In May 1971, Robert Smithson planted a ring of mangrove seedlings approximately one hundred feet in diameter in a shallow lagoon on Summerland Key in the Florida Keys. Rather than constructing a permanent form, Smithson initiated a process of growth, allowing the work to develop through the interaction of plants, sediment, water, and time. Created during a period when Smithson was developing a number of island projects and proposals, Mangrove Ring reflects his interest in landscape formation and the capacity of mangroves to create new land. The work is known through a set of images Smithson took of the sculpture, a unique work in itself, a series of drawings, and Nancy Holt's film Mangrove Ring (1971).

Mangrove Ring belongs to a cluster of island proposals that occupied Robert Smithson around in the early 1970s, including Island Maze, Forking Island, and other speculative island schemes. Many remained drawings; Mangrove Ring was one of the few actually realized. In this ink on paper annotated drawing Mangrove Seedlings Planted in Shallow Lagoon, Summerland Key, Florida he maps out the artwork, showing its scale and location.