Brachychitons, the Australian Bottle TreesBy Geoff Stein (palmbob)
March 15, 2009
Ever since I became interested in plants, I have struggled to find some trees that interested me, too--other than palm trees, that is. I loved the succulents, cacti, palms, cycads, bromeliads and other smaller tropical or desert plants. But I just wasn't that interested in anything tall and tree-like, and my landscapes needed something taller. I grew Bamboo, but that didn't satisfy my urges to find an interesting tree. Then my friend boought a Brachychiton discolor and a B. rupestris. I looked around and found large examples of these two trees and I was hooked!
Brachychiton is a primarily Australian genus (one of the approximately 30 species is from New Guinea) collectively known as the Bottle Trees (or, locally, Kurrajongs). Though many are known for their somewhat swollen trunks, really only one species to me would qualify as something I would call a bottle tree (Brachychiton rupestris). Most of these fat-trunked trees are true ‘pachycauls' or trees that store water in their swollen trunks to survive periods of long and/or extreme drought. Only a handful of these approximately 30 species are known in cultivation. Some of these trees are evergreens (the desert, more bottle-trunked forms) and some are deciduous, flowering primarily as the leaves fall off (the forest growing species). These trees are not generally very cold tolerant and seem best adapted to Mediterranean climates such as those found in the Southwest US, South Africa, much of coastal Australia, and, of course, the Mediterranean. Some species are also quite well adapted to more tropical climates, and even some of the commonly grown species can be found in Hawaii and Florida. These are monoecious trees (both male and female flowers on same tree).
Seed pod of this genus are large and filled with dozens of ovoid 1cm seeds that are obviously quite popular with squirrels (who always outcompete me when I am trying to raid the pods in the local arboretums). Care must be taken when handling these seed pods as the seeds themselves are coated, in most species I have seen, with a dense layer of fuzz, which turns out to be dense matte of spines. These spines are urticating and very hard to get out of one's skin- use gloves or forceps when extracting Brachychiton seeds! Fresh seeds have proven quite easy to germinate. Just plant shallowly in moist potting soil or perlite and keep warm (80F) and most will germinate in less than a few weeks.
seed pod cluster in a Brachychiton populeus (photo by Xenomorf); close up of a seed pot showing the fuzzy spines surrounding the seeds; this third photo is usually how I find the seed pods- empty thanks to the squirrels
Brachychiton acerifolius (aka Illawara Flame Tree, Australian Flame tree, Flame Bottle Tree, Flame Kurrajong) When in bloom this is one of the most spectacular trees I have seen and definitely one I would love to have in my garden had I the room for any trees in my garden. However it is not a reliable bloomer in southern California and some years blooming is better than others. This is in its native Australia a deciduous forest tree, losing its leaves in the dry season and flowering then. Only I suspect the dry season in climates that have one, tend to also be the cooler season. In a tropical climate like Hawaii that has a short dry season in the summers but little temperature fluctuation, the trees lose their leaves and bloom in that short two month period. But in a 'reverse' climate such as that found in southern California when the cold season is also the wettest season, these trees seem ‘confused' and are much less reliable in their blooming patterns, as well as their leaf loss patterns. In southern California this species is mostly evergreen, perhaps having a somewhat sparser foliage during the time of flowering (which can be anywhere from spring to fall). I think this might have something to do with the erratic nature of the flowering in southern California--some trees will fail to flower for years at a time, or flower half-heartedly. Certainly it is rare to see a completely brilliant red-orange leafless tree in full flower as one might come across in the summers of Australia, South Africa or Hawaii. Still, it as an attractive tree regardless.
'typical' look of Brachychiton acerifolius in summer blooms (photos by AustinBarbie and TQGARDEN)
two different trees in spring and summer showing more typical flowering look seen in Southern California- leaves still on and flowers far less visible (still spectacular, though)
Flowers of Brachychiton acerifolius
The name ‘acerifolius' means maple-like, and the leaves indeed somewhat resemble those of a maple tree, at least in overall shape and form. Brachychiton acerifolius has the largest leaves of the commonly grown Brachychitons and can be distinguished from other Brachychitons by the thin, very shiny, somewhat elongated dissected maple-like leaves. The trunks of these trees are not impressively bottle-like and have a smoothish grey bark. It is a somewhat cold sensitive species only tolerating a few degrees of frost below 32 F (0 C). Probably around the world, this is the most commonly cultivated of the Brachychitons.
leaves showing the typical rounded tips (photo by pdb_bermudiana); young Brachychiton acerifolias for sale in southern California
Brachychiton australis (aka Broadleaf Bottle Tree) is one of the least-commonly grown of the ‘common' Brachychitons. I am not sure what its flowers are like (I know they are white) though I have seen these trees on a number of occasions at the local botanical gardens and at a friend's home. Perhaps in southern California they don't flower well. The leaves of this species are also shiny and maple-like, but not elongated. They are somewhat star-shaped with very pointed tips. The trunks of these trees are noticeably greenish even when mature. Branches tend to be rather thick and taper very rapidly giving these trees a clumsy appearance, particularly when leafless. This species is one of the least ornamental of the more common species in my opinion. Brachychiton australis is a deciduous tree and comes from a markedly dry climate. It is not very cold hardy, either, perhaps similar to Brachychiton acerifolius in its sensitivity to cold.
