Trichome micromorphology and its significance in the systematics of Convolvulus L. (Convolvulaceae)

Abstract

Trichomes of 35 species of the genus Convolovulus and one species of the genus Calystegia (C. sepium) were investigated usinglight and scanning electron microscopy. The trichomes show a great variation, which provides valuable data for sections and speciesdelimitation in Convolvulus. Trichomes of Convolvulus are nonglandular, simple, and basifixed or rarely asymmetrically medifixed.Characters of taxonomic interest were the degree of curviness (straight to spiral), orientation relative to the epidermal surface (appressedto erect), and presence of papillae on trichome surface. The trichomes are divided into two basic types: cylindrical and flattenedribbon-like. Our data provide the additional evidence to include Calystegia in Convolvulus; the former is characterized by glabrousshoots supporting its inclusion in the Convolvulus sect. Convolvulus. Using the evolutionary framework provided by recent molecularphylogenetic investigations, the following trends can be proposed in Convolvulus: long cylindrical trichomes are advanced against theflattened ribbon-like ones, densely papillate trichomes are derived against the nonpapillate or loosely papillate ones, long trichomesare advanced against the short ones, and appressed trichomes are primitive compared with the erect ones. In most investigated speciesof Convolvulus, a mixture of various kinds of trichomes has been detected, and the level of advancement should be determined by acollective approach.