Comparative leaf micromorphology and anatomy of the dragon tree group of Dracaena (Asparagaceae) and their taxonomic implications

Małgorzata Klimko,Paul Wilkin,Renata Nowińska,Justyna Wiland-Szymańska

doi:10.1007/s00606-018-1530-3

Abstract

Micromorphological features of the leaf epidermis and the inner structure of leaf tissues of eight arborescent taxa of the genus Dracaena were analysed using light and scanning electron microscopy. The plants are xeromorphic or mesomorphic. Their leaves are isobilateral and amphistomatic, and the stomata are anomocytic and tetracytic. The mesophyll in all the species is divided into an outer chlorenchyma and a central region with colourless water-storage cells, chlorophyll cells and vascular bundles. Water-storage cells have wall bands and reticulate thickenings on the walls. The article describes and illustrates several new quantitative and qualitative leaf characters of the dragon tree group. Our findings can be used to identify the dragon tree group leaves, while the shape of epidermal cells and stomata types may be useful in the identification and classification of fragments of fossil leaves. We conclude that D. ombet and D. schizantha are not two distinct species, but should be treated as subspecies of D. ombet. Leaf characters, especially stomata depth on adaxial epidermis, height of adaxial epidermal cells and the presence and thickness of hypodermal fibre bundles markedly differ between geographical groups: Macaronesian species (D. draco and D. tamaranae), the species found in East Africa and Arabian Peninsula (D. ombet subsp. ombet, D. ombet subsp. schizantha, D. serrulata and D. cinnabari) and Southeast Asian species (D. kaweesakii and D. jayniana).

Highlights

The genus Dracaena Vand. ex L. is currently classified within the family Asparagaceae, subfamily Nolinoideae (APG III 2009), where together with the closely related genera Sansevieria Thunb. and Pleomele Salisb., Dracaena forms the so-called dracaenoid clade
Leaf margin is entire and reddish in Dracaena draco, entire in D. tamaranae (Fig. 1a, b), entire with a distinctive narrow white margin when fresh in D. kaweesakii, entire and undulate widely in D. ombet subsp. ombet (Fig. 1c), serrulate in D. ombet subsp. schizantha and D. serrulata (Fig. 1d, e), dentate in D. cinnabari (Fig. 1f), Outline: The lamina surface in the T.S. on both surfaces is almost flat in D. draco (Fig. 4a) and D. kaweesakii (Fig. 4p, q), flat or slightly undulate in D. cinnabari (Fig. 4k), and slightly undulate in both subspecies of D. ombet (Fig. 4e, g) and D. serrulata (Fig. 4i)
This paper presents for the first time a comparative micromorphological and anatomical study of leaves of the eight arborescent Dracaena taxa

Summary

Introduction

The genus Dracaena Vand. ex L. is currently classified within the family Asparagaceae, subfamily Nolinoideae (APG III 2009), where together with the closely related genera Sansevieria Thunb. and Pleomele Salisb., Dracaena forms the so-called dracaenoid clade. Klimko et al 2017a, b) and Pleomele (Brown 1914) or as Dracaena sensu lato (Bos 1984, 1998; Staples and Herbst 2005). Another approach was applied by Jankalski (2008), who recommended to include Pleomele in the genus Dracaena and to regard non-Hawaiian and Hawaiian Pleomele as two subgenera of Dracaena A recent phylogenetic study of Lu and Morden (2014) has shown that only six Hawaiian Pleomele species form a monophyletic sister group to the Dracaena species and are separated from them as a distinct genus Chrysodracon P.L.Lu & Morden. Non-Hawaiian Pleomele are intermixed with Dracaena, whereas Sansevieria is monophyletic but nested within Dracaena

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