plants use the carbon fixation pathway to increase their photosynthetic efficiency by reducing or suppressing photorespiration, which mainly occurs under low atmospheric concentration, high light, high temperature, drought, and salinity. There are roughly 8,100 known species, which belong to at least 61 distinct evolutionary lineages in 19 families of flowering plants. Among these are important crops such as maize, sorghum and sugarcane, but also weeds and invasive plants. Although only 3% of flowering plant species use carbon fixation, they account for 23% of global primary production. The repeated, convergent evolution from C3 carbon fixation| ancestors has spurred hopes to bio-engineer the pathway into crops such as rice. photosynthesis probably first evolved 30–35 million years ago in the Oligocene, and further origins occurred since, most of them in the last 15 million years. plants are mainly found in tropical and warm-temperate regions, predominantly in open grasslands where they are often dominant. While most are graminoids, other growth forms such as forbs, vines, shrubs, and even some trees and aquatic plants are also known among plants. plants are usually identified by their higher 13C/12C isotopic ratio compared to plants or their typical leaf anatomy. The distribution of lineages among plants has been determined through phylogenetics and was considered well known as of 2016. Monocots – mainly grasses and sedges – account for around 80% of species, but they are also found in the eudicots. The following list presents known lineages by family, based on the overview by Sage. They correspond to single species or clades thought to have acquired the pathway independently. In some lineages that also include and – intermediate species, the pathway may have evolved more than once. grows in deserts. shrub common in steppes of western North America. in Central Asia. has been a model plant. '' uses the pathway under high temperature and light intensity. .
The amaranth family Amaranthaceae contains around 800 known species, which belong to 14 distinct lineages in seven subfamilies. This makes Amaranthaceae the family with most species and lineages among the eudicots. Suaeda aralocaspica and species of the genus Bienertia use a particular, single-cell type of carbon fixation.
The composite family Asteraceae contains three lineages, in two different tribes of subfamily Asteroideae. They include the model genusFlaveria with closely related,, and intermediate species.
The Cleomaceae, formerly included in the caper family Capparaceae, contains three species in genus Cleome. These three species independently acquired the pathway; the genus also contains numerous as well as – intermediate species.
The sedge family Cyperaceae is second only to the grasses in number of species. Prominent sedges include culturally important species such as papyrus and chufa but also purple nutsedge, one of the world's major weeds. Eleocharis vivipara uses carbon fixation in underwater leaves and carbon fixation in aerial leaves.
The spurge family Euphorbiaceae contains the largest single lineage among eudicots. The spurges are diverse and widespread; they range from weedy herbs to the only known trees – four species from Hawaii, including Euphorbia olowaluana and E. herbstii.
Euphorbia subgenus Chamaesyce section Anisophyllum – 350 species
The two species within the same genus have acquired the pathway independently.
Mollugo – 2 species, 2 origins
Nyctaginaceae
Allionia – 2 species
Boerhavia – 42 species
Polygonaceae
Calligonum – 80 species
Portulacaceae
The single genus of this family forms one lineage. CAM photosynthesis is also known. Common purslane is a major weed but also a vegetable.
Portulaca – 100 species, 1–2 origins
Poaceae
The grass family includes most of the known species – around 5000. They are only found in subfamilies of the PACMAD clade. Major crops such as maize, sugarcane, sorghum and pearl millet belong in this family. The only known species with, and intermediate variants, Alloteropsis semialata, is a grass.
