Caricaceae a small family of flowering plants comprising about 35 species in six genera. Carica papaya, the family's most popular representative, is widely grown throughout the World's tropics. It is appreciated not only for its delicious and nutritive fruits, but also because it contains the enzyme papain, which is extensively used in medicines, as meat tenderizer, for softening textiles, silk, and leather, and in beer production. Several other species also have edible fruits and produce papain. For example,Vasconcellea pubescens, and Jacaratia spinosa show promising characteristics for further economic exploitation and development of new crops.

This website provides detailed information on the entire papaya's family. Specifically, data are provided on taxonomy, morphology, reproduction (sexual systems and sex chromosomes), evolutionary relationships , distribution ranges, and biogeography (e.g., how they reached South America from Africa and diversified there). In addition to Carica papaya, I provide detailed information on all wild members of the Caricaceae, including the so-called highland papayas from the Andes (Vasconcellea species) and the closest wild relatives of papaya from Mexico, Guatemala, and El Salvador. For illustrations and detailed information on each genus and species, please use the search form.

Using the tabs above, you can access taxonomic keys for identifying genera and species, and search for herbaria specimens or taxa. You will find georeferenced collections, distribution maps, species descriptions, and illustrations (photos and drawings). For specially designed tutorials and other useful links, click on Resources. All sources of information provided here are listed under References. Links have been added to information and sources online available. Questions, comments, and contributions are especially welcome. Please write to:antunesfc@gmail.com

Morphology

Most members of Caricaceae are trees or shrubs (three Jarilla species from Mexico and Guatemala are herbs). All species produce latex that can be white or light yellow. Leaves vary from entire to deeply lobed or palmate. The flowers in Caricaceae are monoclinous (= unisexual). Male flowers are mostly borne in an inflorescence with more than ten flowers; they have a tubular corolla, filled with sweet nectar; nectaries are located on a small pistillode (nonfunctional ovary); stamens are fused to the corolla throat and distributed in two pentamerous whorls. Female flowers are often solitary or bunched in few-flowered inflorescences (few species present congested female inflorescences); they are devoid of nectar; petals are not fused (with few exceptions); ovaries are divided into one or five chambers (locules); there are five stigmas that are either entire or bifurcated. Fruits are berries with many seeds. The seeds are surrounded by a mucilaginous aril; the testa can be ornamented or not.

The images above show the morphological variation of flowers, fruits, seeds, leaves and habit in Caricaceae. Use the search form to find detailed illustration plates and information on biology and morphology of every species and genera.

Diversity and Distribution

Search for a name of genus or species to generate specific distribution maps based on botanical collections.

Only two species of Caricaceae occur in Africa:Cylicomorpha solmsii in West Africa and Cylicomorpha parviflora in East Africa. Both are large trees restricted to humid montane and submontane forests. All other Caricaceae are distributed in the New World from Mexico to Paraguay. The genus Horovitzia, with its single species H. cnidoscoloides, is only known from the submontane forests of Sierra de Juaréz (Oaxaca) in southern Mexico. The three species of Jarilla are perennial herbs endemic to Mexico and Guatemala. The genus Jacaratia consists of six species of trees distributed in the lowlands of South and Central America. Two of the Jacaratia species are adapted to dry areas (J. mexicana and J. corumbensis) and four to tropical rain forests (J. dolichaula, J. spinosa, J. digitata, and J. chocoensis). The genus with the highest number of species is Vasconcellea, with 20 species and one formally named hybrid. Most Vasconcellea species are found in the northern Andes, making this region the center of species diversity of Caricaceae. Carica papaya (the only species in this genus) is the economically most important species in this family, with an annual production of around 10 million tons. The wild form occurs only in Mesoamerica from southern Mexico to Costa Rica.

What are the evolutionary relationships among the genera of Caricaceae?

