Annona glabra

Annona glabra is a tropical fruit tree in the family Annonaceae, in the same genus as the soursop and cherimoya. Common names include pond apple, alligator apple (so called because American alligators often eat the fruit), swamp apple, corkwood, bobwood, and monkey apple.[2] The tree is native to Florida in the United States, the Caribbean, Central and South America, and West Africa.[3] It is common in the Everglades. The A. glabra tree is considered an invasive species in Sri Lanka and Australia. It grows in swamps, is tolerant of saltwater, and cannot grow in dry soil.

Annona glabra
Fruit

Least Concern  (IUCN 3.1)[1]
Scientific classification
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Magnoliids
Order: Magnoliales
Family: Annonaceae
Genus: Annona
Species:
A. glabra
Binomial name
Annona glabra

Description

The trees grow to up to 12 m. They have narrow, gray trunks and sometimes grow in clumps. The leaves are ovate to oblong, each with an acute tip, 8–15 cm long and 4–6 cm broad with a prominent midrib. The upper surface is light to dark green. Leaves of the A. glabra are said to have a distinct smell, similar to green apples, that can distinguish it from mangroves.[4] The fruit is oblong through spherical and apple-sized or larger, 7–15 cm long and up to 9 cm diameter, and falls when it is green or ripening yellowish. It disperses by floating to new locations, and it is food for many animal species such as wild boar. Reproduction begins around two years of age. A fruit contains 100 or more convex, light yellow-brown seeds, about 1 cm long.[5] A. glabra flowers have a short life-span, and have a diameter of 2-3cm. The flowers have three outer petals as well as three inner petals. Compared to the pale yellow or cream color of the petals, the inner base of the A. glabra flower is a bright red.[4] Its pollen is shed as permanent tetrads.[6]

Ecology

A. glabra thrives in wet environments. The seeds and fruit of this plant can be dispersed during wet seasons where they fall into swamps and rivers. This allows the seeds and fruits to spread to coastlines. A 2008 study found that A. glabra seeds can withstand floating in salt water and fresh water for up to 12 months. About 38% of those seeds can then germinate in soil, though A. glabra roots do not do well with constant flooding.[7] Another study in 1998 found that even under intense flooding, the 12-month lifespan of A. glabra seedlings was unaffected; the growth rate of A. glabra trees did decrease however over a 6-month period. Compared to other Annona seeds and trees, the A. glabra is still more resilient to instances of flooding. [8]

Uses

Unlike the other Annona species, the pulp of the fruit when ripe is yellow through orange instead of whitish.[9] The fruit is edible for humans and its taste is reminiscent of ripe Honeydew melon. It can be made into jam, and it is a popular ingredient of fresh fruit drinks in Maldives. In the older days the seeds were crushed and cooked in coconut oil and applied to hair to get rid of lice [10]

The flesh is sweet-scented and agreeable in flavor, but it has never attained general popular use unlike soursop and other related fruits. Experiments in South Florida have been conducted to use it as a superior rootstock for sugar-apple or soursop. While the grafts initially appear to be effective, a high percentage of them typically fail over time. Soursop on pond-apple rootstock has a dwarfing effect.

Recent research suggests that its alcoholic seed extract contains anticancer compounds that could be used pharmaceutically.[11]

Invasive species

It is a very troublesome invasive species in northern Queensland in Australia and Sri Lanka, where it grows in estuaries and chokes mangrove swamps. The A. glabra tree was introduced to North Queensland sometime around 1912 as both a rootstock for similar Annona species such as Annona atemoya, the custard apple.[12] A. glabra seedlings carpet the banks and prevent other species from germinating or thriving. It also affects farms as it grows along fencelines and farm drains. It also invades and transforms undisturbed areas.[13] This can be observed in the case of Australia’s Eubenangee Swamp National Park where an outbreak occurred due to poor wetland management.[4]

In Australia, A. glabra seeds can be spread by the southern cassowary. Seeds of the fruit have been found in cassowary dung with dispersal distances of up to 5212 m recorded in one 2008 study in the journal Diversity and Distributions. [14] The southern cassowary itself however is an endangered species in Australia. According to the Australian government’s Department of the Environment and Energy, there is only around 20-25% of cassowary habitat remaining. Additionally, part of the government’s recovery plan includes actions towards establishing nurseries filled with plants that the cassowary consumes. [15] Because the A. glabra is among the foods eaten by southern cassowary, revegetation may be necessary to ensure that cassowary have alternative food sources available. When the A. glabra population is controlled, natural vegetation can regenerate without human intervention. [4]

