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Leaf vegetables, also called leafy greens, salad greens, pot herbs, vegetable greens, or simply greens, are plant leaves eaten as a vegetable, sometimes accompanied by tender petioles and shoots. Although they come from a very wide variety of plants, most share a great deal with other leaf vegetables in nutrition and cooking methods.
Nearly one thousand species of plants with edible leaves are known. Leaf vegetables most often come from short-lived herbaceous plants, such as lettuce and spinach. Woody plants of various species also provide edible leaves.
The leaves of many fodder crops are also edible for humans, but are usually only eaten under famine conditions. Examples include alfalfa, clover, most grasses, including wheat and barley. These plants are often much more prolific than traditional leaf vegetables, but exploitation of their rich nutrition is difficult, due to their high fiber content. This can be overcome by further processing such as drying and grinding into powder or pulping and pressing for juice.
Leaf vegetables contain many typical plant nutrients, but since they are photosynthetic tissues, their vitamin K levels are particularly notable. Phylloquinone, the most common form of the vitamin, is directly involved in photosynthesis.
The vitamin K content of leaf vegetables is particularly high, since these are photosynthetic tissues and phylloquinone is involved in photosynthesis. Accordingly, users of vitamin K antagonist medications, such as warfarin, must take special care to limit consumption of leaf vegetables.
If leaves are cooked for food, they may be referred to as boiled greens. Leaf vegetables may be stir-fried, stewed, steamed, or consumed raw. Leaf vegetables stewed with pork is a traditional dish in soul food and Southern U.S. cuisine. They are also commonly eaten in a variety of South Asian dishes such as saag. Leafy greens can be used to wrap other ingredients into an edible package in a manner similar to a tortilla. Many green leafy vegetables, such as lettuce or spinach, can also be eaten raw, for example in sandwiches or salads. A green smoothie enables large quantities of raw leafy greens to be consumed by blending the leaves with fruit and water.
At least 80 different kinds of greens are used, depending on the area and season, including black mustard, dandelion, wild sorrel, chicory, fennel, chard, kale, mallow, black nightshade, lamb's quarters, wild leeks, hoary mustard, charlock, smooth sow thistle and even the fresh leaves of the caper plant.
Preboggion, a mixture of different wild boiled greens, is used in Ligurian cuisine to stuff ravioli and pansoti. One of the main ingredients of preboggion are borage (Borago officinalis) leaves. Preboggion is also sometimes added to minestrone soup and frittata.
Botwinka (or boćwinka) is a soup that features beet stems and leaves as one of its main ingredients. The word "botwinka" is the diminutive form of "botwina" which refers to leafy vegetables like chard and beet leaves.
In the cuisine of the Southern United States and traditional African-American cuisine, turnip, collard, kale, garden cress, dandelion, mustard, and pokeweed greens are commonly cooked, and often served with pieces of ham or bacon. The boiling water, called potlikker, is used as broth. Water in which pokeweed has been prepared contains toxins removed by the boiling, and should be discarded.
Postharvest diseases cause up to 50% losses of leaf vegetables. These are fungal, bacterial, and much less commonly viral. The most important remedy is temperature controlled storage, although also important is prevention of mechanical damage to produce as this provides entryways for pathogens. Uncontaminated water for washing of the vegetables is of lesser but still significant importance.
Common bacterial pathogens include: Xanthomonas campestris pv. vitians, Pseudomonas viridiflava, P. cichorii, and P. marginalis, P. syringae pv. aptata, X. campestris pv. campestris, X. campestris pv. raphani, P. syringae pv. maculicola, P. syringae pv. alisalensis, Pectobacterium spp. including Pectobacterium carotovorum subsp. odoriferum and Pectobacterium aroidearum, Dickeya spp., Pseudomonas marginalis, and Pseudomonas viridiflava.
Common fungal pathogens include: Alternaria brassicicola, A. alternata, A. arborescens, A. tenuissima, A. japonica, Colletotrichum higginsianum, Colletotrichum dematium f. spinaciae, Microdochium panattonianum, Stemphylium botryosum, Cladosporium variabile, Cercospora beticola, C. lactucae-sativae, C. brassicicola, C. acetosella, Botrytis cinerea, Golovinomyces cichoracearum, Podosphaera fusca, Erysiphe cruciferarum, E. polygoni, E. heraclei, Sclerotinia sclerotiorum, and S. minor.
Gotukola (Centella asiatica)