Caricaceae and its sister family Moringaceae are part of the mustard-oil plant order (Brassicales), which also comprises 15 other families of flowering plants, including the Brassicaceae, the cabbage family. Moringaceae is a small family with 13 species distributed in southeastern Asia and Africa. For a general overview of the phylogenetic relationships of Caricaceae within the order Brassicales please refer to the Angiosperm Phylogeny website. The Angiosperm Phylogeny poster provides an overview of current relationships within the flowering plants including morphological, anatomical, and phytochemical traits of the orders, also listing the majority of families.

Within Caricaceae, phylogenetic studies using molecular data have shown that all genera with more than one species are monophyletic. The African Caricaceae are the sister clade of the New World Caricaceae. In the Neotropics, Vasconcellea and Jacaratia form a well-supported clade sister to the remaining three genera, Carica, Jarilla, and Horovitzia see (References).

 

Who are the closest relatives of Carica papaya?

The closest relatives of papaya were long thought to be the Andean mountain papayas (Vasconcellea species). However, this was erroneous and based on a poor understanding of the evolutionary relationships in Caricaceae, as I explain below. Even though Caricaceae consist of only a few genera, the generic circumscriptions have considerably changed throughout the centuries (see taxonomic history). The extensive morphological work of Victor M. Badillo laid the basis for the current classification. Another important advance to understanding the relationships among the genera in Caricaceae came from breeding experiments carried out by Horovitz and Jiménez and their team at the Universidad Central de Venezuela (also Badillo's university).

In 1999, one of the first studies attempting to investigate evolutionary relationships in the family with molecular data (genetic fingerprinting) found a large genetic distance between Carica and Vasconcellea. After that, Badillo reestablished the genus Vasconcellea, emphasizing its genetic distance to Carica papaya and pointing out morphological differences between both genera, number of locules in the ovary, number of leaf veins, stamens hairs, and others. The separation of the two genera was confirmed in subsequent molecular studies, and it is now recognized that, despite considerable morphological similarity, Vasconcellea is not a close relative of Carica (see References).

In my own DNA sequence-based study, I found that the closest relatives of papaya are four dioecious species distributed only in Mexico, Guatemala, and El Salvador: Horovitzia cnidoscoloides, the only species within the genus, is a small tree, completely covered by stinging hairs, endemic to cloud forests in Sierra de Juarez, Oaxaca in southern Mexico. Jarilla is a genus with three species, two of them (Jarilla heterophylla and Jarilla caudata) occurring together in central Mexico and the third (Jarilla chocola) more widely distributed along the Pacific Coast from northern Mexico to Guatemala and El Salvador. Jarilla chocola is distinctive in being an erect herb and having fruits that are pink and have five longitudinal wings. The other two species are more similar to each other, but can readily be distinguished by fruit and flower sizes. The three species are used locally as food and medicine, and are often found in native markets. Both tubers and fruits of the three species produce milky latex, and proteinase activity of a papain-like enzyme has been reported for Jarilla chocola. For detailed description, images, and distribution maps of these species, please use the search form.

Ecological, morphological, and genetic studies of wild Caricaceae other than Vasconcellea and Carica papaya are few. Breeding programs for papaya improvement have focused entirely on hybridization between papaya and highland papayas (see References). Given the new phylogenetic findings, it would be important to have ecological, chemical, and genomic studies of the herbaceous species that are the closest wild relatives of Carica papaya. For the domestication history of papaya from wild populations see Origin and domestication of Carica papaya.

Historical Biogeography

Molecular clocks for angiosperm and Brassicales show that the divergence between Caricaceae and its sister Moringaceae occurred during the Paleocene around 65 Mya(see References). A dated phylogeny of Caricaceae indicates that the family originated in Africa and reached the New World by long-distance dispersal at ca. 35 Mya. The dispersal from Africa to the Neotropics may have involved a floating island carried from the Congo delta via the North Atlantic Equatorial current.

Although the divergence between the African and the Neotropical Caricaceae occurred a long time ago (ca. 35 Mya), the two African species shared a young common ancestor of ca. 3 Mya (from the Plio-Pleistocene). This time coincides with a period in which the climate in Africa changed from wet to dry. This may explain the disjunction of the two species of Cylicomorpha that occur in montane and submontane rainforests of eastern and western Africa, respectively.

