Trees in the Landscape, Part 4: Bombax Ceiba Donald R
WESTERN A rborist Trees in the landscape, Part 4: Bombax ceiba Donald R. Hodel and Paul R. Weissich
ombax ceiba, common- lesser dimensions there, could also Salmalia malabarica (DC.) Schott & ly known as the red silk-cot- find use as a street tree. Wherever it Endl. ton tree, is a large, briefly is grown, though, it is sure to attract Bdeciduous tree occurring in warm attention and be a much admired, if Common Names: red silk-cotton monsoon forests in southern Asia. not spectacular, show-stopping ad- tree, silk-cotton tree, red cotton tree, Easily one of the world’s most spec- dition to any landscape where it is kapok. tacular flowering trees, it is famous adapted. for its large, showy, six-inch flow- Etymology: The genus name Bom- ers with thick, waxy, red petals that Taxonomy and history bax is likely derived from the Greek densely clothe leafless branch tips in Synonyms: Bombax malabaricum DC., bombyx, referring to things of silk or late winter and early spring. Gosampinus malabarica (DC.) Merrill, cotton, and alludes to the abundant, Because of its potentially large size in Hawaii, Bombax ceiba is best used there as a park tree, shade tree, speci- men, and flowering accent for larger Easily one of the world’s most open spaces. It would fulfill these same uses in California and the Desert spectacular flowering trees… Southwest and, because it grows to
Figure 1. (Left) Bombax ceiba can become a large tree in Hawaii, as here in the parking lot of Foster Botanical Garden, Honolulu. Figure 2. (Center) Bombax ceiba has leaves for most of the year and makes a fine shade tree (LosAngeles County Arbore- tum and Botanic Garden, Arcadia, California). Figure 3. (Left) The same Bombax ceiba in Figure 2 is briefly deciduous in later winter and spring and erupts into a riot of large, showy red flowers.
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Figure 4. (Left) Branches of Bombax ceiba are typically arranged in distinct, uniform, and mostly symmetrical whorls or tiers (Los Angeles County Arboretum and Botanic Garden, Arcadia, California). Figure 5. (Center) Branches of Bombax ceiba are typically arranged in distinct, uniform, and mostly symmetrical whorls or tiers (Foster Botanical Garden, Honolulu, Hawaii). Figure 6. (Right) Co-author Paul Weissich provides scale for the trunk of Bombax ceiba which is typically impressive, straight, with buttresses, and often stout (Foster Botanical Garden, Honolulu, Hawaii). silk-like or cottony fibers in the History: The great Swedish bota- Description fruits. The specific epithet or species nist, physician, and zoologist Carl The description is from several sourc- name ceiba is a Spanish derivative of Linnaeus (1707-1778), who laid the es (Barwick 2004, Brown 2011, Flora of a Taino or other Arawakan (South foundations of the modern biological China 2011, McCann 1959, Menninger American indigenous languages) scheme of binomial nomenclature and 1962, Neal 1965, Staples and Herbst name used for a group of large, tropi- is considered the father of modern 2005) and from cultivated trees at The cal trees related to Bombax, many of taxonomy, described and named this Los Angeles County Arboretum and which produce kapok or silk-cotton species in 1753 in his seminal work Botanic Garden in Arcadia, California in their fruits. Species Plantarum. and in Honolulu, Hawaii.
