Lactuca sativa

Why are the seeds of this species difficult? Some wild-collected species of the Asteraceae family can produce a high proportion of empty seeds, which collectors and curators must take account of. The seeds may have physiological dormancy. They are relatively short-lived, so may not remain viable for a long time in storage.

Lactuca sativa (Image: S. Wood, RBG Kew)

Seed Storage

This species has Orthodox seeds - dry to 15-20% eRH and store at -20ºC, or as cool as possible.

The seeds are relatively Short-lived in storage. Monitor viability at least every five years, and more frequently once viability begins to decline. When viability falls close to the regeneration standard, the collection will need to be re-generated or re-collected.

Germination Requirements

Germinate on agar, germination paper or sand at 20ºC. Perform a cut-test on any seeds that have not germinated, to check for empty seeds. All empty seeds are non-viable in germination tests.

The seeds of this species may have non-deep Physiological Dormancy. If germination is low, try using a moist pre-chill treatment before germinating the seeds at their optimum temperature.

Seed Morphology

The production of empty seeds is common in non-domesticated species of the Asteraceae. Empty seeds may have a normal seed coat but an absent or under-developed embryo, or limited storage tissue.

The fruit (3-4 mm) is an indehiscent achene, with a single locule containing a single seed. The achenes are narrowly obovate and compressed, with 5-7 ribs on each face. The tip is formed into a narrow beak, topped by a pappus of 2 equal rows of soft white, simple hairs. The seeds are white, yellowish, grey or brown in colour.

See more images of this species at the Digital Atlas of Economic Plants and the Digital Seed Atlas of the Netherlands.

Taxonomy

Family: ASTERACEAE

Accepted name: Lactuca sativa L.

Synonyms: Lactuca scariola var. sativa Moris

Common name: lettuce

References and Links

Baskin, C.C. and Baskin J.M. (1998). Seeds: ecology, biogeography, and evolution of dormancy and germination. Academic Press, USA.
Black, M., Bewley, J.D. and Halmer, P. (2006). The Encyclopaedia of Seeds: science, technology and uses. CAB International, UK.
Food and Agriculture Organization of the United Nations and International Plant Genetic Resources Institute (1994). Genebank Standards. FAO/IPGRI, Rome, Italy.
International Seed Testing Association (2010). International Rules for Seed Testing: edition 2010. ISTA, Bassersdorf, Switzerland.
Rao, N.K., Hanson, J., Dulloo, M.E., Ghosh, K., Nowell, D. and Larinde, M. (2006). Manual of seed handling in genebanks. Handbooks for Genebanks No. 8. Bioversity International, Rome, Italy.
Purseglove, J.W. (1968). Tropical Crops: dicotyledons. Longman Group Ltd., UK.
Walters, C., Wheeler, L.M., Grotenhuis, J.M. (2005). Longevity of seeds stored in a genebank: species characteristics. Seed Science Research, Vol 15 (1): pp1-20.

AFPD (African Flowering Plants Database) - Conservatoire et Jardin Botaniques de la Ville de Genève, Switzerland, and South African National Biodiversity Institute, Pretoria, RSA: Lactuca sativa.
AVRDC - The World Vegetable Centre, Taiwan: fact sheet on Lactuca sativa.
PROTAbase (Plant Resources of Tropical Africa) - Wageningen, Netherlands: Lactuca sativa.
SID (Seed Information Database) - Royal Botanic Gardens, Kew, UK: Lactuca sativa.
Tropicos - Missouri Botanical Garden, USA: Lactuca sativa.