Lemon balm 391
spread 0.5–1.0 m across. It is characterised by square stems, lemon-scented and
scalloped edge leaves, and flowers that mature from white or yellow to pale blue. The
green leaves, which give off a fragrant lemon smell when bruised, are about egg or
heart shaped and 2–8 cm in length and arranged in opposing pairs on the stems.
Upper leaves are usually bigger than lower leaves. Veins in the leaves can be easily
seen. The small flowers (0.5–1.5 cm size) are produced all summer long. They grow
in loose, small branches from the axils of the leaves on the stems (Fig. 23.1).
Lemon balm is a cross-pollinating species, and has complete perfect flowers with
very short-stalked epidermal glands. The flowers consist of five fused sepals, five
petals, two or four stamens and four lobed ovaries forming 1–4 nutlets. The seeds are
very small about 1–1.5 mm long, ovate, dark brown or black in colour. The weight
of 1000 seeds is 0.5–0.7 g. A long storage period causes a reduction in germination
vigour. Seeds stored for five years may no longer germinate. Lemon balm has a hairy
root system with many lateral roots, which makes the plant more adaptable to different
environmental conditions. The upper parts of the plant die off at the start of winter,
but new shoots re-emerge from the roots at the beginning of spring.
23.2 Chemical composition....................................................................
Much work on chemical composition in both essential oil and different parts of
lemon balm has been reported. Essential oil rate in drug herb changes between 0.02–
0.30%, which is quite low compared to other member of the family Labiatae (Sari
and Ceylan, 2002; Saglam et al., 2004). That is why the production cost and price of
essential oil is very high in the market. The main constituents of the essential oil are
citral (geranial and neral), citronellal, linalool, geraniol, b-pinene, a-pinene, b-
caryophyllene and b-caryophyllene oxide, comprising about 96% of the oil ingredients.
Carnat et al. (1998) explored the chemical composition of essential oil of lemon
balm, and found that major components are citral (neral + geranial) representing
Fig. 23.1 Parts of the lemon balm plant (Melissa officinalis L.).