Pelagophycus is a monotypic genus of kelp. It is found in deep waters off the west coast of central North America. The species Pelagophycus porra, also known as elk kelp, grows in temperatures of no higher than 60 °F (16 °C).

It grows in subtidal forests in the coastal waters off southern California and northwestern Baja California Peninsula, in waters of 20 metres (66 ft) to 90 metres (300 ft) deep, anchored by a holdfast in sedimentary or loose sediment bottoms.

Three ecotypes are recognized:

Pelagophycus giganteus

Pelagophycus porra

Pelagophycus intermedius

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