Consequently, when a bushfire passes through, the wattle seeds do not feel the full effect of the heat. The arils have a distinctive length and form for each species. Acacia melanoxylon has a large aril that is brightly coloured. The very similar species A.implexa has a much smaller cream coloured aril. Obviously their seeds are dispersed in different ways which is why they do not usually grow together.
Pop goes the seed.
A common seed dispersal mechanism is the high speed ejection of the seed from the pod. This is usually caused by the drying and contraction of the pod, resulting in a build up of forces that are suddenly released. This mode is best observed on the hottest day in summer. Although a widespread dispersal mechanism, it must take a long time for a plant species to travel from one valley to the next relying on this method. Fire Banksias, eucalypts and many other Australian plants hold their seeds until fire kills the branch or parent plant, allowing the capsules to open and seeds to be dispersed.