Because of its impact on the environment as an invasive weed, the Australian government classifies the A. glabra as a Weed of National Significance (WONS).[16] Additionally, the A. glabra was considered the highest ranked species in 2003 in a Wet Tropics bioregion weed risk assessment.[12] In Sri Lanka it was introduced as a grafting stock for custard apples and spread into wetlands around Colombo.[5]

Control strategies

Australia

The Australian government views the A. glabra as a weed, and as such offers through its Department of the Environment and Energy a control plan created in 2001 for citizens that aims at eliminating the A. glabra by 20 years. The plan includes six steps that property owners can take to determine how to control and monitor an outbreak of A. glabra as well as how to minimize financial damage. To disincentivize the cultivation and spread of A. glabra by humans, its sale and entry is banned throughout most of Australia.[4]

Options for the control of the A. glabra include fire, chemical, and mechanical controls including combinations of the three types. The best time of year to do so according to the government of Australia is during the time between August to November, which is the dry season. There are currently no studies that have looked at the biological control of A. glabra within Australia. Without studies, any actions taken to eliminate the A. glabra with biological controls could inadvertently affect native Australian apple species that belong to the same family.[4]

  • Leaves
  • Flower
  • Fruit
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References

 This article incorporates text from a publication now in the public domain: Ward, Artemas (1911). "Alligator Apple". The Grocer's Encyclopedia.

  1. Verspagen, N. & Erkens, R.H.J. (2020). "Annona glabra". IUCN Red List of Threatened Species. 2020: e.T142424510A142424521. Retrieved 8 August 2020.
  2. Standley, Paul C. (1922). "Trees and Shrubs of Mexico". United States National Herbarium. 23 (2): 281–282.
  3. "Annona glabra, Annona glabra". Germplasm Resources Information Network (GRIN). Agricultural Research Service (ARS), United States Department of Agriculture (USDA). Retrieved 2009-01-27.
  4. "Control methods and case studies" (PDF). Department of the Environment and Energy. Retrieved 2017-03-25.
  5. Lalith Gunasekera, Invasive Plants: A guide to the identification of the most invasive plants of Sri Lanka, Colombo 2009, p. 112–113.
  6. Tsou, C.-H.; Fu, Y.-L. (2002). "Tetrad pollen formation in Annona (Annonaceae): proexine formation andbinding mechanism". American Journal of Botany. 89 (5): 734–747. doi:10.3732/ajb.89.5.734. ISSN 0002-9122.
  7. Setter SD, et al. (2008). "Buoyancy and germination of pond apple (Annona glabra L.) propagules in fresh and salt water". Sixteenth Australian Weeds Conference: 140–142.
  8. Núñez-Elisea R (1998). "Impact of Flooding on Annona Species". Proc. Fla. State Hort. Soc.: 317–319.
  9. Annona glabra fruit Archived February 18, 2015, at the Wayback Machine
  10. FAO Trees and shrubs of the Maldives
  11. Cochrane CB, Nair PK, Melnick SJ, Resek AP, Ramachandran C (2008). "Anticancer effects of Annona glabra plant extracts in human leukemia cell lines". Anticancer Research. International Institute of Anticancer Research. 28 (2A): 965–71. PMID 18507043.
  12. Setter SD, et al. (2004). "Longevity of pond apple (Annona glabra L.) seeds and implications for management". Fourteenth Australian Weeds Conference: 551–554.
  13. ”Pond apple (Annona glabra) weed management guide”, Department of Sustainability, Environment, Water, Population and Communities, Canberra, at http://www.environment.gov.au/biodiversity/invasive/weeds/publications/guidelines/wons/pubs/a-glabra.pdf
  14. Wescott, David A. (2008). "Cassowary dispersal of the invasive pond apple in a tropical rainforest: the contribution of subordinate dispersal modes in invasion". Diversity and Distributions. 14 (2): 432–439. doi:10.1111/j.1472-4642.2007.00416.x.
  15. "The Southern Cassowary". Department of the Environment and Heritage.
  16. "Adaptive Management: Pond Apple Control In the Catchments of the Russel-Mulgrave and Tully-Murray River Systems" (PDF). Wet Tropics Management Authority. 2004.
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