Purslane (Portulaca oleracea, purslane family Portulaceae) is a very widespread, common plant.
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| purslane, Portulaca oleracea |
So much has been written about it that mostly I'm going to remind you to notice it.
It is easy to identify as a small succulent of roadsides and disturbed areas, pretty much all over the world. The leaves are rounded and can be reddish on the edges. The stems are thick "like pipes" and likely to be reddish. The flowers are small, yellow, and open only in full sunlight. The seedpods are tiny but filled with tinier round, flat black seeds. In my climate, purslane is an annual that requires warm temperatures to germinate, so I rarely see them until late June. After a good rain in July, seedlings are everywhere.
Purslane has a worldwide distribution. It grows on every continent. A study in the 1950s called it the eighth most frequent plant on earth, quite a feat. It is probably more abundant today since we have created more of the open areas it favors and our better roads have opened up rural areas. It is listed as a noxious weed in many places--usually found on "ten worst weeds" lists--not because it is spiny or toxic, but because it is grows so well, crowding out other plants.
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| purslane, Portulaca oleracea Flowers are open; seed pods are brown circles next to the flowers. |
Also, all across the world, purslane is a food plant. It is important in cuisines from the Phillipines to Turkey to France to Mexico. They eat it raw in salads, or cook it with meat or fish, or puree it into sauces. Consequently, purslane has been cultivated for more than 4,000 years. It is commercially grown in southern Europe, parts of Asia, and Mexico. It is also cultivated in the United States, although it is a very minor crop.
Purslane is highly nutritious. It contains significant amounts of omega-3 fatty acids, which are often lacking in vegetarian diets. In addition, it is a good source of vitamins A and C, protein, fiber, and minerals, including iron, calcium, and potassium. The plants also contain antioxidants.
Purslane contains oxalic acid, as does spinach. The levels of oxalic acid found in purslane are safe in a mixed diet, both for humans and livestock, but people advised to avoid oxalic acid should avoid eating purslane. Purslane is sometimes used as fodder and of course pastured livestock feed on it. When fed to poultry, it reduces egg cholesterol.
Purslane was variously used medicinally. The juicy leaves make a soothing ointment for burns and the antioxidants in the plant help prevent infection. It has also been used as a diuretic, for dry coughs, and a general tonic. Generally today, it appears in lists of high quality foods, not in lists of herbal remedies.
Purslane's incredible abundance and ability to grow rapidly are why it is considered such a weed, despite being excellent food. Light is required for germination but otherwise the seeds show no dormancy, germinating when winter temperatures warm and when water is available. The seedlings branch close to the ground and spreads to cover the soil very quickly. Flowering happens when it has enough energy, not based on time of year. The flowers easily self-pollinate. They also outcross a little bit and it is unclear whether that is due to insect or wind pollination. A single plant produced 6,723 seeds within 6 weeks of germinating. Another plant was estimated to produce 101,625 to 242,540 seeds during a single growing season (the number is not exact because counting that many tiny seeds is beyond tedious). Some of the seeds produced will still germinate after 40 years. Compare this to Baker's "ideal" weed (previous post, link): purslane has many of those characteristics.
Purslanes in temperate regions are annuals; where the winter is mild they can be perennial and grow very large.
The ideal weed analysis doesn't address all of purslane's adaptations. The first is being succulent. Purslane stores water in its fleshy leaves, making it a good drought-tolerant crop and an tenacious weed. Secondly, purslane can grow in salty soils. Most crop plants are intolerant of salts in the soil (not just sodium salts but others like potassium compounds) but purslane is much less sensitive, in fact, considered moderately salt tolerant. Again, this makes it an attractive crop and a better weed.
