The scent of Linnaea
Submitted by Tina on 18 May 2018.
Photo by Gunnar Stenhagen
We analysed the scent of Linnea borealis by gas chromatography – mass spectrometry (GC-MS) of adsorbed headspace samples (NJB-01732).
The aim of the study is five-fold.
1. To describe the odour bouquet of L. borealis and compare it from separate localities.
Wittrock had referred to L. borealis as a species ”polymorpha et polychroma”. Is that so also for the composition of its scent?
2. To lay a ground that could inspire studies in pollination biology, primarily the behaviour-guiding roles of the characteristic emitted volatiles.
3. To try and find out the possible systematic and taxonomical value of the scent volatiles.
4. For comparison, also identify volatiles from the related L. amabilis.
5. To provide a contribution to the overriding question: ”why do flowers smell, and why do they smell differently”.
We identified four major volatile compounds, all benzenoids: 1,4-dimethoxybenzene, anisaldehyde, 2-phenylethanol and benzaldehyde.
The chemical composition fits well with descriptions of the Linnaea odour, from Linnaeus onwards. We found small but characteristic differences between three
Swedish populations: Särö – Southwestern Sweden, Säffle – Southcentral Sweden and Abisko – Northern Sweden. Both diurnal and nocturnal samples were taken.
In some cases the nocturnal emittance was stronger, also in accordance with earlier observations.
The scent of a Finnish population of L. borealis, from Raseborg – Southwestern Finland, was also studied. It turned out that it gave off the same benzenoid compounds
as the Swedish populations. But in addition it produced large amounts of (-)-α-pinene and β-pinene.
Another species, which is now placed in the Linnaea genus, L. amabilis, was analysed for comparison. This bushy species also emitted large amounts
of (-)-α-pinene (main component) together with β-pinene and (E)-β-ocimene. But it completely lacked the benzenoids.
Linnaea was published in 1753 with the single species L. borealis. The genus remained monotypic until 2013, when several related genera were
included, raising the number of species to 16. Among these was the beauty bush, Kolkwitzia mirabilis. Ever since the time of Linnaeus the genus Linnaea
has been placed in the family Caprifoliaceae. An alternative proposal has been made, viz. a separate family Linnaeaceae, but this has not been generally accepted.
In our opinion the expanded generic concept of Linnaea fits well into the Caprifoliaceae.
It is presumed that the volatiles attract pollinators: flies, bees and other small insects. The differences in volatiles between the three Swedish populations
of L. borealis and the Finnish one, could hypothetically be explained by separate routes of colonization. But it must also be kept in mind that the biosynthesis of plant volatiles is highly flexible.
All these analyses were carried out with long tested optimal techniques. Molecular formulas for the major volatile compounds (the scent) from L. borealis is given in the Scheme. The strong relationships inbetween the benzenoids a – d, and inbetween the monoterpenes e and f, are obvious.
The odours of the scent components have been described as:
a: ”intensely sweet, floral odour”;
b: ”sweet. Floral and strong aniseed odour”;
c: ”characteristic almond-like odour”;
d: ”characteristic rose-like odour”.
e and f: the pinenes have of course a characteristic pine-tree odour.
Since a and b are quantitatively dominant they may have a dominant influence on the odour bouquet of L. borealis.
by Gunnar L. Bergström and co-authors