Common purslane (Portulaca oleracea). Photo by D. Sillman
(Click on link to listen to an audio version of this blog: My weeds, The Good!
Last week I talked about a few really bad weeds growing in our developing, front yard prairie. There are also some weeds in our little grassland that have so many good qualities that they are, at least, tolerated if not warmly welcomed into our shortgrass community.
The first of these “good weeds” is common purslane (Portulaca oleracea). Purslane has a growth pattern similar to the spurges: it has a central tap root and ground-hugging stems that grow radially out from it. The purslane stems, though, don’t grow quite as densely as the spurges: they leave quite a bit of room in between and around them for the growing grass plants. Purslane is an exotic species from Europe, North Africa and the Middle East (all around the Mediterranean Sea) where it was widely grown and harvested as a food plant! Purslane was also found in human artifacts in North America well before Columbus broke down the plant distribution barriers between the Old World and the New. How it traveled so far from its home range without human assistance is not known.
Common purslane (Portulaca oleracea). Public domain.
Purslane grows very well in hot, dry weather because it, like kochia, is a C4 plant. Purslane is also able, quite uniquely among all other types of plants, to modify its carbon dioxide fixation metabolism in extremely hot, dry weather to use other acids (like crassulacean acid) to fix and store carbon dioxide at night. This ability to switch from C4 metabolism to crassulacean acid metabolism (CAM) gives purslane a significant growth advantage in hot, dry conditions.
The taste of purslane reflects the acids in C4 and CAM metabolisms. Malic acid and oxaloacetic acid are generated in the transfer and storage of the night-absorbed carbon dioxide, and the more acids in the purslane leaflets, the sharper and tarter the flavor! (one purslane grower recommended harvesting the purslane leaflets early in the morning when their night-acquired acid levels would be at their maximum). Oxaloacetic acid consumption, though, can also have some negative health impacts. This acid tends to bind with dietary calcium making it difficult to absorb the calcium into the blood stream (possible leading to low blood calcium and also possibly interfering with high calcium utilizing activities like bone growth and fracture repair). Oxaloacetic acid is also often a major component of urinary calculi (“kidney stones”). In certain people, ingestion of oxaloacetic acid-rich foods or beverages can predispose them to the development of these painful urinary stones.
Purslane is also rich in vitamins (especially E and C) and also contains high levels of dietary minerals (including iron, magnesium, potassium and manganese).It also has significant levels of alpha-linolenic acid (and essential, omega fatty acid!). The nutritional qualities of purslane have led some nutritionists to classify it as a “super-food!” I have eaten salads with purslane and pesto made with purslane instead of basil. It is a very tasty weed!
In addition to being a food source that is probably healthier than anything else grown in your garden, purslane also helps other plants grow and survive. Its ground hugging stems act as a moisture barrier that slows down evaporative water loss from soil, and its tough, hard-soil penetrating roots break up dense soils and allows other plants to more easily root down into the soil profile.
Lambs quarters (Chenopodium album). Photo by D. Sillman
Another “good weed” is, like purslane, actually a highly nutritious food plant masquerading as a weed. Lambs quarters (Chenopodium album) is another Eurasian plant species that has spread widely across the globe. It is a member of a botanical family that contains many of the C4 plant species, although lambs quarters is classified as a C3 (i.e. “normal” carbon dioxide fixer) plant. Also called wild spinach, goosefoot or pigweed, lambs quarters is rich in protein, vitamins (including A, B2, B6 and C) and minerals (including calcium, magnesium, manganese and iron). Its leaves are edible as are the tens of thousands of tiny, black seeds made by each plant.
Lambs quarters residues have been found in Iron Age cooking sites and even in the stomachs of ancient humans whose bodies were preserved in the peat bogs of Denmark. Lambs quarters is cultivated in Northern India where its seeds and leaves are widely used in stews, soups, baked dishes, brewed beverages and more!.
Lambs quarters (Chenopodium album). Photo by Sixth Happiness, Wikimedia Commons
The exotic lambs quarters “weed” is closely related to several North American native plant species that are in the genus Amaranthus. Adding to the ever present, common name confusion, many of these Amaranthus species are often, like the Chenopodium album, referred to as “pigweed.” These native pigweeds (which are C4 plants) were among the first plants actively cultivated by ancient, North American people. The Aztecs, for example, grew and consumed these pigweeds, and they are still grown on subsistence farms in Peru.
Lambs quarters can be a very harmful weed in crop fields. Its rapid growth rate at the end of summer and the abundance of seeds can set up a very damaging and economically significant weed infestation in corn, soybean or sugar beet fields. Lambs quarters also produces large amounts of very fine pollen and is one of the allergens in the late summer/early fall “hay fever” season.
Canadian thistle. Photo by Theraisa K, Wikimedia Commons
A third “good weed” out on our developing prairie is Canada thistle (Cirsium arvense). Canada thistle is usually thought of as a notorious weed in croplands and grazing lands that has severe, deleterious impacts on crop yields and forage capacities. It has, though, many other qualities that mitigate some of its destructive features.
Canada thistle, for example, is one of the best nectar producing plants in all of nature! Its flowers can feed a wide variety of pollinators from honeybees to native bees to butterflies. Entire ecosystems benefit from the increased health and vigor of the pollinating community in ecosystems that include Canada thistle. Canada thistle also produces large quantities of seed (over 1500 seeds per plant!), and many birds (especially goldfinches and other finch species) feed on these seeds though the late summer and fall.
Out on the edges of our front-yard prairie, we are letting purslane, lambs quarters and Canada thistle grow and thrive. We just keep watering it to get the young grass plants rooted and set. We hope next year that it can settle into a more easily managed equilibrium with our increasingly dry climate.