Oriental Lady’s Thumb, Creeping Smartweed, ETC.
SYNONYMS: Persicaria blumei (Meisn.) Nakai, Persicaria blumei var. albiflora Honda, Persicaria buisanensis (Ohki) Sasaki, Persicaria cespitosa var. longiseta (Bruijn) C.F.Reed, Persicaria gentiliana H.Lév., Persicaria satsumensis Nakai, Polygonum blumei Meisn., Polygonum buisanense Ohki, Polygonum cespitosum var. longisetum (Bruijn) Steward, Polygonum gentilianum (H.Lév.) H.Lév., Polygonum longisetum Bruijn
Persicaria longiseta (Bruijn) Kitag. is the correct and accepted scientific name for this species of Persicaria. It was named and described as such by Masao Kitagawa in the Report of the Institute of Scientific Research (Manchoukuo) in 1937. It was first named and described as Polygonum longisetum by Ary Johannes de Bruijn in Plantae Junghuhnianae in 1854.
The genus, Persicaria Mill., was named and described as such by Philip Miller in the fourth edition of The Gardeners Dictionary in 1754. Many species in the Polygonum genus were transferred to the Persicaria genus after that. Plants of the World Online by Kew currently lists 129 accepted species in the Persicaria genus (as of when I am writing this page on 9-13-19). Those numbers could change.
This species has many common names including Oriental Lady’s Thumb, Bristly Lady’s Thumb, Asiatic Smartweed, Creeping Smartweed, Long-Bristled Smartweed, Asiatic Waterpepper, Bristled Knotweed, Bunchy Knotweed, and Tufted Knotweed. With all those names to choose from, iNaturalist.org has chosen to call it Low Smartweed.
Persicaria longiseta isn’t a native of North America although it has made itself quite at home. The website wildflowersearch.org says Persicaria longiseta is only 20% likely to grow in this area. I can tell you without hesitation, this species is 100% alive and well from one end of the farm to the other.
When I decided to identify all the Persicaria species growing on the farm I took my camera and took photos fs all the colonies behind in the pasture behind the chicken house and south of the barn. A few days later I noticed this colony next to the shed in the backyard where my grandparent’s house. It appeared to be the same species that always grows under the porch on the north side of the house and the flower bed there. I usually take photos in the afternoon then look them over and make positive identifications in the evening. As I was trying to ID this colony they appeared to be Persicaria longiseta but I needed to look at their flowers again to make a positive ID. The flowers in the above photo didn’t show me what I needed to know so I went out with the flashlight and magnifying glass (in my boxer shorts) to have a look… Sure enough, the colony is Persicaria longiseta.
There are two very important things that distinguish Persicaria longiseta from the other six species that are growing here on the farm. You have to read farther down to when I took photos of those special characteristics.
As with “most” Persicaria species, they have fairly dark green lance-shaped leaves. The leaves of Persicaria longiseta are normally around 3″ long although the longest I have measured are 4″. Information online says their leaves are alternate with short petioles (the small stem between the leaf and stem of the plant), elliptic, broadly lanceolate or ovate, smooth along the margins and hairless.
The stems are light green to reddish-brown, glabrous, and send stems out usually from the lower nodes. They are decumbent in habit which means they sprawl out on the ground and stand up toward the end. Information online says they grow as long or tall, depending on how you look at it, to 36″ or more.
Ahhh. One of the two distinguishing features of Persicaria longiseta is the cilia growing from the ocrea (sometimes spelled ochrea). The ocrea is basically a sheath that grows at the base of the leaf around the stem and above the node (joint). The cilia look kind of like hair or bristles. The cilia seem to stay attached with P. longiseta while they typically fall off of other species. Even the ocrea dries and falls off of some species.
Another photo of the cilia growing from the ocrea of P. longiseta. The ocrea on Persicaria species is nearly translucent and is formed by the fusion of two stipules. One word seems to lead to another… A stipule is formed at the base of a petiole. Hmmm…
I found more Persicaria longiseta growing along the bank of the pond in the back of the farm on September 4. From a distance, P. longiseta looks very similar to P. setacea and both do have the cilia on their flowers and ocrea. However, P. setacea also has horizontal hairs growing from the sides of their ocrea. I was hoping for that because P. setacea is fairly rare, especially around here as in nonexistent… They grow in the southeast corner of Missouri.
The above photo is a good shot of the cilia growing on the flowers of P. longiseta. The cilia are actually growing from a sheath at the base of each flower.
Sometimes I have no words…
I just take a lot of photos so I can make a positive ID later.
I found a larger colony of Persicaria growing behind the pond bank at the back of the farm on September 9. Sometimes I am on a “mission” and don’t take the time to look around.
Another photo of P. longiseta behind the pond bank.
With age, some of the cilia may fall off of the flowes.
There is a HUGE colony of Persicaria longiseta in front of a couple of large Mulberry trees in the front pasture. Some of their racemes look a little weird…
More bristly ocrea…
There is always a colony of P. longiseta under the porch on the north side of the house. They like to escape into the flower bed…
Here is a colony along the shed behind the garage.
Here is a leaf with a nice thumbprint…
The tiny seeds of Persicaria longiseta are black and shiny. The seeds of all Persicaria species are black and shiny except for P. hydropiper which are black to brownish and dull (not shiny).
Nice 4″ long leaf wit a faint smudge.
The above photo is P. longiseta with P. punctata next to the twin Mulberry trees in the front pasture.
The above photo shows the glabrous stems of P. longiseta branching out t the lower nodes. This single plant was 42″ long, or tall…
Another photo of P. longiseta behind the pond at the back of the farm. In time, new flower stems grow from the upper leaf nodes.
Another shot of the same plant.
Good photo with a lot of hair… You can also see light hairs on the leaf. I get my close-ups using a magnifying glass in front of the lens. It takes patience and A LOT of practice.
Hmmm… I think this photo is a colony in front of the Mulberry trees in the front pasture.
And another area in front of the Mulberry trees.
This whole area in front of the Mulberry trees in the front pasture is full of Persicaria longiseta mingled with P. punctata. You can see the pink glow. There are a few P. pensylvanica mixed with P. punctata around the trees in a few areas. This area slopes toward a low spot (kind of a ditch) where the pond in the front pasture drains in. On the other side of the ditch, close to the pond, P. hydropiper is king.
I mentioned previously Persicaria longiseta grows under the porch and in the flower bed on the north side of the house… Here it is mingling with the Salvia coerulea ‘Black and Blue’ on September 30.
Persicaria longiseta is growing everywhere on the farm that is a good habitat for them. I am finding them in more places all the time…
I enjoyed the experience identifying the seven species of Persicaria growing on the farm. You can read the post about them all by clicking HERE where you will also find links to their own pages.
I have enjoyed photographing and learning about the many wildflowers growing on the farm and other areas. I have grown over 500 different plants and 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 horticulturalist 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.
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