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Centro de Investigaciones Biológicas del Noreste (CIBNOR) 2014

Diversidad y sistemática del género Opuntia s.s., en la región de los Cabos, Baja California Sur, México

Mercado Muñoz, Fermín

Titre : Diversidad y sistemática del género Opuntia s.s., en la región de los Cabos, Baja California Sur, México

Auteur : Mercado Muñoz, Fermín

Etablissement de soutenance : Centro de Investigaciones Biológicas del Noroeste (CIBNOR)

Grade : Maestría en Ciencias en el Uso, Manejo y Preservación de los Recursos Naturales 2014

Résumé
The genus Opuntia is one of the most diverse and complex groups of the Cactaceae, characterized by having flattened stems (cladodes). Currently 93 species of wild prickly pears are recognized in México and are mainly distributed in arid regions, oak woodlands, grasslands and, dry tropical forests. Endemism is correlated with arid climates in México. The Sonora and Chihuahua deserts are especially relevant because they have numerous endemic and micro-endemic species. In the Baja California peninsula, the Cape Region has allowed the development of a large number of endemic species in different groups of plants ; within the Opuntia only three species are recognized to date : Opuntia lagunae, O. bravoana and O. tapona. However, field observations, made by the work team of the Botanical Laboratory of the Centro de Investigaciones Biologicas del Noroeste (CIBNOR), indicate the existence of several morphotypes that cannot be classified by existing keys. Therefore, the main objective of this research was to investigate species diversity for the genus Opuntia in that region. In the Cape Region, 17 nopal morphotypes were identified. Morphological and cytogenetic analyses were conducted to elucidate their taxonomic identity. The morphological analysis consisted of coding 69 morphological attributes to qualitative variables and compared with the cluster analysis to know the levels of similarity between the morphotypes. The cytogenetic techniques were applied to root tips for chromosome counts and karyotype analysis using different asymmetry indices. Morphotypes form two clusters, defined primarily by the presence or absence of recurved leaves in the areoles of pericarp, fruit consistency and growth form. The ploidy range found in Opuntia populations in the Cape Region ranged from diploid (2n=2x =22), triploid (2n=3x=33), tetraploid (2n=4x=44), pentaploid (2n=5x=55), hexaploid (6x=2n=66), and octaploid (2n=8x=88) ; chromosomes were mainly metacentric and submetacentric with minor differences in the size and morphology between morphotypes. These results indicate the existence of at least six new taxa for the genus Opuntia in this region. The greatest diversity of species for the Cape Region is in the deciduous forest and its confluence with the sarcocaule scrub and oak forest.

Mots Clés : Opuntia ; diversidad ; Región de los Cabos ; especies endémicas y microendémicas

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Page publiée le 14 juin 2015, mise à jour le 11 août 2017