The Moreton Bay Chestnut is a medium-sized tropical evergreen tree that bears luxurious shiny leaves and carries a broad rounded crown. Because of its distinctive beauty, it was one of the first ornamental trees introduced into the Santa Barbara area in the 1880s. Surprisingly, it is still considered a rare tree here.
In our Mediterranean climate, its dense canopy is symmetrical and reaches a height and spread of 35- to 45-feet.
Its dark green leaves are pinnately compound (split into leaflets) and can reach up to two feet in length. Each leaf has 9 to 17 leaflets; each leaflet is ovate to oblong in shape (3- to 5-inches long and ¾- to 2-inches wide) and bears a pale green midrib.
Beginning in July and continuing through August, its red to reddish-yellow flowers bloom. These are small (1¼- to 1¾-inches long) and appear in racemes (clusters) on older twigs in the upper crown. Since the flowers are well hidden within the foliage, deliberate inspection from underneath the tree is required simply to see them; but their interesting funnel-like shapes and striking colors make it well worth the effort.
Each flower is “perfect”, meaning that each has both stamens (male flower parts) and pistils (female flower parts). Nevertheless, they still need outside help to be pollinated. This work is done by bees and hummingbirds, which are attracted by the copious amount of pollen and nectar the flowers provide.
After pollination, the small flowers develop their fruit in yellow-green bean pods that are comparatively gigantic – up to 10-inches long and 2½-inches wide! Each pod contains 3 to 5 brown seeds that are circular and rather large (up to 1¼-inches in diameter).
In the fall, the seed pods turn a light brown, drying slowly to split into two long sections – releasing the seeds in December and January. Caveat: unlike the tasty edible seeds of common European and American Chestnut trees, the seeds of Morton Bay Chestnut trees, unless carefully processed, are toxic to humans!
Young trees have bark that is smooth and gray-brown; with age, the bark develops shallow vertical fissures with prominent knobs.
Moreton Bay Chestnut is endemic to tropical and subtropical areas of eastern Australia – on the coast of Queensland (where Moreton Bay is located) and in northeastern New South Wales – and on the southwest Pacific islands of Vanuatu and New Caledonia. In its native tropics, it can grow to the remarkable height of 130-feet.
For thousands of years, Moreton Bay Chestnut has been important to the Aboriginal peoples in Australia as an important source of food, as well as for its wood and bark. The seeds do contain saponins that render them quite inedible without extensive processing – this involves roasting, slicing, mashing, and repeated leaching in water – before they can be eaten as a paste or baked into a thick bread.
Morton Bay Chestnut’s high-quality timber resembles that of walnut trees and, consequently, is prized for fine carpentry and cabinetry. The Aboriginal people used the wood to carve strong spear shafts, and utilized the rugged bark fiber to craft animal traps, fish nets, and woven baskets. European settlers to Australia found it to be a lovely ornamental tree for landscaping – and distributed it to warmer climates worldwide for that purpose.
Moreton Bay Chestnut has many other common names, including “Black Bean”, “Lucky Bean Tree”, and “Bean Tree”. It was given the name “Moreton Bay Chestnut”, because its seeds are visually similar to those of the common chestnut trees, which are in an entirely unrelated plant family, the beech family, Fagaceae. Instead, the Morton Bay Chestnut is in the legume (bean) family, Fabaceae. (Yes, the two plant families also have confusingly similar names.)
Its botanical name is Castanospermum australe. Its genus name, Castanospermum, is derived from a combination of the genus name of the common chestnut trees, Castanea, and the Latin word, “spermum”, meaning “seed”; as combined, this refers to the similar appearance of the seeds. Its specific epithet, “australe”, comes from the Latin word, “australis”, meaning “southern”, which was also applied in the naming of its native continent, Australia.
In our Mediterranean climate, Moreton Bay Chestnut, once established, is a long-lived and very hardy tree. It is adaptable to many types of soil but prefers a well-drained loam. A young tree should not be planted out until it is at least 4-feet tall since younger trees are somewhat tender and difficult to get established. Thereafter, it will need regular watering during at least the first two dry seasons. It can be planted in full sun or partial shade; however, it will benefit from added protection from full sun when still young. Until recently, Morton Bay Chestnut had appeared to be free from plant diseases and insect pests. Unfortunately, it has now been found to be susceptible to attack by “shot hole borer”, a nasty invasive beetle.
Morton Bay Chestnut is easy to propagate from seeds – and the method is very similar to how one grows avocados – freshly collected seeds should be planted in a moist potting mix, exposing about ½ of the seed. Be patient – they can take up to two months to germinate.
Moreton Bay Chestnut has many attributes that recommend it as an ideal ornamental landscape tree for our area. Its uniform growth, stunning evergreen foliage, and fairly well-behaved roots make it useful for streetside planting, as well as for parks and residential gardens.
Curiously, it is not presently generally available in the nursery trade. However, as it can be readily propagated both by commercial nurserymen/women and by home gardeners, it really should be grown and planted in more locations around town.
Moreton Bay Chestnuts can be seen as street trees in our community: an outstanding specimen is in the 1400 block of Crestline Drive; and, two older trees are in the 2100 block of Oak Park Lane. The oldest and largest specimen, reportedly planted in 1883, is located at the southeast corner of the Victorian residence of Stow House in Goleta – It is a lovely old tree and certainly worth a trip to see it.
Tree-of-the-Month articles are sponsored by Santa Barbara Beautiful, whose many missions include the increase of public awareness and appreciation of Santa Barbara’s many outstanding trees and, in a long-time partnership with the City Parks & Recreation Department, the funding and planting of trees along the City’s streets.
Those who wish to honor a special someone can do so with an attractive commemorative marker that will be installed at the base of an existing street tree in the City of Santa Barbara. Because Santa Barbara Beautiful has participated in the planting to date of over 13,000 street trees, there are plenty of trees from which to choose! Application forms are available on the Santa Barbara Beautiful website, www.sbbeautiful.org.
Article and Photos by David Gress