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Biología de la Conservación de Vella pseudocytisus subsp. pauiAbstractVella pseudocytisus subsp. paui is a narrow endemic exclusively found in Aragon(Spain). This shrubby plant forms part of the steppe floristic element in Western MediterraneanBasin. The historical origin of this element is dated at the end of Miocene.Eventually, its range stretched out during glacial Quaternary periods. Closely relatedto this paleogeographic history, at present Vella pseudocytisus is subdivided in threesubspecies, producing a sparsely distributed range with few populations in Spain andNorth Africa.Some parts of the Iberian Peninsula, Anatolia and the Magreb contain the largestextension of Mediterranean steppes and the highest plant diversity for this habitat.Two complementary former habitats may have driven the speciation processes of thecurrent steppe flora. On the one hand, a desert environment closely related to the sub-Sahara region would have shaped a xerotermic floristic element. On the other hand,an inland, continental environment, related to the East Asian region with extremelydry winds and shadow rains phenomena, would contribute to a colder but droughtresistant floristic element.In addition, strong links between the steppe vegetation and the thorny cushionshaped vegetation found in Mediterranean mountains exist. Some examples of thisrelationship are showed for different plant families in this chapter. Woodiness andspinescence are secondary adaptive syndromes that can be found among these plantsgroups and especially in the genus Vella.Populations of Vella pseudocytisus subsp. paui are located along very specific andnarrow climatic gradients following Alframbra and Turia river basins around Teruelcity. The plant grows across hills on gypsum-marl soils taking part of a characteristicshrubby vegetation composed of both limestone and gypsum Mediterranean plants.In addition, some individuals are located in crevices and cliff shelves along some ravinesheavily eroded in the area. Finally, this shrub is able to colonize very recentlydeveloped sites such as road verges, talus slopes, old field lands and hedges amongcultivated fields.IntroducciónVella pseudocytisus subsp. paui (crujiente, arnachilla o cebollada, quepor esos nombres es conocida) es una planta esteparia, endémica aragonesa,que ha sido objeto de interés conservacionista desde que MenéndezAmor (1943) relacionara la especie con el elemento estepario glaciar, señalandosu precario estado de conservación. Posteriormente apareció en laprimera lista de flora amenazada elaborada por la UICN (Lucas y Synge,1978) a instancias de César Gómez Campo, experto en Crucíferas. Algomás tarde, este investigador resaltó la singularidad de los géneros de Crucíferasleñosas, arbustivas o subarbustivas, de los ambientes semiáridosde la península Ibérica y recombinó la nomenclatura del género (GómezCampo, 1981). Vella pseudocytisus forma parte del elemento florístico es-20 El contexto geobotánico