyama and colleagues resolve how the Heterotropa species of the Asarum genus are related at the genetic level. Interestingly, this work will allow for future study of whether the different adaptations of these Asarum species may have been brought about geographically-separated interactions with other organisms.

Obtaining genomic information from non-model plant species, such as those in Asarum, can be difficult. Here the authors make use of a technique known as ddRAD-seq, which is useful for overcoming problems associated with non-model species. From this they get a high-resolution phylogenetic tree of Heterotropa species, from which they can draw conclusions about how geographic distribution and Heterotropa phylogeny are related. All species bar one in the Heterotropa are split into nine clades using the genomic data collected and have broadly distinct distribution patterns. From this the authors can produce an estimated map of how Heterotropa species historically spread to give rise to their current distribution pattern.

It is particularly interesting to consider is what the data collected in this study may be used for in the future. Asarum species are believed to use floral mimicry to attract pollinating insects to their flowers. Floral mimicry involves flowers mimicking attractive features to pollinating insects and may include looking like a possible mate, producing scents like those of a possible mate, or imitating a place where insects themselves commonly mate. Okuyama and colleagues speculate that the diversity of flower structures produced by Heterotropa species may be driven by encountering different groups of pollinators at their different geographic locations (an adaptive radiation). The data gathered here provide an essential bedrock for understanding how Asarum species produced their diversity in structure and function. It will also boost our understanding of the broader methods by which the vast diversity of flowering plants on this planet came about.