Kapok is a large, imposing tree originating from tropical America, its natural range extending from Mexico, through Central America and the Caribbean, to northern parts of South America.
Exceptional specimens may reach heights of up to 40 m (130 ft), though it is more commonly a medium-sized tree 15 to 25 m (50 to 82 ft) tall.
There are two recognised subspecies, Ceiba pentandra var. indica and Ceiba pentandra var. caribaea. The latter easily distinguished by its large, prominent buttresses on mature trees, rising from the ground to 3 to 4 m (10 to 13 ft) in height up the trunk.
Depending on the growing conditions, the trunk may be clear of branches for most of the tree's height or is low-branching. On well-shaped trees, the trunk is tall, straight, round and bulbous, with prominent buttresses near the ground and an umbrella-shaped crown at the top, formed by far-stretching, horizontal branches. The bark is grey and smooth except for stout pyramidal spines on young trees, these becoming absent on mature trees.
The leaves are palmately compound, made up of five to seven dark green leaflets in a close arrangement, casting a deep shade. Leaf-fall occurs in areas with a long or pronounced dry season, leaving the branches bare and exposed.
Flowering occurs in the dry season when the tree is leafless, with blooms of large five-petaled, white or pink cup-shaped flowers. They are borne singly or in clusters of a few and in great numbers, though not every year. Opening just before sunset, they remain open throughout the night to be pollinated by bats, the tree's specialist pollinators.
Fertilised flowers develop into oval fruit 10 to 20 cm (4 to 8 in) long, green when young, becoming dark brown when mature and with a weak shell that can be crushed by hand. At maturity, the shell splits into five longitudinal sections, exposing a mass of wholly creamy-white hairs, inside of which are up to a hundred small roundish black seed.
Image by DEZALB from Pixabay
The hairs or fibres produced by the fruit are known as 'Kapok fibres, which long ago were commercially exploited until replaced by synthetic fibres derived from petroleum. Although not suitable for weaving into fabric because of their smoothness and weakness, their springiness, moth resistance, water-repellency and buoyancy make them useful for stuffing pillows, mattresses, sleeping bags and flotation devices, as well as for insulating against sound and temperature. Yields are estimated at 2.7 to 4 kgs (6 to 9 lbs) of fibre, per tree, per year.
The seed contains about 25% of a pale yellow to brown non-drying oil traded as 'Kapok oil', which is used in much the same way as refined cottonseed oil after refining. It has been used for various purposes, including as lamp oil by traditional people and making margarine and soap in more recent times. Due to high nitrogen, phosphorus, and potassium concentrations, the leftover press cake can be fed to livestock but is largely indigestible and more suitable as organic manure or fertilizer.
The wood is lightweight, averaging around 330 kgs per cubic meter (20 lbs per cubic foot), and has low natural resistance to rot, decay and wood-boring insects. This limits its suitability for construction purposes, other than as a substitute for Balsa (Ochroma pyramidale).
In the coastal parts of the tree's natural range, the trunk of tall, well-formed trees were once crafted into sea-worthy canoes used by fishermen. They were known as 'dug-out canoes' because they were made by hollowing out the wood from the centre, after which the cavity was ribbed for reinforcement and the exterior shaped and painted. The craft of making dug-out canoes from Kapok trees has now mostly died out due to the development of fibreglass canoes.
The flowers produce abundant nectar and are a valuable pollen source for brood-rearing honeybees, making it one of the most important trees for beekeepers in the tropics. The pure honey is pale amber with a characteristic sweet honey taste.
The bark, on wounding, yields a dark gum that swells in water and is similar to tragacanth-type gums except for its colour. Its properties and medicinal use are closest to Karaya Gum (from Sterculia urens). An astringent, it is used in traditional medicine in India as a treatment against bowel complaints.
According to the National Science Foundation of the United States (NSF), the flowers of a single tree can produce up to 190 litres (50 gallons) of nectar per season. This nectar attracts bats that travel up to 19 kilometres (12 miles) between trees, transferring pollen in the process.
Grows naturally in sub-humid to humid subtropical and tropical lowland to mid-elevation climates, generally areas with annual lows of 14 to 25°C, annual highs of 26 to 36°C, annual rainfall of 800 to 5000 mm, and a dry season of 7 months or less.
New plants are usually started from cuttings or seed. Seed are preferred because the trees develop stronger roots, though vegetatively propagated trees will begin to flower and fruit much earlier, when about five to six years old.
Performs best on free-draining clay, loam and sand soils of a moderately acid to slightly alkaline nature, generally with a pH of 4.7 to 7.5, and on sites with full sun exposure.
Kapok is recorded as a weed of the natural environment in Australia and as a low-level weed in other places where it is introduced. However, there does not appear to be any record of it anywhere as a serious weed or invasive species. Its assessment by the Hawaii Pacific Weed Risk Assessment (HPWRA) project has not found it a high weed risk species for Hawaii.
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