Keywords: 
• botany /
• Oncidium flexuosum /
• leaf /
• somatic embryogenesis

Abstract: Young leaves of Oncidium flexuosum Million Dollar were used as explants and cultured in a 1/2 Murashige and Skoog（MS） basic medium with three plant growth regulators for somatic embryogenesis induction. A 60 d in vitro culture in darkness of direct somatic embryogenesis for different leaf positions，seedling characteristics，and leaf size（leaf age） was studied along with the influence of different combinations and concentrations of thidiazuron （TDZ），6-benzyladenine （6-BA），and kinetin （KT） on direct somatic embryogenesis. Results after 60 d showed that leaf tips，adaxial sides，margins，cut ends，and cut central parts formed many somatic embryos and repetitive somatic embryos. From these somatic embryos，a number of protocorm-like-bodies eventually formed. The best leaf explant for somatic embryogenesis induction was a 15 mm leaf from seeding with roots. The best embryogenic responses were with 1/2 strength macro-and micro-elements of MS supplemented with 100.00 mgL-1 myo-inositol，0.50 mgL-1 niacin，0.50 mgL-1 pyridoxine HCl，0.10 mgL-1 thiamine HCl，2.00 mgL-1 glycine，170.00 mgL-1 NaH2PO4，13.90 mgL-1 FeSO47H2O，1 000.00 mgL-1 peptone，0.50 mgL-1 TDZ，250.00 mgL-1 polyvinyl-polypyrrolidone （PVPP），20 000.00 mgL-1 sucrose，and 2 800.0 mgL-1 GelriteTM at a pH of 5.2. Additionally，90% of the leaf explants induced somatic embryos，and 74.6% of the cut ends of leaves as well as 66.9% of the cut central parts of leaf explants induced somatic embryos.［Ch，4 fig. 17 ref.］