What is the capital city of the least populous nation where Himalayan Butterfly Bush grows?
Buddleja crispa: Buddleja crispa, sometimes called the Himalayan Butterfly Bush, is native to Afghanistan, Bhutan, North India, Nepal, Pakistan and China (Gansu, Sichuan, Xizang), where it grows on dry river beds, slopes with boulders, exposed cliffs, and in thickets, at elevations of 1400–4300 m. Bhutan: Bhutan ( ; འབྲུག་ཡུལ་ "druk yul "), officially the Kingdom of Bhutan (འབྲུག་རྒྱལ་ཁབ་ "druk gyal khap "), is a landlocked country in South Asia. Bhutan:  Bhutan is geopolitically in South Asia and is the region's second least populous nation after the Maldives. Bhutan:  Thimphu is its capital and largest city, while Phuntsholing is its financial center.
Thimphu