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The olivine macrocrysts found in oceanites, picrites and magnesian basalts erupted at hotspot volcanoes are generally interpreted either as phenocrysts crystallized from the magma or as xenocrysts extracted from a deforming cumulate. To constrain the origin of these crystals we studied their texture and composition at Piton de la Fournaise volcano, La Réunion. We show that macrocrysts are organized and subdivided into parallel units; this suggests a crystallization by dendritic growth and ripening rather than by a complex combination of paired nucleation, crystal aggregation or synneusis. Dendritic growth is also evidenced by the occurrence of hollow faces, P-rich zones, melt and Cr-spinel inclusions formed from the accumulation of slow diffusing impurities (P, Cr, Al) in the liquid at the contact with rapid-growing olivine. We suggest that early dendritic crystallization may even cause branch misorientations …