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HORT410 - Vegetable Crops
Lettuce and its Relatives - Notes
Lettuce
Common name: lettuce.
Latin name: Lactuca sativa L.
Family name: Compositae (Asteraceae) [Asteraceae Images].
The Latin name (Lactuca) is derived from the Latin root word "lac" or milk.
"Lettuce" derived from the French "laitue" meaning "milk".
"Sativa" means grown from seed.
Harvested organ: leaves, eaten raw, often in salads.
Dicotyledon.
Annual.
Diploid (2n = 18).
Origin: Egypt.
Evidence from Egyptian tomb paintings that lettuce was cultivated before 4,500 B.C.
Derived from the weed Lactuca serriola (prickly lettuce).
Prickly lettuce originally cultivated for forage and oil.
Prickly lettuce is extremely bitter.
Bitterness associated with the production of latex, the milky juice [30KB image] still found in the cultivated varieties when they flower.
Bitter latex is known to be sleep-inducing.
Romans developed broad-leaved, non-heading, non-spiny types that were resistant to early seed stalk formation, had decreased latex content, and produced larger, uniformly germinating seed.
Romans blanched their lettuce (grew them for a period in the dark before harvest) to make them less bitter.
Lettuce history (TAMU).
Modern lettuce types include:
1. Crisphead (iceberg types) - large, heavy, tightly folded heads; brittle or crisp textured; prominently veined leaves; wrapper leaves green; inner leaves whitish-yellow; predominantly outdoor types; widely used in N. America.
2. Butterhead (bibb or Boston lettuce types) - soft leaves; smooth texture; varieties bred for both outdoor summer conditions and greenhouse winter conditions; summer butterheads larger and firmer than the winter types; winter butterheads smaller and less compact; popular in N. Europe.
3. Cos (romaine) - elongated leaves developing into large loaf-shaped heads; slower to bolt than other lettuces; useful as a warm-weather crop; popular in S. Europe and the U.S. (CA and AZ).
4. Leaf - local marketing and home garden lettuce; grown mostly in greenhouses in the winter in northern and eastern regions; outdoor types of leaf lettuce have been developed and are grown mostly in CA and AZ.
Small-seeded.
Usually direct seeded; head-lettuce types sometimes transplanted.
Precision seeders required.
Seed often coated or pelletted.
Anticrustants often used to prevent the soil from crusting over after irrigation during pre-germination.
Days to harvest maturity: 40 days after seeding for leaf lettuce; 70 to 90 days for head lettuce.
CA is the major commercial lettuce producer, followed by AZ.
Lettuce for shipped is often kept fresh by vacuum cooling.
Self-pollinated.
Cool season vegetable.
Optimum growth temperature: 13 to 18 C.
Sensitive to both day length and high temperature.
late spring days and high temperatures prematurely bring on flower initiation causing bolting.
Breeding objectives: resistance to diseases and pests, increased yield and uniformity, improved quality, bolting resistance.
Soil pH optimum: 6.5 to 6.8.
Major insect pests of lettuce in the Midwest:
(see: ID-56: Midwest Vegetable Production Guide for Commercial Growers 2003 - Salad and Green Crops (PURDUE) for information on lettuce and endive varieties, spacing, seeding, fertilizing, and specific lettuce and endive disease, weed and insect control recommendations for the Midwest)
Endive
Common name: endive, or escarole.
Latin name: Cichorium endivia.
Family name: Compositae (Asteraceae) [Asteraceae Images].
Origin: Mediterranean region.
Grown by the Egyptians, Greeks and Romans.
Frost-hardy, annual or biennial.
Dicotyledon.
Lettuce-like.
Mildly bitter in flavor.
Harvested organ: leaves, eaten raw in salads or cooked.
Two major types; broad-leaved and curly-leaved.
Cultivated much like lettuce.
Sometimes blanched before harvest to reduce bitter flavor.
Witloof Chicory
Common names: witloof chicory, Belgian or French endive.
Latin name: Cichorium intybus.
Family name: Compositae (Asteraceae) [Asteraceae Images].
Diploid (2n = 18).
Perennial typically grown as a biennial.
Creamy white, elongated heads, about 5 cm in diameter and from 12 to 18 cm in length.
Blanched heads produced from fleshy storage roots by growing them in the dark at 10 to 15 C in pits, cold frames or houses.
Also grown outdoors for greens.
Dried, roasted, chicory root used as a coffee substitute.
Origin: Mediterranean region.
Grown by the Egyptians, Greeks and Romans.
May have originated from a cross between C. intybus and the wild annual species C. pumilum.
