Allamanda blanchetii A.DC

Common name: Purple Allamanda
Shrubby plant with some climbing stems (scandent shrub) suckering from roots. It often forms a clump about 2 m tall and 2-3 m wide, but can grow much higher when climbing over other vegetation (up to 5 m in height). Stems and leaves with milky sap. Leaves sessile or subsessile, 8-12 cm long, in whorls of usually 4, oblong or obovate-oblong, abruptly acuminate; petioles up to 2 mm long; leaf blades broadly elliptic to orbicular, with trichomes on both surfaces. Flowers have 5 partially overlapping, rounded petals, of pink to reddish purple color, more intense in the throat. Opening from burgundy-brown buds, they stand out against the glossy, bright green leaves, 7-12 cm long, held in whorls of four. Calyx pubescent, corolla 6-9 cm long x 5-6 cm across at limb, rose-purple, darker in throat, tube not basally swollen. The fruits are globose and spiny follicles containing numerous flattened seeds equipped with a membranous wing.

References
1.http://www.flowersofindia.net/catalog/slides/Purple%20Allamanda.html
2.https://www.cabidigitallibrary.org/doi/full/10.1079/cabicompendium.25980468