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In The New phytologist

Plants use roots to access soil resources, so differences in root traits and their ecological consequences could be a mechanism of species coexistence and niche divergence. Current views of the evolution of root diversity are informed by large-scale evolutionary analyses based on taxonomically coarse sampling and led to the "root trait phylogenetic conservatism hypothesis". Here we test this hypothesized conservatism among closely related species, and whether root variation plays an ecological role. We collected root-architectural traits for the species rich Cape rushes (Restionaceae) in the field and from herbaria. We used machine learning to interpolate missing data. Using model-based clustering we classified root syndromes. We modelled the proportion of the syndromes along environmental gradients using assemblages and environmental data of 735 plots. We fitted trait evolutionary models to test for the conservatism hypothesis. We recognized five root syndromes. Responses to environmental gradients are syndrome-specific and thus these represent ecomorphs. Trait-evolutionary models reveal an evolutionary lability in these ecomorphs. This could present the mechanistic underpinning of the taxonomic radiation of this group which has been linked to repeated habitat shifts. Our results challenge the perspective of strong phylogenetic conservatism and root trait evolution may more generally drive diversification.

Ehmig Merten, Linder H Peter


Cape Floristic Region, Restionaceae, ecomorphs, radiation, root traits, trait evolution