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There are over 28,000 cultivars of Rhododendron in the [ https://web.archive.org/web/20110426161301/http : // www.rhs.org.uk/Plants/RHS-Publications/Plant-registers/Rhododendron International Rhododendron Registry ] held by the Royal Horticultural Society .
 organization: Rhododendron; organization: Royal Horticultural Society
Please list all entity words in the text that fit the category.Output format is "type1: word1; type2: word2". 
Option: location, person, organization 
Text: {0} 
Answer:
 organization: Rhododendron; organization: Royal Horticultural Society