Psidium guajava L. (Myrtaceae)

Small evergreen weedy tree from tropical America introduced throughout the tropics for its edible fruits. It is spreading in pasture and agricultural land. On the Galapagos it is displacing evergreen forest composed of many endemic taxa.

Species characteristics

Life form, size, lifespan

Evergreen shrub or small wide-spreading tree 3-10 m high.

Taxonomy, variation and plasticity

Numerous varieties including yellow and red fruited ones. All cultivars are vegetatively propagated.

Reproductive biology

The white flowers are ca. 1.5 cm in diameter and are found singly or in cymes of 2 or 3 flowers. Flowers are pollinated by bees and other insects and cross-pollination accounts for about 35% of the seed set. The large pear-shaped fruit (5 cm long) is an edible berry and contains numerous seeds (size 3-5 mm). It is mainly distributed by cattle. The seed passage through the animals digestive tract does not appear to affect seed germination but seed losses occur as a result of food mastication. Seeds remain viable for several months and will germinate in 3-5 weeks in the warm season. Seed germination rates vary much from year to year and seedling establishment in cow pats is reduced by as much as 50% as shoots of germinated seeds deeply buried in the dung fail to reach the surface.

Resilience and resistance

P. guajava often suckers from roots near the base of the trunk, particularly after a light frost, to which the tree is susceptible. It tolerates temporary waterlogging. Following cutting it coppices readily and the tree spreads by suckering. It can also be propagated by layering or cuttings. P. guajava possesses vesicular-arboricular mycorrhizal associations.

Environmental requirements and successional status

It has an excellent ability to compete with weeds and grass. It can take over sites when it receives full sunlight but can withstand partial shading.

Products and uses

The wood makes excellent firewood and charcoal, and tool handles and implements can be made out of it. The fruits have a very high vitamin C content and red guavas are rich in vitamin A. They are made into preserves, jam, jelly and juice. The tannin-rich leaves and green fruits are used for dyeing and tanning.

Status in native range

Range and abundance

Native to the American tropics where it is widely cultivated.


It grows well in tropical areas of more than 1000 mm of rainfall and can endure droughts of 4 to 5 months.

Site requirements

Found from sea level to 800 m and sometimes up to 1500 m, although its natural limit is unclear due to widespread planting. It favours slightly to strongly acid soils.


It is a common pasture weed in central America either as scattered trees or in pure stands (264 trees/ha).

Pests and diseases

Many insects are reported to cause damage to the plant but particularly to its fruits.

Status in invaded regions

History of introductions and intensity of invasions

At an early date the Spanish brought P. guajava to the Philippines and the Portuguese to India, and it was then spread throughout the tropics. A tree from the Melbourne Botanic Gardens was introduced to Fiji in 1863, where the species has since become a major weed of pastoral, arable and plantation land. First introduced to the Galapagos around 1870 and is now found on three of the populated islands. It has invaded natural forest and covers large areas of these islands.

Patterns of invasion and time-lag

In agricultural areas it becomes a serious pest particularly as a result of root suckering induced by firewood cutting. It competes successfully with crop plants and grasses and soon forms thickets which smother grasses and reduce crop yields. In the Galapagos in 1922 it was already mentioned as a bad plague forming impenetrable thickets. It has replaced most evergreen forest on one of the islands and covers vast areas of the humid zones of four islands. The spread is facilitated by introduced cattle which eat the fruit and excrete the seeds. The dung provides a nutrient rich substrate and appear to reduce grass competition. Cattle also trample vegetation and create open spaces necessary for successful P. guajava seed germination and seedling establishment. Increased fire frequency increase P. guajava dominance.

Site and climate

In the tropics it becomes established under a wide variety of soil and climatic conditions, particularly rainfall.

Floristic region and vegetation types

Usually found on fallow land with highly modified flora. On the Galapagos the invaded vegetation contains a large number of endemic taxa and P. guajava is mostly found in the evergreen forest or scrub.

Pests and diseases

In Fiji P. guajava is attacked by the fungus Botryodiplodia theobromae which also attacks plantation crops. In India wilt is usually fatal where P. guajava occurs on soil with pH > 7.5.

Impact on ecosystem

On the Galapagos Islands P. guajava outgrows native species and forms dominant stands suppressing the native flora. Its spread poses a threat to the survival of some of these endemic species.

Impact on humans and related activities

In Fiji the invasion of pasture land made livestock farming uneconomic in places and also provided an excellent breeding ground for insect pests. Despite the fruit's food value, it is considered a pest. In many regions it supplies valuable firewood and is a good food source.


In the Galapagos restriction to cattle movement is the main factor which can slow the spread of the invasion both by preventing the dispersal of seeds and the production of regeneration sites. Established trees are cut and stumps painted with herbicide. In Fiji P. guajava has been most successfully controlled from arable land using mechanical means.

Ecological differences

Existence of ecological equivalent species and competitive interactions in invaded regions

In the Galapagos most native tree species lack VA mycorrhizal associations and their existence in P. guajava may give it some competitive advantage. The introduced cattle facilitate the spread and regeneration of the invader but not that of endemic species. Some endemic and rare taxa have failed to regenerate following bush fires whereas P. guajava shows a high degree of survival and regeneration.

Differences in status and ecology between invaded and native ranges

The spread in open areas is similar in both native and invaded ranges, however the ability to invade disturbed forest and dominate the native species is only observed on the Galapagos Islands.

Selected references

# Anon (1983) Firewood crops; shrub and tree species for energy production, Vol. 2. National Academy of Science, Washington.
# Anon (1986) Food and fruit-bearing forest species. 3. Examples from Latin America. FAO, Rome.
* Hamann, O. (1991) Indigenous and alien plants in the Galápagos Islands: problems of conservation and development. In Heywood, V.H. & Wyse Jackson, P.S. (Eds) Tropical botanic gardens: their role in conservation and development, pp. 169-192. Academic Press, London.
** Partridge, I. (1979) The guava threat in Fiji. South Pacific Bull. 29(2), 28-30.
** Nowak, J.B., Lawesson, J.E., Adsersen, H. & Vries, T. de (1990) A two-year study of post-fire vegetation dynamics on southern Isabela, Galapagos Islands, Ecuador. Monogr. Syst. Bot. Missouri Bot. Gard. 32, 123-136.
# Purseglove, J.W. (1968) Tropical crops. Dicotyledons. Longman, London.
* Schofield, E.K. (1989) Effects of introduced plants and animals on island vegetation: Examples from the Galápagos Archipelago. Conserv. Biol. 3, 227-238.
• • Somarriba, E. (1988) Guava (Psidium guajava L.) trees in a pasture: population model, sensitivity analyses, and applications. Agrofor. Syst. 6, 3-17.
**# Ellshoff, Z.E., Gardner, D.E., Wikler, C. & Smith, C.W. (1996) Annotated bibliography of the genus Psidium, with emphasis on P. cattleianum (strawberry guava) and P. guajava (common guava), forest weeds in Hawai`i. Coop. Nat. Park Res. Stud. Unit Techn. Rep. 95.

Pierre Binggeli

May 1997