Lettuce

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Lettuce
Poison lettuce (Lactuca virosa), illustration

Poison lettuce ( Lactuca virosa ), illustration

Systematics
Asterids
Euasterids II
Order : Astern-like (Asterales)
Family : Daisy family (Asteraceae)
Subfamily : Cichorioideae
Genre : Lettuce
Scientific name
Lactuca
L.

The lettuce ( Lactuca ) form a genus of plants in the sunflower family (Asteraceae). The milky sap, from which the botanical genus name Lactuca is derived, contains bitter substances that help the plant to ward off predators and pests; on the other hand, they determine the taste of the garden salad , the only type of lettuce with economic significance. Especially in Switzerland which is binding salad traded as lettuce. The approximately 100 species are distributed almost worldwide.

description

Section Lactuca , Subsection Lactuca : Illustration of the poison lettuce ( Lactuca virosa ), Jacob Sturm (1796)
Cup-shaped partial inflorescence of Lactuca virosa with many ray florets
Section Lactuca Subsection Lactuca : Illustration from Storm of the willow lettuce ( Lactuca saligna )
Phaenixopus section : achenes with lettuce pappus ( Lactuca viminea )

Vegetative characteristics

In Lactuca TYPES concerns one- to two-year or rarely perennial herbaceous plants , the plant height, from 15 to about 450 centimeters reach. They form tap roots . All lettuce species contain a whitish milky sap , especially in the stems and inflorescences. The mostly upright stem is mostly branched. The above-ground parts of the plant can be hairy.

The leaves stand together in basal rosettes or are arranged alternately on the stem. The stalked or sessile leaves are simple to pinnate, circular, ovoid, oblong, lanceolate, linear or thread-shaped. They are ciliate on the edge or on the underside along the midrib or have spines there and the leaf margin is smooth, serrated to more or less lobed. The leaf surfaces can be hairy. Stipules are missing.

Generative characteristics

The cup-shaped inflorescences stand together singly or mostly in groups in paniculate or umbrella -shaped inflorescences . Bracts are sometimes present. The small and narrow, rarely large, cup-shaped partial inflorescences are approximately cylindrical to bell-shaped, swell at flowering time, and have a diameter of 2 to 5 (rarely up to 8) millimeters. Their envelope consists of five to thirteen imbricated bracts more or few in two rows, of which the outermost sometimes are shorter. The bottom of the cup is flat to convex without chaff leaves . The single flowers are arranged in one or more rows in a cup-shaped partial inflorescence. All six to over fifty flowers are ray florets . The tongue has five corolla lobes, which clearly shows that the corolla tube is made up of five petals . The petals usually have a yellow, rarely white, bluish to purple color.

The reddish to light brown, white or purple to black achenes have one or more ribs on each side and open into an often thread-like elongated tip on which the pappus sits. The pappus , standing on a disc or on the beak on the upper end of the achenes, consists of one to two or more rows of simple white hairs of equal length, depending on the species.

The basic chromosome number is x = 9.

ingredients

Chemical compounds in Lactuca :
1 - α-lactucerol;
2 - β-lactucerol;
3 - lactucin;
4 - lactucopicrin

Lactuca species contain mainly water and more or less water in the leaves and in the milky sap

The lettuce seeds ( semen lactucae ) contain β-sitosterol and campesterol in the sterol fraction . In addition to lactucin and lactucopicrin, the root contains other bitter substances with a similar structure, e.g. B. Jacquinelin. The lettuce does not contain any alkaloids .

pharmacology

As far as the effects of the ingredients of lettuce are concerned, it has recently been known from a laboratory study that the main bitter substances lactucin and lactucopicrin act against the causative agent of malaria , Plasmodium falciparum , and this effect is ethnobiologically known in Afghanistan - only no lettuce is used there, but the common chicory ( Cichorium intybus ), which contains the same two substances.

It has been claimed that the lettuce milk juice (especially from poison lettuce ) should have a calming and sleep-promoting effect, which has not been scientifically proven (see poison lettuce # ingredients ). Towards the end of the 19th century, according to Riddle, lactucin was considered to be an opium substitute.

Systematics and distribution

There are around 100 types of Lactuca .

