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Abstract
Alternanthera (Amaranthaceae) is a diverse genus largely restricted to the American Tropics that belongs to the alternantheroid clade containing C4 and C3–C4 intermediate species. This research focuses on the study of pollen characters by studying 13 species, representatives of the two major clades and subclades of Alternanthera. General palynological comparisons were conducted with light microscopy (LM), scanning electron microscopy (SEM) and with confocal laser scanning microscopy (CLSM) for exine ultrastructure. Twenty-five characters were measured and described for Alternanthera and among these, 14 pollen characters were used to discriminate pollen groups using cluster analysis and canonical analysis of principal coordinates (CAP). Pollen form and ornamentation, pores number, spines length, number of ektexinous bodies and nanospines on the ektexinous bodies on pore membranes, arrangement of nanopores and spines on structural elements, and metareticula form were taxonomically important and therefore used to construct the first palynological key to the alternantheroid clade species. Our study indicates that the seemingly subtle morphological variation of pollen is useful for recognising three main pollen types within Alternanthera. The much needed palynological terminology for describing the mesoporium in the metareticulate pollen of Amaranthaceae is provided.
Acknowledgements
The authors thank the directors and curators of the herbaria F, GB, MEXU, NY and S for allowing them to examine and sample flowers of loaned material. The authors also thank José Javier G. Quezada Euán (UADY, Yucatán, México) for the use of his laboratory during initial stages of this study; to María Goretti Campos Ríos (CICY, Yucatán, México) for scanning electron microscopy (SEM) images; to Luis Alonso Tellez for valuable help and assistance in the field and to Luciana Camacho for the beautiful design of the light microscopy (LM) and pollen diagrams. The authors thank Ángela Ku (CICY, Yucatán, México) and Jesús E. de A. Bojórquez-Quintal (CICY, Yucatán, México) for help with confocal laser scanning microscopy (CLSM). The authors also thank Jorge Montero (CINVESTAV, Yucatán, México) for discussions about pollen measurements. The authors also greatly appreciate Erick Aguilera-Cauich (CICY, Yucatán, México) and Rubén Andueza (Instituto Tecnológico de Conkal, Yucatán, México) for statistical help. The authors are indebted to Edlin Guerra-Castro (Centro de Ecología, Instituto Venezolano de Investigaciones Científicas, Caracas, Venezuela) and Juan José Cruz-Motta (Departamento de Estudios Ambientales, Universidad Simón Bolívar, Caracas, Venezuela) for help with statistical analyses using PRIMER6 and PERMANOVA.
Disclosure statement
No potential conflict of interest was reported by the authors.
Specimens investigated
Alternanthera caracasana Kunth. Mexico: Zacatecas. 22 September 2001. E.D. Enríquez et al. 3385 (MEXU); Mexico City. 17 September 2010. I. Sánchez-del Pino 121 (CICY); Peru: Cajamarca. 13 December 1987. I. Sánchez 4606 (F).
Alternanthera costaricensis Kuntze. Costa Rica: Province of Alajuela. 3 May 1931. A.M. Brenes 13671 (NY); Costa Rica: Province of Alajuela. 26 June 2000. R. McCauley 136 (MEXU); Panama: Colon. no date. B. Hammel 3976 (MEXU).
Alternanthera echinocephala (Hook. f.) Christoph. Ecuador: Galápagos. 26 May 1967. U. Eliasson & I. Eliasson 2238 (S); Ecuador: Galápagos. 24 June 1964. I.L. Wiggins 18322 (GB).
Alternanthera flava (L.) Mears. Mexico: San Luis Potosi to Tampico, Tamaulipas. December 1878–February 1979. E. Palmer 1146 (NY); Mexico: Veracruz. 10 February 2009. I. Sánchez-del Pino 118 (CICY); s.l. no date. Berlandier 2180 (MEXU).
Alternanthera flavescens Kunth. Mexico: Yucatán. 25 September 2010. I. Sánchez-del Pino 123 (CICY); Colombia: Cartagena. 4 November 1926. E.P. Killip & A.C. Smith 14114 (F); Brazil: Rio de Janeiro. 19 April 1979. M. Alice 25 & A.S. Leão 43 (NY).
Alternanthera galapagensis (Stewart) J. T. Howell. Ecuador: Galápagos. 5 December 1966. U. Eliasson & I. Eliasson 717 (S); Ecuador: Galápagos. 5 December 1966. U. Eliasson & I. Eliasson 726 (GB); Ecuador: Galápagos. 7 December 1966. U. Eliasson & Eliasson 750 (S).
Alternanthera geniculata Urb. Dominican Republic: San Rafael. 6 April 1969. A.H. Liogier 14711 (NY); Dominican Republic: Puerto Frances. 13 March 1969. A.H. Liogier 14395 (NY).
Alternanthera lanceolata (Benth.) Schinz. Mexico: Veracruz. 10 February 2009. I. Sánchez-del Pino 120 (CICY); Peru: Cajamarca. 20 July 1993. I. Sánchez 6544 (F).
Alternanthera macbridei Standl. Peru: Cajamarca. 26 May 1964. P.C. Hutchison & J.K. Wright 5381 (F); Peru: Cajamarca. 21 June 1980. A. Sagástegui et al. 9588 (NY).
Alternanthera littoralis var. maritima (Mart.) A. St.-Hil. United States: Florida. March. A.H. Curtiss 2386 (NY); Bahamas. 15 April 1904. C.F. Millspaugh 2353 (NY); Bahamas. 7 July 1974. D.S. Correll & J. Popenoe 42700 (NY).
Alternanthera obovata Millsp. Mexico: Veracruz. 10 February 2009. I. Sánchez-del Pino 117 (CICY); Mexico: San Luis Potosí. 30 March 1979. J.B. Alcorn 2593 (NY); Guatemala: Izabal. 28 May 1922. P.C. Standley 24639 (NY).
Alternanthera serpyllifolia Urb. Dominican Republic: San José. 9 May 1968. A.H. Liogier 11185 (NY); Dominican Republic: Bayacanes. 31 August 1968. A.H. Liogier 12444 (NY); Cuba: Galse. no date. E.L. Ekman 15705 (NY)
Alternanthera tenella Colla Mexico: Veracruz. 10 February 2009. I. Sánchez-del Pino 116 (CICY); United States: Virgin Island. 21 June 1989. P. Acevedo 2728 (NY); Brazil: Goiás. 23 June 1966. D.R. Hunt & J.F. Ramos 6168 (NY).