Purslane

Known as Ma Chi Xian (pinyin: translates literally as "horse tooth amaranth") in Traditional Chinese Medicine, it is used to treat infections or bleeding of the genito-urinary tract as well as dysentery. The fresh herb may also be applied topically to relieve sores and insect or snake bites on the skin. Eating purslane can dramatically reduce oral lichen planus.

Companion plant
As a companion plant, Purslane provides ground cover to create a humid microclimate for nearby plants, stabilizing ground moisture. Its deep roots bring up moisture and nutrients that those plants can use, and some, including corn, will "follow" purslane roots down through harder soil than they can penetrate on their own. It is known as a beneficial weed in places that don't already grow it as a crop in its own right.

History
Widely used in Greece, archaeobotanical finds are common at many prehistoric sites. In historic contexts, seeds have been retrieved from a protogeometric layer in Kastanas, as well as from the Samian Heraion dating to 7th century BC. Theophrastus in the 4th century BC names purslane, andrákhne, as one of the several summer pot herbs that must be sown in April (H.P 7.12). As portulaca;; it figures in the long list of comestibles enjoyed by the Milanese given by Bonvesin de la Riva in his "Marvels of Milan" (1288).
In antiquity its healing properties were thought so reliable that Pliny advised wearing the plant as an amulet to expel all evil (Natural History 20.120).
Purslane is one of the seven herbs used in the symbolic dish served at the nanakusa-no-sekku, the traditional Japanese new year ritual.
A common plant in parts of India, purslane is known as Sanhti, Punarva, or Kulfa.

Although purslane is considered a weed in the United States, it can be eaten as a leaf vegetable. It has a slightly sour and salty taste and is eaten throughout much of Europe, the middle east, Asia and Mexico. The stems, leaves and flower buds are all edible. Purslane can be used fresh as a salad, stir-fried, or cooked like spinach, and because of its mucilaginous quality it is also suitable for soups and stews. Australian Aborigines use the seeds to make seedcakes. Greeks, who call it andrakla (a?t????a) or glystrida (???st??da), fry the leaves and the stems with feta cheese, tomato, onion, garlic, oregano and olive oil.
Purslane contains more omega-3 fatty acids (alpha-linolenic acid in particular) than any other leafy vegetable plant. Simopoulos states that Purslane has 0.01 mg/g of eicosapentaenoic acid (EPA). This is an extraordinary amount of EPA for land based vegetable sources. EPA is an Omega-3 fatty acid normally found mostly in fish, some algae and flax seeds. It also contains vitamins (mainly vitamin A, vitamin C, and some vitamin B and carotenoids), as well as dietary minerals, such as magnesium, calcium, potassium and iron. Also present are two types of betalain alkaloid pigments, the reddish betacyanins (visible in the coloration of the stems) and the yellow betaxanthins (noticeable in the flowers and in the slight yellowish cast of the leaves). Both of these pigment types are potent antioxidants and have been found to have antimutagenic properties in laboratory studies.
100 grams of fresh purslane leaves (about 1 cup) contain 300 to 400 mg of alpha-linolenic acid. One cup of cooked leaves contains 90 mg of calcium, 561 mg of potassium, and more than 2,000 IUs of vitamin A. One half cup of purslane leaves contains as much as 910 mg of oxalate, a compound implicated in the formation of kidney stones. However, note that many common vegetables, such as spinach, also can contain high concentrations of oxalates.
When stressed by low availability of water, purslane, which has evolved in hot and dry environments, switches to photosynthesis using Crassulacean acid metabolism (the CAM pathway): at night its leaves trap carbon dioxide, which is converted into malic acid (the souring principle of apples), and in the day, the malic acid is converted into glucose. When harvested in the early morning, the leaves have 10 times the malic acid content as when harvested in the late afternoon, and thus have a significantly more tangy taste.

Portulaca oleracea (Common Purslane, also known as Verdolaga, Pigweed, Little Hogweed or Pusley), is an annual succulent in the family Portulacaceae, which can reach 40 cm in height. About 40 varieties are currently cultivated. It has an extensive old-world distribution extending from North Africa through the Middle East and the Indian Subcontinent to Malesia and Australasia. The species status in the New World is uncertain: it is generally considered an exotic weed; however, there is evidence that the species was in Crawford Lake deposits (Ontario) in 1430-89 AD, suggesting that it reached North America in the pre-Columbian era. It is naturalised elsewhere and in some regions is considered an invasive weed. It has smooth, reddish, mostly prostrate stems and alternate leaves clustered at stem joints and ends. The yellow flowers have five regular parts and are up to 6 mm wide. The flowers appear depending upon rainfall and may occur year round. The flowers open singly at the center of the leaf cluster for only a few hours on sunny mornings. Seeds are formed in a tiny pod, which opens when the seeds are ready. Purslane has a taproot with fibrous secondary roots and is able to tolerate poor, compacted soils and drought.