Latin Name: Sonchus asper
Common Names: Prickly sow thistle, spiny sow thistle, sharp sow thistle, rough milk thistle
Season: Early spring
Edible: Yes
Flavor: Good
Medicinal and nutritional value: Vitamin rich, antioxidant strong, liver and kidney purifying
Identification difficulty: Beginner
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| The leaves of this plant are at a good stage for harvest |
Despite the texture, prickly sow thistle is one of the edible wild plants I look forward to the most every spring.
If you can work around the prickles, which is easy enough to do when planning dishes that need to be pureed (like sauces and soups), you are rewarded with a wonderfully rich leafy green. The flavor is generally very mild with only a slight bitterness, comparable to swiss chard or belgian endive, to add complexity. Most everyone who eats leafy greens will enjoy properly prepared prickly sow thistle.
Perhaps even better, prickly sow thistle is extremely common
Nutritional & medicinal benefits
The sow thistle family (Sonchus) is one of the ones where a significant amount of research has been done into nutrition and potential medicinal benefits. Sow thistles have long been accepted as health foods, associated with liver and kidney purification.
Recent studies have shown that the sow thistles, particularly the prickly sow thistle, are antioxidant powerhouses. Antioxidants have been shown to reduce the effects of aging, both on the body and mind. They also lower your cancer risk.
While antioxidant extractions are available in pills, syrups, etc., studies show that the best way to gain the positive effects of antioxidants might simply be to incorporate a large number of antioxidant-rich foods into your diet.
All three sow thistles were found to be rich dietary fiber and in vitamin E, though smooth sow thistle (Sonchus arvensis) had the highest concentrations. Like most leafy greens, sow thistles have a lot of valuable minerals, including potassium, calcium, magnesium, iron, zinc, sodium and selenium. Smooth sow thistle is the best of the 3 for potassium, common sow thistle has the highest concentration of iron and prickly sow thistle offers the most calcium.
As an added bonus, sow thistles DO NOT have large amounts of oxalic acid, even though they exhibit red coloration. They contain less than 10% of the oxalic acid found in spinach or swiss chard, for example, and less than 5% of the oxalic acid in purslane.
To learn more about the antioxidant properties of prickly sow thistle, check out this article from the National Library of Medicine.
To learn more about the nutritional qualities of the sow thistle genus, please read this article from the National Library of Medicine.
History as a food crop
There are three, common, wide-spread sow thistles: Common sow thistle (Sonchus oleraceus), prickly sow thistle (Sonchus asper) and smooth sow thistle (Sonchus arvensis). They are native to Europe, particularly the Mediterranean regions. They are now found throughout temperate North and South America, Australia and New Zealand, the Middle East, and much of Asia and Africa.
Despite the name, common sow thistle is not the most common, at least not in my North American experience; perhaps in the Mediterranean it is. In the Northeast US, I found common sow thistle and prickly sow thistle found in about even amounts, but here in Texas, prickly sow thistle is everywhere, and common sow thistle is . . .well, quite uncommon. Smooth sow thistle, arguably the most difficult to identify when young, seems to be the least common.
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A good-sized haul of prickly sow thistle leaves,
ready to cook and eat |
Our earliest record of sow thistles as a food comes from the ancient Greeks, who considered it to be strengthening, and used the non-prickly varieties in salads, especially during winter time when greens were scarce.
Europeans in the middle ages valued the sow thistles for animal feed. The name "sow thistle" comes from farmers feeding the plant to sows with piglets; it was believed that this plant increased lactation.
As traditional agriculture became the standard in Europe and European colonies, like the U.S., sow thistles came to be regarded as common weeds, and a great deal is spent to eradicate them.
But that is not always the case in areas where sow thistles have spread.
As European agricultural practices spread with colonization, many native species of plants, which were essential food sources for the native peoples, were wiped out. Eurasian plant species had evolved a centuries-long history of competition, due to exposure to other plant species spread via trade routes. As a general rule, these plants could out-compete native species, which is why dandelions, plantains, sow thistles and others are considered common weeds today.
But many native peoples have embraced the "weeds" traditional agriculture rejects, and have used them to supplement or replace native plants that have been decimated. Sow thistles in particular are consumed by the Māori of New Zealand and the by the native peoples of the rural Brazilian rainforest regions.
In addition to the three most wide-spread sow thistles there are many regional species, especially in Africa and some hype-local species in places like the Canary Islands, some of which are used for food.
Prickly sow thistle identification
Note: the entire above-ground portion of the plant is edible.
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| Prickly sow thistle at the perfect stage for harvesting leaves |
Growth season & features
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An early basal rosette, the raised leaves are good
for harvesting |
Sow thistles are annual plants that begin their growing season as a basal rosette in early spring. A basal rosette is when leaves create a circle on the ground around a central attachment to the root system below. In Texas this is usually early March but can be mid-February in mild winters. In the Northeast I generally found them in mid-April.
