Dwarf Conyza, Dwarf Fleabane, Dwarf Horseweed
Synonyms of Erigeron divaricatus (2) (Updated on 8-16-22 from Plants of the World Online): Conyza ramosissima Cronquist, Leptilon divaricatum (Michx.) Raf.
Erigeron divaricatus Michx. is the accepted scientific name for this species. It was named and described as such by André Michaux in Flora Boreali-Americana in 1803.
The genus, Erigeron L., was named and described as such by Carl von Linnaeus in the second volume of the first edition of Species Plantarum in 1753.
Conyza ramosissima Cronquist is another commonly used scientific name, which Plants of the World Online says is a synonym. It was named and described as such by Arthur John Cronquist in the Bulletin of the Torrey Botanical Club in 1943.
The genus, Conyza Less., was named and described as such by Christian Friedrich Lessing in Synopsis Generum Conyza ramosissima in 1832. Species of the Conyza genus have been moved to Erigeron.
As of 8-16-22 when I am updating this page, Plants of the World online lists 446 species in the Erigeron genus. It is a member of the plant family Asteraceae with 1,676 genera. Those numbers could change as updates are made on POWO.
The above distribution map for Erigeron divaricatus is from the USDA Plants Database, although they use the name Conyza ramosissima. Areas in green are where the species is native and blue where it has been introduced. The map on Plants of the World Online doesn’t show as broad a range. The USDA Plants Database gets their data from BONAP, however they don’t list Erigeron divaricatus OR Conyza ramosissima… Maps are to get a general idea and actual distribution could be different. No maps are perfect.
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.
THERE ARE A FEW LINKS AT THE BOTTOM OF THE PAGE FOR FURTHER READING AND TO HELP WITH A POSITIVE ID.
Hello everyone! This page is about a common but often overlooked species. I have noticed quite a few of them growing in the cracks of the driveway since I can remember but I never bothered to identify them. I decided to take a few photos and use iNaturalist to find out what they were. I was kind of surprised to find out they were Erigeron divaricatus which is a member of the plant family Asteraceae. Common names include Dwarf Conyza, Dwarf Fleabane, Dwarf Horseweed, and possibly others. It is a dwarf cousin of the much taller Erigeron canadensis (Syn. Conyza canadensis commonly known as Horsetail,Marestail, and so on.
The Erigeron divaricatus is an odd plant growing no more than about 10″ tall. The plants in my driveway get mowed off, but that doesn’t keep them from flowering. They have a grayish appearance because they are covered (stems, leaves, and flowers) with white antrorse hairs (laying flat against the stem and facing forward/upward.
The flowers, as you can imagine, are very small and you wouldn’t guess it was even a member of the Asteraceae family at all from a distance. It does, however, have the essentials that make it so. The ray flowers (petals) and disc flowers emerge from a flattish receptacle which are enclosed by cup or bell-shaped involucral bracts. After flowering, the fruit dries and the seeds remind you of miniature dandelions…
There isn’t much information online about this species, but I find the history of the scientific name interesting. The two major databases I use, Plants of the World Online by Kew (Royal Botanical Garden) and Tropicos (from the Missouri Botanical Garden) both say the “accepted” scientific name is Erigeron divaricatus. It was named and described as such by André Michaux in 1803. Then, in 1818, Constantine Samuel Rafinesque attempted the name Leptilon divaricatum, which apparently didn’t stick… THEN, probably in 1943 when Arthur John Cronquist named the species Conyza ramosissima, there was a little confusion. Apparently, Mr. Cronquist decided to move the species from Erigeron to Conyza but there was already a Conyza divaricata (Sprengel 1826), so he proposed the name be changed to Conyza ramosissima… Then in 1995, Harold Ernest Robinson changed Conyza divaricata to Vernonanthura divaricata, but that is an entirely different plant.
So, the name Conyza ramosissima stuck for a while and MOST websites are using that name as the accepted scientific name.
As I mentioned, I rely on Plants of the World Online and Tropicos for up-to-date accepted scientific names. Before POWO, I used The Plant List which was taken over by World Flora Online. I found it interesting WFO says both Erigeron divaricatus and Conyza ramosissima are “ambiguous” names. Ummm… Ambiguous means doubtful or uncertain. WHAT IS THAT?!?!?! Botanists always have an opinion even though they may not agree. I was told by a wise retired botanist and professor of botany that accepted names don’t necessarily mean correct names. I had to think about that for a while but I realized he was right. I had to change what I was saying from “correct and accepted” to just “accepted.”
The International Plant Names Index (IPNI) is used by both Plants of the World Online and Tropicos. IPNI is a plant names database which includes (or will eventually include) all scientific plant names. It includes links to the original publication where the person naming the plants was published, which is important. For example, Conyza is listed as:
Conyza Less., Syn. Gen. Compos. 203 (-204) (1832), nom. cons.
The “nom. cons.” means nomen conservandun. The name has specific nomenclatural protection and has been retained even though it violated one or more rules which would otherwise keep it from being a legitimate name. For example, the authur (Less.) perhaps violated a rule when naming the plant or published the description.
EARLIER, Carl Linnaeus himself must have described (or possibly even named) the genus Conyza, because there is a listing for:
Conyza L., Sp. Pl. 2: 861 (1753), nom. rej.
Hmmm… The “nom. rej.” means nomen rejiciendum. That is for a name that has been recjected in favor of a name that has been conserved under certain rules of the ICN (International Code of Nomenclature). Well, that is weird. On page 861 and 862, Mr. Linnaeus described several species of Conyza in the second volume of the first edition of Species Plantarum… In 1753! So, how is it that his Conyza is recected over Lessing’s Conyza of 1882?
The weird thing is, when I read the original publication where Mr. Lessing supposedly named Conyza (Synopsis Generum, page 203), it says Conyza L. That means he gave credit to Linnaeus for naming the genus, not himself… So, how is it Conyza Less. was the conserved name? I have no clue!
Maybe the confusion was enough to make the Conyza genus a synonym of Erigeron, and Conyza ramosissima a synonym of Erigeron divaricatus… Linnaeus still wins. 🙂
Linnaeus described several species Erigeron right after Conyza… Well, I am not a botanist so it is easy for me to be somewhat confused… When I attempt to read the rules of nomenclature on the ICBN website, I am kicked out because I don’t have permission.
Actually, anyone can use either name since the naming of both species were documented in valid publications. There are rules, you know. BUT, the genus name Conyza was not actually validly published and one of more rules were broken and was considered “nom. rej.” (n
I will add more photos, and proper descriptions…
I have enjoyed photographing and learning about the many wildflowers growing on the farm and in other areas nearby. My farm is 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 200 species of wildflowers (most have pages listed on the right side of the page). 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 variable from location to location, so that can be 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 email@example.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)
FLORA OF NORTH AMERICA (GENUS/SPECIES)
USDA PLANTS DATABASE
MSU-MIDWEST WEEDS AND WILDFLOWERS
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 the most reliable and up-to-date plant database and they make updates on a regular basis. 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. 🙂