Some species of lettuce are difficult to distinguish visually, e.g. B. the members of the group Lactuca serriola / Lactuca saligna / Lactuca virosa . In addition, according to more recent studies, the members of the Lactuca sativa / Lactuca serriola / Lactuca dregeana / Lactuca altaica group show no genetic differences and are therefore probably con- specific .

A classification that is often used is that of gene pools , which are grouped around the garden salad. The primary gene pool for lettuce is the species Lactuca serriola / Lactuca dregeana / Lactuca altaica and Lactuca aculeata . These can easily be crossed with Lactuca sativa and are therefore an immediately available source for improving salad. The secondary gene pool consists of Lactuca saligna and Lactuca virosa , which makes crossing difficult. Finally, in the case of the tertiary gene pool, crossing is only possible with radical methods; it consists of the types of sections Phaenixopus , Mulgedium and Lactucopsis (see below).

There are about ten species of lettuce in North America , 33 in tropical East Africa , 40 in Asia and 17 in Europe . European species grow in temperate and warm regions. The northern border runs at about 50 to 55 ° north latitude, with the exception of Lactuca sibirica , which can occur up to 70 degrees. The westernmost species is Lactuca tatarica at 9 ° West. Most species live at altitudes from 200 to 600 meters with exceptions up to 2000 meters ( Lactuca alpestris , Lactuca tatarica , Lactuca altaica and Lactuca tenerrima ). Most of the European species are found in the Mediterranean , many of them only there.

During an excursion through parts of Central Europe, Lactuca serriola in particular was found. Only in Provence and Italy was there greater biodiversity. It should be noted, however, that the route of the excursion did not touch the Rhine-Main-Moselle area, for example, where several rarer species are native.

Types (selection)

The 17 species occurring in Europe are divided into several sections and subsections:

Phaenixopus section : lettuce ( Lactuca viminea )
Lactucopsis section : Illustration of the oak lettuce ( Lactuca quercina )
Section Lactuca Subsection Lactuca : Garden salad ( Lactuca sativa )
Section Lactuca Subsection Cyanicae : Blue lettuce ( Lactuca perennis )
  • Phaenixopus Section (Cass.) Benth. : The inflorescence is pyramidal or spike-like with single or tufted cups. Heads with four to eight flowers.
  • Mulgedium Section (Cass.) CB Clarke : The inflorescence with descending branches and a few cups. Numerous flowers.
    • Lactuca sibirica Benth. ex Maxim. : The homeland is Northern Europe, Eastern Europe, Siberia, China, Japan, Mongolia and Far Eastern Russia.
    • Tatar lettuce ( Lactuca tatarica C.A.Mey. ): It is native to Northern Europe, Eastern and Southeastern Europe, Poland, Slovakia, Western Asia, the Caucasus, Central Asia, India, Pakistan, Siberia, Mongolia, China and North America. There are two subspecies.
  • Section Lactucopsis (Sch. Bip. Ex Pančić) Rouy : The inflorescence is usually umbelliferous. Cups with six to 15 flowers.
    • Lactuca aurea (Schultz-Bip. Ex Panć.) Stebbins : It is endemic to the Balkan Peninsula from Croatia and Serbia to Romania, Greece and the European part of Turkey.
    • Oak lettuce ( Lactuca quercina L. ): It is native to Europe, Western Asia, India and the Caucasus. There are two subspecies.
    • Lactuca watsoniana Trelease : Endemic to the Azores .
  • Lactuca section : The inflorescence is a dense panicle of many cups. Cups with 10 to 50 flowers.
    • Subsection Lactuca . These species are ruderal and prefer rough terrain.
      • Garden salad ( Lactuca sativa L. ): It is only cultivated.
      • Spiny lettuce ( Lactuca serriola L. ): This species is by far the most common in Central Europe.
      • Willow lettuce ( Lactuca saligna L. ): Home is Europe (except north), North Africa, Asia Minor.
      • Poison lettuce ( Lactuca virosa L. ): Home is sub-Mediterranean Europe, Western Asia, North Africa, North America.
      • Lactuca altaica fish. et CA Mey. : The homeland is Southeast Russia, Central Asia, Siberia and Xinjiang .
      • Lactuca livida Boiss. et Reut. : It is also called Lactuca virosa subsp. livida (Boiss. & Reut.) Ladero & A. Velasco to Lactuca virosa . It is endemic to central Spain .
    • Subsection Cyanicae : Surprisingly, according to the latest research, these species seem to be the furthest removed from garden lettuce and should therefore be excluded from the genus Lactuca .
      • Blue lettuce ( Lactuca perennis L. ): Home is sub-Mediterranean Europe.
      • Lactuca intricata Boiss. (Syn .: Lactuca graeca Boiss. ): It occurs in Greece, Macedonia, Albania, in the Aegean Sea and in Turkey.
      • Lactuca tenerrima Pourr. : It occurs in Morocco, Spain, Gibraltar, Andorra, France and the Balearic Islands.

