The mark, Chu xiu gong zhi, may be translated, 'Made for the Chuxiu Palace' or the 'Palace of Assembled Elegance'.
A blue and white dish of this same pattern and large size bearing the same unusual seal mark, and another of larger size (64cm.) with the additional yellow glaze are illustrated by G. Avitabile, From the Dragon's Treasure, London, 1987, nos. 157 and 156 respectively. The author speculates on p. 109 that they were 'made on the occasion of the 50th anniversary of Cixi (1884),' 'probably for the renovated palace.'