dinsdag 18 augustus 2015

Helichrysum color

How Many Helichrysum Species Exist and Why is Their Color so Fade-Resistant?

The genus Helichrysum belongs to the family Asteraceae and encompasses more than 500 different species, with hotbeds of biodiversity centered in the Mediterranean basin, South Africa, and Australia — three geographically and geologically unrelated areas.1 This split distribution is presumably the result of parallel evolution from one or more ancestral and now-extinguished species. The name Helichrysum (from the Greek helios = sun and krysos = gold) makes reference to the bright yellow color of the flowerheads, which is particularly striking in full sun and also remarkably persistent in the dried plant. The name of the plant in many European languages — perpetuino and semprevivo in Italian, immortelle in French, everlasting in English, siempreviva in Spanish — recalls this property. The yellow color of Helichrysum’s flowerheads has been tied to the presence of the chalcone (a particular type of flavonoid) isosalipurposide,2 and its steadfastness may be due to stabilizing co-pigments, to the anatomy of the flower that preserves the bracts’ vacuolar contents from air oxidation, or to a combination of these factors. On the other hand, recent investigations of H. italicum failed to detect the presence of chalcones3 — which are probably typical of the Northern species H. arenarium Moench.4 — but found kaempferol-type flavonols instead.3 Therefore, the exact nature of the yellow pigment from H. italicum and, in general, of the resistance of Helichrysum flowerheads to fading, seem unclear. Interestingly, when mixed with mulberry (Morus spp., Moraceae) leaves and fed to silkworms, the flowerheads of H. italicum induce the production of naturally yellow silk, a material used in central Sardinia for the production of folk garments (Figure 2). Ancient Romans and Greeks decorated the statues of gods with wreaths of Helichrysum flowerheads, a practice mentioned by classic writers since the 7th century BCE. This use may seem curious, since existing classic statues are now the color of the original materials from which they were made (e.g., marble or bronze). However, they were originally vividly colored, and the yellow hue of Helichrysum in full sun would have given the effect of a gold crown on a polychromous figure.

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