The group of Ochrophytes (Ochrophyta), owes its name to the ochre shade of most of the species of this phylum. Ochrophytes are an extremely diverse group of algae, in which we will find species as disparate as diatoms or brown algae among others.

They are characterized by the presence of chlorophylls a, c1, c2, c3, β-carotene and xanthophylls, the majority pigment being β-carotene, and therefore its coloration. As a reserve substance, they mainly use chrysolaminarine. Despite the fact that photoautotrophy is the majority, that is, they obtain the organic compounds through photosynthesis, there are heterotrophic species in which they obtain the organic compounds through the phagocytosis of other organisms.

We can classify the ochrophytes in the following classes:

  • Phaeophyceae, or brown algae or Pheophytes, owe their coloration to a high amount of fucoxanthin in their chloroplasts. The shades of this group of algae range from olive green to brown, depending on the amount of fucoxanthin present in their chloroplasts. They use laminarine as a reserve substance. They are exclusively multicellular algae, with a cell wall formed by alginate and cellulose. We will find them almost exclusively in marine habitat, except for the genera Heibaudiella, Pleurocladia, Bodanella and Sphacelaria. A total of about 2,000 species are known, organized in 265 different genera. The Pheophytes present a wide variety in terms of size and shape of the species. They are the largest and fastest growing seaweeds (Macrocystis laminae can grow up to 50 cm per day, while stipe can grow up to 6 cm per day). They live mostly on the rocky coasts of temperate or subpolar waters, dominating the intertidal zone, although there are also species of free floating life, such as Sargassum bacciferum, which forms extensive floating formations, giving its name to the Sargasso Sea.

  • Chrysophyceae, predominantly single-celled freshwater individuals of low hardness (low calcium concentration). They have two flagellums located perpendicularly between them. Their chloroplasts have chlorophylls a, c1 and c2. Those species covered by siliceous scales, these adopt a radial conformation. The genera with cocoid and filamentous species are mainly located in cold water springs or streams, where they grow forming gelatinous masses both in rocks and wood. The vast majority are sensitive to changes in the environment. When these changes occur they form stomatocysts, a kind of spores, covered by a wall of silica.

  • Synurophyceae, unicellular or colonial algae, related to the Chrysophyceae. They are characterized by having two scourges, both parallel to each other. Another characteristic is the presence of silica scales, which are attached to each other. Their chloroplasts have chlorophyll a and c1. They form an important component of biomass in freshwater environments and are able to thrive in lakes with acidic pH.

  • Eustigmatophyceae, known as yellowish-green algae, are unicellular algae present in fresh, brackish and salt water, as well as in terrestrial habitats. They have only chlorophyll a and β-carotene in their chloroplasts. The vast majority of species produce zoospores.

  • Pinguiophyceae, are unicellular planktonic marine microalgae whose size does not exceed 40 µm. They possess an unusual and high concentration of polyunsaturated fatty acids (eicosapentaenoic acid), and as a consequence of this characteristic their name is derived, since 'Pingue' in Latin means fat. This, together with the absence of a cell wall, makes the species belonging to the class of Penguiophyceae a preferential source for obtaining unsaturated fatty acids for food.

  • Dictyochophyceae, we are dealing with unicellular algae without a capsule and with amoeboid morphology, being together with the Xanthophyceae, practically the only amoeboid algae.

  • Pelagophyceae, mostly spherical unicellular algae of small size (3-5 µm) that are part of the ultra-plankton. Several members of this class are of economic importance, as they cause brown tides (Aureoumbra lagunensis and Aureococcus anaphagefferens).

  • Bolidophyceae, flagellated picoplantonic algae and phylogenetically close to diatoms. This small class of algae, unlike diatoms, does not have a siliceous coating.

  • Bacillariophyceae, also known as diatoms. They are a group of unicellular algae with brown tones, which possess a rigid capsule of siliceous nature and formed by two halves that fit between them in the form of a box. There are diatoms in both fresh and marine waters.

  • Raphidopyceae, are large (30 - 80 µm) unicellular organisms with a globoid or elongated oval morphology. They lack a cell wall. Freshwater species have a greenish coloration, while marine species tend to be more yellowish due to the presence of fucoxanthin in their chloroplasts. Many marine species tolerate a wide range of salinity (3% - 50%) as well as temperatures. Also, certain marine species (e.g. Chattonella antiqua and Heterosigma carterae) can produce neurotoxic compounds, capable of generating red tides.

  • Xanthophyceae, the vast majority of species inhabit freshwater or terrestrial environments, and only a small number are found in salt water. They are generally characterized by having 2 flagella, as well as by the absence of fucoxanthin in their chloroplasts.

  • Phaeothamniophyceae, are the only class of algae in which both fucoxanthin and heteroxanthin coexist in chloroplasts. We find both filamentous and cocoid algae species.