Lactuca

Lactuca, commonly known as lettuce, is a genus of flowering plants in the family Asteraceae. The genus includes at least 50 species, distributed worldwide, but mainly in temperate Eurasia.

Its best-known representative is the garden lettuce (Lactuca sativa), with its many varieties. "Wild lettuce" commonly refers to the wild-growing relatives of common garden lettuce. Many species are common weeds. Lactuca species are diverse and take a wide variety of forms. They are annuals, biennials, perennials, or shrubs. Their flower heads have yellow, blue, or white ray florets. Some species are bitter-tasting.

Most wild lettuces are xerophytes, adapted to dry habitat types. Some occur in more moist areas, such as the mountains of central Africa.

Diversity
There are different concepts of the species within Lactuca. It is not clear how many distinct species are known, and estimates vary from 50 to 75 so far.

Species include:


 * Lactuca acanthifolia (Crete, Turkey)
 * Lactuca aculeata (Asia Minor)
 * Lactuca acuminata
 * Lactuca adenophora
 * Lactuca alpestris (Crete)
 * Lactuca alpina (syn. Cicerbita alpina) (Europe) - alpine sow-thistle, alpine blue-sow-thistle, tall blue lettuce
 * Lactuca altaica (Eurasia)
 * Lactuca attenuata (Africa)
 * Lactuca aurea (Europe)
 * Lactuca azerbaijanica (Iran)
 * Lactuca biennis (North America) – tall blue lettuce, blue wood lettuce
 * Lactuca calophylla (Africa)
 * Lactuca canadensis (North America) – Canada wild lettuce, tall lettuce
 * Lactuca corymbosa (Congo)
 * Lactuca crambifolia (Turkestan)
 * Lactuca cyprica (Cyprus) - Cyprus lettuce
 * Lactuca deltoidea
 * Lactuca dissecta (Asia)
 * Lactuca dolichophylla (Asia)
 * Lactuca dregeana (South Africa) – melkdissel, slaaidissel
 * Lactuca dumicola
 * Lactuca erostrata (Pakistan)
 * Lactuca fenzlii
 * Lactuca floridana (North America) – Florida lettuce, woodland lettuce
 * Lactuca georgica (Asia)
 * Lactuca glaucifolia (Asia)
 * Lactuca graciliflora (Asia)
 * Lactuca graminifolia (Americas) – grassleaf lettuce
 * Lactuca haimanniana
 * Lactuca henryi
 * Lactuca hirsuta (North America) – downy lettuce, hairy lettuce
 * Lactuca hispida
 * Lactuca homblei (Zaire, Zambia)
 * Lactuca imbricata (Africa)
 * Lactuca indica (Asia) - Indian lettuce
 * Lactuca inermis (Africa, Arabian Peninsula)
 * Lactuca intricata (Albania, Greece, Turkey)
 * Lactuca jamaicensis (Jamaica)
 * Lactuca kanitziana
 * Lactuca kochiana
 * Lactuca lasiorhiza (Africa)
 * Lactuca ludoviciana (North America) – biannual lettuce
 * Lactuca macrophylla
 * Lactuca mira
 * Lactuca muralis
 * Lactuca mwinilungensis (Zaire, Zambia)
 * Lactuca nana (Africa)
 * Lactuca orientalis (Asia, Egypt)
 * Lactuca palmensis (Canary Islands)
 * Lactuca paradoxa
 * Lactuca parishii
 * Lactuca perennis (Europe) – blue lettuce, mountain lettuce
 * Lactuca persica
 * Lactuca petrensis
 * Lactuca quercina (Eurasia)
 * Lactuca racemosa
 * Lactuca raddeana (Asia)
 * Lactuca rechingeriana
 * Lactuca rosularis (Iran, Turkmenistan)
 * Lactuca saligna (Eurasia) – willow lettuce, least lettuce, narrow-leaf lettuce
 * Lactuca sativa – lettuce, garden lettuce
 * Lactuca scarioloides (western Asia)
 * Lactuca schulzeana (Angola, Cameroon, Zaire)
 * Lactuca schweinfurthii (Africa)
 * Lactuca serriola (Africa, Asia, Europe) – prickly lettuce, compassplant, scarole, milk thistle
 * Lactuca setosa (Africa)
 * Lactuca sibirica (Eurasia)
 * Lactuca singularis (Spain)
 * Lactuca songeensis
 * Lactuca spinidens (Tajikistan, Turkmenistan)
 * Lactuca stebbinsii (Angola)
 * Lactuca takhtadzhianii (Armenia)
 * Lactuca tatarica (Northern Hemisphere) – blue lettuce
 * Lactuca tenerrima (southern Europe, Morocco)
 * Lactuca tetrantha (Cyprus)
 * Lactuca tinctociliata
 * Lactuca triangulata (Asia)
 * Lactuca triquetra
 * Lactuca tuberosa (Eurasia)
 * Lactuca ugandensis
 * Lactuca undulata (Asia)
 * Lactuca viminea (Africa, Asia, Europe) – pliant lettuce
 * Lactuca virosa (Europe, northern Africa) – bitter lettuce, great lettuce
 * Lactuca watsoniana (Azores)
 * Lactuca winkleri (Tajikistan)

Ecology
Lactuca species are used as food plants by the larvae of many Lepidoptera species.

Etymology
'Lactuca' is derived from Latin and means 'having milky sap'. 'Lactuca' and 'lactic' (of or relating to milk) have the same root word, 'lactis'.