The plant will very quickly grow raised leaves from the rosette that stretch upward. This is the best time to gather the leaves, when they aren't against the ground (the leaves on the ground tend to be tough and fibrous) but before the stalk is branching.
I also harvest the leaves when the central stalk has formed but is young, 4-6 inches long, even if it already has flower buds. But once the plant starts branching the leaves usually loose flavor and become stringy.
This plant to the left is already branching at the top. The leaves will generally be less flavorful at this stage, but this plant seemed to be unusually healthy and well-watered, and some of the leaves were still tender and not stringy.
If left unchecked, prickly sow thistle can grow to around 3' 6" tall (about a meter), but will most often be under half that height in areas that are mowed or otherwise landscaped.
Not every plant will produce branches though all will produce a cluster of flower stalks at the top of the central stem, if allowed to grow long enough.
Leaf shape & features
The leaves are the most important Identification feature for prickly sow thistle.
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Leaf progression. When very young (left), the leaves are spoon-shaped and not lobed.
As the plant matures the leaves will become increasingly large, dark, lobed and the prickles will become more defined. All of these leaves are from a young plant. |
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| The lower leaves in the basal rosette are deeply lobed |
Each leaf in the basal rosette stage is long and narrow, about 3 times as long as it is wide. The leaves are deeply lobed, which means they appear to have cut outs on the sides; they somewhat resemble dandelion leaves.
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Leaves from a 8" tall plant, dark green and
purple, from cold expos
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The leaves are generally bright green but will be darker in cooler weather. If they are exposed to near freezing conditions during their growth they will have red or purple zones, or even become purple entirely. This isn't a concern for the forager, as the purple leaves are just as edible. The central midvein of the leaf is thick, well-defined and white but will turn pink, red or purple in cold weather.
The leaves on the upper stalk or branching stems are a different shape from the leaves at the base. These grow as teardrops, are not deeply lobed, and the rounded base clasps around the stem. These leaves are smaller, less flavorful and often papery.
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| Leaves as they appear on the upper stalk or branching stems. |
The entire margin (edge) of each leaf is rimmed with prickles where the leaf pinches itself together into soft spikes. Unlike thorns, prickles are not especially hard, and will bend easily if pressed. When touching them I would describe the sensation as prickly (lol) rather than painful.
This is one way to distinguish a sow thistle from a true thistle as true thistles have hard spines or spikes on the leaf edge that will pierce the skin if pressed. But more on that in the look-a-like section below.
While in the elevated basal rosette shape, the prickles on the leaves create rather beautiful fractal patterns as viewed from above.
Stem/stalk features
The central stalk of the plant is hollow, ribbed or lined on the outside, translucent green, patched or streaked with red/pink and exudes copious amounts of thick, opaque white sap when damaged. This sap will oxidize when exposed to air and turn the plant matter brown.
One important ID feature of prickly sow thistle is that the stalk will snap easily and cleanly, rather than bending or stretching.
Flower & buds
What appears to us as a single yellow flower is actually many dozens of ray flowers clustered together into a single flower head. Sow thistle flowers closely resemble dandelion flowers, and, like dandelions, this clustered growth will ensure each flower releases dozens of seeds, which will also turn into fluffy white tufts to be born away by the wind.
Unlike dandelion flower heads, which contain so many individual ray flowers that they bend back over themselves and their seed stage resembles a sphere, sow thistle heads always resemble a disc or an 80s flattop hairstyle. You can easily see the green bracts from which the flowers come below, and the seed head will only ever be a half-sphere.
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In this image, the yellow circled are flower buds,
while the rest are spent flower heads. |
The plant will almost always produce multiple flower heads from the central stalk and if conditions are ideal will also have several branches each ending in multiple flower heads.
The flower buds are shaped like fat hourglasses and will be tightly tucked in on the top, with no yellow or white showing until right before blooming. The spent flowers most often look like teardrops or diamonds and will usually have a tuft of darkening yellow at one end.
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From left to right: youngest bud, mature bud, bud about to open, spent flower,
spent flower beginning to close, fully closed spent flower |
After growing as a bud, blooming, and tucking the flowers back into the calyx in a teardrop, the spent flower will once again re-open to release the seeds which are at the base of white cottony tufts, denser and more opaque than those of a dandelion.
A healthy, well-developed plant might have 4-7 flowers, 2-4 spent flowers and a dozen or more buds simultaneously, and will continue to bud and flower throughout the growing season unless the plant is cut or the weather becomes too hot or dry. In the Northeast, un-mowed sow thistles would often survive until the frosts in October, but here in Texas they generally die off in late spring, June at the latest.
