Rhododendron thomsonii – This species forms a large shrub to small tree with deep blood red pendulous, bell-shaped blooms that emerge from April to May. This native of Nepal and Bhutan eventually develops peeling red bark on older specimens. R. thomsonii has deep green rounded foliage and prefers open woodland. Grows 6′ high in 10 years. Zone 7.
Rhododendron moupinense – A real beauty from western China with fragrant white flushed pink blooms (with rosy-purple spots in the throat) from February to April. The 1.5″ long leaves emerge a bronze-red in spring and it is best positioned in part sun. This is the parent of such cultivars as ‘Olive’, ‘Bo-Peep’ and ‘Pink Snowflakes’. Grows 3′ tall and wide. Zone 7.
Rhododendron niveum – An RHS Award of Garden Merit winner with unusual smokey-purple to mauve-purple blooms held in erect trusses of 15 to 20 flowers from April to May. This native of India and Bhutan has dark green leaves with white to pale brown indumentum on the reverse. R. niveum is best placed in part sun and grows 4-5′ tall in 10 years. Zone 7.
Rhododendron calophytum – Another very large species that eventually forms a big shrub or small tree. This Award of Garden Merit winner from southwest China and Tibet bears white to pale pink bell-shaped blooms with maroon spots in early spring. It also has huge green leaves that reach 12″ long by 3″ wide. Grows to 30′ tall (shorter in cultivation). Zone 6.
Rhododendron lutescens – A highly attractive species from southwest China with primrose yellow flowers (1.5 to 2″ across with green spots and protruding stamens) held in showy trusses of 3 to 6 individual blooms from March to April. The new growth is bronzed, turning a matte green at maturity. It prefers part to full sun and grows 7-15′ high. Zone 7.