Abstract
Interspecific hybridization is a major mechanism for generating evolutionary novelty in plants. Halophytic Spartina species are often abundant in coastal salt marshes around the world, and they frequently hybridize. Despite a large body of knowledge on the ecology and evolution of Spartina species, taxonomic resources for distinction of complex taxa in the genus are scarce. The general aim of this study was to characterize parental species S. maritima (native) and S. densiflora (invasive) and their reciprocal hybrids formed in the Gulf of Cadiz (Southwest Iberian Peninsula). Our approach was to quantify and compare morphological and anatomical characters of tufts, culms, leaves and inflorescences and the limits of their variation in different ecological settings. Our results document discriminating trait variables from populations of both hybrids that can be used to distinguish them from their parental species and each other. From these findings and the verification of type specimens, we describe two new nothotaxa, Spartina × onubensis subsp. onubensis and Spartina × onubensis subsp. tartessiana, and develop taxonomic keys for identification of the four studied taxa. Floral traits such as the length of the terminal spike, the spikelet and its glumes and lemma allow us to differentiate S. densiflora (with lower values) from the other three taxa. The presence of exerted stamens, shorter culms and shorter leaf blades separated S. maritima from both hybrids. Each hybrid can also be distinguished since S. × onubensis subsp. onubensis develops more spikes per inflorescence and consistently has longer leaves than S. × onubensis subsp. tartessiana.
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Acknowledgements
Blanca Gallego-Tévar thanks the University of Seville for a research contract (Plan Propio de Investigación). M.D. Infante-Izquierdo acknowledges to Ministerio de Educación, Cultura y Deporte, Spanish Government, for the FPU Grant (Ref. FPU14/06556). F. Muñoz-Rodríguez thanks Ministerio de Economía, Industria y Competitividad of Spanish Government for the research project CGL2017-85204-C3-3-P. The authors thank the Directorate of the Tinto, Odiel, Piedra and Guadiana Natural Parks for supporting field work conducted in this study. A cooperative agreement between the United State Department of Agriculture, Agricultural Research Service (USDA-ARS) Invasive Species and Pollinator Health Research Unit and the University of Seville facilitated this collaboration.
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Online resource 1. Phenotypic inheritance for 32 plant morphological and anatomical characters of the reciprocal hybrids between native Spartina maritima and invasive S. densiflora.
Online resource 2. Analyses of sediment samples from the microenvironments supporting native S. maritima, invasive S. densiflora and its reciprocal hybrids in the Gulf of Cadiz (Southwest Iberian Peninsula).
Online resource 3. Holotype of Spartina × onubensis subsp. onubensis.
Online resource 4. Holotype of Spartina × onubensis subsp. tartessiana.
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Infante-Izquierdo, M.D., Gallego-Tévar, B., Sánchez-Gullón, E. et al. Morphological and anatomical evidence supports differentiation of new interspecific hybrids from native Spartina maritima and invasive S. densiflora (Poaceae, subfamily Chloridoideae). Plant Syst Evol 305, 531–547 (2019). https://doi.org/10.1007/s00606-019-01591-5
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DOI: https://doi.org/10.1007/s00606-019-01591-5