How long after a citrus seedling has germinated does it rely on the cotyledon for energy? I've always assumed they remain attached to the seedling longer than they are actually needed.

Hi Mark, maybe you are talking about the first two true leaves? I say that because typically the cotyledons remain under ground.

I found the following abstract of a research paper which doesn't answer your question directly, but it gives very useful and relevant information about cotyledons. Link is below, unfortunately you have to pay to get the full paper.

http://www.springerlink.com/content/mr71v6012222w820/

Cotyledon detachment inhibits development but does not affect precocious flowering of ‘Duncan’ grapefruit

Doron Holland, Mohamad Abu Abied, Sahar Nachman and Shoshana Saad

Abstract
The role of cotyledons in seedling development and precocious flowering was studied in 'Duncan' grapefruit (Citrus paradisi Macf), a cultivar that displays a high frequency of precocious flowering. Cotyledons were detached from the embryo and the embryos were germinated in vitro to form plantlets. Cotyledon detachment dramatically affected the development of 'Duncan' seedlings. The decotyledonized plants were stunted, with small narrow leaves and thin and underdeveloped roots. Decotyledonization did not change significantly the number of leaves developed. Despite the dramatic effects of the cotyledons on seedling development, decotyledonized 'Duncan' seedlings retained their ability to flower precociously. We conclude that although normal growth and development of 'Duncan' grapefruit seedlings is cotyledon-dependent, the ability to flower precociously does not depend on the presence of cotyledons during in vitro germination.

Until the first true leaves develop, and begin to produce photosynthates. - Millet (713-)