May-flowering species in the Rhododendron species collection

Rhododendron hippophaeoides forms bushes up to 1.5 m tall with narrow leaves that are silvery-grey on the upper side and produces clusters of pale lavender-blue, relatively large flowers up to 2.5 cm wide. Found in the wild in Yunnan and Sichuan, usually in bogs at 2,400-4,800 m elevation.   

Small shrubs up to 50 cm (up to 1 m according to Flora of China) tall, both sides of the small, elliptic leaves dotted with scales, as are the central portions of calyx and mauve-pink petals. Grows at 3900–4300 m elevation in south-west Sichuan.    

Another low-growing up to 1 m (can reach 1.5 m according to Flora of China) mountain-top shrub, with dark green leaves, the pink-brown scales on undersides distinguishing it from many similar cultivars sold under the same name. Flowers are violet-blue. Distributed in the wild in Yunnan at 3,000-4,900 m.   

A variable species, upright to creeping, 30-90 (-150) cm tall, with fruity-aromatic leaves. The flowers are small, range in colour from white to pink, the corolla notably tubular at the base, containing the reproductive parts, with spreading lobes. Grows in the Himalayas from Nepal to Tibet and Sikkim at 3,000-5,000 m.  

Shrub up to 2 m tall, foliage and flowers dotted with scales, producing clusters of purple flowers with corolla lobes spreading from the base, up to 3 cm diameter, and darker markings on the dorsal lobes. Distribution in Bhutan, Sikkim and Tibet at 2,500-4,300 m elevation.  

An upright shrub growing to 1-3(-7) m height particularly notable for its robust, waxy, narrow bell-shaped, up to 5 cm long hanging flowers that vary in colour between subspecies and varieties from yellow through to red or purple. Native to forests from eastern Nepal to south-eastern Tibet at 1,900-4,000 m elevation.

Forms trees up to several (1-5) m tall, Rhododendron augustinii can be recognised by the hairs on the branches, the light green 12 by 5 cm leaves with hairs on the young midribs, and 5 cm broad lavender-blue flowers. From Hubei and Sichuan at 1,000-3,400 (-4,200) m elevation.  

A deciduous bush up to 4 m tall expanding by underground suckers. Yellow, scented flowers up to 5 cm in diameter are produced in June. Native to south-east Europe north into Poland.

Elegant deciduous shrub up to 2-3 m tall with characteristic regular branching pattern and leaves held in groups of 4-5 with red margins. Open, white bell-shaped flowers nestle amongst the foliage at the end of May. From Honshu, Japan.  

Shrubs up to 1 m tall with glaucous green leaves grow in bogs and wet forest margins in its native North America from Labrador south to New York State. Produces light to darker violet-pink (or white) flowers in May. 

Rhododendron hyperythrum forms dense up to 1.5 m tall shrubs with narrow, consistently rolled-in leaves (not caused by drought or cold), and large white flowers produced in May. Native to Taiwan at 900-1,200 m elevation.

Shrubs or small trees growing up to 2–8 m tall, distinguished by the flattened, winged petioles holding thickly leathery, broadly elliptic leaves. Striking inflorescences of up to 15 large, bell-shaped pink flowers produced in May. From Nanchuan, China at 1,800–2,200 m elevation.    

Endangered (EN): see conservation of threatened Rhododendron species at the University Gardens.