Some 100-150, see text.
Annona 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 110 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 Mexico to approximately 1000 BC.
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. Several annonacaeous species have been found to contain acetogenins, a class of natural compounds with a wide variety of biological activities.
Annona species are taprooted, evergreen or semideciduous, tropical trees or shrubs. This fruit typically grows in areas which do not get below 28 degrees; Cuba, Jamaica, and the Philippines, however it has been known to grow in certain areas of Florida.
- Trunks: The 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.
- Leaves: Leaf blades can be leathery or thin and rather soft or pliable, bald or hairy.
- Flowers: The flowering stalks rise from axils, or occasionally from axillary buds on main stems or older stems, or as solitary flowers or small bundle 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 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. Numerous stamens that are ball, 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 distinct stigma, with one or two ovules per pistil; the style and stigma are club-shaped or narrowly conic.
- Fruits: 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: Dynastid scarab beetles appear basic 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.
The compound annonacin contained in the seeds of some members of Annonaceae such as Annona muricata (soursop) is a neurotoxin and it seems to be the cause of a neurodegenerative disease. The only group of people known to be affected 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 demonstrated for the first time that the plant neurotoxin annonacin is responsible for this accumulation.
Selected species 
The following is a list of some of the more important species. Many of them have significant agricultural, medicinal, pharmaceutical, and other uses. Synonyms appear in the sublist.
Insects and diseases 
Annona species are generally disease-free. They are susceptible to some fungi and wilt. Ants are a problem, since they promote mealybugs on the fruit.
- Natural Resources Conservation Service (NRCS). "PLANTS Profile, Annona L.". The PLANTS Database. United States Department of Agriculture. Retrieved 2008-04-16.
- Germplasm Resources Information Network (GRIN) (1996-09-17). "Genus: Annona L.". Taxonomy for Plants. USDA, ARS, National Genetic Resources Program, National Germplasm Resources Laboratory, Beltsville, Maryland. Retrieved 2008-04-18.
- "Annona". Integrated Taxonomic Information System. Retrieved 2008-04-16.
- Flora of North America. 1. Annona Linnaeus, Sp. Pl. 1: 536. 1753; Gen. Pl. ed. 5, 241, 1754 3. Retrieved 2008-04-20.
- Austin, Daniel F. (2004). Florida Ethnobotany. CRC Press. p. 95. ISBN 978-0-8493-2332-4.
- Warrington, Ian J. Warrington (2003). "Annonaceae". Apples: Botany, Production and Uses. CABI Publishing. ISBN 0-85199-592-6. Retrieved 2008-04-20.
- University of Southampton (March 2002). "Factsheet No. 5. Annona" (PDF). Fruits for the Future. Department for International Development, International Centre for Underutilised Crops. Retrieved 2008-04-20.
- Pilar Rauter, Amélia; A. F. Dos Santos and A. E. G. Santana (2002). "Toxicity of Some species of Annona Toward Artemia Salina Leach and Biomphalaria Glabrata Say". Natural Products in the New Millennium: Prospects and Industrial Application. Springer Science+Business Media. pp. 540 pages. ISBN 1-4020-1047-8. Retrieved 2008-04-20.
- Esposti, M Degli; A Ghelli, M Ratta, D Cortes, and E Estornell (1994-07-01). "Natural substances (acetogenins) from the family Annonaceae are powerful inhibitors of mitochondrial NADH dehydrogenase (Complex I)". The Biochemical Journal (The Biochemical Society) 301 (Pt 1): 161–7. PMC 1137156. PMID 8037664.
- Gottsberger, Gerhard (28 April 1988). "Comments on flower evolution and beetle pollination in the genera Annona and Rollinia (Annonaceae)". Plant Systematics and Evolution (Springer Science+Business Media) 167 (3–4): 189–194. doi:10.1007/BF00936405. Retrieved 2008-04-20.
- Informationsdienst Wissenschaft: Tauopathie durch pflanzliches Nervengift, 4. Mai 2007
- Germplasm Resources Information Network (GRIN). "GRIN Species Records of Annona". Taxonomy for Plants. USDA, ARS, National Genetic Resources Program, National Germplasm Resources Laboratory, Beltsville, Maryland. Retrieved 2008-04-16.
- Robert Vieth, Master Gardener. "Cherimoya". Minor subtropicals. Ventura County Cooperative Extension. Retrieved 2008-04-20.
- Jorge Pena and Freddie Johnson (October 1993). "Insect Pests of Annona Crops" (PDF). Other Fruits With Insecticides Known to Have Labels for Use. Department of Entomology, University of Florida. Retrieved 2008-04-19.
- Jonathan H. Crane, Carlos F. Balerdi, and Ian Maguire (April 1994). "Sugar Apple Growing in the Florida Home Landscape". Fact Sheet HS38. Institute of Food and Agricultural Sciences, University of Florida. Archived from the original on 11 April 2008. Retrieved 2008-04-19.
- Bridg, Hannia (2001-05-03). "Micropropagation and Determination of the in vitro Stability of Annona cherimola Mill. and Annona muricata L.". Zertifizierter Dokumentenserver der Humboldt-Universität zu Berlin. Archived from the original on 24 April 2008. Retrieved 2008-04-20.
- Media related to Annona at Wikimedia Commons
- Data related to Annona at Wikispecies
- Type Collections of Neotropical Annonaceae - Annona — has pictures and details on these and other Annona species