Bottle tree seed pods. Close-up of open seed pods of the bottle tree (Brachychiton populneus). Inside are numerous bright yellow seeds, which are attractive to birds as food. As a seed passes through a bird's digestive tract, the tough outer seed coat is weakened, thus aiding germination of the seed when it later passes out of the bird in its faeces. The bottle tree is native to Australia. It is an evergreen tree, and can reach 9 to 13 metres in height. The seed pods measure between 1 and 7 centimetres in length. They are lined with fine hairs that can cause irritation if touched. The seeds of the bottle tree can be ground and used as a coffee substitute.