Lignotubers:
Australian
plants have to survive extremely harsh conditions. Fire is common in many
Australian environments. Native plants have developed a number of strategies
to survive fairly frequent burning. Some species have woody fruits and cones
to protect their seeds during fires (eg Banksias and Hakeas). Acacias have
hard seed coats that require heat to break dormancy. Eucalypts and some
members of the Proteaceae family have a swelling at the base of the stem at
soil level or just below. This swelling is known as a lignotuber and contains
dormant buds, which burst into life when the top growth is destroyed (usually
by fire). These dormant buds produce suckers that develop into stems. Mallees
are eucalypts with multiple stems produced from a lignotuber. The illustration
shows the growth of a New England Mallee (E. codonocarpa). In this case
the lignotuber is almost one metre (three feet) in diameter. The lignotuber
and multiple stems have arisen due to the influence of bush fires. When this
species grows in sheltered situations, protected from fire, or in cultivation
then a single stem usually develops.