Trebouxiophyceae

Members of the Trebouxiophyceae are microscopic or macroscopic organisms which exist in a variety of forms: non-flagellate coccoid or elliptical single cells, unbranched filaments, blades, or colonies of cells. Chloroplasts are diverse in morphology and placement and may be axial and stellate (e.g. Prasiola), numerous and discoid (e.g. Eremosphaera), or parietal. Pyrenoids may be present or absent. Ultrastructure Trebouxiophyceaen algae are characterized by a combination of plesiomorphic traits. It has basal bodies of its flagella in a counterclockwise orientation, non-persistent, metacentric spindles during telophase, and phycoplast-mediated cytokinesis. The presence of counterclockwise basal bodies are shared with Ulvophyceae, the metacentric spindles are shared with walled prasinophytes, and the non-persistent spindles and phycoplasts are also present in Chlorophyceae. Some members do not produce flagellated stages at all. ==Ecology==

Trebouxiophycean algae are common and widespread, and found in a variety of habitats. Terrestrial species live most commonly in places such rocks, soils or tree bark. Trebouxia (also the namesake of the class) and Asterochloris are the most common and widespread phycobionts of lichens; it is estimated that Trebouxia is associated with over 20% of all lichen-forming fungi worldwide. Research on lichens has historically focused more on the fungal partner (the mycobiont) over the phycobionts. Research on trebouxiophycean phycobionts has been hampered by the time-consuming nature of identification. Because the morphology of these algae is often heavily influenced by the environment, reliable identification relies on molecular techniques such as DNA barcoding. However, recent research has discovered considerable diversity. It was previously thought that a specific mycobiont associates with only one type of phycobiont; however, it is now accepted that multiple trebouxiophycean algae can associate with a single species or even a single thallus. The host organisms are diverse and include ciliates (e.g. Paramecium), Hydra and freshwater sponges. Paramecium bursaria is a well-studied example and model organism for endosymbiosis. The hosts may have an obligate or a facultative relationship with the symbionts. Desmococcus on beech 02.jpg|Desmococcus, a terrestrial alga growing on the bark of a beech tree Eremosphaera viridis 361793586.jpg|Eremosphaera, found in freshwater plankton Prasiola stipitata Suhr (AM AK307212-6).jpg|Prasiola stipitata growing on a rocky shore Trebouxia 2 - Miguel Varona - Cuaderno de Campo del Treparriscos.jpg|Trebouxia, a common phycobiont of lichens Paramecium bursaria.jpg|The ciliate Paramecium bursaria with endosymbiotic trebouxiophycean algae Anthopleura xanthogrammica 1.jpg|Anthopleura xanthogrammica; the green color is due to endosymbiotic Elliptochloris marina Prototheca wickerhamii.GMS.jpg|Photomicrograph (stained) of Prototheca wickerhamii infection in a human Phyllosiphon arisari 244841554.jpg|Parasitic alga Phyllosiphon arisari causing yellow spots on Arisarum ==Evolution and phylogeny==

The clade Trebouxiophyceae likely originated about 600–800 million years ago, The closest relatives of Trebouxiophyceae are Chlorophyceae and Ulvophyceae; together, they form a monophyletic group termed the UTC clade (also known as core Chlorophyta). The ancestral trebouxiophycean alga was likely a sexual organism; later lineages appear to have independently lost the ability to reproduce sexually many times. It is hypothesized that the production of autospores became advantageous in terrestrial environments, since flagellated cells require water for movement. ==Taxonomy==

The taxonomy of algae has traditionally been based on morphological characters; however, microalgae typically have few morphological characters, and therefore morphological classifications are limited by convergent evolution and cryptic diversity. Therefore, modern taxonomic classifications involve an integrative species concept combining morphological and molecular data. Higher-level relationships within Trebouxiophyceae are not yet fully resolved. As of 2025, AlgaeBase accepts the following orders: • Chlorellales • Microthamniales • Phyllosiphonales • Prasiolales • Trebouxiales • Watanabeales Genera and families without intervening taxonomy include: • Micractiniaceae • Ragelichloridaceae • Apatococcus • Autumnella • Chlorolobion • Chloropyrula • Elliptochloris • Eremochloris • Glaphyrella • Koliellopsis • Lemmermannia • Leptochlorella • Leptosira • Lunachloris • Neochlorella • Rhopalosolen • Xerochlorella • Xylochlorella == Usage ==

The microalga Chlorella has been used by researchers to study basic elements of biochemistry and physiology, as an simpler analog of land plants. Biochemical research involving Chlorella has resulted in two Nobel Prizes: in 1931, Otto Heinrich Warburg was awarded the Nobel Prize in Physiology or Medicine for his research on cellular respiration, and in 1961, Melvin Calvin was awarded the Nobel Prize in Chemistry for studying carbon dioxide assimilation in plants, using Chlorella as a model. Some trebouxiophycean microalgae are under interest as potential sources of biofuels or other products, such as proteins and lipids. Botryococcus is of particular interest as a producer for biodiesel, since it produces a high amount of lipids. A few algae in Trebouxiophyceae are edible, such as Prasiola, which is edible and locally harvested for food Japan and Myanmar. In the mid-twentieth century, Chlorella was seen as an economical source of food and an answer to the global food crises of the time. Since then, improvements in crop yield have caused a decline in interest in Chlorella as food; == See also ==