A tree from the forests of West and Central Africa, Parkia bicolor has large, reddish, pendent flower heads that are pollinated by fruit bats at night.
About this species
The genus Parkia was named by the renowned British botanist Robert Brown in honour of the explorer Mungo Park, who mentioned these trees in the account of his travels in West Africa in the late 18th century. Parkia bicolor is one of three African species in this genus, the others being P. biglobosa, a characteristic tree of West African savanna woodland (and the species actually seen by Park), and P. filicoidea, another forest species, mostly from central and eastern Africa. All of the African species of Parkia have pendent, reddish flower heads that resemble pom-poms and are pollinated by fruit bats, also known as pteropodid bats.
Geography & Distribution
Parkia bicolor occurs across western and central Africa, from Guinea in the west as far as eastern Congo, and south to the Cabinda region of Angola. It occurs in rain forest up to 1,200 m, and often also in gallery forest and swamp forest, usually in regions with more than 2,000 mm of rain per year.
Widely spreading buttresses (woody fins acting as supports) of Parkia bicolor (Image: Xander van der Burgt)
A tree up to 35 m tall (sometimes even taller), with a tall bole (unbranched part of the trunk) about 1 m in diameter, widely spreading buttresses and a well-developed, briefly deciduous crown. The leaves are bipinnate (divided into leaflets which divide again), and up to 35 cm long. Each of the numerous pinnae bears 30 or more pairs of small, slightly curved leaflets. The individual flowers are small, and are massed into bluish-red or orange-red flower heads that are borne on tough, pendent stalks. In each flower head, fertile flowers form a round to elongated ball at the tip. The sterile flowers have long filaments which form a fringe at the base, and this fringe overhangs a ring of specialised nectar-secreting flowers in the middle. The fertile flowers have a 5-lobed corolla, 10 stamens (male parts), and a single ovary with a long terminal style and about 20 ovules. The flowers open in late afternoon and last for one night. The pods (fruits) are up to 40 cm long x 1.5–3.5 cm broad, twisted and strap-like but swollen over each seed. They hang in bunches in the crown, each bunch arising from the woody, central part of the old flower head. The flattened seeds are 11–15 x 7–10 mm and surrounded by a small amount of yellowish floury pulp that is eaten by dispersers, such as monkeys.
A remarkable study by the German biologist Regine Grünmeier, in Cameroon, showed that the flower heads of Parkia bicolor are visited at night by several species of pteropodid fruit bats, including the specialised nectar-feeding bat Megaloglossus. The pollination of P. bicolor featured in a wildlife documentary about Korup National Park, by the film-maker Phil Agland. When bats pollinate the flowers they land on the flower heads, lick nectar that has exuded from the specialised nectar-flowers and become dusted with pollen. Several non-flying nocturnal mammals, such as pottos, African dormice and bushbabies, are also attracted to the flower heads and can act as pollinators. In the late afternoon and early morning, honeybees and birds also visit in search of nectar and pollen.
Many bat-pollinated plants have white or drab flowers but those of Parkia are unusual as they are either reddish, as in P. bicolor, or yellow (as in species from Asia, Madagascar and some from South America). This is thought to be due, at least in part, to the fact that the bats involved in pollination have relatively good eye-sight and the flower heads are highly reflective when fresh. On starlit nights the flower heads are visible to the bats (and other nocturnal mammals), either against the sky or the tree’s foliage.
However, the floral scent of Parkia bicolor is entirely typical for a bat-pollinated plant, being musty and slightly unpleasant. Analyses using gas chromatography have shown that the odour of this species is due to various terpenoids (or isoprenoids) and fatty acid derivatives. Sulphur-containing compounds are not present, although they do contribute to the smell of some other bat-pollinated flowers, such as Adansonia digitata, the African baobab.
Threats & Conservation
Taking into account its entire geographical range, Parkia bicolor is not considered threatened at present, although in several countries its distribution is decreasing as forests are destroyed. Although not considered threatened, P. bicolor illustrates an important principle in conservation biology. Numerous types of animal are involved in its pollination and dispersal, and in addition it has various pests and diseases, indicating a complex web of relationships that is especially typical of tropical rain forests. An understanding of the relationships within this web can be important in developing conservation strategies – if pollinators and dispersers are not conserved along with plant species, then the plants’ long term survival cannot be assured. In trees of the rain forest canopy, such as P. bicolor, pollination and dispersal occur high above the ground, making these interactions particularly difficult to study.
Conservation assessments carried out by Kew
Parkia bicolor is being monitored as part of the Sampled Red List Index Project, which aims to produce conservation assessments for a representative sample of the world’s plant species. This information will then be used to monitor trends in extinction risk and help focus conservation efforts where they are needed most.
Until recently the wood of Parkia bicolor was considered inferior, but because stands of many commercial timber species are becoming depleted, this species is assuming more importance, especially for local construction and joinery. The wood is also used for plywood and pulpwood.
The fruit pulp is edible and the fermented seeds are used as a condiment. The fruit is used in west Africa as bait for catching fish and squirrels. Several parts of the tree are used in traditional medicine. For example, macerated bark is used to treat eye complaints, powdered bark is used to treat wounds and sores, and a leaf pulp is rubbed onto smallpox and chicken pox.
The tree is sometimes retained when forest is cleared for agriculture, as its open, widely spreading crown is useful for shading crops.
Research is needed to determine sustainable levels of harvesting natural stands for timber and other products.
This species at Kew
Dried and spirit-preserved specimens of Parkia bicolor are held in Kew’s Herbarium, where they are available to researchers by appointment. The details of some of these specimens, including some images, are available on-line in the Herbarium Catalogue.
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