noun, plural: elaiosomes
Elaiosome is an organelle that stores fat and is therefore rich in oil. It is a fleshy structure abundant in lipids and proteins. It occurs in seed tissues (e.g. chalaza, funiculus, hilum, raphe-antiraphe) or fruit tissues (e.g. exocarp, receptacle, flower tube, perigonium, style, spicule).1 It may vary in shape. In certain plants, elaiosomes in seeds act as dispersal agents. For instance, seeds with elaiosomes attract ants and therefore are taken into the ants' nest wherein the elaiosome are fed to the larvae while the seed is discarded where it ultimately germinates under favorable conditions. Caruncle, the protuberance at or surrounding the hilum of a seed of spurge (i.e. plants belonging to genus Euphorbia), contains elaiosome. Seeds that have a caruncle are referred to as carunculate whereas those that do not have a caruncle are called ecarunculate.
Word origin: Greek elaion (oil) + some
1 Gorb, E. & Gorb, S. (2003). Seed Dispersal by Ants in a Deciduous Ecosystem. Kluwer Academic Publishers, Dordrecht, the Netherlands.