Essential oil composition and glandular trichome structure of the weather prophet Dimorphoteca pluvialis

Dimorphoteca pluvialis (L.) Moench, usually known as weather prophet, African daisy, or Cape marigold, is an Asteraceae commonly found in gardens due to its appealing white to yellowish flowers. Recently, its use as a non-food oilseed crop has been investigated due to the high amounts of dimorphecolic acid (Δ9-hydroxy,10t,12t-octadecadienoic acid), a highly reactive C₁₈ fatty acid with value for the manufacture of paints, inks, lubricants, plastic and nylon. However, information on the essential oil (EO) composition of its plant tissues is scarce. The present work focused on characterizing the glandular trichomes, the main site for secretion of natural products, of shoots and sepals and analysing the EO composition of shoots and flowers of D. pluvialis, extracted by hydrodistillation for 15, 30 or 60 minutes. Shoot surface displayed sharp and elongated non-glandular protection trichomes, while the sepals additionally showed shorter and wider non-glandular trichomes. A capitate trichome with a biseriate peduncle and a multiseriate head was the only type of glandular trichome identified. A histochemical analysis of the glandular head revealed the presence of acid lipids, terpenic and phenolic compounds. The extracted EOs showed high amounts of trans-2-hexenal, a C₆ aldehyde that protects plants against harmful substances, but is considered toxic for humans. This study described, for the first time, the composition of EOs of D. pluvialis plants.