Evolving the structure: climatic and developmental constraints on the evolution of plant architecture. A case study in Euphorbia

Abstract

Plant architecture strongly influences ecological performance, yet its role in plant evolution has not been explored in depth. By testing both phylogenetic and environmental signals, it is possible to separate architectural traits into four categories: development constraints (phylogenetic signal only); convergences (environmental dependency only); key confluences to the environmental driver (both); unknown (neither).We analysed the evolutionary history of the genus Euphorbia, a model clade with both high architectural diversity and a wide environmental range. We conducted comparative analyses of 193 Euphorbia species world-wide using 73 architectural traits, a dated phylogeny, and climate data.We identified 14 architectural types in Euphorbia based on trait combinations. We found 22 traits and three types representing convergences under climate groups, 21 traits and four types showing phylogenetic signal but no relation to climate, and 16 traits and five types with both climate and phylogenetic signals.Major drivers of architectural trait evolution likely include water stress in deserts (selected for succulence, continuous branching), frost disturbance in temperate systems (selected for simple, prostrate, short-lived shoots) and light competition (selected for arborescence). Simple architectures allowed resilience to disturbance, and frequent transitions into new forms. Complex architectures with functional specialisation developed under stable climates but have low evolvability.

Hydraulic prediction of drought‐induced plant dieback and top‐kill depends on leaf habit and growth form

“…It is reported that woody plants in dry environments show a more segmented hydraulic system than those in wet habitats (Schenk et al, 2008), and growth of multiple, segmented basal stems (i.e., modular systems) represent a common syndrome of plants in arid systems (Anest et al, 2021). Moreover, the degrees of modularity also differ among growth forms.…”

“…Drought can be particularly severe for plants in arid and semi‐arid habitats, where long and intense periods of water stress occur during the dry season. Plant species growing in semi‐arid environments, particularly shrubs and trees, tend to have modular hydraulic systems and typically have multiple aboveground clonal stems with high redundancy (Anest et al, 2021; Schenk et al, 2008); the aboveground tissues may partially or completely die during severe disturbances such as fire and drought (hereafter define as branch ‘dieback’ or ‘top‐kill’, definitions are provided below), but the species retain living belowground organs that support resprouting, allowing the species to recover post‐drought (Bond & Midgley, 2001; Bond & Midgley, 2003). This strategy may reduce the risk to whole‐plant death under extreme drought (Schenk et al, 2008).…”

Bringing Raunkiær with plant architecture: unveiling the climatic drivers of architectural evolution in Euphorbia

“…Fig.1Diversity of architectures in Euphorbia. In the recently published article in NewPhytologist,Anest et al (2021; doi: 10.1111/nph.17296) identified 14 architectural types within the genus, which are all exemplified here. For description of each architectural type, the reader is referred to the Table1of their paper.…”

“…In this issue of New Phytologist , Anest et al . (2021; pp. 1278–1295) use an unusually integrative approach involving architectural analysis, phylogenetic methods and climatic modelling to decipher the drivers of architectural evolution in the species‐rich genus Euphorbia .

‘In sum, Anest et al .

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“…Fig.1Diversity of architectures in Euphorbia. In this issue of NewPhytologist,Anest et al (2021; pp. 1278-1295 identified 14 architectural types within the genus, which are all exemplified here.…”