Systematics and Evolution

Our work in systematics and phylogenetics is focused on identifying the underlying causes of diversification. We integrate phylogenetics with ecology, biogeography, genomics, and morphometrics to identify how the evolution of traits corresponds to the divergence of lineages. By understanding when, where, and why lineages have diversified, we are better equipped to quantify and protect biodiversity.

Phylogenetic Structure of Gene Tree Incongruence in Capsiceae

Global Biogeography of Cyperaceae

We found that the Cyperaceae originated in the American tropics about ~85 million years ago (a), likely traveling through what was then a temperate Antarctica to reach Australia. The sedges then diversified in the Northern Hemisphere. Three massive increases in diversification rate occurred during the evolution of the sedges – and two of these were in temperate regions (b). This has resulted in temperate regions containing almost as many – if not more – species than tropical regions, even though the sedges originated in the tropics and have only been in temperate zones for 60 million years (a). This is because rates of diversification are overall much lower in the tropics (c). Read more here. After observing this pattern, we wanted to more know about what might have happened in the temperate regions to promote such rapid rates of diversification. See more below.

Evolution of geography and niche space in North American sedges

While some sedges are widespread, most have very narrow and non-overlapping distributions. After observing this pattern, we suspected that geography likely played an important role in the diversification of the family. In a global analysis using about 3 million herbarium records, we found that species richness in clades is highest when:

• Clades are widespread.

• The ranges of individual species don’t overlap

• The range of individual species is small relative to the total range of the clade.

We also found that species that occur in sympatry are often unrelated to each other – it is far more likely that distantly related species co-occur than it is for closely related species to co-occur.