Author(s): Rita M. Lopez Laphitz (corresponding author) , Cecilia Ezcurra , Romina Vidal-Russell 
Identifying and delimiting species has always been a complex endeavor in systematics. The question of what defines a species is contentious, as evidenced by the existence of a large number of different species concepts (de Queiroz 2007). In systematics, being able to efficiently and accurately delimit species is basic because this taxonomic level is the fundamental study unit of different fields such as biogeography, ecology, and conservation. However, one of the major problems linked to species delimitation has been to distinguish between species concepts and species criteria (Wiens and Servedio 2000). One of the practical yet conservative strategies taken by many researchers has been to apply evidence from diverse sources to support the recognition of species. These include fixed or non-overlapping differences in morphological, behavioral, or ecological characters, molecular divergence, or geographic isolation. In this study, we recognize non-overlapping patterns of morphological variation as the primary criterion for inferring species boundaries. This is based on the idea that morphological discontinuities suggest that some evolutionary force may be preventing two distinct lineages from homogenizing (Stuessy 1990; Wiens and Servedio 2000). Morpho-species (Cronquist 1978) or pheno-species (Sokal and Sneath 1963) are those concepts that follow this basic criterion that has been applied in most of the morphological systematic studies (e.g. Lehnebach 2011; Lopez Laphitz et al. 2011; Nagahama et al. 2014). As posed by Wheeler and Meier (2000), even though a species definition may or may not make reference to characters (morphological or not), all concepts use character data to infer species boundaries, and most of those data are morphological. In this sense, we use the morpho-species criterion in an empirical example focusing on Quinchamalium Molina, a morphologically variable, geographically extended, and taxonomically understudied genus from southern South America.
Quinchamalium is a small genus of yellow-flowered hemiparasitic perennial herbs (Fig. 1
Fig. 1.: Morphological variation in plants of Quinchamalium . A. Bariloche, Argentina. B. Paposo, Chile. C. Portillo, Chile. D. Huasco, Chile. Photographs by C. Calviño and R. Vidal Russell.
) distributed throughout the Andes in open habitats across a wide elevational range (0-3,800 m a.s.l.). The genus was established by Molina in 1782 based on a specimen from Chile, and since then, 33 species names have been published within it. At present, Quinchamalium is thought to include approximately 21 species (Brako and Zarucchi 1993; Zuloaga et al. 2009; Jørgensen et al. 2014; Appendix 1), but the limits between these species are in many cases obscure (Dawson 1944). The genus is distributed from northern Peru to southern Chile, Argentina and Bolivia, covering a wide geographic area (Appendix 1). Despite this, the 21 accepted South American species mentioned before have not yet been treated in one single taxonomic study that includes them all. Consequently, no diagnostic key is available where the total number of recognized species of Quinchamalium are comparable. In the past, taxonomic treatments (Presl 1849; Philippi 1857; Miers 1880) included quantitative morphological traits related to flower and leaf morphology....