Systematics, ecology and phylogeographic significance of Olea europaea L. ssp maroccana (Greuter & Burdet) P. Vargas et al., a relictual olive tree in south-west Morocco

Within the genus Olea, the olive (Olea europaea. L.) possesses the largest geographic distribution, and several subspecies have been described. South- west Morocco harbours an endemic olive, O. europaea ssp. maroccana (Greuter & Burdet) P Vargas et al., located in the western part of the High Atlas ( mainly on the southern slope of the Idaou-Tanane massif) and in the western Anti Atlas. The existence and the taxonomic position of this tree have lon g remained uncertain, but the combination of several morphological traits i s unique. Nuclear and cytoplasmic DNA polymorphism also demonstrate that th is tree is a well-differentiated and relictual taxon, probably originating from an ancestral unit within tropical Africa. Our findings refute the opin ions of several authors who consider ssp. maroccana to be intermediate betw een the cultivated olive, (O. europaea ssp. europaea) and the Saharan olive (O. europaea ssp. laperrinei (Batt. & Trab.) Cif.). According to cpDNA and mtDNA analysis, the Moroccan olive and the Canarian olive (O. europaea ssp . guanchica P. Vargas et al.) are related and belong to the same sub-taxon. This biogeographical affinity is strongly supported by other recent phylog enetic studies. The long-term viability of ssp. maroccana is threatened by several factors: (1) limited distribution and reduced numbers of individual s within isolated populations, (2) fragmentation processes related to human and livestock pressures, and (3) putative gene flow between this taxon and the cultivated olive. In order to ensure the long-term survival of this en demic olive, a specific program of conservation should be implemented in th e near future. (C) 2001 The Linnean Society of London.