Habit/Conformation: medium to large, long-lived, briefly deciduous Join TAC during the flowering period in late TAC or the Tree Advisory Committee enables everyone to share their winter to early spring, mostly tropi- experiences and observations managing specific trees in our landscape cal, frequently spiny tree, 40 to 130 and urban forests for this series Trees in the Landscape. TAC is free, feet tall, 15-60 feet wide (Figs. 1-3), easy to join, and open to everyone. Simply send me an e-mail expressing canopy mostly upright and broadly your desire to participate in TAC. I will e-mail all TAC members notify- columnar to rounded, moderately ing them which tree species I will be profiling in an upcoming issue of open, mostly symmetrically and Western Arborist. TAC members can then respond to me about their experiences and observations managing that tree. Upcoming species to regularly branched, typically with be covered in this series include Sapindus saponaria, Acacia pendula, distinctly and uniformly spaced and Alectryon excelsus, among others. whorls or tiers of spreading to up- ward-pointing branches (Figs. 4-5) Join TAC by e-mailing me: giving the tree the appearance of a
39 Summer 2012 WESTERN A rborist soft hairs; stamens yellowish but red tinged toward the tips, anthers black, in 2 whorls, outer whorl divided into 5 bundles of 9-20 each, inner whorl of 10-15 surrounding the style, less than half as long but reaching rim of re- curved petals, about three-quarters as long as style (Fig. 14); style exceeding stamens, red, 5-lobed tip; late winter to spring when tree is leafless.
Fruits: a capsule, 4-6 × 1.8-2 inches (Fig. 15), ovoid, pointed, longitudi- nally ribbed, densely covered with grayish white hairs, splitting open along 5 seams to reveal white, cot- tony, silky material (Fig. 16); seeds small, black or brown, embedded in cottony material (Fig 17); late spring to summer.
Figure 7. (Upper left) Bark of Bombax ceiba is smooth and greenish gray on Distribution and ecology young trees (Los Angeles County Arboretum and Botanic Garden, Arcadia, Cali- Red silk-cotton tree is widespread fornia). from India to Sri Lanka, Nepal, Bhu- Figure 8. (Upper center) Bark of Bombax ceiba becomes rough and checked on tan, Bangladesh, Myanmar, Thailand, older trees (Foster Botanical Garden, Honolulu, Hawaii). Laos, Cambodia, Vietnam, southern China, Malaysia, Indonesia, Papua Trunk: impressive, straight, often Flowers: solitary but densely placed New Guinea, northern Australia, and stout, 1-5 feet in diameter (Fig. 6), near branch tips, conspicuous and the Philippines. However, its exact often short and thick on cultivated very showy (Figs. 10-12), 4-7 × 4-7 origin is unclear because it has been specimens in open sites but a straight, inches (Fig. 13); calyx cup-shaped, so widely cultivated for centuries in symmetrical bole 50-125 feet to the 3-5-lobed, 0.8-1 inch long, outer or many warm, seasonally dry and hu- first branch on forest specimens grow- lower surface glabrous, inner or upper mid areas in southern Asia. Its natural ing under favorable conditions; surface densely covered with yellow- habitat, though, is likely hot, humid, invariably buttressed at the base on ish silky hairs; petals 3.1-4 × 1.4-2.2 seasonally dry, mostly lowland, large specimens (Fig. 6), the but- inches, recurved, dull to bright red, tropical moist, deciduous monsoon tresses extending up the trunk for less frequently orange-red, orange, forests in river valleys and hillsides 15-25 feet. or rarely white, thick, fleshy, waxy, to about 3,700 feet elevation. The satiny, densely covered with short, climate is warm-humid tropical with Bark: smooth and greenish gray on young trees (Fig. 7), becoming rough, Figure 9. (Lower center) Leaves of Bombax ceiba are palmately compound and checked, with irregular vertical fis- to 24 inches long (Los Angeles County Arboretum and Botanic Garden, Arcadia, sures and gray-white to silver-gray, California). greenish gray, or brown (Fig. 8), typi- Figure 10. (Lower right) Bombax ceiba flowers towards the tips of leafless cally with sharp, straight, stout, tan branches in late winter and spring (Los Angeles County Arboretum and Botanic to brown, conical prickles to 0.5 inch Garden, Arcadia, California). long, these sometimes enveloped by expanding bark.
