Probably everybody knows the popular game in which one person seeks to determine whether the object of their affection returns it or not, by using the “petals” of a “flower”, usually a daisy. Well, the term daisy can refer to many species. Here, we will focus on the Southern daisy, Bellis sylvestris Cir., which is a plant belonging to the Asteraceae (or Compositae) family. This means that this beautiful “flower” is actually a flower head, composed by several small flowers, the yellow ones in the middle and the white ones that are usually mistaken for petals. This plant species is widespread in Europe and is very similar to the common daisy, Bellis perennis L., so much that it is hard to differentiate them.
The name might come from the Latin bellus = beautiful. However, a very similar word, bellum, means war. This has been proposed as an alternative etymology, inspired by the wound-healing properties of some plants of this genus. The specific name sylvestris refers to its most common habitat (woods), although it can also be found in meadows, pastures, olive plantations, etc. The two species also share common names in many languages. The English name seems to come from day’s eye, since the flowers open in the morning. The Italian name is margherita, probably directly coming from the Latin for pearl, margarita. I find quite funny the German for this daisy, Wald-Gänseblümchen,a literally wild geese little flower.
The Southern daisy is an edible and officinal plant (1). The young leaves are eaten as salad. However great care should be taken, and plants collected in the wild should always be identified by experts: there is a lot of toxic plants out there! The leaves and flowers have diuretic, depurative, purgative, and diaphoretic properties (1). The plant, like the common daisy, is also used in traditional medicine for skin treatments, due to its anti-inflammatory properties, as well as to treat common cold and infections of the upper respiratory tract (1).
Herbal parts of this species are rich in caffeic acid derivatives, phenols, flavonoids, phenolic acids, terpenes, and triterpenoid saponins (1,2,3,4). Although all these compounds have interesting properties, we will focus now on saponins.
What is a saponin?
A saponin is a specialized metabolite made up by a lipid skeleton, which can either be a triterpene or a steroid, bound to one or more sugar chains of variable length and branching.
If you are just a little bit familiar with phytochemicals, at this point something will probably pop up in your mind: if we consider how many modifications of a triterpenoid and a steroid skeleton are possible, we can already imagine a huge diversity. Well, if we also consider the high variability of the sugar types, length of the chain(s), possible glycosylation sites, and so on…then the diversity we can imagine (and that plants can actually produce) is amazing. However, nature has even more fantasy: sometimes further chemical units (small phenolics, acetyls, etc.) can be linked either to the lipid or to the sugar moieties.
The combination of the hydrophobic aglycone backbone and the hydrophilic sugar units makes these compounds highly amphipathic and confers them foaming and emulsifying properties.b These structural features and peculiar physicochemical properties suggest important roles in plants and make these compounds useful for a series of application in food, cosmetics and pharmaceuticals.
From the plants’ perspective, making these metabolites comes with a cost, so they are surely not just playing chemist, but each single molecule could have a specific role. On the other hand, a modularity in building these compounds, based on different combinations of the initial building blocks, could be a good strategy to lower the overall costs. For some saponins the role is known, but there is still a lot to discover for most of them.
Saponins from Bellis sylvestris
The saponins isolated so far from Bellis sylvestris are characterized by the lipid backbone of bayogenin (a derivative of oleanolic acid) that can then be even further modified (2,3,4). Among these saponins, many were also reported from Bellis perennis.
Besylvosides I-VI were specifically isolated from Bellis sylvestris. They are also characterised by bayogenin as aglycone, linked to a sugar chain of variable length, and in one case, Besylvoside VI, with two glycosylation sites (2). These saponins have been tested for their phytotoxic activityc against a target species (2). Basically, small seedlings of the target plant were grown in presence of the saponins. For some of these, a mild phytotoxic effect was observed, which means that the plants were not growing as well as the control plants. While the detrimental effects were more evident for the aboveground part of the target plants, a weird phenomenon was observed, with the roots bending upwards. This phenomenon was reported also for another saponin in a different experimental system (5) and it was hypothesized that saponins are interfering with the gravitropic response of the target plants. In other words, the roots are not growing anymore downwards. The right direction of root growth is important for the plant and the disruption of the mechanisms controlling it results in perturbation of plant growth and performance. By interfering with the normal root orientation of seedlings of other species, the Southern daisy could win space and resources for its own offspring. However, these are mainly hypotheses that surely need to be further explored. The lack of toxicity of these compounds for the daisies themselves, as well as the way the compounds are released into the soil, their stability, etc. should be demonstrated.
These saponins were all reported from the leaf and stem parts of Bellis sylvestris. It is not known yet whether they are present also in the flower heads and roots, but this should be the case if we consider the close similarity to Bellis perennis.
The role of these saponins still needs to be clarified and possible antifungal, antimicrobial, nematocidal properties or, more in general, plant defence related activities should be taken into consideration.
a. The common daisy is simply Gänseblümchen.
b. This explains their name, from the latin sapo=soap.
c. The ability to inhibit the growth of another plant. There are, indeed, some plant derived chemicals able to influence growth and other important parameters of other plant species (positively or negatively). In case of phytotoxicity we take into account negative effects.