Weed’s tale: the beguiling marsh pennywort

Thursday, July 6, 2017

Kenneth Setzer Fairchild Tropical Botanic Garden

As published in the Miami Herald, JULY 06, 2017 7:30 AM

Lawns are thought of, and to an extent are, deserts of biodiversity with seemingly little of interest to the bio-curious. But there’s almost always something waiting to be appreciated. Out walking the dog, weeding, planting, getting the mail — these are chances to peek into your lawn and see what’s really there.

I’ve spotted mating pearly crescent butterflies and weird mushrooms like the Pisolithus arhizus, the dyemakers’ false puffball mushroom. The appearance of the mushroom near my live oak revealed that they are probably engaged in a beneficial, symbiotic entanglement deep underground.

One visitor that doesn’t require much searching through your lawnscape to see is called manyflower marsh pennywort, a mouthful of a common name for Hydrocotyle umbellata (hydro-coat-a-lee).


Hydrocotyle or pennywort is a common weed on heavily watered lawns. KENNETH SETZER Fairchild Tropical Botanic Garden

Much of the info available on this plant is on how to eradicate it from your lawn, but to me that’s crazy. It’s native to the southeast, actually a huge portion of the United States according to the USDA plants profile, and it’s absolutely beguiling to my eyes. The leaves are like little lily pads popping up on stems like something out of Wonderland. There’s a handy botany term of good use here: peltate, meaning the stem (the petiole) attaches to the leaf not at the leaf’s margin, but from underneath. Nasturtium leaves also exhibit this; in fact marsh pennywort foliage looks quite like nasturtium.

Pennywort thrives along shores in freshwater wetlands, or in nearly any damp areas like overwatered lawns. If you dig one out of the ground carefully, you will find that what appear to be individual plants are mostly connected to an underground stem as a single entity. They’re just like holiday lights hanging from a single wire; in this way they can form dense mats.

The subterranean stems also occasionally send up flower stems (aka peduncles). The flowers are absolutely tiny and easily missed. Appropriately, since it’s in the carrot family (Apiaceae, or possibly now reclassified into Araliaceae, the ivy family) the flowers resemble tiny carrot flowers in white bunches shaped like a “Y” called umbels.


Pennywort grows well in water provided foliage can reach the surface. KENNETH SETZER Fairchild Tropical Botanic Garden

Possibly because of their use as aquarium plants, some species of pennywort have morphed into non-native invasive weeds around the world, such as in parts of the United Kingdom and Australia, where they may infest waterways.

Seven or so species are supposedly found in Florida, including H. bonariensis, and H. ranunculoides. They’re all pretty much called dollarweed or pennywort, and while similar looking, H. ranunculoides has a notch in the leaf and it is rebelliously non-peltate.

You can harvest Hydrocotyle and cultivate it yourself in garden ponds or dish (more like bowl) gardens. Gently dig up soil around the stems, pulling slightly to loosen and uncover the underground stem. You’ll find short roots growing from nodes along the stem. As long as you have one of these root nodes, the plant should survive, though more is perfectly fine.

In my own pond, I’ve tucked the roots into a pot already containing a plant, and the Hydrocotyle has behaved itself while providing some interest near water level. It will also do fine in plain water with no soil. A small container of water in sun will soon be filled with the disc-shaped leaves, covering the water’s surface thus discouraging mosquitoes.

Hydrocotyle growing in a vessel on a brightly lit windowsill makes a statement of simplicity, and will flourish without soil for months. What’s a weed, anyway, except a plant you haven’t yet stuck in a pot?