Brachychiton rupestris is endemic to Queensland, Australia, but both of today’s photos are of cultivated plants in California.
This species grows as a pachycaulous tree, meaning it has an unusually thick-stemmed trunk. Young Brachychiton rupestris trees have straight trunks. As they mature, reaching the age of 5-15 years, these succulent-like trees begin to store large amounts of water between their inner bark and their trunk. The tree’s trunk swells until it becomes round like a big bottle, giving this species its common name of Queensland bottle tree. Brachychiton rupestris‘s water reserve allows it to survive extended periods of drought. It can even survive for three months after being uprooted. This plentiful source of moisture was well-used by the aboriginal people of Queensland, who would eat the secretions produced from wounds in the tree’s trunk, as well as eat most other parts of the tree.
The first photo displays the seeds and pod of Brachychiton rupestris. It forms groups of 3 to 5 boat-shaped follicles (dry fruit from one carpel that contains multiple seeds). Each follicle holds 4 to 8 (up to 12) seeds. The seeds are surrounded by a hairy coating which will irritate unprotected skin. Brachychiton rupestris seeds germinate readily and can be grown in most soil types. Botanical gardens around the world feature this awe-inspiring species, but the best place to see it is in its homeland. It is commonly planted as a street tree in Queensland. The town of Roma, Queensland, features an avenue planted with over 100 Brachychiton rupestris in honour of fallen WW1 soldiers. In the same town is the purported largest Queensland bottle tree in the world, measuring over 9 meters in circumference.