In the New World, Caricaceae began to diversify in Central America where all Neotropical genera are still occurring today. It seems that Caricaceae reached South America from Central America about 27 Mya. It was during the intense mountain building in the northern Andes that the Vasconcellea/Jacaratia clade began to differentiate. Today, most Vasconcellea species occur in the North Andean region, implying a strong effect of the Andean uplift in the diversification of this clade. On the other hand, Jacaratia consists of only lowland species, and its diversification may have been more affected by the Miocene climatic cooling. A single species (Jacaratia chocoensis) occurs in the Andean foothills. The expansion of dry woodlands and grasslands during the late Miocene (12-7 Mya) may have favored the occupation new habitats by species like Jacaratia mexicana and J. corumbensis. For detailed description, images, and distribution maps of these species, please use the search form.

Origin and domestication of Carica papaya

Identification of historic ancestors of papaya is not possible by means of phytoliths, and fossilized pollen grains are rare. The resulting absence of fossil and archeological records of Caricaceae makes it difficult to infer the place of origin and domestication of this important crop. Although some authors in the past suggested a South American origin, nowadays Central America is considered the center of origin and domestication of Carica papaya. The first to suggest this was Alphonse De Candolle in 1883 (read online), and the father of modern research into crop origin, Nikolai Ivanovich Vavilov in his "Origin and Geography of Cultivated Plants", also preferred a Central American domestication, perhaps by the Mayas, as opposed to domestication by the Incas in the Andean region.

Fieldwork over the past 20 years has shown that populations of the wild form of papaya occur only in Central America (map below), supporting the place of origin of Carica papaya in that region. The most distinctive feature of the wild form is its fruits, which are globose or ovoid and much smaller than the cultivated forms. Fruits of the wild papaya maximally reach 7 cm in diameter when mature). They also have a thinner layer of pulp (mesocarp) than the cultivated papayas and in general are not edible by humans, although they are tasty and sweet. Early civilizations from Mexico and Central America probably were the first people to regularly use papaya plants either as food or as a stomach medicine. The Olmec, Maya, and Aztecs also domesticated many other crops, such as maize and cotton. Much older domestication in southwestern Mexico, before 5000 BC, greatly predating the Mayan farming cultures, is also possible (as suggested for other crop species by Pohl et al. 1996).

Click here to find more information on Mesoamerican civilizations who domesticated other crops in that region.

The wild form of papaya was first formally named as Carica peltata by Hooker and Arnott in1840 (read online) based on a collection made in 1835 by Andrew Sinclair, during the World circumnavigation of Her Majesty's Ship the Sulphur, perhaps one of the best-documented journeys ever. Although the ship stopped in El Realejo several times, the type specimen was collected in Realejo, in February 1838. At that time, El Realejo belonged to Guatemala, but today is in Chinandega, northern Nicaragua. The wild papaya was again described in 1909 under the name Carica jamaicensis by Ignatz Urban in his Symbolae Antillanae based on a collection made by William H. Harris in Jamaica. He described a plant with small fruits (2.3-2 cm), only consumed by birds.

 

Sexual systems

Flowering plants (angiosperms) have a wide variety of sexual systems that differ in how male and female structures (stamens and pistils) are distributed on the plants of a population and sometimes also in the time when the male and female structures are functional. The flowers can be perfect (= bisexual or hermaphroditic) or imperfect (= unisexual or monoclinous). Hermaphroditic flowers bear stamens (male) and carpels (female). Monoclinous flowers either are staminate (having only functional stamens, thus male) or pistillate or carpellate (having only functional carpels, female). In this website, I will use the terms male flowers and female flowers to distinguish the two types of monoclinous flowers.

