Date palm as a keystone species in Baja California peninsula, Mexico oases

•Date palms were introduced to the Baja California peninsula oases by Jesuit missionaries.•The palms readily naturalized, and form part of unique species guilds in the oases.•Date palms play a role of an ecological keystone species.•Date palms also serve as cultural keystone species in the oasis villages.

Based on historical records, Jesuit missionaries were the first to introduce date palm (Phoenix dactylifera L., Arecacea) to the mission oases of the Mexican Baja California peninsula. Seedling date palms readily naturalized and have partially, and in some cases almost entirely replaced the native fan palm, Washingtonia filifera and Washingtonia robusta in the oases. These wild and introduced palms form the over-story for smaller cultivated trees, shrubs, and open gardens of mixed perennial and annual cultivars in complex agro-ecosystems. They also grow in dense stands along the oases arroyos where they may be “owned” by various oasis residents and semi- to carefully managed, or comprise wild populations beyond the periphery of the oasis settlements. These palms serve as ecological and cultural keystone species, altering oasis microclimates and providing shade for understory crops, shelter and food resources for resident and migratory fauna, and building materials and food for oasis human residents. I explore the agro-ecological role of the date palm in Baja California peninsula oases.