Arguably the most famous 50p, commemorating 250 years of the Royal Botanical Gardens in Kew, which is also a UNESCO World Heritage Site.  This is currently the most scarce 50p coin in circulation with mintage figures of just 210,000.
 
Obverse: Ian Rank-Broadley Portrait
Reverse: Depicting the Chinese Pagoda found at Kew Gardens encompassed by a leafy vine plant (designed by Christopher Le Brun).