Bulb tunic anatomy and its taxonomic implication in Allium L. (Amaryllidaceae: Allioideae)

Abstract

Allium is taxonomically a difficult genus with blurred taxonomic borders at all taxonomic ranks. In this research, anatomy and morphology of bulb tunics in 42 species of the genus representing its 16 currently recognized sections and 6 subgenera (Allium, Cepa, Reticulatobulbosa, Amerallium, Polyprason and Melanocrommyum) were investigated. Our results indicated the following characters to be most informative at sectional and subgeneric levels: features of calcium oxalate crystals and subepidermal cell layer of the outermost bulb tunic, type of tracheids, and bulbils presence. Three main types of crystals, i.e. prismatic, sand and druses, were fairly common among the investigated species except for the members of A. sect. Acanthoprason (A. subg. Melanocrommyum) that often lack crystals. The subepidermal layers of outer tunics were mostly composed of hexagonal, rectangular, or elongated cells but A. paradoxum (A. subg. Amerallium, sect. Briseis) showed the pentagonal type and A. longisepalum (A. subg. Amerallium, sect. Molium) the elliptic type of subepidermal cells. The members of A. sub. Melanocrommyum showed various types of tunic cells and crystals.

Keywords:

• Calcium oxalate crystals
• laticifer
• systematics
• tracheid member
• subgeneric classification
• Iran

Abbreviations:

• Bs: bulb shape
• Bt: bulb type
• B: bulbils presence
• Tt: tunic texture
• Tc: tunic color
• Ss: shape of subepidermal cell
• As: alignment of subepidermal cell
• Ts: type of subepidermal cell
• Tw: type of anticlinal wall
• Ct: crystal type
• Cn: crystal number
• Dc: distribution of crystal
• T: type of tracheid
• S: starch
• L: laticifer
• R: rhizome
• Bl: bulb length
• Bw: bulb width
• Sl: subepidermal cell length
• Sw: subepidermal cell width
• Cl: crystal length
• Cw: crystal width

Acknowledgments

The authors gratefully acknowledge anonymous reviewers for their very helpful comments, leading to improvement of the manuscript. Shahin Zarre is thankful to Alexander von Humboldt Stiftung (Germany) and University of Tehran for their support.

Notes

1. According to a new sampled specimen the lower part of scape is also smooth and shiny in this species, but Fritsch and Abbasi (2013) did not address this feature definitely due to insufficiency of materials.