Only in the New World occur (selection):

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Individual evidence

  1. a b c d John L. Strother: Lactuca Linnaeus. , Pp. 258-262 - online with the same text as the printed work . In: Flora of North America Editorial Committee (Ed.): Flora of North America North of Mexico. Volume 19: Magnoliophyta: Asteridae, part 6: Asteraceae, part 1 (Mutisieae – Anthemideae). Oxford University Press, New York and Oxford, 2006, ISBN 0-19-530563-9 .
  2. ^ A b Reuben A. Sessa, Mark H. Bennett, Mervyn J. Lewis, John W. Mansfield, Michael H. Beale: Metabolite Profiling of Sesquiterpene Lactones from Lactuca Species. In: Journal of Biological Chemistry Volume 275, No. 35, 2000, pp. 26877-26884, doi : 10.1074 / jbc.M000244200
  3. W. Blaschek et al. (Ed.): Hager's Handbook of Pharmaceutical Practice. Volume 3: Drugs L - Z. 5th edition. Springer-Verlag, Berlin 1998, ISBN 3-540-61619-5 , p. 17 ff.
  4. Theodore A. Bischoff, Charles J. Kelley, Yvette Karchesy, Maria Laurantos, Phuc Nguyen-Dinh, Abdul Ghafoor Arefi: Antimalarial activity of Lactucin and Lactucopicrin: sesquiterpene lactones isolated from Cichorium intybus L. In: Journal of Ethnopharmacology Volume 95, No. . 2-3, 2004, pp. 455-457, doi : 10.1016 / j.jep.2004.06.031 .
  5. J. Storm's flora of Germany in illustrations after nature. I – XV, 2nd revised edition, KG Lutz, Stuttgart 1900–1907, Volume XIV, p. 110.
  6. John Marion Riddle: Dioscorides on Pharmacy and Medicine. With a foreword by John Scarborough , Austin (Texas) 1985 (= History of science series. Volume 3), pp. 28 and 38.
  7. Wim JM Koopman, Martin J. Zevenbergen, Ronald G. Van den Berg: Species relationships in Lactuca sl (Lactuceae, Asteraceae) inferred from AFLP fingerprints. In: American Journal of Botany. Volume 88, No. 10, 2001, pp. 1881-1887, abstract .
  8. ^ Wim JM Koopman: Zooming in on the lettuce genome. Species relationships in Lactuca sl, inferred from chromosomal and molecular characters. In: Wageningen University dissertation. Volume 3233, June 21, 2002, download .
  9. a b Aleš Lebeda, Ivana Doležalová, Eva Křístková, Barbora Mieslerová: Biodiversity and ecogeography of wild Lactuca spp. in some European countries. In: Genetic Resources and Crop Evolution. Volume 48, No. 2, 2001. pp. 153-164. doi : 10.1023 / A: 1011265614395
  10. a b c d e f g h i j k l m n o Lactuca in the Germplasm Resources Information Network (GRIN), USDA , ARS , National Genetic Resources Program. National Germplasm Resources Laboratory, Beltsville, Maryland. Retrieved April 13, 2018.
  11. a b c d e f g Werner Greuter (2006+): Compositae (pro parte majore). In: Werner Greuter, E. von Raab-Straube (Ed.): Compositae. : Lactuca data sheet In: Euro + Med Plantbase - the information resource for Euro-Mediterranean plant diversity.

Web links

Commons : Lattich ( Lactuca )  - album containing pictures, videos and audio files