Comparative investigation about the trichome morphology of Common oregano (Origanum vulgare L. subsp. vulgare) and Greek oregano (Origanum vulgare L. subsp. hirtum)

• O. vulgare subsp.vulgare and subsp. hirtum have different density and size of trichomes.
• The essential oil concentration differs between both O. vulgare subspecies.
• The subsp. hirtum is characterized by larger size of peltate trichomes.
• The subsp. hirtum is characterized by denser peltate trichomes.
• Both forms of glands have an important role for essential oil accumulation.

The genus Origanum is divided in several species and subspecies. Common oregano (Origanum vulgare L. subsp. vulgare) and Greek oregano (Origanum vulgare L. subsp. hirtum) are two important subspecies which are characterized by different content of essential oil synthesized in glandular trichomes. Investigations with light microscopy and scanning electron microscopy were carried out to determine the morphological parameters of the leaves and trichomes of O. vulgare subspecies cultivated in a pot experiment under field conditions. It was found that Greek oregano is characterized by higher density of peltate as well as capitate glandular trichomes on adaxial leaf side compared to common oregano. The size of peltate glandular trichomes of Greek oregano was significantly larger on both sides (abaxial and adaxial) of the leaves compared to common oregano whereas no difference between both subspecies was observed regarding the size of capitate glandular trichomes. It can be concluded that higher essential oil content of Greek oregano is caused by the combination of both higher density and larger size (larger volume) of peltate glandular trichomes.

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