Clockwise Vines, Counterclockwise Vines

 

Coral Honeysuckle (Lonicera sempervirens) flowers.
Rowan County, North Carolina. 

Charles Darwin was fascinated by the growth of vines.  In 1865 he published his research in a book called On the Movement and Habits of Climbing Plants.  Among the many topics Darwin addressed was twining, how vines wrap around a support or each other to climb. He reviewed a well know observation that for a given species, the vine twines in only one direction, either clockwise or counterclockwise.   

 About 90% of twining vines grow counterclockwise but a significant minority go the other way.  A few plants can twine in either direction.  The reason for this interesting observation has been a topic of debate and research for centuries.  Many explanations have been proposed, including the movement of the sun across the sky and the Coriolis effect.  The latter is caused by the rotation of the Earth and causes hurricanes to spin counterclockwise in the northern hemisphere and clockwise in the southern.  Neither of these ideas is correct. It turns out that the twining direction of plants is genetically determined.

There are about 180 species of honeysuckles (Lonicera  sp.) and they are native to North America, Europe and Asia. All honeysuckles twine clockwise, that is, when you look at a honeysuckle vine it grows up from right to left, spiraling clockwise up its support. Coral Honeysuckle (Lonicera sempervirens) is a native of eastern North America.  With its opposite leaves and pink, tubular flowers, this striking vine is a magnet for pollinating insects and Ruby-throated Hummingbirds (Archilochus colubris).  All this pollination leads to large red fruits of Coral Honeysuckle that are a prized food for birds. 

Coral Honeysuckle flowers.
Rowan County, North Carolina.

Coral Honeysuckle Fruits.
Rowan County, North Carolina. 

Coral Honeysuckle vines twining clockwise.
Rowan County, North Carolina. 

Carolina Jessamine (Gelsemium sempervirens), is a vine found in the southern United States and down into Mexico and Central America. It has glossy evergreen leaves and brilliant yellow tubular flowers. Carolina Jessamine twines in a counterclockwise direction when growing up trees in a forest or on an arbor in a garden.  This beautiful vine has a darker side, it produces the alkaloid gelsemine.  This neurotoxin is found in all parts of the plant including the nectar.  Although many insects collect the nectar there are cases on record of Carolina Jessamine poisoning honeybees.  This usually happens when no other nectar sources are available. People can also be affected by ingesting Carolina Jessamine.  Symptoms of human poisoning include nausea, diarrhea, blindness and death.  This toxin is so notorious that Agatha Christie had a character use gelsemine in one of her books to commit murder.   

Carolina Jessamine (Gelsemium sempervirens) in flower. 
A Clouded Sulphur (Colias philodice) is drinking nectar. 
Rowan County North Carolina. 

Carolina Jessamine vines twining counterclockwise.
Rowan County, North Carolina. 

Asymmetry abounds in nature.  People can be left-handed or right handed, male fiddler crabs have one giant and one small front claw, even some organic molecules come in mirror image forms.  So, take a look at some vines and see which direction they turn.