Coastal plain pennywort - H. bonariensis .
Water pennywort - H. umbellata
Whorled pennywort - H. verticillata .
It is hard to think of this nice, cozy, round, scalloped-margin plant being a weed. The leaves are on an elongated stem. It can be grown as a ground cover or in a bog garden. Plant in the muddy margins of a pond. Bright filtered light or full sunlight.
Found in moist and wet sites. Can be seen from Maine to Florida and west to California, and in places like Nova Scotia, West Indies, Mexico, and Central and South America.
It is considered a weed (just a plant "out of place" - see Emily's definition) in lawns that are overwatered.
Very similar to Dichondra carolinensis (Carolina Dichondra or Ponyfoot) which is kidney shaped with the stem coming out of the kidney like indentation. The Dollarweed is umbrella like with scalloped margins with the stem coming out of the middle of the leaf.
It is a perennial weed with rhizomes sometimes tubers.
Emily: My absolute favorite water garden plant
A reader writes: I just did a Google search for "dollarweed" to see what negatives were out there on my ABSOLUTE FAVORITE water garden plant.
I actually purchased this plant at Lowe's several years ago, where it was sold with only its scientific name, Hydrocotyle umbellata, attached, and as an "oxygenator," with no information as to what it really was, or did... I had to do net-searches to discover it was also called Pennywort, and it was only after a couple of years I actually heard the term "Dollarweed" and only last year I finally saw it online.
I grow mine primarily in a 55-foot stream that connects my small upper pond with my larger (450-gallon) lower pond, and it lives year-round here in Zone 7b/8a, although I often have my pump off in the winter because I need to do maintenance, so it just goes dormant until the water runs again.
All it has to for rooting substrate in the stream is a thin layer of "egg rock" and whatever mulm has settled into and beneath that, yet it FLOURISHES each year, to the point that annually I send several large (2-gallon) Ziplock bags full of this stuff to water gardening internet friends all over the country... Iowa, Indiana, Michigan, Maryland, North Carolina and several other states...
With all the FUSS over it being a WEED, I finally did a USDA search to make sure it IS a native plant, and they indicate it IS and DON'T call it a weed at all.
Here's a picture of some growing, prolifically, in a section of my stream...
Emily: How do I kill it?
Dear Emily: My husband and I thought we were moving into our dream home.
We live on 10 acres. The entire area around my house and to the front of the property is totally covered (thick) in dollar weed, which I believe I am severely allergic, I'm absolutely miserable. What can I do? Does mowing help with the allergies or bother them more?
A: Mowing and trimming the dollarweed seems to encourage more growth. Dollar weed appears because there is over watering in the area where it grows.
Yes, sometimes mowing stirs up the dryness and the oils of a certain plant material to bother some people. Dollar weed is a southeastern problem and getting rid of it is very difficult.
Emily: Not My Pennywort!
Dear Emily: You've got the wrong plant. Dollarweed is not the same as our Pennywort that we grow and make a drink out of.
A: Another problem with common names. Dollarweed and pennywort are used either interchangeably or regionally in mostly Southeast United States. This is not the same plant as the pennywort eaten or used to make a drink in India, Southeast Asia (and some other parts of Asia), and Northern Australia.
This Asian pennywort is called Asiatic Pennywort or Indian Pennywort and Goto-Kola. We have seen the scientific name listed both as Centella asiatica and Hydrocotyle asiatica. We have not seen many references for this plant in US gardening books and do not know if it is grown regularly here. One of our references (Botanica) says that it will grow in US zones 9 - 12. Botanica says that it is cultivated in Asia for its many medicinal uses.