In botany, C4 carbon fixation is one of three known methods of photosynthesis used by plants. C4 plants increase their photosynthetic efficiency by reducing or suppressing photorespiration, which mainly occurs under low atmospheric CO2 concentration, high light, high temperature, drought, and salinity. [2] [3] There are roughly 8,100 known C4 species, which belong to at least 61 distinct evolutionary lineages in 19 families (as per APG IV classification [4] ) of flowering plants. [1] Among these are important crops such as maize, sorghum and sugarcane, but also weeds and invasive plants. [1] Although only 3% of flowering plant species use C4 carbon fixation, they account for 23% of global primary production. [5] The repeated, convergent C4 evolution from C3 ancestors has spurred hopes to bio-engineer the C4 pathway into C3 crops such as rice. [1] [5]
C4 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. C4 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 C4 plants. [1]
C4 plants are usually identified by their higher 13C/12C isotopic ratio compared to C3 plants or their typical leaf anatomy. [5] The distribution of C4 lineages among plants has been determined through phylogenetics and was considered well known as of 2016 [update] . Monocots – mainly grasses (Poaceae) and sedges (Cyperaceae) – account for around 80% of C4 species, but they are also found in the eudicots. [1]
The following list presents known C4 lineages by family, based on the overview by Sage (2016). [1] They correspond to single species or clades thought to have acquired the C4 pathway independently. In some lineages that also include C3 and C3–C4 intermediate species, the C4 pathway may have evolved more than once. [1]
The large acanthus family Acanthaceae includes one genus with C4 species, found in dry habitats from Africa to Asia. [8]
While many species in the ice plant family Aizoaceae use crassulacean acid metabolism (CAM), one subfamily with drought-tolerant and halophytic plants includes C4 species: [9]
The amaranth family Amaranthaceae (including the former goosefoot family Chenopodiaceae) contains around 800 known C4 species, which belong to 14 distinct lineages in seven subfamilies. This makes Amaranthaceae the family with most C4 species and lineages among the eudicots. [1] Suaeda aralocaspica and species of the genus Bienertia use a particular, single-cell type of C4 carbon fixation. [1] [10]
The composite family Asteraceae contains three C4 lineages, in two different tribes of subfamily Asteroideae. [1] [18] They include the model genus Flaveria with closely related C3, C4, and intermediate species. [1]
The borage family Boraginaceae contains one widespread C4 genus, Euploca, which has also been treated as part of a distinct family Heliotropiaceae. [22]
The Cleomaceae, formerly included in the caper family Capparaceae, contains three C4 species in genus Cleome . These three species independently acquired the C4 pathway; the genus also contains numerous C3 as well as C3–C4 intermediate species. [1] [24] [25]
In the carnation family Caryophyllaceae, the C4 pathway evolved once, in a clade within the polyphyletic genus Polycarpaea. [1] [26]
The sedge family Cyperaceae is second only to the grasses in number of C4 species. Prominent C4 sedges include culturally important species such as papyrus ( Cyperus papyrus ) and chufa ( C. esculentus ) but also purple nutsedge ( C. rotundus ), one of the world's major weeds. Eleocharis vivipara uses C3 carbon fixation in underwater leaves and C4 carbon fixation in aerial leaves. [1]
The spurge family Euphorbiaceae contains the largest single C4 lineage among eudicots. The C4 spurges are diverse and widespread; they range from weedy herbs to the only known C4 trees – four species from Hawaii, including Euphorbia olowaluana (up to 10 m) and E. herbstii (up to 8 m). [1] [6]
Contains a C4 genus with a single species.
Includes the only known aquatic C4 plants. [1]
The two C4 species within the same genus have acquired the pathway independently.
The single genus of this family forms one C4 lineage. CAM photosynthesis is also known. Common purslane ( Portulaca oleracea ) is a major weed but also a vegetable. [1]
The grass family includes most of the known C4 species – around 5000. They are only found in subfamilies of the PACMAD clade. Major C4 crops such as maize, sugarcane, sorghum and pearl millet belong in this family. The only known species with C3, C4 and intermediate variants, Alloteropsis semialata , is a grass. [1]
Amaranthaceae is a family of flowering plants commonly known as the amaranth family, in reference to its type genus Amaranthus. It includes the former goosefoot family Chenopodiaceae and contains about 165 genera and 2,040 species, making it the most species-rich lineage within its parent order, Caryophyllales.
C4 carbon fixation or the Hatch–Slack pathway is one of three known photosynthetic processes of carbon fixation in plants. It owes the names to the 1960s discovery by Marshall Davidson Hatch and Charles Roger Slack that some plants, when supplied with 14CO2, incorporate the 14C label into four-carbon molecules first.
