Mertensia maritima is a species of flowering plant in the borage family, and is known by the common names oyster leaf in North America, oyster plant in the British Isles, and sea bluebells.

It is restricted to gravelly sea shores, usually within reach of the highest winter tides in the Northern Hemisphere, reaching north to the northern parts of Canada, Greenland and Svalbard.

It is a perennial herb producing a stem approaching 50 centimeters in maximum length. The inflorescence forms a cluster of flowers which are first reddish, and later bright blue.

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