Leaves: palmately compound, to 24 inches long (Fig. 9); petiole 4-8 inches long; leaflets 3-7, digitately arranged, 3-10 × 0.6-3 inches, oblong to oblong lanceolate, leaflet stalks 0.6-1.6 inches long, tip pointed, glabrous (without hairs or other coverings).
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Figure 11. (Upper left) Flowers of Bombax ceiba are solitary but typically densely placed near branch tips (Los Angeles County Arboretum and Botanic Garden, Arcadia, California). Figure 12. (Upper right) Flowers of Bombax ceiba are densely placed, large, and showy (Los Angeles County Arboretum and Botanic Garden, Arcadia, California). a mostly distinct summer maximum However, red silk-cotton trees do best in 1968 is now about 60 feet tall and rainfall pattern. Mean annual rainfall and tend to become gregarious on wide and has a trunk about five feet is variable throughout the region and deep sandy, well drained loams on al- in diameter. Two trees received by the ranges from 30 to 175 inches (Mub luvium near rivers and streams (Mub Los Angeles County Arboretum and 2007). Growth and development are 2007). It sometimes occurs on heavier Botanic Garden in Arcadia, California best in areas where rainfall is more but well drained soils on slopes. in 1979, which originated as scion evenly distributed throughout the material grafted on to Ceiba speciosa year. Humidity is usually always Propagation and growth rate (formerly Chorisia speciosa), are now high. Mean maximum temperatures Red silk-cotton tree is primarily 30 to 40 feet tall, spread for 25 to 35 for the warmest months range from propagated from seeds but cuttings, about 85 to 95 F with maximums air layers, and grafting are also Figure 14. (Lower right) Stamens ranging from 100 to 122 F. Mean possible. Sow seeds immediately of Bombax ceiba are yellowish with minimum temperatures in the coolest after collection by scattering over a reddish tinged tips and clustered in months range from 50 to 75 F with pre-moistened, clean, disease-free bundles (Los Angeles County Arbo- minimums ranging from 36 to 63 F (pasteurized), well drained seed or retum and Botanic Garden, Arcadia, (Mub 2007). Frosts are rare but occur potting mix and cover with about California). at the higher altitudes and latitudes one-eighth inch of the medium. of its distribution. Keep evenly moist at a temperature Soils are also variable and range from of 70 to 80 F and protect from wind, clays and clay loams to sandy alluvium. dryness, and extreme cold and heat. Transplant into individual containers Figure 13. (Lower left) Flowers of when seedlings are sufficiently large Bombax ceiba are large, up to seven to be handled easily. Grow seedlings inches across (Los Angeles County Ar- in light shade but acclimate to full boretum and Botanic Garden, Arcadia, sun quickly. California). A moderately growing species, red silk-cotton tree can attain about 60 feet in height with a trunk four to five feet in diameter in 40 years in Ha- waii and about 40 feet in height with a trunk about 18 inches in diameter in 30 years in southern California’s Mediterranean climate. A tree in the parking lot of Foster Botanical Garden in Honolulu and grown from a young seedling collected in the Philippines
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Figure 15. (Left) Fruits of Bombax ceiba are a pointed, longitudinally ribbed capsule (Foster Botanical Garden, Honolulu, Hawaii). Figure 16. (Center) Fruits of Bombax ceiba split open along five seams to reveal white, cottony, silky material (Foster Bo- tanical Garden, Honolulu, Hawaii). Figure 17. (Right) Seeds of Bombax ceiba are small, black or brown, and embedded in the cottony material (Foster Botani- cal Garden, Honolulu, Hawaii).