Third, purslane has both C4 and CAM photosynthesis. These are adaptations to drought; C4 and CAM are two different ways plants reduce the water vapor lost when taking in carbon dioxide (to do photosynthesis and grow). C4 plants have compartmentalized their leaves and because of the compartments, lose much less water when taking in carbon dioxide and releasing oxygen. CAM plants store the oxygen produced by photosynthesis during day, and only release it at night, when, even in deserts, humidity is higher and less water is lost. What is truly remarkable about purslane is that it easily switches between these two systems, using C4 most of the time, but, when stressed by lack of water, switching to CAM. The result is a plant much less limited by drought than most other plants.
This botanical curiousity--switching to CAM from C4--is detectable in the taste of purslane. In CAM photosynthesis, plants stash carbon in malic acid all night and then convert it to sugars in daylight. The relatively high concentrations of malic acid make the taste of purslane sharper (more acidic) first thing in the morning. As the malic acid is turned to glucose, the taste mellows. This effect is not present when purslane is doing C4 photosynthesis, which is usually. Check out the change in taste when your purslane is under water stress.
The scientific name Portulaca is based on a traditional Roman name for the plant, of unknown meaning. The species epithet oleracea means "of the vegetable garden," a plant used in cooking. The common name purslane is a version of portulaca, so its meaning is equally unknown. Purslane is by far the most widely used common name, but you might find it referred to as garden or winter purslane (there are other species of purslane), Cuban spinach, miner's-lettuce (thought there is a different plant that usually gets that name), pigweed (again, there are other pigweed), pussley and pursley (notice the similarity to parsley), little hogweed, and, redroot. In French Canada it is pourpier, in Mexican Spanish verdolaga.
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| purslane, Portulaca oleracea |
This is an incredibly useful and successful plant that we mostly just walk over. Next time you see purslane, look for flowers, crush a leaf to appreciate how it would sooth to skin irritations, and notice if it is growing in a difficult environment. (I'd also say taste it, but only do that if you think the leaves are clean of environmental pollutants.) Lots to observe. Purslane is a remarkable plant.
Comments and corrections welcome.
Note: I didn't deal with its origins because purslane is known from archaeological sites in Europe, Asia and the Americas 2,000 years ago. That "impossible" distribution needs a blog of its own. Coming soon.
References
Kumar, A., S. Sreedharan, P. Singh, E. G. Achigan-Dako, and N. Ramchiary. 2021.Improvement of a Traditional Orphan Food Crop, Portulaca oleracea L. (Purslane) Using Genomics for Sustainable Food Security and Climate-Resilient Agriculture. Frontiers in Sustainable Food Systems. https://doi.org/10.3389/fsufs.2021.711820 link (Accessed 8/9/22)
Matthews, J. F., D. W. Ketron and S. F. Zane. 1992, The biology and taxonomy of the Portulaca
oleracea L. (Portulacaceae) complex in North America. Rhodora. 95: 1266-183.
Needham, J. 1986. Science and Civilisation in China. VI: 1. Biology and Biological Technology. Cambridge University Press, Cambridge.
Oxford English Dictionary. "portulaca, n" Oxford English Dictionary online (U. Nebraska) (Accessed 8/6/22)
Sage, R. F. 2016. A portrait of C4 photosynthesis on the 50th anniversary of its discovery. Journal of Experimental Botany. 67 (14):4039-4056
Shaw, H. Hunter, 2020. All About Purslane. Angler, Gardener, Cook.com. link
Simopoulos, A., H. A. Norman and J. E. Gillaspy. 1995. Purslane in human nutrition and its potential for world agriculture. pp. 47-74 IN; A. Simopoulos editor. Plants in Human Nutrition. World Rev Nutri Diet, Basel, Kargar. Vol 77.
Ventura, Y., A. Eshel, D. Pasternak and M. Sagi. 2015. The development of halophyte-based agriculture. Annals of Botany. 115(3) 529-540.
WebMD editors. Health benefits of purslane. WebMD.com link (Accessed 8/12/22)
Wisconsin Horticulture Common purslane link (Accessed 8/9/22).
Kathy Keeler, A Wandering Botanist
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