Globe Artichoke
Common name: globe artichoke, or French artichoke.
Latin name: Cynara scolymus.
Family name: Compositae (Asteraceae) [Asteraceae Images].
Diploid (2n = 34).
Thistle-like.
Harvested organ: immature flower bud, surrounded by many leaf-like bracts; the thickened bracts (phyllaries), heart (receptacle) and choke (flower buds) are eaten.
Origin: central and western Mediterranean over 2,500 years ago.
Closely related species: cardoon (Cynara cardunculus) and Cynara syriaca Boiss.
Globe artichoke probably developed these relatives by the Greeks and Romans.
Artichoke history (TAMU).
Entire U.S. artichoke crop is produced in the mid-coastal area of CA.
Requires a moderate climate; frost-free winters and cool summers.
Propagation usually by division rather than by seeds.
Perennial - plantings productive for 3 to 7 years.
Mature plant grows to about 1.5 m.
Leaves blue-green, sometimes spiny.
Flower stalks bearing a central bud and 2 or 3 secondary buds also arise from the central crown.
Artichokes are harvested year-round but mostly in the spring.
Jerusalem Artichoke
Common name: Jerusalem artichoke.
Latin name: Helianthus tuberosus.
Family name: Compositae (Asteraceae) [Asteraceae Images].
Cold-hardy, frost tolerant.
Autumn-blooming sunflower.
Harvested organ: tuberous, potato-like roots (rhizomes).
Origin: native of N. America
Cultivated by the American Indians before the 16th century.
Introduced to Europe in the 17th century.
Sources of information:
Welty, C., Weinzierl, R., Oloumi-Sadeghi, H. Leaf crops. In "Vegetable Insect Management With Emphasis on the Midwest", (ed. R. Foster, B. Flood), Meister Publishing Co., Willoughby, Ohio (1995).
Nonnecke, I.L. "Vegetable Production", Van Nostrand Reinhold, NY (1989).
Phillips, R., Rix, M. "The Random House Book of Vegetables", Random House, NY (1993).
Lorenz, O.A. Lettuce. In "The Software Toolworks Multimedia Encyclopedia", Version 1.5, Grolier, Inc. (1992).
Maynard, D.N. Artichoke, chicory, and endive. In "The Software Toolworks Multimedia Encyclopedia", Version 1.5, Grolier, Inc. (1992).
Kalloo, G. Chicory, Cichorium intybus L. In "Genetic Improvement of Vegetable Crops", (ed. G. Kalloo, B.O. Bergh), Pergamon Press, Oxford, U.K., pp. 535-540 (1993).
Kalloo, G. Endive, Cichorium endivia L. In "Genetic Improvement of Vegetable Crops", (ed. G. Kalloo, B.O. Bergh), Pergamon Press, Oxford, U.K., pp. 541-542 (1993).
Pink, D.A.C., Keane, E.M. Lettuce, Lactuca sativa L. In "Genetic Improvement of Vegetable Crops", (ed. G. Kalloo, B.O. Bergh), Pergamon Press, Oxford, U.K., pp. 543-571 (1993).
Pecaut, P. Globe artichoke, Cynara scolymus L. In "Genetic Improvement of Vegetable Crops", (ed. G. Kalloo, B.O. Bergh), Pergamon Press, Oxford, U.K., pp. 737-746 (1993).
Kalloo, G. Jerusalem artichoke, Helianthus tuberosus L. In "Genetic Improvement of Vegetable Crops", (ed. G. Kalloo, B.O. Bergh), Pergamon Press, Oxford, U.K., pp. 747-750 (1993).
Midwest Vegetable Production Guide for Commercial Growers, ID-56, eds. R. Foster, D. Egel, E. Maynard, R. Weinzierl, H. Taber, L.W. Jett, B. Hutchinson, Purdue University Cooperative Extension Service, 2003.
Desphande, S.S., Salunkhe, D.K. Lettuce. In "Handbook of Vegetable Science and Technology: Production, Composition, Storage, and Processing", (ed. D.K. Salunkhe, S.S. Kadam), Marcel Dekker, Inc., NY, pp. 493 - 509 (1998).
Kadam, S.S., Salunkhe, D.K. Celery and other salad vegetables. In "Handbook of Vegetable Science and Technology: Production, Composition, Storage, and Processing", (ed. D.K. Salunkhe, S.S. Kadam), Marcel Dekker, Inc., NY, pp. 523 - 532 (1998).
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David Rhodes
Department of Horticulture & Landscape Architecture
Horticulture Building
625 Agriculture Mall Drive
Purdue University
West Lafayette, IN 47907-2010
Last Update: 01/07/08
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