Grasses, by their high productivity even under very low pCO2, their ability to survive repeated burning and to tolerate long dry seasons, have transformed the terrestrial biomes in the Neogene and Quaternary. The expansion of grasslands at the cost of biodiverse forest biomes in Madagascar is often postulated as a consequence of the Holocene settlement of the island by humans. However, we show that the Malagasy grass flora has many indications of being ancient with a long local evolutionary history, much predating the Holocene arrival of humans. First, the level of endemism in the Madagascar grass flora is well above the global average for large islands. Second, a survey of many of the more diverse areas indicates that there is a very high spatial and ecological turnover in the grass flora, indicating a high degree of niche specialization. We also find some evidence that there are both recently disturbed and natural stable grasslands: phylogenetic community assembly indicates that recently severely disturbed grasslands are phylogenetically clustered, whereas more undisturbed grasslands tend to be phylogenetically more evenly distributed. From this evidence, it is likely that grass communities existed in Madagascar long before human arrival and so were determined by climate, natural grazing and other natural factors. Humans introduced zebu cattle farming and increased fire frequency, and may have triggered an expansion of the grasslands. Grasses probably played the same role in the modification of the Malagasy environments as elsewhere in the tropics.

Aim Grasses (Poaceae) are found in all major habitats of Madagascar and have a particular importance in C4 grasslands, whose origins are controversial. We aimed to estimate the number, age and origins of endemic grass lineages in the Madagascar region, and to compare the diversification of C3 and C4 taxa. Location Madagascar and the surrounding Indian Ocean islands, integrated within a global dataset. Methods We estimated 11 time‐calibrated molecular phylogenies including 73% of Madagascar's known grass flora (65% of endemics), using two calibration scenarios. Integrating the available sequences from worldwide grass species, a total of 1928 accessions were analysed. We tested range evolution models, estimated ancestral ranges, and compared the patterns of lineage accumulation between endemic C3 and C4 grasses. Results We recovered 69 lineages endemic to or with an estimated origin in the Madagascar region, 25 of them C3 and 44 C4. Range evolution analysis suggests widespread distance‐scaling of dispersal and strongest historical links to Africa. Extant grass diversity largely accumulated since the Miocene, with parallel increases in C3 and C4 taxa. Two large C3 groups in the “Forest shade clade” (Paniceae: Boivinellinae) and the bamboos (subtribe Hickeliinae) have an estimated origin in the Madagascar region. Divergences and crown ages of endemic C4 lineages largely coincide with the Miocene grassland expansion. Main conclusions Madagascar's extant grass flora is the result of multiple overseas dispersals, predominantly from Africa, and diversified from the Miocene onwards. C3 grasses are characterized by two large presumed in situ radiations of shade grasses in the Paniceae and bamboos. Endemic C4 lineages result from twice as many immigration events, resulting in smaller clades. Ages of C4 lineages are consistent with a Pliocene or Late Miocene origin of grasslands in Madagascar, but estimating the nature and expanse of such early grasslands will require further research.

BackgroundHeterogeneous 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.ResultsHere 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.ConclusionsUsing 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.Electronic supplementary materialThe online version of this article (10.1186/s12870-017-1199-8) contains supplementary material, which is available to authorized users.

Despite the substantial area covered by grasslands in Madagascar (65%), the taxonomy of the grasses (Poaceae), which represent the main plant component of these vegetation types, is still understudied. Inventories and detailed specimen identification work from 1 2 localities in the Itremo Massif Protected Area allowed us to compile a list of grasses present in the area. In total, members of eight subfamilies, 56 genera, and 99 species have been recorded from the Itremo Massif. Grasslands cover 75% of the Itremo Massif Protected Area and are dominated by Panicoideae (65%) and by C 4 plants. The genera Eragrostis and Panicum, with nine and eight species respectively, are the best represented genera in Itremo. Eragrostis betsileensis and Tristachya betsileensis are the two species known to be local endemics. Twenty species are endemic to the central highlands, and a further 1 4 species are restricted to Madagascar. Five ecological groups of grasses were identified in the Itremo Massif: shade species in gallery forests, open wet area species, fire grasses, anthropogenic disturbance associated grasses and rock-dwelling grasses. Grasslands of the Itremo Massif are likely to be at least partly natural as shown by their richness in terms of endemic and native grass species. Conservation of such grasslands is thus an important issue, not only for grasses but for all species that inhabit these open canopy habitats. RÉSUMÉMalgré la superficie importante occupée par les formations herbeuses de Madagascar (65%), la taxonomie des graminées (Poaceae) dominant ces écosystèmes reste mal connue. Les inventaires effectués dans 1 2 localités de l'Aire Protégée (AP) du

Six temperate woody bamboos (Arundinarieae, Bambusoideae) from Madagascar were described in the genus Arundinaria during the 1920s to 1960s. However, recent phylogenetic studies imply that Arundinaria is restricted to North America, and taxonomic affiliation of the Malagasy temperate woody bamboos remained ambiguous. In search of phylogenetic affinity of these bamboos, herbarium observation, fieldwork, and molecular phylogenetic analysis have been carried out. Four of them and one potential new species were sampled for molecular phylogenetic analyses in the context of the tribe Arundinarieae. Maximum likelihood and Bayesian analyses indicated that those species were closely related to Oldeania alpina distributed in continental Africa, but not Arundinaria, Bergbambos, Fargesia (including Sinarundinaria), Thamnocalamus, or Yushania, in which they were placed at one time or another. On the grounds of molecular phylogeny, morphology, and phytogeography, the Malagasy temperate woody bamboos should be treated as members of the genus Oldeania. Arundinaria humbertii and A. ambositrensis are conspecific. A new species, Oldeania itremoensis, is described and illustrated. The other two temperate woody bamboo species in Madagascar not sampled in the molecular phylogeny are also transferred to Oldeania on the basis of morphology.

Madagascar's fragile ecosystems are vulnerable to invasive plants but accounting for these in a poorly known and undercollected group is challenging due to an insufficient knowledge base. We record three species of grasses (Poaceae) new to Madagascar. Ehrharta stipoides Labill. is a potentially dangerous introduction due to its invasiveness in frequently burned ecosystems. Enteropogon prieurii (Kunth) Clayton is not recorded as invasive but is frequently misidentified due to its similarity to Chloris virgata Sw. The new record of Vulpia myuros (L.) C. C. Gmel. is from a collection made 50 years ago.