Anther Wall Development, Microsporogenesis, and Microgametogenesis inAbolbodaandOrectanthe: Contributions to the Embryology of Xyridaceae (Poales)

Abstract

Editor: Patrick S. Herendeen Premise of research. Xyridaceae includes two subfamilies with a total of five genera. Xyridoideae has only the single genus Xyris, and Abolbodoideae includes the remaining genera. The inter-and intrafamilial relationships among Xyridaceae have not yet been clarified, and this study therefore aimed to investigate the anther wall and pollen grain development in Abolboda and Orectanthe species, searching for characters that can be used in taxonomic and phylogenetic analyses.Methodology. Anthers from flowers at different stages of development were examined using both LM and SEM.Pivotal results. All studied species present the following: monocotyledonous type of anther wall development, single-layered endothecium with band-like thickenings in the mature anther, single ephemeral middle layer, multilayered and plasmodial tapetum, successive microsporogenesis, and spherical inaperturate pollen grains. Characteristics such as reduced type of anther wall development, single-layered and secretory tapetum with uninucleate or binucleate cells, and elliptical sulcate pollen grains with a reticulate exine are present in Xyris and differentiate this genus from Abolboda and Orectanthe. The characteristics reported for Xyris are also present in Mayacaceae, which used to form the xyrid clade of Poales with Eriocaulaceae and Xyridaceae. Abolboda and Orectanthe share with Eriocaulaceae the monocotyledonous type of anther wall development with an ephemeral middle layer, an endothecium with band-like thickenings, and pollen grain exine with projections. The presence of a multilayered tapetum is exclusive to Abolboda and Orectanthe among the Xyridaceae and also among the Poales.Conclusions. The embryological characteristics support the division of Xyridaceae into two subfamilies. In contrast with the megasporogenesis and megagametogenesis, the microsporogenesis and microgametogenesis characteristics were quite variable within the xyrid clade, with successive microsporogenesis being the only characteristic shared by Xyridaceae, Eriocaulaceae, and Mayacaceae.

Evolution and diversity of the angiosperm anther: trends in function and development

“…Both secretory and plasmodial types are common in dicots and monocots. The secretory tapetum probably had several independent origins (Oriani and Scatena 2015) and is regarded as the most primitive form (Furness and Rudall 1998;Pacini et al 1985). The early divergent angiosperm Amborella has a secretory tapetum (Tobe et al 2000), which also appears to be the most common type in primitive dicotyledons (Furness and Rudall 1998).…”

“…The tapetum is almost exclusively single layered; multilayered tapeta are very rare in angiosperms, and in monocotyledons, it has been reported only in Abolboda and Orectanthe in the Xyridaceae family (Oriani and Scatena 2015 ). The number of layers of the anther wall seems to be critical for pollen production, with changes in the tapetum being particularly detrimental, with additional tapetum layers resulting in male sterility (Cecchetti et al 2015 ; Chaubal et al 2000 , Feng and Dickinson 2010 ).…”