Linden trees (Tilia spp.) are ornamental plants used in parks, gardens, and urban green spaces. This research was carried out with the aim of dormancy breakage and seed germination improvement in mature and immature seeds of T. rubra subsp. caucasica f. angulata Rupr. collected from middle altitude (500 m) and high altitude (1500 m) of Hyrcanian forests, north of Iran. In 1st experiment, mature and immature seeds with pericarp were followed by 1) cold stratification (CS) without pretreatment, 2) imbibed with 30% NaOH + CS. Also, the mature and immature seeds without pericarp were imbibided in 1) Gibberelic acid (GA₃) + CS, 2) kinetin (KN) + CS.
The highest seed germination belonged to mature seeds without pericarp imbibed with GA₃ or KN as well as to immature seeds with pericarp, cold stratified. The highest germination speed (%) allocated to immature seeds with pericarp, cold stratified, and the maximum mean germination time belonged to mature seeds without pericarp, imbibed with GA₃. In 2nd experiment, treatments were used the same as in the 1st experiment. The highest germination (%) allocated to seeds without pericarp of high altitude, treated respectively with GA₃ + CS,
and KN + CS. The highest germination speed (%) belonged to seeds with pericarp collected from middle altitude, treated respectively with CS and imbibed with GA₃ + CS. The greatest mean germination time allocated to seeds without pericarp of high altitude, treated respectively with CS and imbibed with KA + CS. Generally, in the case of access only to seeds originating from middle altitude, it is better to expose immature seeds with pericarp to CS. If seeds of both middle and high altitudes are sufficient, it is advisable to imbibe immature, seeds without pericarp of high altitude with GA₃ or KN followed by CS.