Genus of flowering plants in the family Asteraceae
Crepis, commonly known in some parts of the world as hawksbeard or hawk's-beard (but not to be confused with the related genus "Hieracium" with a similar common name), is a genus of annual and perennial flowering plants of the family Asteraceae superficially resembling the dandelion, the most conspicuous difference being that "Crepis" usually has branching scapes with multiple heads (though solitary heads can occur). The genus name "Crepis" derives from the Greek "krepis", meaning "slipper" or "sandal", possibly in reference to the shape of the fruit.
The genus is distributed throughout the Northern Hemisphere and Africa, and several plants are known as introduced species practically worldwide. The center of diversity is in the Mediterranean.
Ecology.
"Crepis" species are used as food plants by the larvae of some Lepidoptera species including the broad-barred white moth. The fly "Tephritis formosa" is known to attack the capitula of this plant.
Seeds of "Crepis" species are an important food source for some bird species.
Reproduction.
"Crepis" can reproduce sexually or asexually. "Crepis" is insect-pollinated, typically by bees and other generalist pollinators. Species in this genus are able to produce viable seeds through hybridization. Some of these hybrids (depending on their parent species) can reproduce themselves. As an aster, flowers of "Crepis" are closely clustered on a capitulum, which is surrounded by petal-like rays. Asexual reproduction (or autogamy) between flowers on the same capitulum has been observed in the genus.
Apomixis in "Crepis".
As with several other genera in Asteraceae, multiple "Crepis" species exhibit apomixis, a form of asexual reproduction where flowers produce clonal seeds without need of fertilization. Unlike sexually-reproducing individuals, which are diploid, apomicts are typically polyploid, with three or more sets of chromosomes. The mechanism of apomixis in "Crepis" is apospory, wherein diploid tissue arises during meiosis in the ovule. Through apospory, asexual seeds can develop spontaneously in the flowers of a non-apomictic "Crepis".
"Crepis" is part of the Cichorieae tribe in Asteraceae, and is one of several genera of that tribe that exhibits apomixis. The largest group of asexual species is found in North America, and is referred to as the "North American "Crepis" agamic complex" The agamic complex may have first arisen in the Pliocene, between 5.3 and 2.6 million years ago. At least one Eurasian "Crepis" species, "C. tectorum", has been observed to self-fertilize. Another agamic complex is thought to exist in Asia. Species known to produce apomicts in"clude C." "acuminata, C." "barbigera, C. intermedia," and "C. occidentalis." Polyploid individuals may still be able to carry out sexual reproduction and therefore produce sexual offspring, allowing for the formation of new polyploid hybrids.
Reproductive interference.
Apomictic individuals can prevent reproduction in sexual individuals in multiple ways. Like other apomictic species in Cichorieae, polyploid apomicts may still produce viable pollen that can be transferred to sexual diploids through the normal process of pollination. The mixed apomict-sexual parantage may produce a polyploid hybrid (as has been observed when the apomictic "C. barbigera" breeds with diploid species "C. atribarba"). Seed set in the diploid may be reduced, or the pollen may produce hybrid seeds that are unable to reproduce or survive to a normal lifespan. The pollen from the apomict may also prevent germination of pollen from a diploid flower. When pollen from a polyploid individual fertilizes diploid flowers, the resultant seeds are typically polyploid, which lowers the diploid population over generations.
As a result of this reproductive interference, sexual reproduction between diploid plants is reduced when apomicts enter a population. Because diploid species require pollen exchange to reproduce and apomicts can produce seeds by parthenogenesis, apomicts do not suffer any reproductive consequences in a mixed diploid-polyploid population. Meanwhile, the reproductive success of sexually-reproducing diploids falls, resulting in diploids being found more often in populations isolated from apomicts.
Evolutionary implications.
Although apomixis has been considered a "blind alley of evolution", research into apomictic species and species complexes has cast doubt on this. Apomictic clades elsewhere in Cichorieae have demonstrated an ability to "revert" to a sexual mode of reproduction, reducing the risk of extinction through lack of introgression. Speciation in "Crepis" has occurred through its ability to self-fertilize, hybridize, and form polyploid apomicts.
Apomixis can facilitate range expansion in ways that sexual reproduction does not. Apomicts do not require input of genetic material for another individual, and can therefore produce seeds on maturity without the aid of pollinators. This allows apomictic populations to expand into new geographic areas more rapidly than sexual ones. Because apomixis in "Crepis" involves multiple ploidy levels, there is sufficient genetic variation for adaptation to novel ecosystems. Additionally, some "Crepis" apomict species have the ability to hybridize with other apomicts, resulting in genetic recombination alongside parthenogenesis.
Uses.
In Crete, Greece the leaves of "Crepis commutata" which are called () are eaten raw, boiled, steamed or browned in salads. Another two species on the same island, "Crepis vesicaria", called (), () or () and a local variety called () or () have both its leaves and tender shoots eaten boiled by the locals.
Secondary metabolites.
The genus "Crepis" is a rich source of costus lactone-type guaianolides, a class of sesquiterpene lactones.
Phenolics found in "Crepis" include luteolin-type flavonoids and caffeoyl quinic acid derivatives such as chlorogenic acid and 3,5-dicaffeoylquinic acid. Moreover, "Crepis" species contain the caffeoyl tartaric acid derivatives caffeoyl tartaric acid and cichoric acid.
Diversity.
There are about 200 species in the genus.
Species include:
References.
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