Different types of foliar trichomes in the family Boraginaceae

The objective of this study, is description of different types of trichome in Boraginaceae. The foliar trichome of certain members of Boraginaceae including Anchusa ovata, Asperugo procumbens, Buglossoides arvensis, Heliotropium ellipticum, Lappula barbata, Myosotis silvatica, Onosma dichroanthum, O. microcarpum and Symphytum asperum are studied. In Boraginaceae, trichome as epidermal attachments have various shapes, structure and function such as protect and support the leaf. A trichome is formed by single- or multi-celled, branched or unbranched, living or dead. Trichome as observed in Boraginaceae includes four types: a) simple unicellular short trichome (Anchusa ovata), b) bicellular simple trichome which is unbranched and cystolith commonly present at the bases of the trichome surrounded by 1-3 layeres of subsidiary cells (Asperugo procumbens, Heliotropium ellipticum), c) multicellular, which trichome is extremely large (O. microcarpum), and d) glandular, multicellular trichome consists of two or three stalk cells, and a terminal more or less spherical gland cell (Symphytum asperum). The function of trichome within Boraginaceae is also evaluated in this study. Rough trichome such as cystolith-like trichome in above-mentioned species, decreases air movement on the leaf surface and creates a zone of still air through which water vapor diffuses when moving from the leaf interior to the relatively dry air of the surrounding atmosphere. This is also avoiding transpiration losses by influencing the water diffusion boundary layer of the transpiring leaf surface. It is well known that plants from dry habitats possess progressively more pubescent leaves or densely covered with trichome (Onosma dichroanthum and O. microcarpum). In addition to directly influencing transpiration, trichomes may also indirectly influence water economy of plants through temperature regulation.