Knotgrass or Not
Lessons in source verification (Polygonum aviculare)
What are the toughest nuisance plants your average person encounters day-to-day?
Around here, in the rainy UK, that list would include things like the common dandelion (Taraxacum officinale), butterfly bush (Buddleja davidii), hedge bindweed (Calystegia sepium) and field bindweed (Convolvulus arvensis).
Taraxacum officinale has the best propagation mechanism of all. I recall blowing out the fluffy seed heads as a child and this delight transcends generations.
Take any British train and you’ll observe resplendently healthy Buddleja davidii growing out of creosote saturated train line gravel.
As for Calystegia sepium and Convolvulus arvensis… well, anyone who has these tentacled plants in their annual vegetable plot will need no introduction.
I would be hard-pressed to distinguish field bindweed and hedge bindweed in a line up though. Their lookalike appearance has led to similar common names, which makes sense, but has some dangerous implications. Apparently, hedge bindweed (Calystegia sepium) has edible stalks and roots but field bindweed (Convolvulus arvensis) doesn’t. I should probably talk about this in a later article, but I digress.
Another on this list of tough “nuisances” is Common Knotgrass (Polyganum aviculare).
I have an interesting relationship with Common Knotgrass. It’s the first and last time I have applied weedkiller. This happened on the driveway of a rental property more than a decade ago.
In my defence I had tried to remove the plant by hand only to discover that it had grown up through a plastic membrane and up through several inches of gravel.
The Common Knotgrass bounded back of course, shrugging off my rustbucket’s constant engine oil leak. My story is one that has repeated itself across innumerable driveways across the world.
Of course, back then I didn’t know this plant was Polyganum aviculare.
An unassuming plant, it belongs to the Polygonaceae family which features the Japanese Knotweed dread-god and minor demon Rumex, amongst others. This family has a solid pedigree of inducing stomach ulcers in gardeners and landscapers the world over.
I rediscovered Common Knotgrass in the barren compacted soil of my local park, right between a high foot-traffic gate.
At the time, I didn’t know this was the same humble plant as that weedkiller soaked driveway almost a decade ago. I mentally tucked it away, “Common Knotgrass”, I said to myself, “What an interesting name, is it related to Knotweed?”.
And the memory finally emerged, shouldering through the cracks of others, just like that heroic driveway plant.
Of course I brought my new found love of nature to bear and discovered many things about the Common Knotgrass. My initial forays told me that the Vietnamese consume it regularly as a bitter vegetable. “They call it rau đắng”, I joyfully told some friends.
Except I was wrong.
There are quite a few articles (including wikipedia) proclaiming this, but after quite a lot more digging I’m fairly certain that rau đắng is Glinus oppitisifolus.
Glinus oppitisifolus is used in many Vietnamese recipes including
Cao lầu which is “a regional Vietnamese noodle dish, from the city of Hội An, in central Vietnam's Quảng Nam Province. It typically consists of pork and greens on a bed of rice noodles made from rice which has been soaked in lye water”.
Mì Quảng which is “rice noodles, meat, and herbs, most commonly served with a small amount of broth, which is generally infused with turmeric. Peanut oil can also be added to make the dish more flavorful. Wide rice noodles are placed atop a bed of fresh herbs in a bowl (or vice versa), and then warm or lukewarm broth and meat are added. The broth is usually strongly flavored and only a small amount of it is used, generally enough to partially cover the vegetables.”
These delicious recipes make it all the more a shame that Glinus oppitisifolus has been confused with Polyganum aviculare in many internet sources. The common names for both being “bitter leaf” in Vietnamese might be at the heart of this mistaken identity.
So where does this leave Polyganum aviculare, or Common Knotgrass?
Recipes for this are not so common. Compared to the abundance of recipes for its alter ego, I had to explore ethnobotanical research papers to find where P. aviculare has been consumed.
Another name for P. aviculare is pigweed - yes, it’s fed to pigs and other animals as fodder. Since we’re anatomically quite similar to pigs, the common name is an important clue that we can consume it too.
In the Gümüşhane province of Turkey, it is prepared for food by boiling and roasting. More generally in Turkey, Common Knotgrass is also prepared by stewing “with bulgur or rice after mixing them with fried onion”.
On either side of the Turkish-Georgian border Common Knotgrass is boiled and stewed. The above ground and young shoots are prepared in a broadly accommodating dish called “Pkhali” which includes “boiling, squeezing, and chopping the plants, then either stewing them with onion in oil or occasionally with eggs, or mixing them together with garlic, coriander, and walnut”.
In the same border region, it is also prepared in soups, made into a pickle or put into a wrap (sarma).
West of Turkey, we find that some parts (unknown) of Common Knotgrass have been used in porridge by the “Germanic people” but I can find no sources for this. Given how it can be stewed, this makes sense to me.
And finally, if you’re still unconvinced, the famous Tollund man was found preserved in a bog in Denmark with Common Knotgrass seeds in his stomach. What better accreditation than that of a 2,400 year old man?
Final Thoughts
Whilst Polyganum aviculare does not sit in the same culinary pantheon as Glinus oppitisifolus there is definitely a solid Turkish-Georgian base to build on.
Unfortunately my property does not have have Common Knotgrass (also known as Prostrate Knotgrass) but I’m sure I can acquire some from a consenting neighbour’s driveway. I’ll be sure to share my culinary explorations if I can gather enough.
The lesson in this article is not to trust common names too much (in any language!). The deeper lesson is to question whatever article you’re reading. If it sounds too good to be true, maybe it is! Read multiple sources and see if they agree. Please be mindful of this if you read the sources I have given - the Wikipedia article is guilty of this, for instance.
Until next time.
Further Reading
Gümüşhane province, cooking P. aviculare by boiling and roasting
P. aviculare used as animal feed and “gastroprotective effect through its reducing power and phenolic content”
P. aviculare stewed, boiled in “Pkhali”, in sarmas, pickled, soup in Turkish-Georgian border region
The usual wikipedia article which confuses P. aviculare and G. oppitisifolus - be careful!
An example of confusing P. aviculare with G. oppitisfolus - still educational though, just be careful
One of the articles that clued me into the mistaken identity
The only article I found that recognises the confusion between the two plants
Is the bottom photo G. oppitisifolus?