Comparative micro-anatomical investigation of genus Heliotropium (Boraginaceae) found in Turkey

Abstract

The genus Heliotropium L., belonging to family Boraginaceae in Turkey comprises 16 species. The species of this genus occur in a diverse range of environments. In this investigation, we describe and compare the leaf and stem anatomy in seven Turkish Heliotropium (H) taxa, the species are H. bovei Boiss., H. dolosum De Not., H. myosotoides Banks & Sol., H. haussknechtii Vatke., H. samoliflorum Bunge subsp. erzurumicum Donmez., H. suaveolens M. Bieb., and H. thermophilum Kit Tan, A.Çelik & Gemici., using standard protocol for light microscopy. Three of these seven investigated species i.e., H. thermophilum, H. haussknechtii, and H. samoliflorum subsp. erzurumicum are endemic to Turkey. This is first investigation of most of these species and little is known about the vegetative anatomy in these taxa. Leaf and stem characters described here related to epidermis, cuticle, indumentum, crystals, stomata, mesophyll, papillae and vascular system. Findings have shown that epidermal cells number, stomatal size, number of layers of hypodermis, collenchyma, cortex cells, palisade and spongy layers, number of subsidiary cells, shape and structure of crystals, and trichomes are of taxonomic value for this genus, and are valuable for species identification. Nearly all species have single layer epidermis. Three types of calcium oxalate crystals: styloids, druses, crystals sands were observed in stems and leaves of these species. Leaves are amphistomatic and anomocytic stomata type were observed in all species. Although the investigated specimens represent a limited range of taxa, the results of this study highlight the importance of stem and leaf anatomical features in assessing the taxonomic similarities between Heliotropium species. © 2019 Elsevier GmbH