Brachychiton australis in Southern California; leaves showing typical shiny, pointed stars; typical greenish trunk
Brachychiton bidwillii (aka Rusty Kurrajong) is a pretty rare tree in cultivation, but not unheard of. I had several of these at my old house and they were fairly slow growing trees in zone 9b Southern California. I have seen large ones in the Los Angeles Arboretum, but never seen those monsters in flower. This is a fuzzy-leaved species deciduous forest species noted for its large, spectacular red-pink bell-shaped flowers. This is a species that seems to have no problem blooming in southern California, but blooming times are somewhat inconsistent, with some plants blooming in spring and others blooming later in the year. New leaves start out an attractive rust color and are very fuzzy, then mature to a bright, flat green with a very short coating of fuzz on them. Leaves of juvenile plants are exaggeratedly dissected, but mature trees have more star-shape, maple-like leaves. Trunks are grey and not the least bit bottle-like. This plant seems to be a bit more cold tolerant than the above two tolerating temps into the low 20s briefly.
Brachychiton bidwillii in Southern California; smaller seedling in flower (no leaves) in late spring; flowers of Brachychiton bidwillii
mature leaves in first photo; new fuzzy reddish leaves in middle photo; young tree half way between losing all its leaves and making flowers
Brachychiton discolor (Pink Flame Tree, Brush Kurrajong or Lacebark Tree) is one of the more commonly grown Brachychitons in southern California landscaping. Though it is certainly not what I would call a common tree, I do see several in most suburbs of Los Angeles, and most botanical gardens have at least one of these. These are really large trees, easily the largest of all the common Brachychitons, and, to me, one of the messiest trees, dropping massive amounts of leaves at one time of the year (usually spring) followed by a massive flower drop in late summer. Brachychiton discolor is the most reliably flowering of all the common Brachychitons, producing huge volumes of pink, bell-shaped flowers in summer that make this a strikingly beautiful tree in summers. Leaves are large, slightly fuzzy, and maple-leaf-shaped. The trunk is roughly grooved and grey (unlike most of the other Brachychiton trunks which are much smoother). This is a rainforest tree but seems quite happier in drier Mediterranean climates. I have not ever seen cold damage to this tree so I can handle temps well into the low 20s, and I don't know how much colder. I have tried to bonsai this species and it has actually done quite well in a small pot developing a wonderful, fat, twisted root... but it tends to still grow tall, and is obviously not hugely happy being root bound only holding a modest number of leaves and failing to flower for me (so far).
Brachychiton discolor in full flower; second photo of very old tree in full leaf (both in Southern California)
flowers of Brachychiton discolor
mature leaves (photo by Kelli); and immature leaves; last photo is of my 'bonsaid' specimen
Brachychiton populneus (aka Bottle Tree, Black Kurrajong etc.) is easily the most commonly used Brachychiton in public planting projects in southern California and is a fairly common street tree. Sadly, to me at least, it is the least interesting of the cultivated Brachychitons, perhaps because it is so common? It has simple ovoid to 3-pointed, slightly curled small bright green leaves and fairly small, non-descript off-white flowers, with pinkish, spotted centers, that are barely noticeable. This is an evergreen species (desert tree) so the flowers are doubly hard to pick at unless one looks closely. The trunks of this species are markedly tapering and at least look somewhat bottle-like, and the trees somewhat resemble giant bonsai trees. The trunk color is a light tan with a hint of green under the paper-thin bark and quite smooth.
mature example of Brachychiton populneus as street tree in Southern California; leaves; trunk (photo by Xenomorf)
Brachychiton rupestris (Narrowleaf Bottle Tree, Queensland Bottle Tree, Queensland Kurrajong) is my personal favorite species of Brachychiton. This to me is the true bottle tree as these plants develop grossly thickened trunks, often immensely so, that taper almost comically, just like a bottle. Trunks have a thin layer of tan bark and usually some of the pale green color from beneath shows through. The leaves of this species are quite variable with some specimens having very narrow leaflets forming three to 6 points, to plants that have wider leaves that look a lot like the Brachychiton populneus 3-point leaves (perhaps this is a natural hybrid, as these are both desert species?). Immature plants have simple, narrow lancelote dark green leaves. Like Brachychiton populneus, Brachychiton rupestris is an evergreen with similarly small and often insignificant pale pink flowers with spotted throats. I have one of these in the yard and though the flowers may be small and not all that easy to notice from a distance, these trees drop hundreds upon hundreds of flowers all summer long making it a disappointingly messy tree for growing in a succulent garden.
Mature Brachychiton rupestris examples in Southern California
flowers of Brachychiton rupestris; young green trunk; young plants being grown for sale, Southern California
various leaf forms of Brachychiton rupestris: simple lanceolate, trident dissected and the most popular form, the super-thin leaflet form
This is one of the easier trees to bonsai, and stems will still become quite stout and impressive even if roots are moderately bound. These twisted, swollen roots can then be raised up to increase the ornamental effect of these pot-bound plants. Cold tolerance is excellent (from my point of view at least) with no problems encountered in most cooler inland southern California climates. This is an incredibly drought- and wind-tolerant plant, needing no water whatsoever once established.
Old plant growing as a bonsai with its roots lifted up out of pot; my own plant started as a bonsaid specimen showing a nice twisted, swollen stem/root
my own plant, growing up over a few years... and now its ripped apart the planter box... oops
Below are a few photos of other species of Brachychiton I have encountered in southern California in botanical gardens, but I have never seen these in private gardens, for sale at nurseries or used in public landscaping.
photos of Brachychiton muerllerianus in Southern California botanical garden