Glandular trichomes and essential oils of Helichrysum stoechas

The aerial organs of Helichrysum stoechas bear a dense woolly indumentum with two types of trichomes: nonglandular trichomes, extremely long, simple, uniseriate and multicellular; and biseriate, glandular trichomes with 10–14 cells. Glandular trichomes are abundant on the leaf abaxial surface, particularly on the intervein areas, on the inflorescence, at the receptacle on interfloret positions, on the corollalobes, and on the ovary surface. Secretion accumulates in a subcuticular spaceformed above the top of the upper tier of secretory cells and is released to the outside by cuticle rupture. The essential oils isolated from the flowers and from the leaves collected during the flowering period were obtained in a yield of 0.3% (v/w) and0.8% (v/w), respectively. The analyses performed by GC and GC-MS revealed that the monoterpene hydrocarbon fraction was dominant in both oils, attaining 93% and98% of the total oils from the flowers and leaves, respectively. a-Pinene was the major component in both oils, amou...