Common Purslane (Portulaca oleracea), also known as Verdolaga, Pigweed, Little Hogweed or Pusley.
Photo by José Luis Gálvez
Summarized from the Wikipedia article linked above (see article for references) unless otherwise referenced:
Apparently the leaves, stems and flower buds (the latter of which I've never seen) are edible and in fact eaten regularly in Europe, Asia and Mexico. There are 40 varieties cultivated. The plant has adapted to grow extensively from North Africa, through south Asia to Australia during past centuries. There is some evidence of this species in North America in the pre-Columbian era. The little yellow flowers appear only if rainfall conditions are optimum and only for a few hours on sunny mornings. Likely why I've never seen them. Like most weeds, the plant grows well in poor quality, drought-prone soils.
Purslane is a succulent herb reported to have a peppery, slightly sour and/or salty taste and can be eaten similar to spinach (fresh in salads, stir-fried or cooked). It is considered to have similar taste to spinach and similar texture to okra [>]. It is also good in soups due to its mucilaginous quality. At one time Australian Aborigines used the seeds to make seedcakes. It is best harvested in morning or evening [>].
Purslane contains more Omega-3 fatty acids (alpha-linolenic acid in particular) than any other leafy vegetable plant. It contains an extraordinary amount of EPA (Eicosapentaenoic acid) for land based vegetable sources. EPA is an Omega-3 fatty acid normally found mostly in fish, some algae and flax seeds. But note that fish oil typically contains 750 mg/tsp of EPA (source: bottle in our fridge) compared with 0.01 mg/g in Purslane. Doing the math, you need to eat 75 kg of Purslane to get the equivalent EPA from 1 tsp of fish oil. Purslane also contains vitamins (mainly vitamins A, C, some B and carotenoids), as well as dietary minerals, such as magnesium, calcium, potassium and iron. It also contains potent antioxidants.
Hmm, maybe I can cut back on my vegetable plantings and encourage growth of Purslane instead!