Phytomer

Phytomers are functional units of a plant continually produced by root and shoot meristems throughout a plant's vegetative life-cycle. The phytomer unit originates at the shoot (or root) apex, and typical phytomer consists of a node to which a leaf is attached, a subtending internode, and an axillary bud at the base of the leaf. Each component of a phytomer can continue to differentiate and grow. Increases in phytomer can be measured using the rate of phyllochron (rate of appearance of leaves n a shoot). Related to the phyllochron is the plastochrone, which is the rate of leaf primordia initiation. Since many more leaf primordia are initiated than leaves develop, the plastochrone develops at a much faster rate (sometimes as much as twice as quickly) as the phyllochrone.

Initially, a young plant will only produce phytomers at its apical meristems but later in development, secondary meristems will begin to form and phytomers will be formed on this lateral plant growth.

References

Howell, S.H. (1998). Molecular Genetics of Plant Development. Cambridge University Press 104. ISBN 0-521-58784-0

McMaster, G. S. Phytomers, phyllochrons, phenology and temperate cereal development. J. Agric. Sci. 143, 137 (2005).