Just found several orchid stamps hiding in my different collections.
International Stamp Exhibition, POLSKA 1973, issued by Hungary on May 11, 1973:
200th birth anniversary Charles Darwin, issued by GB on February 12, 2009:
The Millennium of Exploration - Charles Darwin, issued by Mongolia on October 5, 2000:
Vanda cathcari orchid, issued by Mozambique in 2011 to commemorate death centenary of the botanist Joseph Dalton Hooker, Charles Darwin's friend:
The orchid design taken from "Illustrations of Himalayan plants (1855)" by Walter Hood Fitch (1817-1892):