As the weather begins to hint of September crispness, there are a couple of island wildflowers that signal the shift. You’ll know that change is in the air when swamp rose mallow and sea lavender reach their peak. Swamp mallow (Hibiscus moscheutos) is Nantucket’s native wild hibiscus. Rather than living in true swamps, this big and bold wildflower thrives in salt marsh edges, salt ponds, and other wet shoreline habitats. Instead of a shrub with woody stems like most hibiscus, rose mallow’s soft green stems regrow from the ground each season to a remarkable height — usually three or four feet tall. Not to be outdone by its tropical cousins, rose mallow produces very large blooms, four to eight inches in diameter, which here on Nantucket are typically a solid bright pink. Sometimes the centers of the flowers are a darker shade of pink or red. A version with pale or white petals surrounding a very dark center may be more common in other parts of the rose mallow’s range, which extends from New Hampshire (recently colonized in 2005) westward to the Great Lakes region and south all the way to Texas. Botanists have sometimes considered the different color patterns to be separate subspecies, but since the differences are along a gradient rather than strongly separated they are now regarded as one species with wide variability.
Rose mallow seems almost too showy to be real! A close look reveals that each petal has distinct veins, giving the flower a pleated appearance. In the center of the flower is a large curving structure where all of the flower’s reproductive parts are fused together in one column. Central parts of the column are female, while the male anthers, loaded with golden pollen, branch out around the column. Emerging from the tip of the column are several styles tipped with round sticky pads that receive the pollen when a flower is visited by an insect.
Who pollinates a rose mallow? A visit to the plants growing in my garden bed revealed a number of ants and small beetles harvesting pollen, but they would be unlikely to carry pollen to the stigmas if they can’t reach the nectar hidden inside the column. Bumblebees and other species of native long-tongued bees do visit the flowers for the nectar, and there is even a specialist native bee that feeds solely on hibiscus flowers, called the rose mallow bee (Ptilothrix bombiformis). As its species name suggests, it’s a heavy-bodied bee with a strong resemblance to bumblebees (Bombus spp.). If you happen to spend some time in a rose mallow patch observing pollinator visits, it’s worth a look for this bee; furry like a bumblebee but with longer, lankier back legs, the rose mallow bee is known to mate inside the hibiscus flowers, the males following females on their rounds as they feed. Because of its ability to feed on both the pollen and the nectar, the rose mallow bee is probably the ideal pollinator for our hibiscus. As far as we know, it has never been documented on Nantucket, so it would be an exciting find.
Surprisingly, rose mallow is adaptable enough that you can even grow it in your garden, and various cultivars are available from nurseries. The ones in my garden bed were a bit of an accident, when seed from plants grown for restoration use decided to germinate in the middle of my lettuce patch. So far it seems to do fine mixed in with the vegetables. Rose mallow truly thrives in the rich wet soil of our pond shores and marshes, but compost-enriched soil and a bit of supplemental watering can make it a part of your yard. A sunny spot that naturally collects runoff, such as a rain garden or near the downspout of your gutters, would be perfect. The more water and the richer the soil, the bigger the blooms.
Another August wildflower found on our shores is sea lavender (Limonium carolinianum). Unlike the flamboyant rose mallow, sea lavender’s haze of color in the salt marsh is made up of hundreds of tiny lavender colored flowers. Growing among the salt marsh grasses, sea lavender may be fully submersed at the highest tides. It has a few interesting adaptations to be able to tolerate this salty, amphibious life style; sea lavender leaves are tough and leathery, somewhat succulent and covered with a waxy outer layer to protect them from drying out. When things get too salty, it’s able to pump saline water out of special pores on the leaf surfaces to maintain the correct balance. The flowers are on tall stalks, elevated above all but the highest of tides, and attracting insects that can cross pollinate the plants.
Demand for sea lavender’s delicate flowers meant that it was nearly wiped out in some New England marshes. Its colorful flowers are easily dried for flower arrangements, and were picked and sold in large bundles. If over-harvested, too few are left to produce seed for new generations. It takes several years for a seedling to grow large enough to flower and set seed. Researchers have found that it just takes only seven years of over-harvesting to deplete a marsh’s sea lavender by 75%.
Both of these late summer wildflowers contribute to the biodiversity and natural beauty of our shores. They add a splash of color to what would otherwise be areas populated almost entirely with cattail or salt marsh grasses. To view sea lavender in bloom, check out conserved marshes like Eel Point, Folgers, and Masquetuck. The best way to enjoy this salt marsh plant is to walk along the sandy areas of the shore where the fiddler crab armies roam, and take in the fields of green with areas of misty lavender blooms. Rose mallow is easy to find at the Land Bank’s Bamboo Forest along Madaket Road, while Squam Pond, Sesachacha, and Miacomet Pond also have established rose mallow patches that require a bit more exploring.
*Please note, this blog post was originally published in The Inquirer and Mirror on August 31, 2017 in the article series called Island Ecology. The Foundation’s Science staff regularly contribute to our local newspaper and reprint the articles here soon after.
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