Morphological and anatomical study of stevia leaves (Stevia rebaudiana (Bertoni) Hemsley)

Abstract

Topicality. Stevia rebaudiana (Bertoni) Hemsley is a perennial plant that originates from Paraguay and southern Brazil. In Ukraine the plant is cultivated. Stevia is a natural low-calorie sweetener with a wide range of health care properties. It is used as a hypoglycemic, anticarcinogenic, antioxidant, bactericidal, antiviral, anti-inflammatory and antihypertensive agent.

Aim. The aim of our study was to analyse the morphological and anatomical structure of Stevia rebaudiana (Bertoni) Hemsley leaves.

Materials and methods. Stevia leaves were harvested on the research area of the cultural flora department of M. M. Gryshko National botanical garden NAS of Ukraine during the mass blossoming of plants in 2016. Specimens production was carried out by conventional methods. We used a microscope MC 10 (glasses X5, X10, 15, lenses X10, X40). Photomicrographs were made with a camera Samsung PL50. We analysed the agents of epidermis from the surface (edge, the middle of the upper and lower sides of the leaf blade, its cross cut), cross cuts of a petiole.

Results and discussion. Morphological structure: leaves are opposite, short, without stipules, lanceolate or ovoid, with a serrated edge, gently wrapped down. Reticulated nervation. The leaf is more pubescent on the lower side, over the nerves and along the edge of the leaf blade. The leaves are more pubescent on the top of the plant. The colour of the leaf blade on top is green and on bottom is a little lighter. The taste is sweet, spicy with a slightly bitter aftertaste. The smell is pleasant, fragrant. Microscopic analysis: epidermis of a leaf blade is covered with multicellular hairs and glands. The cells of the upper epidermis are with thin, sinuous walls, few stomata, anisocytic type. Many simple hairs of different thickness and length. The cells of the lower epidermis have sinuous walls and stroke cuticle, many stomata. The anatomical structure of the blade is amfistomatic, dorsiventral. On cross cuts the petiole is oval, with a small notch on the adaxial side and with small side wings. The main area of the petiole takes parenchyma. The leading system of the petiole consists of five rounded vascular bundles: one central, two lateral of about the same size and two small, located closer to the wings of the petiole. Bundles are collateral, with a small area of the phloem, small, without the mechanical elements. The epidermis of a petiole is with hairs and glands.

Conclusions. The main morphological and anatomical characteristics of Stevia rebaudiana (Bertoni) Hemsley leaves were found on the basis of macro and microscopic analysis, that were used during the drafting of the quality control methods project on a new herb “Stevia leaves”.