Annona

''Annona'' (from Taíno ''annon'') is a genus of flowering plants in the pawpaw/ sugar apple family, Annonaceae. It is the second largest genus in the family after '' Guatteria'', containing approximately 166Species of Annona
on The Plant List. Retrieved 2013-05-28. species of mostly Neotropical and Afrotropical trees and shrubs.

The generic name derives from ''anón'', a Hispaniolan Taíno word for the fruit. Paleoethnobotanical studies have dated ''Annona'' exploitation and cultivation in the Yautepec River region of Medicoto to approximately 1000 BC. Plants of the genus have several common names, including sugar-apple, soursop, and guanabana.

Currently, seven ''Annona'' species and one hybrid are grown for domestic or commercial use, mostly for the edible and nutritious fruits; several others also produce edible fruits. Many of the species are used in traditional medicines for the treatment of a variety of diseases, though their efficacy has yet to be validated scientifically. Several annonaceous species have been found to contain acetogenins, a class of natural compounds with a wide variety of biological activities. The first complete genome for a species in this genus (''Annona muricata'') was published in 2021.

Description

''Annona'' species are taprooted, evergreen or semideciduous, tropical trees or shrubs. The plants typically grow in areas where air temperature does not drop below , especially Cuba, Jamaica, Central America, India the Philippines and Calabria (southern Italy). However, they have also been known to grow in certain parts of the Andes mountains in South America and in Florida.

The woody trunks have thin bark that has broad and shallow depressions or fissures which join together and are scaly, giving rise to slender, stiff, cylindrical, and tapering shoots with raised pores and naked buds. Leaf blades can be leathery or thin and rather soft or pliable, bald or hairy.

The flowering stalks rise from axils, or occasionally from axillary buds on main stems or older stems, or as solitary flowers or small bundles of flowers. Usually, the three or four deciduous sepals are smaller than the outer petals that do not overlap while in bud. Six to eight fleshy petals are arranged in two whorls—the petals of the outer whorl are larger and do not overlap; inner petals are ascending and distinctively smaller, and nectar glands are darker pigmented. The numerous stamens are ball-shaped, club-shaped, or curved and hooded or pointed beyond anther sac. Numerous pistils, attached directly to the base, are partially united to various degrees with a distinct stigma, with one or two ovules per pistil; the style and stigma are club-shaped or narrowly conic.

One fleshy, ovate to spherical fruit is produced per flower. Each fruit consists of many individual small fruits or syncarps, with one syncarp and seed per pistil. Seeds are bean-like with tough coats; the seed kernels are toxic.

Pollination occurs via Dynastid scarab beetles, which appear to be basic generalists within the genus ''Annona''. Those species of ''Annona'' which are more morphologically derived, as well as all '' Rollinia'' spp., possess reduced floral chambers and attract small beetles such as Nitidulidae or Staphylinidae.

Toxicology

The compound annonacin and dozens of other acetogenins contained in the seeds and fruit of some members of Annonaceae such as ''Annona muricata'' (soursop) are neurotoxins and seem to be the cause of a Parkinson-like neurodegenerative disease. The only group of people known to be affected by this disease live on the Caribbean island of Guadeloupe and the problem presumably occurs with the consumption of plants containing annonacin. The disorder is a so-called tauopathy associated with a pathologic accumulation of tau protein in the brain. Experimental results published in 2007 demonstrated for the first time that the plant neurotoxin annonacin is responsible for this accumulation.

Selected species

There are 169 accepted ''Annona'' species, as of April 2021, according to Plants of the World Online.

*''Annona acuminata''
*''Annona acutiflora''
*''Annona ambotay''
*''Annona angustifolia''
*''Annona asplundiana''
*''Annona atabapensis''
*''Annona aurantiaca''
*''Annona bullata''
*''Annona cacans'' – araticum-cagão
*''Annona cascarilloides''
*''Annona cherimola'' – cherimoya
*''Annona chrysophylla'' – graines
*''Annona conica''
*''Annona cordifolia''
*''Annona coriacea''
*''Annona cornifolia''
*''Annona crassiflora'' – araticum do cerrado, marolo
*''Annona crassivenia''
*'' Annona cristalensis''
*''Annona cubensis''
*''Annona deceptrix''
*''Annona deminuta''
*''Annona dioica''
*''Annona diversifolia''
*''Annona dolichophylla''
*''Annona ecuadorensis''
*'' Annona ekmanii''
*''Annona foetida''
*''Annona fosteri

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