Laminariales

(botany) An order of brown, large, structurally complicated, often highly differentiated members, commonly called kelps, of the algal class Phaeophyceae; distinctive features include a life history in which microscopic, filamentous, dioecious gametophytes alternate with a massive, parenchymatous sporophyte, and a mature sporophyte typically consisting of a holdfast, stipe, and one or more blades.

An order of large brown algae (Phaeophyceae) commonly called kelps. Four families are recognized: Chordaceae, Laminariaceae, Alariaceae, and Lessoniaceae. Definitive features include a life history in which microscopic, filamentous, dioecious gametophytes alternate with a massive, parenchymatous sporophyte; growth of the sporophyte effected by meristems; and production of unilocular zoosporangia in extensive sori on blades of the sporophyte. See also Phaeophyceae.

A mature sporophyte consists typically of a holdfast, stipe, and one or more blades. The holdfast usually comprises a cluster of rootlike structures (haptera); in a few species it is discoid or conical. The stipe, which varies in length from a few millimeters in Hedophyllum to more than 100 ft (30 m) in Macrocystis (giant kelp), may be branched or unbranched and may bear one or more blades.

Kelps are largely confined to cold waters of both hemispheres, displaying a peak of diversity, abundance, and luxuriance all around the North Pacific. Only Lessonia and Ecklonia (both Lessoniaceae) are characteristic of the Southern Hemisphere, but Macrocystis is bipolar, occurring abundantly in subantarctic waters. Kelps are lacking in Antarctica, where their ecological niche is filled by members of the brown algal family Desmarestiaceae. Some kelps are found in the intertidal zone, usually on rocks exposed to heavy waves, but most are subtidal.

The principal use of kelps is in the alginate industry. Various kelps are used extensively for human food in Japan. In China Laminaria japonica has been established as an important maricultural crop plant. Ecologically, such kelps as Macrocystis and Nereocystis are particularly important because they form protective canopies harboring special communities of smaller seaweeds, invertebrates, fishes, and the sea otter. See also Algae; Alginate.