Recent advances in molecular phylogenetics and a series of important palaeobotanical discoveries have revolutionized our understanding of angiosperm diversification. Yet, the origin and early evolution of their most characteristic feature, the flower, remains poorly understood. In particular, the structure of the ancestral flower of all living angiosperms is still uncertain. Here we report model-based reconstructions for ancestral flowers at the deepest nodes in the phylogeny of angiosperms, using the largest data set of floral traits ever assembled. We reconstruct the ancestral angiosperm flower as bisexual and radially symmetric, with more than two whorls of three separate perianth organs each (undifferentiated tepals), more than two whorls of three separate stamens each, and more than five spirally arranged separate carpels. Although uncertainty remains for some of the characters, our reconstruction allows us to propose a new plausible scenario for the early diversification of flowers, leading to new testable hypotheses for future research on angiosperms.

Dombeya sevathianii, a new endemic species from Mauritius, is described and illustrated. Based on its morphology, D. sevathianii belongs to the section Assonia as defined by Arènes and is closely related to D. populnea, endemic to La Réunion and Mauritius. These affinities are confirmed by a previous molecular study. The morphological diagnostic features for D. sevathianii are the cupuliform and entire epicalyx, and the absence of staminodes within the androecium. Given its known restricted distribution and small population, the species should be considered Critically Endangered (CR) as per the Red List Criteria of the International Union for the Conservation of Nature.

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Abstract-Dombeya formosa (Malvaceae s. l. or Dombeyaceae), a new species endemic to La Réunion, is described and illustrated. The species is distinguishable by its ovate leaves with round or slightly cordate bases, round to lightly acute apices and glabrescent abaxial surfaces, subulate and persistent stipules, umbellate inflorescences, and acute apices of floral bracts. Dombeya formosa is morphologically close to Dombeya punctata Cav. but differs from it in having ovate leaves and acute apices on floral bracts. Dombeya formosa is also morphologically similar to D. ficulnea Baill. but can be distinguished from it by its persistent and subulate stipules as well as the glabrescent adaxial surface of its leaves. Our study, focusing on 16 quantitative floral characters, demonstrates that there is a clear morphological distinction between D. formosa, D. punctata, and D. ficulnea. In comparison to the other two species, Dombeya formosa possesses smaller flowers and additionally shows cryptic dioecy along with flower-size dimorphism between sexes. Amongst the Mascarene Dombeyoideae, it is the only species distributed up to an altitude of 2,100 m. The phylogenetic position of Dombeya formosa is consistent with the morphological features and locates the species within the clade endemic to La Réunion characterized by umbellate inflorescences.Keywords-Dioecy, Dombeyaceae, Dombeyoideae, phylogeny, taxonomy.Dombeya is one of the most species-rich genera (Judd et al. 2002) within Malvaceae s. l. with ca. 215 species, and most of its diversity is found in Madagascar (Skema and Dorr 2010). Dombeya also occurs in continental Africa (Seyani 1991) and in several oceanic archipelagos of the South West Indian Ocean biodiversity hotspot, such as the Mascarenes (Friedmann 1987, Le Péchon et al. 2009. The flora and fauna of this archipelago are characterized by high rates of endemism. Dombeya is one of the most striking examples with 14 species (20 taxa) strictly restricted to the archipelago, only one being indigenous and also present in Madagascar and Africa (Friedmann 1987;Le Péchon et al. 2011). This genus plays a structuring role for both the preservation and the function of the ecosystems on these islands, from lowland to tropical montane cloud forests and particularly in the tropical wet and cloud forests found on La Réunion (Cadet 1980;Blanchard 2000). Another notable feature for the Réunion Island Dombeya is the magnitude of variations for both vegetative and reproductive characters among and within the different species (Jacob de Cordemoy 1895;Friedmann 1987;Humeau et al. 1999aHumeau et al. , 2000. Polymorphism of morphological characters has led to a taxonomic conundrum because of the difficulties to draw boundaries between close taxa.Since the 18th century, several studies described the diversity of the Mascarene Dombeyoideae (Cavanilles 1787; De Candolle 1823; Lindley 1844; Baker 1877). The first global taxonomic treatment at the scale of the archipelago was included in La flore de l'île de La Réunion (Jacob de Cordemoy 18...

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