Caricaceae flowers are usually unisexual, although bisexual flowers are occasionally found. There is only one species (Vasconcellea monoica) that bears male and female flowers on the same plant (monoecious), all others are dioecious with male and female flowers on different individuals (male and female plants). Dioecy is a relatively rare sexual system among angiosperms occurring only in ca. 6% of species. In rare cases, individuals of one sex may produce flowers of the other sex or hermaphroditic flowers (see above). In Caricaceae, this has been documented in Vasconcellea pubescens, Jacaratia mexicana, and in Carica papaya where male plants may produce some female and some hermaphroditic flowers. A detailed study of tree sex ratio in natural populations is from Aguirre (2007) on Jacaratia mexicana who found that male plants with perfect flowers may represent up to 25% of the trees in a population or be absent. Species with fruit-producing males (hermaphrodites) are classified as trioecious, and this certainly applies to the cultivated papaya. In plantations, the morph ratios are heavily skewed by people's preference for the fruits of hermaphrodite papaya (i.e., males with fruits) that are preferred for the facilities of self-pollinated plants and also for the cylindrical shape of the fruits, which makes them easier to pack and transport than the spherical fruits of true females. Interestingly, in Africa, spherical fruits are preferred for their supposedly superior taste. On the other hand, more recently Cháves_Pesqueira et al. (Ref) have shown that the wild form of papaya is strictly dioecious (i.e. there is no hermaphrodites plants) and highly susceptible to habitat fragmentation.

Sex chromosomes

Following the discovery of morphologically distinct sex chromosomes in plants (in liverworts in 1917) a general search for sex chromosomes began among dioecious flowering plants, especially crop plants, including papaya. So far, 11 of the 34 species of Caricaceae had their chromosomes counted. The number is 2n = 18, with no morphological distinction between autosomes and sex chromosomes.

Experiments designed to find out sex segregation ratios from crosses among the three sexual systems of Carica papaya show that when hermaphrodite papayas are self-pollinated, it produces 2 hermaphrodites to 1 female (2 : 1). Female plants pollinated with pollen from an hermaphrodite plant generate 1 female to 1 hermaphrodite (1 : 1), and if a female plant is fertilized with pollen from a male plant the result is 1 female to 1 male (1 : 1). These ratios of offspring inheritance were the first evidence of sex chromosomes in papaya. Indeed already in the early 1940s it was suggested that papaya has three distinct chromosomes with a complex of genes confined to a small region in which recombination is suppressed, and that males and hermaphrodites are heterozygotes with a lethal gene what explains the 2 : 1 ratio.

Genome sequencing confirmed that sex determination in Caricaceae is of the XX-XY type, and that the hermaphrodite plants are determined by a slightly different Y chromosome named Yh. The X chromosome carries recessive genes responsible for the supression of stamens and development of female sex organs. The typical Y and the Yh have a small sex-specific region that is about 10 % of the chromosomes physical size. The male-specific region (MSY) present in the Y contains all information necessary to determine the male plants (i.e., a gene that promotes stamen development and a dominant mutation that suppresses the development of female sex organs). In the same way, a hermaphrodite-specific region (HSY), present in the Yh, determines the hermaphrodite individuals (i.e., contains a functioning male fertility allele and a recessive gene that promotes the development of carpels). To avoid that the male and female sterile mutations revert to hermaphroditism, recombination between the two sex-determining regions must be suppressed. This causes the degeneration of a large number of Y-linked genes, and if a seedling carries two Y alleles or a Y and a Yh allele, it will die. The XY system is reported also for Vasconcellea goudotiana, V. pubescens, V. parviflora, and V. pulchra (see references)

Carica papaya was one of the first woody plants to have its genome completely sequenced. However, in order to understand the evolution of the sex chromosomes in Caricaceae it will be important to sequence the genomes of its closest relatives and of the African species. So far, there have only been comparisons between Carica and Vasconcellea, which is clearly insufficient (see the phylogeny).

Taxonomic history

In total, more than 200 names for Caricaceae taxa have been published, of which I recognize 34 species and one hybrid (Vasconcellea × heilbornii). To see all accepted names and their respective synonyms, please use the search form.