feet, and have trunks 15 to 18 inches within USDA Zones 9 to 11. It is likely fertilizers, a well drained soil is best in diameter. to excel in most places in Hawaii and for optimal growth. Brown (2011) reports that the red perhaps might have the potential to A long, warm to hot growing sea- silk-cotton tree in Florida flowers become weedy there if grown in wet- son is likely best for the red silk-cotton when about eight to ten feet tall from ter areas. tree and if planted in frost-free but seed and can grow to 30 feet tall in five Despite its tropical origins, the cooler coastal areas, situating the tree years in tropical areas. In India, the red silk-cotton tree is amazingly cold on the south or west side of a building red silk-cotton tree grows to about 20 tolerant, and has withstood tempera- or other structure that could trap and feet tall with a trunk about four inches tures in the middle 20s F with little collect heat in the day and release at in diameter after five years, to 32 feet or no damage in the December 1990 night might enhance performance. tall and seven inches in diameter after and January 2007 freezes in southern There is no information about how 10 years, to 50 feet tall and 11 inches California. However, it might be intol- the red silk-cotton tree would per- diameter after 20 years, and 61 feet erant of lower temperatures and this form in turf grass or groundcovers tall and 13 inches in diameter after 30 extreme cold will likely limit where it where it might be over-irrigated and years (Mub 2011). can be grown successfully. Its moder- -fertilized but one of the trees at the ate growth rate, though, might result Los Angeles County Arboretum and Environmental tolerances in relatively slow recovery during Botanic Garden in Arcadia, California Little is known about the environ- the growing season if damage does is growing adequately in turf grass. mental tolerances of the red silk-cot- occur. Menninger (1962) reports that Perhaps, through judicious, mea- ton tree; thus, we need to extrapolate it is hardy to at least 20 F. sured applications of fertilizers and information from its native habitat Although largely undocumented, irrigation, growth could actually be and the one place where it grows in the red silk-cotton tree, once estab- retarded without losing quality. southern California. It is not listed lished, might tolerate extended peri- in Sunset (Brenzel 1995) but appears ods with little or no water, a notion Uses adapted to Sunset Zones 18 through extrapolated from its natural mon- Because of its eventual large size, 24 in southern California and perhaps soon forest habitat where little or no width, and trunk diameter in Hawaii, Zone 13 (low desert) in southwestern rain falls for several months. A fairly the red silk-cotton tree needs to be California, eastern Arizona, and ex- tough and rugged species, it appears carefully placed in the urban forest treme southern Nevada. In northern to tolerate some harsh conditions, in- and landscape. Some appropriate California hard freezes and/or lack cluding heat, wind, smog, aridity, and uses in Hawaii include park tree, of summer heat might restrict growth restricted root space. Brown (2011) shade tree, specimen, and flower- but it should be evaluated in Zones 15 reported that the red silk-cotton tree ing accent for larger open spaces. through 17 in the Bay Area. It might has low salt tolerance but in the Phil- It is too large for street tree use in also perform adequately for many ippines co-author Weissich observed Hawaii although it might be suitable years in Zone 12 in Arizona, gaining large specimens growing well only for a wide (at least 10 feet) median. It sufficient size before a hard freeze, a few feet from the edge of Manila would fit these same uses in southern like the one of 2011, seriously dam- Bay where their roots were likely California and, because of its slower ages or even kills it. Much of this area in contact with sea water. Although growth rate and smaller size, could, in the southwestern United States falls mostly not particular about soils or in some instances, find use as a street
