Once more into the Wiggy Wig Bush!

New Zealand is an island (well, two islands) and has been for millions of years. Geographic isolation has resulted in many an evolutionary quirk occurring within both the island’s flora and fauna and as it stands today 80% of the country’s trees, ferns and flowering plants are classified as ‘endemic’, meaning that they naturally occur no where else on Earth. One such quirk is the rather splendid and unusual growth habit known as Divarication. Divaricate plants have small leaves and wide angled branches that grow in a characteristic, interlacing ziggidy-zaggedy manner producing a dense, highly tensile shrubby mass. While plants exhibiting this form are found throughout the world, they are nowhere as prominent as within NZ’s flora.  Around 10% of the country’s woody plants display this growth habit with specimens occurring across 18 different taxonomic plant families. Bizarrely, certain plants, such as the Kōwhai tree (Sophora microphylla) have a divaricate form as the juvenile stage of their development before adopting a more conventional branching arrangement as they mature. A prime example of a plant with a strongly divaricated habit is our old friend the Wiggy Wig Bush (Muehlenbeckia astonii) with its highly geometric, molecular shaped branching.

The Wiggy Wig Bush- A fine example of Divarication

Close up zig zag

A number of theories have arisen to explain the penchant for divarication of New Zealand’s plant life.  Some have postulated that the dense and tangled branch growth had evolved as a defensive response to the browsing of the now extinct Moa, a large flightless bird similar to the modern day emu. Indeed, such a theory would explain the juvenile divaricate habit of certain plants as once of a mature height they would no longer be at risk from browsing animals. Others claim that divarication aids plants in protection from dry and windy climatic conditions by acting as a windbreak, reducing transpiration from the plant’s inner leaves and limiting water loss.  The inner depths of a divaricate shrub also provide a hospitable environment for native lizards such as skinks and geckos. In return for acting as agents of fruit and seed dispersal, the lizards are provided shelter and protection by the interwoven branches of the plant.

The Moa in action

A range of plants exhibiting a divaricated growth habit can be viewed in the Native plants section of the Dunedin Botanic Gardens.