The Strangest Hibiscus of All

August 29, 2013

Nature Notes by Bill Dunson

 

I have to admit that I am a huge fan of hibiscus flowers. My first love was the rose mallow (Hibiscus moscheutos) which provides a spectacular flower display in coastal marshes of MD and VA. Later I became aware of the amazing variety of hybrids and cultivars of the tropical Hibiscus rosa-sinensis in FL. Then there are various other members of the mallow family (Malvaceae) which are remarkable on their own, such as rose of Sharon, hollyhock, cotton and okra.

But for those of us that are committed to making our gardens maximally receptive to butterflies and other native pollinators, there is a dark side to hibiscus culture. Many of the most commonly grown species do not seem to be very attractive to butterflies and hummingbirds. Indeed it appears that the most showy flowers of both cold hardy and tropical varieties are mainly attractive to bumblebees because of the pollen they supply. Some species such as rose of Sharon and Turk’s cap do also offer nectar and will attract hummingbirds, orchard orioles, and bumblebees.

Many hibiscus flowers are open only for about one day, which is strange in comparison with some other flowers with much longer life spans. But the most extreme of the short-lived hibiscus flowers is the famous “flower of an hour,” Hibiscus trionum. They are an exotic, weedy invader from the eastern Mediterranean region which prefers disturbed ground. I noticed this remarkable plant in our garden recently and enjoyed the brief opening of its flowers which lasts only a few hours. The flower is quite beautiful with white petals and a dark red, iridescent center. This bulls-eye pattern is considered to function as a means of guiding pollinators to the flower. But what could be the purpose of having a flower obviously designed to attract pollinators which only lives a few hours? Apparently this is a strategy for this weedy species to maximize its output of seeds. The flower waits a short time for pollinators to appear to effect cross pollination, but if they don’t, the female stigma bends over and contacts the anthers leading to self pollination.

The beauty and variety of hibiscus flowers is spectacular as are the evolutionary mechanisms which have led to their specific colors, shapes and associations with pollinators. None are stranger than the short lived flower of an hour which has developed an unusual method to allow for genetic variation derived from some cross pollination, while insuring by delayed self pollination that the flowers will be producing a large number of seeds required for this invasive species to colonize disturbed habitats.

Bill Dunson, Englewood, FL & Galax, VA
wdunson@comcast.net

Bill Dunson

About Bill Dunson

Bill Dunson, born in rural Georgia, skipped 12th grade and went directly to Yale. Bill subsequent-ly received a PhD in Zoology from the University of Michigan, studying softshell turtles. Bill is Professor Emeritus of Pennsylvania State University thanks to a career spent entirely at that institution, teaching and doing research on the physio-logical ecology and ecotoxiciology of reptiles, amphibians and fish. Always curious about nature, Bill has dedicated his life to learning and sharing his knowledge with others. He has served on many advisory boards here in Southwest Florida to preserve the water that gives life to our region.

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