Ectocarpales is a very large order

Order (biology)

In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 in the brown algae

Brown algae

The Phaeophyceae or brown algae , is a large group of mostly marine multicellular algae, including many seaweeds of colder Northern Hemisphere waters. They play an important role in marine environments, both as food and for the habitats they form...

 (class Phaeophyceae). The order includes families with pseudoparenchymatous (Splachnidiaceae) or true parenchymatous (Scytosiphonaceae) tissue. Pseudoparenchymatous refers to a filamentous alga with cells packed very close together to give an appearance of parenchymatous tissue, the latter being composed of cells which can truly divide in three dimensions, unusual among the algae

Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

. Filamentous algae are composed of cells that divide along a single plane, allowing only elongation to form filaments of one or more rows of cells. Algae that can divide in two planes can form sheet-like thalli

Thallus (tissue)

Thallus, from Latinized Greek θαλλός , meaning a green shoot or twig, is the undifferentiated vegetative tissue of some organisms in diverse groups such as algae, fungus, some liverworts, lichens, and the Myxogastria. Many of these organisms were previously known as the thallophytes, a polyphyletic...

 or bodies. Cells that can divide in a third plane potentially allow for the organism to develop a more complex body plan, and diversification of body plans into an erect thallus of some sort and a holdfast for attaching the upright portion to the substrate.

AlgaeBase uses the following families for this order:

• Acinetosporaceae Hamel ex J Feldmann
• Adenocystaceae F Rousseau, B de Reviers, M-C Leclerc, A Asensi, and R Delépine
• Chordariaceae Greville
• Chordariopsidaceae Kylin
• Ectocarpaceae C Agardh
• Mesosporaceae
• Myrionemataceae Nägeli
• Pylaiellaceae

AlgaeBase places Ralfsiaceae in its own order, the Ralfsiales

Ralfsiales

Ralfsiales is an order of crustose brown algae containing two families.-External links:...

, and Splachnidiaceae in the Scytothamnales

Scytothamnales

Scytothamnales is an order of brown algae ....

.