The ecological performance of plants (i.e., ability to compete for resources and overcome disturbances) largely depends upon plant architecture. However, the role of architecture in plant evolution has been weakly explored.  

The genus Euphorbia L. is well suited as a model group to study the evolution of architecture as it has high growth form diversity comprising single stemmed short-statured plants, rosettes, shrubs and trees. 

In a study published in New Phytologist, researchers from the Xishuangbanna Tropical Botanical Garden (XTBG) made the first attempt to classify Euphorbia traits according to their architecture. They investigated how architectural traits can explain the structural evolution of Euphorbia and specifically tested whether climate has been a major evolutionary driver of architecture in the clade. 

Combining phylogenetic analyses with regression modelling, the researchers separated architectural traits into four evolutionary categories: development constraints (phylogenetic signal only); convergences (environmental dependency only); key confluences to the environmental driver (both); unknown (neither). 

Using a large phylogeny with 193 Euphorbia species, they screened a total of 73 structural traits (22 representing convergences under climate groups; 21 showing phylogenetic signal but no relation to climate; and 16 with both climate and phylogenetic signals), and identified 14 architectural types with different structural properties and levels of complexity. 

They found that plant architecture in Euphorbia was strongly associated with three main climatic groups, namely deserts where water is limiting (cold and hot deserts grouped together), temperate zones subject to freezing winter temperatures, and tropical systems that are frost-free and include aseasonal wet systems to seasonally dry systems. 

"The result is not exhaustive because we only describe 10 percent of the genus," said Artémis Anest, first author of the study. 

"Our results provide insights into the colonization of arid and temperate systems, the evolution of complex plant architecture, and how the elaboration of structure can allow the emergence of new functions," said Dr. Kyle W. Tomlinson of XTBG.