The first description of a Caricaceae species dates from 1648, when Georg Marcgrave in his Historiæ rerum naturalium Brasiliæ libri octo described and illustrated Jaracatia brasiliensibus, pointing out some distinctive features of the genus, such as the palmately compound leaves. The name, probably was derived from the Tupi name of the plant, Yarakatiá that is still used locally in many regions of Brazil.

The first names assigned to papaya are reported from 1696 where Hans Sloane referred to the two sexes of papaya from Jamaica asPapaya major (the male papaw tree) and Papaya minor (the female papaw tree). Images of Sloane's collections from Jamaica are available here. It was in 1753 that Carl Linnaeus published the genus Carica describing two species (C. papaya and C. posoposa) based on plants growing in the green-houses of George Clifford in The Netherlands. The short description of C. posoposa given by Linnaeus unfortunately does not allow one to link it to any species, and none of three BM specimens associated with Hortus Cliffordianus 462, cited by Linnaeus, is a Caricaceae.

Pablo de La Llave (1832), a director of the National Museum of Natural History of Mexico, was the first to describe one of the unusual herbaceous Caricaceae (see section on the closest relatives of papaya). To mark the new species' distinctness he placed it in a separate genus, Mocinna, honoring the Mexican naturalist José Mariano Mociño. Realizing that Mocinna La Llave was a later homonym of Mocinna Lag. (an Asteraceae), Henry Hurd Rusby (1921) proposed the substitute name Jarilla, derived from the Spanish vernacular name Jarrila.

The first Vasconcellea to be described was V. quercifolia, based on collections from Rio Grande do Sul collected and named by A. Saint-Hilaire (1864). The name honors the Jesuit priest Simão de Vasconcellos, who was one of the first to write a history of Brazil (read online). For more details on Vasconcellea and V. quercifolia, please use the search form.

The first taxonomic treatment was carried out by Alphonse De Candolle (1864) who dealt with the family under the name Papayaceae and recognized three genera: Papaya with three species; Vasconcellea with 15 species divided in two sections (Hemipapaya and Euvasconcellea), and Jacaratia with four species. Twenty-five years later Solms-Laubach (1889) accepted 28 species of Caricaceae in two genera, Jacaratia with five species and Carica with three sections: section Vasconcellea with 16 species, section Hemipapaya with two species, and section Eupapaya with three species. He did not mention any herbaceous or Central American species.

The first Caricaceae from Africa, collected by Paul Rudolph Preuss in the year 1890 in southwestern Cameroon, was described by Urban (1893) and named Jacaratia solmsii, to honor Solms-Laubach. Based on collections made by Carl H. E. W. Holst in the year 1893 in the Usambara mountains of Tanzania, Urban (1901) described a second African species and transferred both species to a separate genus, Cylicomorpha.

Victor Manuel Badillo Francieri (1920-2008), a Venezuelan taxonomist expert on Caricaceae and Asteraceae, greatly improved our knowledge of the papaya family. Badillo had an acute sense of observation, extensive field experience and the intuity to use information from other disciplines, such as the results of breeding experiments by his colleagues Salomón Horovitz and Humberto Jiménez (see References), and the results of the first studies using molecular data that begun in the late 1990s (see References).

Badillo published extensively on Caricaceae from 1967 until 2001 (see References) when he reestablished Carica and Vasconcellea as separate genera (as first suggested by De Candolle in 1864). He took into account the chloroplast DNA results of Aradhya et al. (1999) who found that Carica papaya was a distinct evolutionary lineage, and that Vasconcellea species (previously included in Carica) were closer related to Jacaratia mexicana. Badillo's most important contribution was a monograph of the family published in 1971. In 1968 he was awarded for his work on Caricaceae by the association of professors of the Universidad Central de Venezuela.

The only recent revision of one of the genera is that of Jarilla by Carlos Díaz Luna and José Lomeli (1992), who greatly enlarged our understanding of this small group of herbs with their first-hand knowledge of the plants, both in the field and herbarium.

Please refer to the search form to find more on nomenclature (synonyms and accepted names), illustrations, distribution maps, images of specimens and other detailed information on each of the taxa (species or genus).

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