Morphological diversity of glandular trichomes in Urticalean Rosids

ABSTRACT

Glandular trichomes are epidermal structures that produce, store and release a variety of chemical compounds. Their high morphological diversity allows their taxonomic use at various levels. Therefore, their description and standardization of terminology become challenging. Cannabaceae is a well known family of Urticalean Rosids because of the presence of cannabinoid-secreting trichomes in Cannabis sativa. Other Urticalean Rosid families (Moraceae, Ulmaceae and Urticaceae) are neglected in this regard. Thus, the morphology and distribution of glandular trichomes were studied in Cannabaceae and Ulmaceae species and compared with published data for Moraceae and Urticaceae. Surface and anatomical analyses were performed on vegetative and floral organs. Urticalean Rosids show at least 15 types of glandular trichomes, 12 of them capitate and three filiform. In particular, Trema micrantha, a Cannabaceae species, has six different types. A trichome with biseriate stalk and pluricellular head, found in Trema micrantha and Pteroceltis tatarinowii, was not previously reported. Glandular trichomes are widely distributed in the plant body, which may be related to protection against herbivory. The greatest difficulty was the large quantity of terms and the lack of morphological details of the glandular trichomes in previous studies. A standardization of the terminology of glandular trichomes was therefore proposed.

Keywords:
anatomy; Cannabaceae; Moraceae; terminology; Ulmaceae; Urticaceae