![]() The flowers are pendant or rarely erect, pentamerous, succulent erect and appressed sepals sometimes surpassing the corolla, petals usually connate at the base, variously colored (white, greenish or reddish, or with maculae at the apex), with ten free stamens alternate or epipetalous and five nectaries. Plants are characterized by a rock-dwelling habit, the leaves are terete, greenish or purple, sometimes conspicuously glaucous-farinose, the inflorescence is axillar, a scorpioid cyme or cincinnus, with somewhat imbricate succulent bracts. Species grow in xerophytic scrub or less commonly in oak forest, and on vertical rock cliffs. Most of the species in this genus have been described from a single locality ( von Poellnitz 1937, Moran 1989, 1991, Brachet et al. Pachyphytum Link, Klotzsch & Otto is another genus in Crassulaceae mostly endemic to central Mexico comprising 19 described species, with a distribution centered on the Mexican Plateau, extending from southern Tamaulipas to northern Michoacán ( von Poellnitz 1937, Moran 1963, 1989, 1991, García-Ruiz et al. Jacobsen, and Thompsonella Britton & Rose ( Carrillo-Reyes et al. However, most of the series are poly- or paraphyletic according to recent phylogenies, retrieved in clades embedded with species from Cremnophila Rose, Graptopetalum Rose, Sedum L. The main traits used to recognize the 17 series are type of pubescence on the aerial stems, type of inflorescences and shape and length of the corolla ( Walther 1972). Flowers have mostly expanded succulent erect sepals, and bright colored succulent petals connate at the base ( Kimnach 2003). Plants of Echeveria have leaves arranged in rosettes, with variable type of inflorescence (lateral spike, raceme, cyme, scorpioid cyme or cincinnus, thyrsoid). In the last 50 years, the circumscription of Echeveria has remained unchanged and is divided into 17 series based on morphological and chromosomal evidence ( Walther 1972, Kimnach 2003, Pilbeam 2008). Berger (1930) considered Thompsonella and Dudleya Britton & Rose to be part of Echeveria, yet both genera were reestablished later ( Clausen 1940, Moran 1951). ![]() Oliveranthus Rose and Urbinia Rose were two taxa segregated at the beginning of the last century ( Britton & Rose 1903), however these genera were not approved by taxonomists. Since then, Echeveria has undergone few changes. It was split from Cotyledon by De Candolle in 1828 by including all New World species that have a lateral inflorescence. is a genus in the Crassulaceae comprising approximately 140 species distributed in the New World, from Texas to Argentina with the highest diversity in the mountainous areas of southern Mexico ( Moran 1967, Walther 1935, 1972, Kimnach 2003).
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