Turion (botany)

A turion (from Latin turio meaning "shoot") is a specialised overwintering bud produced by aquatic herbs, especially in the genera "Potamogeton", "Aldrovanda" and "Utricularia". Turion are produced in response to unfavourable conditions such as decreasing day-length or reducing temperature. They are derived from modified shoot apices. They are often rich in starch and sugars enabling them to act as storage organs. Although they are hardy (frost resistant), it is probable that their principal adaptation is their ability to sink to the bottom of a pond or lake when the water freezes. Because water expands anomalously at lower temperatures, water at 4^o C (39^oF) is denser than colder water and stays at the bottom, and it is in this water that the turions over-winter before rising again in the spring. Some turions are also drought resistant allowing them to survive in evanescent pools.

The presence of humic acids may speed up the formation of turions.

References

* "Turion Overwintering Of Aquatic Carnivorous Plants", International Carnivorous Plant Society, Science Newsletter, June 1999 - Lubomír Adamec, Academy of Sciences of the Czech Republic, Institute of Botany. [http://www.carnivorousplants.org/cpn/samples/Science281Turion.htm]