Oppositeleaf Spotflower

Acmella repens

ak-MEL-uh  REE-penz

Synonyms of Acmella repens (26) (Updated on 11-29-23 from Plants of the World Online): Acmella nuttaliana Raf., Acmella occidentalis Nutt., Acmella oppositifolia var. repens (Walter) R.K.Jansen, Anthemis repens Walter, Anthemis trinervia Sessé & Moc., Ceratocephalus beccabunga Kuntze, Ceratocephalus repens (Walter) Kuntze, Ceratocephalus subhirsutus Kuntze, Spilanthes americana f. ciliatifolia A.H.Moore, Spilanthes americana f. lanitecta A.H.Moore, Spilanthes americana f. longiinternodiata A.H.Moore, Spilanthes americana var. parvula (B.L.Rob.) A.H.Moore, Spilanthes americana var. repens (Walter) A.H.Moore, Spilanthes beccabunga DC., Spilanthes beccabunga var. parvula B.L.Rob., Spilanthes ciliata var. diffusa A.H.Moore, Spilanthes cocuyensis Cuatrec., Spilanthes diffusa Poepp. & Endl., Spilanthes disciformis var. phaneractis Greenm., Spilanthes lateraliflora Klatt, Spilanthes lehmanniana Klatt, Spilanthes nuttallii Torr. & A.Gray, Spilanthes orizabaensis Sch.Bip. ex Klatt, Spilanthes phaneractis (Greenm.) A.H.Moore, Spilanthes repens (Walter) Michx., Spilanthes subhirsuta DC.

Acmella repens (Walter) Rich. ex Pers. is the accepted name for this species of Acmella. The genus and species were described as such by Christiaan Hendrik Persoon in Synopsis Plantarum in 1807. He gave credit to Louis Claude Marie Richard for naming the genus and species. It is sometimes cited as Acmella repens (Walter) Rich. or Rich. ex Pers. It was first named and described as Anthemis repens by Walter Thomas in Flora Caroliniana in 1788.

As of 11-29-23 when this page was last updated, Plants of the World Online still lists 32 species in the Acemella genus. The genus is a member of the plant family Asteraceae with 1,702 genera. Those numbers could change as updates are made on POWO. The number of genera in this family fluctuates up or down quite often.

The above distribution map for Acmella repens is from Plants of the World Online. Areas in green are where the plant is native and purple is where it has been introduced. The map on the USDA Plants Database for the United States and Canada is the same. The species may be more widespread than the maps show.

The map on iNaturalist shows where members have made observations. Anyone can join and it is a great website to confirm and share your observations. The maps on iNaturalist are continually updated as members post new observations.

Acmella repens is found growing in the United States in Missouri and Texas eastward in the south part of the country toward the east coast, Mexico south through parts of South America, Costa Rica, and Cuba.

 THERE ARE A FEW LINKS AT THE BOTTOM OF THE PAGE FOR FURTHER READING AND TO HELP WITH PLANT IDENTIFICATION.

I have only noticed this plant growing in a small spot along the northwest corner of the barn. I think I first noticed it growing here a few years ago. I took photos, and maybe misidentified it because I can’t find the older photos. I have gotten more into wildflower ID so I make sure I take ample photos of the entire plant whereas a few years ago I probably just took photos of the flowers. It takes a lot more than just flowers sometimes to make a positive ID.

This plant only seems to show up in the yard by the barn late in the season. I either don’t notice it since I mow this area weekly or it just emerges. They may grow in other areas on the farm but this is the only spot I have noticed it so far. They seem to be a low-growing sprawling plant, so they may grow unnoticed among taller weeds (I mean wildflowers) and grass.

Acmella reptans is a herbaceous perennial that grows in swampy areas, low wet woods, borders of pods, and areas beginning to dry out. 

 This plant has several types of leaves on the same plant. Leaves are mainly opposite while upper leaves may be alternate. Leaves are petiolate, narrowly lanceolate to broadly ovate, and bluntly or sharply pointed. Margins of leaves are finely to coarsely and bluntly to sharply toothed. Leaf surfaces are smooth (glabrous) or covered with short, soft hairs (pubescent) along the veins.

The spreading (or sprawling) stems are up to 36” long (3 m), finely ridged or grooved, with pubescent hairs. Stems often root at their lower nodes. Stems can be green, reddish, or a combination of the two.

The undersides of the leaves show prominent veins and midribs. Some are kind of chalky looking which is from fine hairs.

They have a fibrous root system, sometimes rhizomatous. The spreading (or sprawling) stems are up to 36” long (3 m), finely ridged or grooved, with pubescent hairs. Stems often root at their lower nodes.

Here is a smaller leaf that is more narrowly lance-shaped and not so deeply lobed.

 

The single flower heads emerge from the top of the plant’s branches and central stem. Flower heads consist of 5-15 yellowish ray florets (petals) and a cluster of disc flowers in the center. A series of 6-16 chaffy bracts surround the flower. The cone of disc flowers elongates as the plant matures. For a better technical description, see the link to Missouri Plants below.

I haven’t noticed this species since 2019. I will keep an eye out for it next to the barn and in other areas. This species flowers from July through October…

There isn’t that much online about the Acmella repens and some of the websites showed plants with different leaves…

I have enjoyed photographing and learning about the many wildflowers growing on the farm and other areas. I live on a small farm in Windsor, Missouri in Pettis County (Henry County is across the street and Benton and Johnson aren’t far away). I have grown over 500 different plants and identified over 250 species of wildflowers (most have pages listed on the right side of the blog). I am not an expert, botanist, or horticulturalist. I just like growing, photographing, and writing about my experience. I rely on several websites for ID and a few horticulturalists I contact if I cannot figure them out. Wildflowers can be somewhat variable from location to location, so sometimes it gets a bit confusing. If you see I have made an error, please let me know so I can correct what I have written.

I hope you found this page useful and be sure to check the links below for more information. They were written by experts and provide much more information. Some sites may not be up-to-date but they are always a work in progress. If you can, I would appreciate it if you would click on the “Like” below and leave a comment. It helps us bloggers stay motivated. You can also send an email to me at thebelmontrooster@yahoo.com. I would enjoy hearing from you especially if you notice something is a bit whacky.

FOR FURTHER READING:
PLANTS OF THE WORLD ONLINE (GENUS/SPECIES)
INTERNATIONAL PLANT NAMES INDEX (GENUS/SPECIES)
TROPICOS (GENUS/SPECIES)
FLORA OF NORTH AMERICA (GENUS/SPECIES)
WORLD FLORA ONLINE (GENUS/SPECIES)
WIKIPEDIA (GENUS/SPECIES)
MISSOURI PLANTS
DAVE’S GARDEN
iNATURALIST
WILDFLOWER SEARCH
USDA PLANTS DATABASE
THE NATIONAL GARDENING ASSOCIATION
LADY BIRD JOHNSON WILDFLOWER CENTER

NOTE: The data (figures, maps, accepted names, etc.) may not match on these websites. It depends on when and how they make updates and when their sources make updates. Some websites have hundreds and even many thousands of species to keep up with. Accepted scientific names change periodically and it can be hard to keep with as well. Some of the links may use a name that is a synonym on other sites. In my opinion, Plants of the World Online by Kew is one of the most reliable and up-to-date plant databases and they make updates regularly. I make updates “at least” once a year and when I write new pages or add new photos but I do get behind. We are all a work in progress. 🙂