Comparative Ontogeny of Hermaphrodite and Pistillate Florets in Helianthus annuus L. (Asteraceae)

Aslıhan Çeti̇nbaş,Meral Ünal

doi:10.15835/nsb427576

Abstract

The inflorescence of Helianthus annuus L. has two types of flowers (or florets) on a single capitulum; central hermaphrodite disc florets and peripheral pistillate ray florets. In both florets, reproductive development starts with the conversion of apical meristem into floral meristem that will produce floral organ primordia. The only difference between hermaphrodite and pistillate florets in apical meristem stage is that apical meristem of the pistillate florets is not as apparent and curvaceous as apical meristem of the hermaphrodite florets. The differentiation of apical meristem into floral meristem is in the same progress in both florets. In hermaphrodite florets, flower organs; petals, stamens and carpels develop from floral meristem. Differentiation of five petal primordia takes place in the same way in both florets. Firstly filament and then anther differentiates in a stamen. Two carpel primordia appear below the stamen primordia in hermaphrodite florets. In following stages, carpel primordia are lengthened and formed inferior ovary, style, stigma respectively. In pistillate florets, flower organs; petals and carpels develop from floral meristem. They pass directly from the periant initiation to the start of carpel formation. Stamen primordia don’t appear and the further development of carpel primordia stops in a short time, as a result, stigma and style do not exist in pistillate florets. However, an inferior ovary with no ovule forms. In the capitulum of hermaphrodite florets, the development takes place in a centripetal manner; it starts firstly on the outermost whorl, and it proceeds towards inner whorl. However, this is not the case in pistillate florets.

Highlights

Helianthus annuus is a member of Asteraceae (Compositae), which is the largest family of flowering plants, with approximately 1620 genera and more than 23.600 species (Anderberg et al, 2007)
Flower organs; sepal, petal, stamen and carpel develop from floral meristem (Atsmon and Galun, 1960; Malepszy and Szczytt, 1991), but further development of stamen or pistil is selective, resulting in unisexual flowers (Haughn and Somerville, 1988; Rastogi and Sawhney, 1988)
The purpose of this study is to find out the comprehensive description of hermaphrodite and pistillate florets ontogeny

Summary

Introduction

Helianthus annuus is a member of Asteraceae (Compositae), which is the largest family of flowering plants, with approximately 1620 genera and more than 23.600 species (Anderberg et al, 2007). The family Asteraceae is characterised by a capitulum which is a specialised indeterminate inflorescence containing one to hundreds of flowers (or florets) (Harris, 1999). The inflorescence of H. annuus has two types of florets on a single capitulum; hermaphrodite and pistillate. The outer whorl is defined by pistillate ray florets (Heiser, 1976; Hurd et al, 1980). The remainder of the capitulum is filled with hermaphrodite, disc florets (Frankel et al, 1977; McGregor, 1976; Knowles, 1978). Flower organs; sepal, petal, stamen and carpel develop from floral meristem (Atsmon and Galun, 1960; Malepszy and Szczytt, 1991), but further development of stamen or pistil is selective, resulting in unisexual flowers (Haughn and Somerville, 1988; Rastogi and Sawhney, 1988)

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