River plants etc. go missing (5)
I believe the answer is:
indus
'river' is the definition.
(Indian river)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for indus that I've seen before include "9 of Pakistan" , "River giving its name to an early civilisation" , "Main river of Pakistan" , "River rising in Tibet" , "Important river" .)