Anther and ovule development in Pittosporopsis and its implications for the systematics of Metteniusaceae (Metteniusales)

Authors: KONG, DONG-RUI - Ludong University; Schori, Melanie; LI, LU - Southwest Forestry University; LUO, YAN - Chinese Academy Of Sciences; HU, DECHANG - Ludong University

Submitted to: FLORA
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2022
Publication Date: 5/19/2022
Citation: Kong, D., Schori, M., Li, L., Luo, Y., Hu, D. 2022. Anther and ovule development in Pittosporopsis and its implications for the systematics of Metteniusaceae (Metteniusales). FLORA. https://doi.org/10.1016/j.flora.2022.152078.
DOI: https://doi.org/10.1016/j.flora.2022.152078

Interpretive Summary: The genus Pittosporopsis has recently been classified as a member of the family Metteniusaceae, but the reproductive details of its flowers have not been studied closely or compared to other members of the family. We studied flower buds to examine their male and female parts as they developed and found several features that are shared with other family members. Unusual features included two layers enclosing the developing egg and starch grains in the sac around the egg. The two-layered condition is shared with one other member of the family, and starch grains are known from a closely related family. As more members of the family are studied, we will learn more about patterns of floral development in the larger group of plants that includes this and related families.

Technical Abstract: Pittosporopsis Craib, previously considered a member of the Icacinaceae sensu lato (s.l.), was transferred recently to the expanded Metteniusaceae, a family of 11 genera that needs morphological reevaluation to assess possible synapomorphies given its new circumscription. We investigated the anther and ovule developmental characters of Pittosporopsis and compared them with those of other members of Metteniusaceae as well as Icacinaceae s.l. to the extent possible. These characters are important to establish morphological synapomorphies of Metteniusaceae and to provide insights into embryology of the early diverging clades of core asterids. Within the family, Pittosporopsis shares several uncommon embryological characters with both Metteniusa H. Karst. and Emmotum Ham., such as a connective with numerous tanniferous cells and two superposed ovules within one locule. The ovule of Pittosporopsis is bitegmic, the third report of this condition (after Emmotum and Quintinia Baker f.) in the recently recircumscribed campanulids. Characters not shared with other members of Metteniusaceae include an unusual outward protuberance in the anther wall derived from the division and enlargement of endothecial cells, and a hypostase connecting the embryo sac and the ovular vascular bundle. Interestingly, a hypostase is known from Bruniaceae, which is sister to the core campanulids. Although further studies are needed to fully characterize the embryology and floral development of Pittosporopsis and the other genera now placed in Metteniusaceae, our study provides new insights into the embryology of the first diverging campanulid clades.