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On our last ELC campus field trip with the Orchid Island Garden Club on January 19th we hiked along the impoundment dike on the South end of the property in the ecotone (or ecological transition zone) between the mangrove forest, brackish marsh, and coastal upland. What’s so special about ecotones is that they are places where at least two different ecosystems mix, which makes them biodiversity hubs.
One of the more common (and one of the most ornamental) plants on the impoundment dike that we saw is Sea Ox-eye Daisy (Borrichia frutescens.) This long-lived perennial shrub grows up to three feet tall and, as a halophyte (a salt tolerant plant), it can most commonly be found in the harsh conditions of salt marsh, coastal strand, the backside of beach dunes, or on mosquito impoundment dikes.
In the landscape, sea ox-eye daisy makes a beautiful addition with its silver pubescent leaves amongst other mostly coastal wildflowers like yellowtop (Flaveria linearis) and horsemint (Monarda punctata), or in moist to wet conditions together with sea purslane (Sesuvium portulacastrum) and christmasberry (Lycium carolinianum.) The flowers are yellow dime sized daisies that are lined with spine-tipped bracts (the tiny supportive leaves behind the flower.)
While it’s not so much of a bee attractant (at least the author rarely sees bees visiting the flowers), sea ox-eye daisy is primarily pollinated by a wide range of butterflies, including the florida white (Appias drusilla), great southern white (Ascia monuste; see photo of the impoundment dike at Pelican Island NWR), gulf fritillary (Agraulis vanillae), many skippers and Sulphur (Phoebis) butterflies.
Whenever you see this plant look out for brown outgrowths on the upper stems (see photo), especially from spring to summer. Those are the gulls of the midge Asphondylia borrichiae (a tiny non-biting fly), named after its host plant. The female midge injects her eggs into the plant tissue that is capable of growth (also called meristem.) The larvae’s saliva then changes the local biochemistry of the plant so that it creates a gall that houses between one and eight larvae in little chambers covered with a fungal layer that the larvae feed on.
At least four species of wasps are known to parasitize these galls by injecting their own eggs into them. The wasp larvae then feed on the pupae or larvae of the midge. Most of these wasps are also known to hyperparasitize each other in the gall chambers. About 3% of the midges that are not parasitized are said to be predated by birds.
This is just one of many examples showing why exotic plants can never be a substitute for natives. Native plants have undergone a coevolution with wildlife and both are dependent on each other and form a complex ecosystem.
If you want to learn more about Florida, visit the Environmental Learning Center and join us on a guided kayak excursion.
