Floral morphology and anther development in diandrous orchid Paphiopedilum purpuratum with their taxonomic implications

Abstract

The taxonomy of Paphiopedilum Pfitz. has been disputed and needs more data for clarification. Floral morphology and anther development in P. purpuratum were observed using microscope and paraffin section. The results were as follows: (1) It was supported that P. purpuratum should be placed in Paphiopedilum subgenus Paphiopedilum sect. Barbata by some floral features, including a single flower, sepal white with veins, petal spotted with blackish-maroon, pouch of a lip auriculate on both sides, and a staminode lunate. (2) At the early stage, anther primordium developed into a pair of laterally juxtaposed thecae. An incomplete sterile septa was differentiated in the center of each theca, giving rise to two arc-shaped microsporangia. When anther split, the sterile septum was discomposed and degenerated resulting in a mass of sticky pollens from two pollen sacs were fused into a unit. (3) The developed anther wall consisted of an epidermis, an endothecium, a middle layer, and a tapetum, conforming to the monocotyledonous type. Both tapetum and the inner tapetum cells contained 2 nuclei. At the stage of 2-celled grains, degeneration occurred in the epidermis and tapetum layers, while the endothecium became thickened fibrously. (4) Microspore mother cells underwent a simultaneous cytokinesis resulting in microspore tetrads with varied arrangements of tetrahedral, isobilateral, and decussate types, and the meiotic activity of microspore mother cells in the same theca was obviously asynchronous and different meiosis phases could be observed. (5) Microspores produced 2-celled pollens via a mitosis, which could be retained in pollen tetrads or released as monad. Based on the data available, some key features are selected for taxonomy and conservation biology of Paphiopedilum in Cypripedioideae, including the differentiation of incomplete sterile septum, the monocotyledonous type of anther wall, the binucleated tapetum, differentiation of the inner tapetum, simultaneous cytokinesis, the sticky pollens, and so on. This study provides new information for taxonomy and conservation biology of Paphiopedilum, as well as of Cypripedioideae.

Keywords

• paphiopedilum
• cypripedioideae
• anther wall development
• microsporogenesis
• male gametogenesis
• pollen dispersal unit
• taxonomy