Plain and clear about German backing Congress (9)

I believe the answer is:

serengeti

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'plain' is the definition.
(I've seen this before)

I cannot understand how the rest of the clue works.

(Other definitions for serengeti that I've seen before include "region in Tanzania" , "Tanzanian plain renowned for its wildlife" , "area of Tanzania" , "Tiger seen in Tanzania's great National Park" , "place to watch game" .)

I've seen this clue in The Times and The Sunday Times.

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