Morphology and histochemistry of the glandular trichomes of Isodon rubescens (Hemsley) H. Hara [Lamiaceae]: A promising medicinal plant of China

Isodon rubescens, a perennial herb indigenous to China, with medicinal application, potentially has economic value. The morphology of the glandular trichomes was investigated with light microscopy. At the same time the chemical content was analyzed by applying chemical reagents and fluorescence microscopy. This morphoanatomical and histochemical study revealed that leaves of I. rubescens possess one type of non-glandular and two types of glandular trichomes, with the latter differing both anatomically and in the composition of their secondary metabolites. Non-glandular trichomes were uniseriate with an ornamented surface. Peltate and capitate glandular trichomes comprised one basal cell, one stalk cell and one head. The head of mature peltate glandular trichomes consisted of four-twelve secretory cells while that of the capitate glandular hairs was comprised of two cells. Peltate glandular trichomes containing compounds of terpenoid nature are probably the main site of oridonin and ponicidin accumulation. The fluorescent stain of peltate and capitate glandular trichomes indicated the possible presence of phenolic compounds.   Key words: Isodon rubescens, Lamiaceae, glandular trichomes, microscopy, histochemistry, terpenoids, phenolic.