Embryology of Spathoglottis plicata Blume: A Reinvestigation and Additional Data

Abstract

Spathoglottis plicata Blume is very popular among terrestrial orchids because it is attractive, easy to grow and can flower all year round. The aim of this study was to reinvestigate the embryological characters using classical paraffin embedding and sectioning, along with ovule clearing and scanning electron microscopy analyses. The simultaneous cytokinesis results in decussate, isobilateral, linear, T-shaped and tetrahedral microspore tetrads. Mature pollen grains are two-celled with perforate sculpturing. The anther wall is comprised of an epidermis, two to three layers of endothecium, one layer each of middle layer and one layer of binucleate glandular tapetal cells. At anthesis, the mature anther wall is composed of epidermis and fibrous endothecium. At 9 d after pollination (DAP), the mature ovules are anatropous, bitegmic and tenuinucellate. The megaspore tetrad is linear. Development of the embryo sac conformed to the Polygonum type. The pollen tube enters the embryo sac through the micropyle (porogamy), and double fertilization is observed at 15 DAP. The zygote divides transversely to form a two-celled proembryo. The basal cell becomes the suspensor initial cell, whereas the terminal cell divides transversely to form a linear three-celled proembryo. The proembryonal tetrad is T-shaped. Embryogenesis is of the Onagrad type. The suspensor is single-celled, hypertrophied and cap-, globular- or saclike. Fruit opens at 30 DAP. Seeds are fusiform in shape with longitudinally oriented testa cells with a smooth periclinal seed surface and straight anticlinal walls. The mature globular embryo is acotyledonous and lacks differentiation. Furthermore, cleavage polyembryony gives rise to twin embryos.