A natural hybrid, an autopolyploid, or a new species? An integrative case study of a distinctive Costus species (Costaceae) from the Atlantic Forest of Brazil

Abstract

Sixteen species of Costus s.s. are cited to Brazil, all of which can be found in the Brazilian Amazon, while only three also grow in the Atlantic Forest: C. arabicus, C. scaber, and C. spiralis. Studies of the genus from the Brazilian Atlantic Forest evidenced a distinctive fourth taxon, similar overall to C. spiralis, which is an ornithophilous species, however the flower morphology of this new taxon indicates it to be melittophilous. Hybridization and polyploidy (allopolyploidy or autopolyploidy) may play a role as an important source for evolutionary events, especially in recent speciose lineages such as Neotropical Costus. Here we investigated the evolutionary origin of this interesting Costus species using an integrative approach. This approach comprised a morphological analysis, cytogenetic analyses (chromosome counts, CMA/DAPI staining, and fluorescent in situ hybridization), genome size estimations, and a molecular phylogenetic reconstruction (using the plastid regions rps16 and trnL-F, and the nuclear ITS and ETS), aiming to answer the following questions: is it a hybrid?; is it an autopolyploid of C. spiralis?; or, if it is a different species, is it even phylogenetically related to C. spiralis or C. arabicus? The studies performed did not indicate any evidence of polyploidy, however, a chromosomal polymorphism was observed between the populations of the taxon studied. The phylogenetic position of this peculiar taxon with C. erythrophyllus, C. spiralis, and C. varzearum also excludes the putative partial heritage of C. arabicus which had been previously hypothesized. Our results confirm that it is a new, undescribed species, which is confirmed by our morphological observations of floral features. A complete taxonomic treatment of the new species is provided, including a key for the species of the genus in the Atlantic Forest.

Key words:

• Cytogenetics
• integrative taxonomy
• phylogeny
• pollination syndrome
• Zingiberales

Acknowledgements

We are indebted to those who funded our field research, including the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Fundação de Amparo à Ciência e Tecnologia de Pernambuco (FACEPE), and the U.S. National Science Foundation. The authors thank Regina Carvalho for the line drawing and Scott Heald for his review of the English of the manuscript.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Supplemental data

Supplemental material for this article can be accessed here: http://dx.doi.org/10.1080/14772000.2020.1729890.

Associate Editor: Oscar Pérez Escobar

Additional information

Funding

This work was supported by the Conselho Nacional de Desenvolvimento Científico e Tecnológico and the U.S. National Science Foundation under Grant number DEB-0946618; and by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brasil (CAPES) – Finance Code 001.