Plant Tissue Culture Strategies for Sustainable Conservation of Zanthoxylum Zanthoxyloides (Lam) Zepern & Timler in Nigeria: A Systematic Review

Zanthoxylum zanthoxyloides (Lam.) Zepern. & Timler (Rutaceae), commonly known as the African prickly ash or Senegal prickly ash, is one of the most ethnobotanically and pharmacologically important medicinal trees of sub-Saharan Africa. In Nigeria, it is used in various areas of therapy, including antimicrobial, analgesic, antipyretic, and anticancer applications, and forms part of the primary healthcare of many traditional communities. Although the species has significant socioeconomic and ecological importance, its populations are declining at an accelerating rate due to uncontrolled harvesting, substantial habitat fragmentation, forest clearance, and the recalcitrant nature of its seeds, which renders conventional ex situ seed banking largely ineffective. Plant tissue culture (PTC) provides a scientifically sound, scalable, and cost-effective platform to overcome these conservation deficits. This review systematically assesses the entire range of in vitro methods applicable to the conservation of Z. zanthoxyloides, including seed sterilisation and germination stimulation, callus induction and organogenesis, somatic embryogenesis, micropropagation via axillary shoot proliferation, synthetic seed technology, and cryopreservation—with specific reference to vitrification and encapsulation-dehydration protocols. The review critically evaluates published literature on the genus Zanthoxylum and the broader family Rutaceae, identifies important species-specific knowledge gaps, examines the infrastructural and regulatory environment for implementation in Nigeria, and proposes a prioritised ten-year research agenda. It is argued that long-term conservation of this species requires the integration of in vitro procedures with molecular characterisation, community engagement, and enabling policy reform—an approach that is both scientifically feasible and a national imperative.