Summer 2012 42 WESTERN A rborist tree although there might be some is- elevate the canopy if desired. Once in amounts of white, cottony material sues with flower litter (see below). For the landscape only judicious thinning that, once liberated from the fruits street-tree use in southern California out to reduce canopy density might be (Fig. 18), floats through the air and minimum parkway width and cutout necessary. Trees would benefit from litters the landscape for some distance size are probably six feet and trees regular irrigation and fertilizer until (Fig. 19). must have lower branches removed established, especially during the to raise the canopy for vehicular and growing season, but once established Pests and diseases pedestrian clearance. Maintaining an appear to perform adequately in turf Little or no information is available elevated canopy also allows the hand- or non-turf areas with occasional ir- on the subject but the red silk-cotton some trunk and symmetrical branch- rigation and no fertilizer. However, tree appears free of serious pests and ing habit to be easily admired and regular irrigation might be critical diseases. appreciated. An unusually prickly in hot interior valleys and the low trunk might pose a hazard to unwary desert. Weed/invasive species risk passersby. The incredible late winter Little is known of the weed/ invasive to early spring floral display make Problems/litter species risk of the red silk-cotton tree the red silk-cotton tree an eye-catch- The red silk-cotton tree is largely free but it is likely not a threat in California ing and show-stopping specimen or of serious problems. Its wood might and the Desert Southwest. It might accent in the landscape. not be prone to breakage, even in be a threat in Hawaii, especially in high winds; although a small sample, wetter areas. Pruning/management the two trees in Arcadia, California, The red silk-cotton tree has a strong an area hard hit by the great wind Availability tendency for straight, upright, single- storm of November 30-December 1, Despite its many attributes and popu- leader growth and retention of lower 2011, had little or no branch break- larity in other parts of the world, the branches and likely needs little train- age. Mature trees can produce an red silk-cotton tree is unknown in the ing and pruning in the nursery and abundance of flowers and subsequent nursery industries in California, Ari- landscape. Even if the leader is bro- fruits. Petals are large and fleshy and, zona, Nevada, and Hawaii. However, ken, it will readily form a new leader because they drop abundantly during it is easily propagated by seeds, which and continue upright growth. Provide the intense flowering period, might can be procured from trees in Hawaii adequate space in the nursery and be an unacceptable nuisance along (which see below) or from mail-order retain lower branches to encourage streets, sidewalks, and other paved suppliers. maximum trunk caliper. Because of areas that people frequent. Similarly, strong, straight, upright growth and the large leaves drop during a very Trees in California and Hawaii symmetrical, whorled, spreading short period in mid-winter and might Only two specimens of the red silk- branches, staking is probably mostly be particularly annoying for a short cotton tree are known in California, unnecessary if trees are given ade- time. Although fruits have yet to both at the Los Angeles County Arbo- quate space. Nursery trees might only form in California, likely because of retum and Botanic Garden in Arcadia. need light pruning to reduce canopy an absent pollinator, and they gen- In December they drop their leaves density and, when nearing readiness erally remain on the tree, they can and put forth their incredible floral for sale, to remove lower branches to be problematic because of the vast display from February into April (Figs. 2-3). The largest tree in Hawaii, Figure 18. (Left) Fruits of Bombax ceiba contain vast amounts of white, cottony an orange-flowered form brought by material that, once liberated, float through the air (Foster Botanical Garden, co-author Paul Weissich from the Honolulu, Hawaii). Philippines in 1968, is in the parking Figure 19. (Center) The white cottony material contained in the fruits of Bom- lot of Foster Botanical Garden in Ho- bax ceiba can litter the landscape for some distance (Foster Botanical Garden, nolulu and always prompts interest Honolulu, Hawaii). when in flower in January and Febru- ary (Fig. 1). Another tree in Hawaii of unknown age is along Leahi St. at the Queen Kapiolani Rose Garden in Kapiolani Park in Honolulu (Figs. 20- 21). It is about 40 feet tall and wide and has a short trunk about three feet in diameter that branches into a double leader about 10 feet above the ground. Several specimens near the entrance to Hoomaluhia Botanical
