Not to be semantically confused with : Bastard Balm (Melittis melissophyllum) [a plant with similar name but which also belongs to the same dead-nettle Family] nor with Melilotus officinalis (Ribbed Melilot).
Some similarities to : Gipsywort but those leaves do not smell of lemons when crushed. Also, the leaves of Balm are oval, whilst those of Gypsywort are much longer than wide.
Uniquely identifiable characteristics
Distinguishing Feature : the unexpected smell of lemons when the leaves are crushed.
No relation to :
Lemons [a tropical tree bearing yellow fruit with similar name].
The only plant (at least in the UK) belonging to the Melissa Genus, although there are many cultivars. It is not known whether the above photos are a cultivar, but they were growing on a public right of way within the grounds of a house. It is a perennial herb.
Balm, or Lemon Balm, contains Eugenol and numerous other terpenes and their derivatives. Specifically 1-octen-3-ol,
β-Bourbonene, Caffeic Acid, Caryophyllene, Caryophyllene Oxide,
Cis-3-hexen-1-ol (leaf alcohol, which has an intense grassy-green odour of freshly cut grass), cis-Ocimene,
Eugenyl-acetate, γ-Cadinene, δ-Cadinene,
Geranial, Geraniol, Geranyl Acetate, Germacrene D,
Octyl-benzoate, Oleanolic Acid,
Stachyose, Succinic Acid, Thymol, Trans-Ocimene and Ursolic Acid. Strangely, it lacks Limonene which smells of oranges but which is present in the peel of Lemons.
Lemon Balm can exist as two or more Chemotypes, where exactly the same species of plant can produce differing secondary metabolites, which might depend upon the region it is growing in or on environmental factors.
LEMON SCENTED MONOTERPENOIDS
The leaves not only smell lemony, but also have a citrusy taste like the non-native
Lemongrass. Balm is used to flavour ice-creams and herbal teas. Its flavour derives from four of the main constituents of the essential oil from Lemon Balm: 24%
Linalyl Acetate (aka
Linalool Acetate) and 12% Caryophyllene. Citral has two conformational isomers, the (E)-isomer is known as Citral A aka
Geranial, the (Z)-isomer as Citral B aka
Neral. Shown is Citral A, Geranial, which has a strong
lemon odour (the odour of Citral B, Neral is less intense). It is used in perfumery whenever a hint of citrus is required and is present in the essential oil of the non-native?
Lemon Myrtle (Backhousia citriodora) at a whopping 90-98%, in
Lemongrass (Cymbopogon citratus) at 65-85%, in Balm/Lemon Balm at just 11%, Lime fruits at 6-9% and
Lemon fruits at 2-5%.
Rhodinal) also smells of lemon fruits and it too is a major component of Lemongrass (Cymbopogon citratus) and other plants that smell of lemons. It is a highly effective repellent of mosquitoes and also has strong anti-fungal properties.
MINTY SCENTED MONOTERPENOIDS
Linalyl Acetate has a taste similar to its fruity minty smell. It is the Acetate of Linalool which it usually occurs in plants together with, and is a major component in