Alternanthera is a genus of flowering plants in the family Amaranthaceae. It is a widespread genus with most species occurring in the tropical Americas, and others in Asia, Africa, and Australia. Plants of the genus may be known generally as joyweeds, or Joseph's coat. Several species are notorious noxious weeds.
The Salicornioideae are a subfamily of the flowering plant family Amaranthaceae. Important characters are succulent, often articulated stems, strongly reduced leaves, and flowers aggregated in thick, dense spike-shaped thyrses. These halophytic plants are distributed worldwide. Many are edible
The Gomphrenoideae are a subfamily of the Amaranthaceae.
Orobanchaceae, the broomrapes, is a family of mostly parasitic plants of the order Lamiales, with about 90 genera and more than 2000 species. Many of these genera were formerly included in the family Scrophulariaceae sensu lato. With its new circumscription, Orobanchaceae forms a distinct, monophyletic family. From a phylogenetic perspective, it is defined as the largest crown clade containing Orobanche major and relatives, but neither Paulownia tomentosa nor Phryma leptostachya nor Mazus japonicus.
Atriplex is a plant genus of about 250 species, known by the common names of saltbush and orache. It belongs to the subfamily Chenopodioideae of the family Amaranthaceae s.l.. The genus is quite variable and widely distributed. It includes many desert and seashore plants and halophytes, as well as plants of moist environments. The generic name originated in Latin and was applied by Pliny the Elder to the edible oraches. The name saltbush derives from the fact that the plants retain salt in their leaves; they are able to grow in areas affected by soil salination.
Chamaesyce is a genus of plants in the family Euphorbiaceae. Recent phylogenetic studies have shown that Chamaesyce is deeply nested within the broader Euphorbia. Specifically, Chamaesyce is very closely related to plants like Euphorbia pulcherrima, the popular poinsettia. Currently, all species have now been reclassified as species of Euphorbia. Specifically, this group now belongs to Euphorbia subgenus Chamaesyce section Anisophyllum. Taxonomically speaking, Chamaesyce is considered a synonym of Euphorbia.
Neotatea is a plant genus in the family Calophyllaceae. It is found in northwestern South America, primarily southern Colombia and Venezuela. There are four species currently recognized in the genus.
Halimione portulacoides, commonly known as sea purslane, is a shrub found in Eurasia.
The Cleomaceae are a small family of flowering plants in the order Brassicales, comprising about 220 species in two genera, Cleome and Cleomella. These genera were previously included in the family Capparaceae, but were raised to a distinct family when DNA evidence suggested the genera included in it are more closely related to the Brassicaceae than they are to the Capparaceae. The APG II system allows for Cleomaceae to be included in Brassicaceae. Cleomaceae includes C3, C3–C4, and C4 photosynthesis species.
Suaeda is a genus of plants also known as seepweeds and sea-blites. Most species are confined to saline or alkaline soil habitats, such as coastal salt-flats and tidal wetlands. Many species have thick, succulent leaves, a characteristic seen in various plant genera that thrive in salty habitats.
Aerva is a genus of plants in the family Amaranthaceae. Its species are native to the palaeotropics, throughout continental Africa, Madagascar and smaller islands, through parts of the Middle East, India, and southeast Asia. Aerva javanica is an alien in northern Australia.
Flaveria is a genus of plants in the family Asteraceae. They are sometimes called yellowtops. Some are annual or perennial herbs and some are shrubs. They bear yellow flowers in heads, with zero, one, or two ray florets in each head. These plants are found in the Americas, Asia, Africa, and Australia.
Suaeda aralocaspica is a species of plant in the family Amaranthaceae that is restricted to the deserts of Central Asia. It is a halophyte and uses C4 carbon fixation but lacks the characteristic leaf anatomy of other C4 plants (known as kranz anatomy). Carrying out complete C4 photosynthesis within individual cells, these plants instead are known as single‐cell C4 system or SCC4 plants. This makes them distinct from typical C4 plants, which require the collaboration of two types of photosynthetic cells. SCC4 plants have features that make them potentially valuable in engineering higher photosynthetic efficiencies in agriculturally important C3 carbon fixation species such as rice. To address this, the 467 Mb genome of S. aralocaspica has been sequenced to help understanding of the evolution of SCC4 photosynthesis and contribute to the engineering of C4 photosynthesis into other economically important crops.
The Suaedoideae are a subfamily of plants in the family Amaranthaceae.
Bienertia is a flowering plant genus that currently is classified in the family Amaranthaceae s.l.. For long time, the genus was considered to consist only of one species, Bienertia cycloptera, but in 2005 and 2012, two new species have been separated.
Rhinantheae is a tribe with less than 20 genera of herbaceous plants in the family Orobanchaceae.
Hedbergia decurva, formerly Bartsia decurva, is a species of flowering plants in the family Orobanchaceae.
Hedbergia longiflora, formerly Bartsia longiflora, is a species of flowering plants in the family Orobanchaceae.