Revisión taxonómica y biogeográfica del género Acalypha l. (Euphorbiaceae) para la región del Océano Indico Occidental

• Autores: Iris Montero Muñoz
• Directores de la Tesis: José María Cardiel Sanz (dir. tes.), Geoffrey A. Levin (codir. tes.)
• Lectura: En la Universidad Autónoma de Madrid ( España ) en 2021
• Idioma: español
• Tribunal Calificador de la Tesis: Mauricio Velayos Riguez (presid.), Emma Ortúñez Rubio (secret.), Paul E. Berry (voc.)
• Programa de doctorado: Programa de Doctorado en Biología por la Universidad Autónoma de Madrid
• Enlaces
  • Tesis en acceso abierto en: Biblos-e Archivo
• Resumen

  • Acalypha, with around 500 species, is one of the most diverse genera of the Euphorbiaceae family (subfam. Acalyphoideae). Acalypha includes mainly trees and shrubs of pantropical distribution, although some herbs reach temperate regions. It inhabits a wide variety of habitats, from tropical humid forests to sub-desert areas, and from sea level up to 4,000 m. The greatest diversity of species occurs in tropical America, followed by the African continent. In the current classification, three subgenera are recognized: subgenus Acalypha, which includes 90% of the species, subgenus Linostachys, and the monotypic subgenus Androcephala, only known from Madagascar.

    The Western Indian Ocean Region (WIOR) includes Madagascar, the Comoros Islands, the Mascarene Islands, the Seychelles Archipelago, and the Scattered Islands. The geology of this region is complex; Madagascar and most of Seychelles islands were part of the Indian subcontinent until their separation during the Mesozoic, remaining isolated for 90 million years. Comoros, the Mascarenes, and the coral islands of Seychelles, have a much more recent volcanic origin. The dominant climate is tropical, with great contrasts, especially in Madagascar. The vegetation is very diverse; Madagascar has humid forests in the east, dry deciduous forests in the west, and spiny thickets in the south; in the north, there is a mixture of dry and humid forest formations; in addition, there is high mountain vegetation. In the surrounding islands, we find littoral vegetation, deciduous forests, evergreen forests of medium-altitude, ericoid vegetation, and some mangroves. WIOR is considered one of the main world hotspots. The WIOR, and especially Madagascar, has been the subject of extensive botanical exploration, from the mid-17th century, with the arrival of the first French settlers, to the present day. Currently, the Vahinala Project, led by the Missouri Botanical Garden, has registered c. 241,000 collections of vascular plants of Madagascar. In Madagascar, c. 13,000 species of vascular plants, 82% endemic, are estimated. Despite this richness, the threats to conservation of its flora and fauna are immense. Madagascar has lost 44% of its original forest cover due to slash and burn agriculture, mining, logging, and the proliferation of exotic species. The situation in the other islands is similar.

    Previous studies of Acalypha from the WIOR have been few. In the last revision of the genus for Madagascar, 23 species were recognized (Leandri, 1942). In Comoros, Mascarenes and Seychelles, 7, 2 and 3 species are respectively mentioned (Voeltzkow, 1919; Coode, 1979, and Hemsley, 1919).

    The aim of this work is to carry out a taxonomic and biogeographic revision of Acalypha of the WIOR, to know the existing species, their habitat and distribution, evolution, and conservation status. To achieve this objective, we studied Acalypha specimens from 38 herbaria and carried out an exhaustive nomenclatural revision. We examined 2,327 herbarium specimens, corresponding to 1,694 collections, from the WIOR, and we also reviewed many specimens from continental Africa. A comparative morphological study was carried out, as well as micromorphological analysis. We also georeferenced all the collections to make distribution maps, to analyze the diversity and endemicity, and to evaluate the conservation status of each species. A red list was developed according to IUCN criteria. For molecular phylogenetic analysis, we used 174 sequences of 104 Acalypha species worldwide. The molecular marker used was the ITS region. Phylogenetic inference was performed using different methods: Maximum Likelihood, Approximate Maximum Likelihood and Bayesian Inference.

    As a result, we recognize 48 species of Acalypha from WIOR, (41 native, and 7 introduced), and we consider 92 names as synonyms, 27 of them for the first time. We designate lectotypes for 41 names. Twelve species (25%) have been described as new to science; these are A. ankaranensis, A. baretiae, A. cardielii, A. ercillae, A. gillespieae, A. isaloensis, A. leandrii, A. levinii, A. mayottensis, A. nusbaumeri, A. rabesahalana, and A. tremula.

    The new species are supported by morphological and molecular data. We present original descriptions, illustrations and distribution maps of all species, and an identification key. Madagascar includes 39 species, Mascarene Islands 8, Comoros 7, Seychelles 4, and the Scattered Islands one. The endemicity of Acalypha in the WIOR approaches 100%; in Madagascar it is 94%, in the Mascarene and Seychelles 100%, and in the Comoros archipelago 50%. We also describe for the first time in Acalypha the presence of brachyblasts, perulate axillary buds, and pocket-shaped domatia. As micromorphological characters, we describe four types of epidermal crystals, and a great variety of epicuticular waxes.

    We confirmed the WIOR as the main center of diversity of Acalypha in the Paleotropics. The species of this region represent 10% of the total species of the genus, and 42% of the African species. The red list presented includes 23 species with any of the threat categories; we estimate that 22% of them could be extinct.

    Phylogenetic studies confirm Acalypha as monophyletic, and also support its African origin. The studies do not confirm clearly the classification into subgenera proposed by Pax & Hoffmann (1924); subgenus Acalypha is confirmed as monophyletic, but the results regarding the subgenera Linostachys and Androcephala are inconsistent in the different analyzes. The WIOR species of the subgenus Acalypha do not form a monophyletic group; they are placed into four clades highly supported in the three analyzes. The species placed in these clades have morphological affinities. These results support the existence of different dispersal events from continental Africa to Madagascar, and from Madagascar to the different archipelagos. Madagascar is the main area from which Acalypha colonized the rest of the islands, but our results indicate that there may have been a dispersal event between continental Africa and the archipelagos. Acalypha urophylla it is shown to be a complex of several species, and A. integrifolia and A. marginata are confirmed as distinct species. The phylogenetic results are limited, due to the difficulties that we had during the extraction and amplification of the DNA; therefore, some clades are not well resolved and their relationships vary in the different analyzes. We consider it necessary to expand the sampling and incorporate additional molecular markers.