In Buddhism, udonge (優曇華) (uḍumbara in Hindi) is a plant said to bloom only once in three thousand years. Due to this, in China and Japan it is used as a word for an auspicious sign, a good omen, or a rare and fabulous thing. In The Tale of the Bamboo Cutter, the Jeweled Branch of Hourai was called udonge.
"Udonge" can also refer to the plantain flower or to the eggs of the lacewing insect (which resemble a flower).
Udonge in Touhou
Udonge, apart from the varieties mentioned above, is also a type of tree which grows in the Lunar Capital. While normally barren, in the presence of impurity it sprouts beautiful seven-coloured jewels, allowing it to act as a early-warning system.
The Jeweled Branch of Hourai is the branch of an udonge which has been brought to Earth; the Lunarians use these to sow conflict on Earth, since its beauty will grow in accordance to the impurity of its holder who will then take it as a sign of their authority.
Kaguya Houraisan owns a bonsai udonge, as well as a Jeweled Branch which was already in her possession. The bonsai remained unbloomed until the spell of eternity over Eientei was lifted following the events of Imperishable Night.