Croton is a very large genus of flowering plants in the spurge family (Euphorbiaceae), subfamily Crotonoideae, formally established by Linnaeus in Species Plantarum (1753). The name comes from the Greek krótos, meaning "tick," a reference to the resemblance of the seeds of some species to the parasitic arachnid. The genus is one of the largest in its family: Wikipedia cites over 1,100 species, GBIF lists 1,741 descendant taxa within the genus, and older floras (such as SEINet) give a conservative figure of "600+," reflecting both ongoing taxonomic revision and differing concepts of how many infraspecific names should count.
A critical point of confusion: the popular tropical houseplant sold in nurseries as "croton," with brilliantly variegated red, orange, and yellow foliage, is not a member of this genus at all. That plant is Codiaeum variegatum, which was once classified under Croton but is now placed in the separate genus Codiaeum (still within Euphorbiaceae). True Croton species are predominantly wild trees, shrubs, and herbs of tropical and subtropical regions and are rarely grown as ornamentals.
The genus is pantropical, with some species extending into temperate zones; Madagascar alone harbors as many as 150 endemic species. Habit ranges from small annual herbs through shrubs to canopy trees. Morphologically, plants are monoecious or dioecious; calyces are typically 5- to 7-lobed; petals usually equal the sepals in staminate flowers; stamens are inflexed in bud; seeds bear a caruncle; and the indumentum is often distinctively stellate (star-shaped hairs). Small flowers are arranged in condensed, spike-like terminal inflorescences.
Several Croton species are economically or culturally important. Croton tiglium, native to South and Southeast Asia, is the source of croton oil, a notoriously violent purgative now considered unsafe and excluded from many pharmacopoeias because its phorbol-ester constituents are powerful tumor promoters. Croton eluteria (cascarilla) yields an aromatic bark used to flavor liqueurs such as Campari and certain vermouths. Croton megalocarpus, a Kenyan tree, produces nuts containing roughly 35 percent oil that is harvested as an economical biofuel. Other well-known members include the South American Croton lechleri (sangre de grado, "dragon's blood"), the North American Croton capitatus (woolly croton) and Croton californicus (California croton), and the Hong Kong endemic Croton hancei. Ecologically, the foliage supports a variety of insects, including the larvae of Lepidoptera such as Schinia citrinellus.
Etymology
The genus name Croton derives from the ancient Greek krótos, meaning "tick" — a reference to the small, ovoid seeds of some species, which were thought to resemble the parasitic arthropod. The name was carried into modern botanical nomenclature by Linnaeus when he formally described the genus in 1753.
Distribution
Croton is pantropical in distribution, with the bulk of its species diversity in the tropics and subtropics of both the Old and New Worlds; a smaller number of species extend into temperate regions. Madagascar is a particularly important center of endemism, with up to about 150 species found nowhere else. Representatives reach into North American floras as well — for example, Croton lindheimerianus, an annual species, is cited from southwestern and adjacent North American floras.
Taxonomy notes
Croton L. was published by Linnaeus in Species Plantarum (1: 1004, 1753) and sits in the spurge family Euphorbiaceae, subfamily Crotonoideae, within order Malpighiales (class Magnoliopsida, phylum Tracheophyta). It is one of the largest genera in the family: Wikipedia cites more than 1,100 accepted species, GBIF currently lists 1,741 descendant taxa, and older floras use the more conservative "600+."
A persistent source of confusion is that the showy variegated foliage plant sold as "croton" or "garden croton" in horticulture is Codiaeum variegatum, not a Croton at all. Codiaeum was historically lumped into Croton but is now treated as a separate genus, also within Euphorbiaceae. When the name "croton" appears in ornamental-plant contexts it almost always refers to Codiaeum; the true Croton genus is overwhelmingly composed of wild tropical trees, shrubs, and herbs rarely seen in cultivation.
Ecology
Croton species occupy an exceptionally broad range of tropical and subtropical habitats, in habits ranging from short-lived annual herbs through shrubs to substantial canopy trees. Flowers are small and arranged in condensed, spike-like terminal inflorescences; individual plants may be monoecious or dioecious depending on species. The genus supports a variety of insect herbivores — larvae of certain Lepidoptera, including Schinia citrinellus, are recorded as feeding on Croton foliage.
Cultural & economic uses
Several Croton species have long histories of human use. Croton tiglium, native to China, India, Indonesia, and other parts of Southeast Asia, is the source of croton oil; in traditional Chinese medicine it is bā dòu and is counted among the "50 fundamental herbs," while in South Asia its seeds are known as jamālgoṭa and are detoxified with cow's milk before any medicinal use because of their severe purgative toxicity. Croton oil's phorbol-ester chemistry (including crotonoleic acid, glyceryl crotonate, crotonic acid, crotonic resin, and various phorbol derivatives) is now understood to be co-carcinogenic, and the oil is excluded from most modern pharmacopoeias. Historically, the bark of C. tiglium has even been used as arrow poison and the seeds to poison fish.
On more benign ground, Croton eluteria (cascarilla) yields an aromatic bark long used to flavor liqueurs such as Campari and certain vermouths, and Croton megalocarpus, a Kenyan tree, produces nuts whose oil — about 35 percent of nut weight — is harvested as a renewable biofuel feedstock.
History
The genus was formally established by Carl Linnaeus in Species Plantarum (1: 1004) in 1753, making it one of the earliest validly published genera in the spurge family. Subsequent generic recircumscriptions removed the variegated ornamental species now treated as Codiaeum variegatum, separating the showy "garden croton" of horticulture from the much larger, mostly wild Croton sensu stricto.
