List of C4 plants

A farmer among high maize plants
Maize (Zea mays, Poaceae) is the most widely cultivated C4 plant.[1]

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. Monocots – mainly grasses (Poaceae) and sedges (Cyperaceae) – account for around 80% of C4 species, but they are also found in the eudicots.[1] Moreover, almost all C4 plants are herbaceus, with the notable exception of some woody species from the Euphorbia genus, such as the tree Euphorbia olowaluana.[6] The reason behind C4 metabolism extreme rarity in trees is debated: hypotheses vary from a possible reduction in photosynthetic quantum yield under dense canopy conditions, coupled with an increased metabolic energy consumption (inherent to C4 metabolism itself), to less efficient sunflecks utilization.[7]

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]

Spiny plant with pale violet flowers
Blepharis attenuata (Acanthaceae) grows in deserts.
Dense bush with yellow flowers in dry habitat
Shadscale (Atriplex confertifolia, Amaranthaceae) is a halophytic shrub common in steppes of western North America.[1]
Bush in very dry desert habitat
Black saxaul (Haloxylon ammodendron, Amaranthaceae) provided fuel for caravans following the Silk Road in Central Asia.[1]
Plant with inflorescence of white flowers
Cleome gynandra (Cleomaceae) has been a C4 model plant.[1]
Dense papyrus stand on river bank
Papyrus (Cyperus papyrus, Cyperaceae) has been of major cultural importance.[1]
Prostrate purple plants growing on sidewalk
Spotted spurge (Euphorbia maculata, Euphorbiaceae) commonly grows in sidewalk cracks in North America.[8]
Bright green foliage of aquatic plant
The aquatic Egeria densa (Hydrocharitaceae) uses the C4 pathway under high temperature and light intensity.
Cut sugarcane
Sugarcane (Saccharum officinarum, Poaceae) is grown for sugar and bioethanol.[1]
Prostrate plant with shiny, fleshy leaves
Purslane (Portulaca oleracea, Portulacaceae), a weed and ancient vegetable, uses both C4 and CAM photosynthesis.[1][9]
Grass with inflorescence in front of blue sky
Rhodes grass (Chloris gayana, Poaceae) is a major forage grass in tropical areas.[1]
Spiny fruits devloping on plant
The spiny fruits of puncture vine (Tribulus terrestris, Zygophyllaceae) may even puncture tyres.[1]
  1. ^ a b c d e f g h i j k l m n o p Cite error: The named reference Sage2016 was invoked but never defined (see the help page).
  2. ^ Cite error: The named reference SageSage2012 was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference ChristinOsborne2014 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference APGIV was invoked but never defined (see the help page).
  5. ^ a b c Cite error: The named reference Kellogg2013 was invoked but never defined (see the help page).
  6. ^ Elliott, Liam (2020-05-22). "To C4 or not to C4 if you're a tree? Some possible answers". Botany One. Retrieved 2024-04-30.
  7. ^ Young, Sophie N R.; Sack, Lawren; Sporck-Koehler, Margaret J.; Lundgren, Marjorie R. (2020). "Why is C4 photosynthesis so rare in trees?". Journal of Experimental Botany. 71 (16): 4629–4638. doi:10.1093/jxb/eraa234. PMC 7410182. PMID 32409834. Retrieved 2024-05-01.
  8. ^ Cite error: The named reference YangBerry2011 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference KochKennedy1982 was invoked but never defined (see the help page).