Historical biogeography of the Yucatan Peninsula, Mexico: a perspective from ferns (Monilophyta) and lycopods (Lycophyta) SANTIAGO RAMÍREZ-BARAHONA 1 , ANDRÉS TORRES-MIRANDA 1 , MÓNICA PALACIOS-RÍOS 2 and ISOLDA LUNA-VEGA 1 * 1 Departamento de Biología Evolutiva, Facultad de Ciencias UNAM, Ciudad Universitaria, Apartado postal 70-399, México 04510, Distrito Federal, México 2 Instituto de Ecología A. C., Apartado postal 63, Xalapa, Veracruz 91000, México Received 11 May 2009; accepted for publication 18 June 2009 Based on known data sets and maximum entropy distribution data of fern and lycopod species registered in the Yucatán Peninsula, track and parsimony analyses were undertaken to evaluate the contribution of these groups to the establishment of biogeographical relationships of the peninsula with other areas. The resulting generalized tracks clearly agree with the geological origin of the peninsula and the previously recognized relationship with the Greater Antilles is not supported for ferns and lycopods. Instead, a Central American generalized track connects the Yucatán Peninsula with south-eastern México and Central America. Floristically, the peninsula harbours 66 species of ferns and lycopods. Seven are registered for the first time in the Yucatán Peninsula and one is a new species for México. These species do not follow the latitudinal pattern expected if ecological factors, such as humidity and rainfall, were the most important in determining their distributions. Groups of areas recognized with parsimony analysis of endemicity could not be defined as provinces as a result of the lack of endemic species. Nevertheless, a regionalization scheme based on maximum entropy distribution data and supported by track analyses is proposed. Two separate districts are recognized within the Yucatán Peninsula: arid/dry Yucatán in the north and El Petén (humid) in the south. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 775–786. ADDITIONAL KEYWORDS: floristics – grid-cell analysis – maximum entropy modelling – parsimony analysis of endemicity – regionalization – track analysis. INTRODUCTION From a biogeographical viewpoint, the Yucatán Pen- insula may be broadly defined as a province compris- ing the entire territory of the Mexican states of Campeche, Quintana Roo, and Yucatán; adjacent por- tions of Tabasco and Chiapas; the El Petén depart- ment in Guatemala; and the northern half of Belize (Fig. 1) (Lundell, 1934; Miranda, 1958; Morrone, 2006). Accepting small differences in its delimitations (Barrera, 1964); Estrada-Loera, 1991); Espadas- Manrique, Durán & Argáez, 2003)), the peninsula is well accepted as a distinct biological province. The ‘core’ of the Yucatán Peninsula (sensu Ibarra-Manríquez et al., 2002), entirely comprises the Mexican states of Campeche, Quintana Roo, and Yucatán. This area consists of an unconfined flat lying karst landscape, which is recognized as being quite different from the rest of México in terms of geogra- phy, geology, diversity, and biota richness (Lundell, 1934; Smith, 1940; Goldman & Moore, 1946; Miranda, 1958; Barrera, 1964; Rzedowski, 1978; Estrada-Loera, 1991; Ferrusquía-Villafranca, 1993; Morrone, 2006), consequently, highlighting the need for the conserva- tion of this diverse and unique region (Spellerberg & Sawyer, 1999). The region is devoid of surface water and is undergoing rapid change, which has increased concerns with respect to conservation and fresh water *Corresponding author. E-mail: ilv@hp.fciencias.unam.mx Biological Journal of the Linnean Society, 2009, 98, 775–786. With 6 figures © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 775–786 775