The endemic ‘sugar canes’ of Madagascar (Poaceae, Saccharinae: Lasiorhachis) are close relatives of sorghum

International audienceCrop wild relatives are important but often poorly known. This is the case for subtribe Saccharinae (Poaceae: Andropogoneae), which includes sugarcane (Saccharum) and sorghum (Sorghum). We present a phylogenetic and taxonomic account of the Malagasy endemic genus Lasiorhachis, previously included in Saccharum. New plastome and nuclear sequences were assembled from genome skimming data. Phylogenetic analyses of whole plastomes place Lasiorhachis as sister to Sorghum and only distantly related to the interbreeding Saccharum complex. This is also supported by analyses of nuclear ITS and partial assemblies for eight low-copy regions. Some nuclear regions suggest that Lasiorhachis is closer to Sorghum section Sorghum than other Sorghum spp. sometimes segregated as Vacoparis. We present a full taxonomic treatment of Lasiorhachis with an identification key, synonymy, typification, descriptions, drawings and a distribution map of the three species, all endemic to the central highlands of Madagascar. Lasiorhachis species occupy contrasting ecological niches and at least one of them, L. viguieri, has significance for ecosystem function. As crop wild relatives of sorghum, Lasiorhachis species should be included in germplasm collections

Description of five new species of the Madagascan flagship plant genus Ravenala (Strelitziaceae)

International audienceMadagascar's emblematic traveller's tree is a monospecific genus within Strelitziaceae, the family of the South African bird of paradise. Until now, this endemic genus consisted of a single species: Ravenala madagascariensis Sonn., which is grown everywhere in the tropics as an ornamental plant. The plant is immediately recognizable for its huge fan-forming banana-like leaves and is locally referred to in Magagascar by several vernacular names. "Variants" have been mentioned in the literature, but without any attempt to recognize formal taxa based on diagnostic features. In this paper, we formally describe five new species and fix the application of the name R. madagascariensis to the populations growing on the eastern coast of Madagascar, with the epitype growing in the marshy Fort-Dauphin area in the south. This paper has numerous implications for conservation biology and other domains of life sciences, due to the importance of this genus for the conservation of Madagascan ecosystems, the ornamental plant trade, as well as for its invasive status in several tropical areas

The Genus Sartidia (Poaceae:Aristidoideae) in Madagascar

The uncommon southern African and Malagasy genus Sartidia in the Aristidoideae, Poaceae resembles the closely related Aristida but has a C-3 photosynthetic system, 3-5-veined lower glumes, and a ventrally grooved caryopsis. We present a revision of Sartidia in Madagascar with two species. Sartidia isaloensis is described as new based on its interrupted inflorescence structure, small spikelets, and short awns. A leaf anatomical study and a delta C-13 analysis confirm that S. isaloensis is a C-3 species. Sartidia perrieri is likely extinct in the wild. We present descriptions, typification, illustrations, distribution maps, an identification key, and IUCN conservation assessments. A key to the Aristidoideae in Madagascar is also included

Grass diversification in Madagascar: In situ radiation of two large C 3 shade clades and support for a Miocene to Pliocene origin of C 4 grassy biomes

International audienc

Negative correlation between rates of molecular evolution and flowering cycles in temperate woody bamboos revealed by plastid phylogenomics

Abstract Background Heterogeneous rates of molecular evolution are universal across the tree of life, posing challenges for phylogenetic inference. The temperate woody bamboos (tribe Arundinarieae, Poaceae) are noted for their extremely slow molecular evolutionary rates, supposedly caused by their mysterious monocarpic reproduction. However, the correlation between substitution rates and flowering cycles has not been formally tested. Results Here we present 15 newly sequenced plastid genomes of temperate woody bamboos, including the first genomes ever sequenced from Madagascar representatives. A data matrix of 46 plastid genomes representing all 12 lineages of Arundinarieae was assembled for phylogenetic and molecular evolutionary analyses. We conducted phylogenetic analyses using different sequences (e.g., coding and noncoding) combined with different data partitioning schemes, revealing conflicting relationships involving internodes among several lineages. A great difference in branch lengths were observed among the major lineages, and topological inconsistency could be attributed to long-branch attraction (LBA). Using clock model-fitting by maximum likelihood and Bayesian approaches, we furthermore demonstrated extensive rate variation among these major lineages. Rate accelerations mainly occurred for the isolated lineages with limited species diversification, totaling 11 rate shifts during the tribe’s evolution. Using linear regression analysis, we found a negative correlation between rates of molecular evolution and flowering cycles for Arundinarieae, notwithstanding that the correlation maybe insignificant when taking the phylogenetic structure into account. Conclusions Using the temperate woody bamboos as an example, we found further evidence that rate heterogeneity is universal in plants, suggesting that this will pose a challenge for phylogenetic reconstruction of bamboos. The bamboos with longer flowering cycles tend to evolve more slowly than those with shorter flowering cycles, in accordance with a putative generation time effect

Late Miocene origin and recent population collapse of the Malagasy savanna olive tree (Noronhia lowryi)

International audienceDebates regarding the origin of tropical savannas have attempted to disentangle the role of human, biotic and abiotic factors. Understanding the origins of savanna remains essential to identifying processes that gave rise to habitat mosaics, particularly those found in the Central Plateau of Madagascar. Documenting the evolutionary history and demography of native trees occurring in open habitats may reveal footprints left by past and recent environmental changes. We conducted a population genetic analysis of an endangered Malagasy shrub (Noronhia lowryi, Oleaceae) of the Central Plateau. Seventy-seven individuals were sampled from three sites and genotyped at 14 nuclear and 24 chloroplast microsatellites. We found a highly contrasting nuclear and plastid genetic structure, suggesting that pollen-mediated gene flow allows panmixia, while seed-based dispersal may rarely exceed tens of metres. From a phylogeny based on full plastomes, we dated the surprisingly old crown age of maternal lineages back to ~6.2 Mya, perhaps co-occurring with the global expansion of savanna. In contrast, recent demographic history inferred from nuclear data shows a bottleneck signature ~350 generations ago, probably reflecting an environmental shift during the Late Pleistocene or the Holocene. Ancient in situ adaptation and recent demographic collapse of an endangered woody plant highlight the unique value and vulnerability of the Malagasy savannas

How ancient forest fragmentation and riparian connectivity generate high levels of genetic diversity in a microendemic Malagasy tree

International audienceUnderstanding landscape changes is central to predicting evolutionary trajectories and defining conservation practices. While human-driven deforestation is intense throughout Madagascar, exceptions in areas like the Loky-Manambato region (North) raise questions. Such regions also harbor a rich and endemic flora, whose evolutionary origin remains poorly understood. We assessed the genetic diversity of an endangered microendemic Malagasy olive species (Noronhia spinifolia Hong-Wa) to better understand the vegetation dynamic in the Loky-Manambato region and its influence on past evolutionary processes. We characterized 72 individuals sampled across eight forests through nuclear and mitochondrial restriction associated sequencing data (RADseq) and chloroplast microsatellites (cpSSR). Combined population and landscape genetics analyses indicate that N. spinifolia diversity is largely explained by the current forest cover, highlighting a long-standing habitat mosaic in the region. This sustains a major and long-term role of riparian corridors in maintaining connectivity across those antique mosaic-habitats, calling for the study of organismal interactions that promote gene flow