How to tell yellow oleander (Allamanda) and yellow oleander (Thevetia) apart?

Allamanda neriifolia and Thevetia peruviana belong respectively to the genera Allamanda and Thevetia in the family Apocynaceae. The two are similar in form and are often confused. Here they are distinguished from three aspects: leaves, flowers and fruit.

Leaves: Allamanda neriifolia has leaves in whorls of 3 to 5, elliptical or ovate-oblong, 6 to 12 cm long, with acuminate tips and cuneate bases; Thevetia peruviana has alternate leaves, linear-lanceolate, 10 to 15 cm long, long-tapered at both ends, flowering from May to August.

Flowers: Allamanda neriifolia has terminal inflorescences and an orange-yellow corolla; Thevetia peruviana has cymose terminal inflorescences, with large, yellow, fragrant flowers, flowering from May to December.

Fruit: The fruit of Allamanda neriifolia is a capsule, spherical, with long spines; the fruit of Thevetia peruviana is a drupe, flatly triangular-spherical.

Distinguishing Rosa xanthina and Rosa primula

Rosa xanthina and Rosa primula are both deciduous shrubs in the genus Rosa of the family Rosaceae, and both are spring-blooming ornamental shrubs. The two can be distinguished by the following points.

Plant form: Rosa xanthina is a clumping shrub; Rosa primula is an upright shrub.

Branches: Rosa xanthina has hard, straight prickles on the branchlets; Rosa primula has broad, flat, straight prickles on the branchlets.

Leaves: Rosa xanthina has 7 to 13 leaflets, broadly ovate to nearly round, 0.8 to 1.5 cm long, with bluntly serrate margins, slightly pubescent on the underside when young, without glandular dots; Rosa primula has 9 to 15 leaflets, elliptical to obovate, 0.6 to 2 cm long, with finely pointed, gland-tipped biserrate margins, hairless on both sides, with glandular dots on the underside.

Flowers: Rosa xanthina has solitary, yellow flowers; Rosa primula has pale yellow to white flowers.

Fruit: The fruit of Rosa xanthina is reddish-brown; the fruit of Rosa primula is dark red.