43 Summer 2012 WESTERN A rborist ers of the red silk-cotton tree secrete nectar. Barwick (2004) and Mub (2007) note that the fleshy petals and heavy nectar are attractive to birds, squir- rels, and bees, all of which may act as pollinators. However, fruits have yet to form on the red silk-cotton tree in California although the trees have been flowering for many years. Widely planted and highly re- vered from India to southern China, the red silk-cotton tree has many uses. Known as the semal tree in India, a gummy secretion is obtained from the bark and sold as semal gum for me- dicinal use. The cottony fibers in the fruits are a substitute for kapok and used to stuff mattresses, pillows, and cushions although they are inferior to that of true kapok, Ceiba pentandra. The fleshy sepals and perhaps pet- Figure 20. (Left) This Bombax ceiba at Queen Kapiolani Rose Garden in Kapiolani als of young flowers are cooked and Park, Honolulu, Hawaii is about 40 feet tall and wide and has a short trunk about eaten as a vegetable. The soft wood three feet in diameter that branches into a double leader about 10 feet above has been employed for matches and the ground. tea boxes while the fibrous inner bark Figure 21. (Center) Co-author Paul Weissich provides scale for the same tree in makes suitable cordage. All parts of Figure 16 that is now devoid of leaves in late March and bears numerous fruits. the tree, including roots, bark, flow- ers, and fruits, have local medicinal/ ethnobotanical uses to treat a variety Garden in Kaneohe and accessioned January. About the same time the of ailments (Ecosensorium 2011). The in 1986 are about 50 feet tall, spread dark brown buds are forming and en- tree is so highly revered that, accord- for 45 feet, and have trunks nearly two larging and they open from February ing to Chinese historical records, the feet in diameter. Staples and Herbst to April on the leafless tree. Individual King of Nam Yuet, Chiu To, gave one (2005) report that a red silk-cotton tree flowers are short lived, about five to to the emperor of the Han Dynasty in is at The Queens Medical Center in seven days, but, because flowers ma- the 2nd century B. C. Honolulu but we have not seen it. ture at various times, the most intense flowering period can last for a month Acknowledgements Notes with sporadic flowering preceding Susan Eubank, librarian, and James Bombax and related genera, including and following this intense period E. Henrich, botanist, both at the Los Adansonia, Cavanillesia, Ceiba, Chiran- (Brown 2011). The ground beneath Angeles County Arboretum and thodendron, Durio (durian), Fremon- flowering tree is typically littered Botanic Garden in Arcadia provided todendron (California native flannel with flowers and can attract squirrels, information about the Bombax ceiba in bush), Pachira, and Pseudobombax, deer, and other mammals that feed The Arboretum. Matt Ritter, author among others, comprise about 25 to upon the floral litter. When flowering and botany professor at California 30 genera and 250 species of mostly heavily with no leaves the tree is par- Polytechnic State University at San tropical trees with large, showy flow- ticularly striking and can be seen from Luis Obispo; Ken Greby, an unusu- ers, some of them of rather large habit a great distance as a red blaze against ally knowledgeable arborist; Angela that were once included in the Bomba- the blue sky. New leaves emerge Liu, consulting arborist; and James caceae. However, recent research has when flowering is finished, and fruits E. Henrich critically reviewed the shown that the Bombacaceae is not complete development rapidly, split manuscript and offered valuable that distinct from the Malvaceae and open, and release the cottony material suggestions. is mostly now treated as a subfamily with embedded seeds prior to or after of this latter, widely circumscribed the tree has completely renewed its Donald R. Hodel is the Environ- family. leafy canopy. mental and Landscape Horticul- Leaves of the red silk-cotton tree Squirrels and other animals eat the ture Advisor for the University of turn yellow and fall in December and fleshy petals (Menninger 1962). Flow- California Cooperative Extension
Summer 2012 44 WESTERN A rborist in Los Angeles, a position he has held for over 28 years. Don devel- Literature Cited ops and implements educational Barwick, M. 2004. Tropical and Subtropical Trees. Timber Press, Portland, and applied research programs for OR. the professional tree and land- Brown, S. H. 2011. Bombax ceiba. Univ. Florida Fact Sheet, IFAS Extension, scape management industries. He Lee County, Southwest Florida. specializes in the selection and Ecosensorium. 2011. Bombax ceiba or semal tree. On-line: http://www. management of trees and palms. ecosensorium.org/2011/02/bombax-ceiba-or-semal-tree.html. Accessed:
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