Padmanabhan, P., Murch, S. J., Sullivan, J. A. and Saxena, P. K. 2014. Development of an efficient protocol for high frequency in vitro regeneration of a horticultural plant Primulina tamiana (B.L. Burtt) Mich. Möller & A. Webber. Can. J. Plant Sci. 94: 1281-1287. A rapid and efficient in vitro regeneration system was established for Primulina tamiana, an attractive ornamental plant of horticultural importance. The successful regeneration protocol employed induction of shoot organogenesis on leaf explants. Among the various plant growth regulators evaluated, thidiazuron (TDZ) proved to be the most effective in inducing rapid de novo shoot formation. The highest shoot regeneration frequency within the shortest time from leaf explants was obtained on medium enriched with 2.5 µM TDZ. Furthermore, leaf segments were found to be a more suitable explant for in vitro shoot regeneration compared with petiole explants. The abaxial side of the leaf segments, which was in contact with the culture medium, generated more shoots than the adaxial side. Scanning electron microscopic studies carried out at various stages of de novo shoot differentiation demonstrated that shoot organogenesis involved the formation of actively dividing regions from the epidermal and subepidermal layers of the explants. In vitro rooting of the regenerated shoots was attempted using two different auxins, IAA (3-indoleacetic acid) and 3-indolebutyric acid (IBA) (0, 0.1, 0.5, 1.0, 2.0, and 5.0 µM). The optimum concentration for root induction was found to be 5 µM IBA. Approximately, 98% of the regenerated plants survived transfer and acclimation to greenhouse conditions.