The evolutionary ecology of C-4 plants

C4 photosynthesis is a physiological syndrome resulting from multiple anatomical and biochemical components, which function together to increase the CO2 concentration around Rubisco and reduce photorespiration. It evolved independently multiple times and C4 plants now dominate many biomes, especially in the tropics and subtropics. The C4 syndrome comes in many flavours, with numerous phenotypic realizations of C4 physiology and diverse ecological strategies. In this work, we analyse the events that happened in a C3 context and enabled C4 physiology in the descendants, those that generated the C4 physiology, and those that happened in a C4 background and opened novel ecological niches. Throughout the manuscript, we evaluate the biochemical and physiological evidence in a phylogenetic context, which demonstrates the importance of contingency in evolutionary trajectories and shows how these constrained the realized phenotype. We then discuss the physiological innovations that allowed C4 plants to escape these constraints for two important dimensions of the ecological niche – growth rates and distribution along climatic gradients. This review shows that a comprehensive understanding of C4 plant ecology can be achieved by accounting for evolutionary processes spread over millions of years, including the ancestral condition, functional convergence via independent evolutionary trajectories, and physiological diversification

Centropodieae and Ellisochloa, a new tribe and genus in Chloridoideae (Poaceae)

There has been confusion among taxonomists regarding the subfamilial placement of Merxmuellera papposa, M. rangei, and four species of Centropodia even though many researchers have included them in molecular studies. We conducted a phylogenetic analysis of 127 species using seven plastid regions (rps3, rps16-trnK, rps16, rpl32-trnL, ndhF, ndhA, matK) to infer the evolutionary relationships of Centropodia, M. papposa, and M. rangei with other grasses. Merxmuellera papposa and M. rangei form a clade that is sister to three species of Centropodia, and together they are sister to the remaining tribes in Chloridoideae. We provide the carbon isotope ratios for four species indicating that Merxmuellera papposa and M. rangei are photosynthetically C3, and Centropodia glauca and C. mossamdensis are C4. We present evidence in favor of the expansion of subfamily Chloridoideae to include a new tribe, Centropodieae, which includes two genera, Centropodia and a new genus, Ellisochloa with two species, Ellisochloa papposa and E. rangei. The name Danthonia papposa Nees is lectotypified

Cleaning up the grasses dustbin: systematics of the Arundinoideae subfamily (Poaceae)

International audienceAmong the 12 subfamilies currently considered in the systematics of Poaceae, the Arundinoideae have long been considered as a dustbin group, with a diversity of forms putatively hiding incertae sedis. Because this subfamily has been poorly investigated using molecular markers for the last two decades, the present study provides the first complete phylogeny of the Arundinoideae based on five plastid DNA loci sequenced for 12 genera, and analysed with and without plastome data from previous studies. The refined Arundinoideae appear to be a robust evolutionary lineage of Poaceae, divided into three tribes with some biogeographical patterns: (1) tribe Arundineae, the most heterogeneous tribe, including Eurasian Arundo, Australian Amphipogon and Monachather, and South African Dregeochloa; (2) tribe Crinipedeae (described here), including Crinipes, Elytrophorus, Styppeiochloa and Pratochloa (described here), with a South and East African distribution; and (3) tribe Molinieae, including Hakonechloa, Molinia and Phragmites, with a Eurasian distribution. Despite reduction in size, this small subfamily conserves a high diversity of morphological forms, with several small but highly differentiated genera. Finally, the molecular dating approach provides an evolutionary framework to understand the diversification of Arundinoideae, refuting Gondwanan vicariance between genera and suggesting capability for long distance dispersal