Dollarweed - What Good Is It?

Talk about a plant that everybody loves to hate!  Dollarweed (Hydrocotyle sp.) is a native plant, also known as pennywort, that loves to grow in the same conditions that also favor lawn grass:  bright sun, plentiful water, low surrounding vegetation.  It's hardy and it requires essentially no care.  With its single, round, silver dollar sized leaves, it is easily recognizable and it boldly stands out in a mass of linear grass leaves.  As such, dollarweed has gained great notoriety - heaven forbid that a non-grass plant disturb the carpet-like splendor of a lawn!

If you look at dollarweed simply as a plant, however, it's really rather attractive.  The bright, shiny green leaves reflect sunlight and are held aloft on pliable, sturdy stems. 

The flowers are umbels of white that are not glamorous, perhaps, but that are quite attractive in a quiet, lacy way.

 This photo shows how the umbels open up as they get older.

This morning, as I took photos, the insects I found on these flowers in a garden bed were tiny ants.  Truthfully, I didn't even see the ants until I opened the photos up on my computer screen.

Perhaps dollarweed's biggest flaw as a garden plant is that it doesn't tend to form solid mats but, instead, prefers to interweave through other plants, refusing to stay neatly in one place.  It's also difficult to completely eradicate from a lawn or flower bed with underground rhizomes that break off readily at each node. 

Because it's a native plant, I've wondered how dollarweed fits into the ecosystem here, but I haven't taken the time to really study it.  All I've noticed on the plant in my yard is an occasional leaf miner.   I'm not sure what insect is doing this particular leaf mining - the larva of a fly? of a moth? of a sawfly? of a beetle?  Any of these different types on insects have certain species whose larvae are leaf miners, feeding on the leaf tissue between the upper and lower surfaces of leaves.

A couple weeks ago, I noticed a closeup photo of the bloom of dollarweed on Instagram.   Responding to the photo, which was identified only by the scientific name, presumably to minimize automatic knee-jerk negative responses, I commented on my interest about how this plant worked in the ecosystem.  The poster replied back with a list of Hymenopterans (bees, ants, and wasps) that had been observed by scientists in 2015 on dollarweed flowers at Archbold Biological Station here in Florida. (See note below.)

Here's the list "floridaplants" sent, comprised of 10 solitary wasps and one native bee.  As you scan it, be sure to note the prey that these wasps use for feeding their young: orb weaver spiders, beetles, flies, leafhoppers or planthoppers, leafhoppers, flies, flies, flies, moth caterpillars, and moth caterpillars.

Episyron conterminus posterus - a spider wasp specializing in orb weavers to provision their nests
Cerceris blakei - a digger wasp that provisions its nest with beetles
Ectemnius rufipes ais - a square-headed wasp that nests in dead wood, provisioning its nest with flies
Epinysson melippes - a solitary wasp that provisions its nest with leafhoppers or planthoppers
Hoplisoides dentriculatus dentriculatus - a sand wasp that provisions its nest with leafhoppers
Oxybelus emarginatus - a prong-backed flyhunter wasp that provisions its nest with flies
Tachysphex apicaulis - a square-headed wasp that provisions its nest with flies
Tachysphex similis - a square-headed wasp that provisions its nest with flies
Leptochilus acolhuus - a mason wasp provisioning its nest with moth caterpillars
Parancistrocerus salcularis rufulus - a mason wasp provisioning its nest with moth caterpillars
Halictus poeyi - Poey's Furrow Bee, a small native bee in the sweat bee family that provisions its nest with nectar and pollen

Wouldn't it be great to get some free, round-the-clock pest control in your gardens?  Especially pest control that specializes in controlling some of the insects above without, at the same time, killing praying mantids, honeybees, or monarch butterflies?

Well, you can have exactly that sort of pest control - IF you leave dollarweed and other small, flowering plants alone in your lawn, instead of treating them like public enemy #1.  In fact, this sort of situation is why Greg and I don't use chemicals on our lawn.  If it grows low, is generally green, and can be mowed, we let it be.  Because of their relationships with native pollinators, I prefer to have native plants as weeds in my grass - rustweed and some of the sedges, for example, as well as dollarweed - but it's almost impossible to have native broadleafed plants without also having non-natives, so we "live and let live".  

The only one of the insects in the list above that I've knowingly observed in my yard is the native bee, Halictus poeyi, Poey's Furrow Bee, shown in the photo above on Gaillardia and identified on BugGuide.net.  Coincidentally, it's the only one of the insects on the Archbold Biological Station's list with a common name. That doesn't mean the wasps aren't an important part of the natural web of nature, too, it just means that people haven't paid a lot of attention to them.  They're generally small.  They're not very colorful.  They don't bother people. Until recently, it's simply that nobody has paid much attention to them.  Generally, scientists often don't know which species, exactly, each wasp specializes in utilizing as prey for food for its larvae.

What a shame that we've ignored these important parts of the ecosystems in our yards and gardens...but what an interesting chance for everyday gardeners to help restore the balance of nature.  Literally as well as figuratively.  Best of all, this ability to help restore Earth's ecosystems is as easy as refraining from using chemicals on our lawns.  Seems like a no-brainer to me.


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Note:  According to the Instagram poster "floridaplants", self described as a botanist, this is the list of wasps and bees that were observed nectaring at dollarweed, Hydrocotyle umbellatus, at Archbold Biological Station in Florida.  The scientific paper (?) is Deyrup, M.A. and M.D. 2015. Database of observations of Hymenoptera visitations to flowers of plants on Archbold Biological Station, Florida, USA.  Unfortunately I haven't been able to get a copy of this database online, so I'm going out on a limb here and assuming the information is accurate.  After all, it's not like many people have the interest or ability to make up a list of scientific names like this.