FLORAL STRUCTURE AND DEVELOPMENT REVEAL PRESENCE OF PETALS IN PHYLLANTHUS L. (PHYLLANTHACEAE)

• Published in: International journal of plant sciences Vol. 177; no. 9; pp. 749 - 759
• Main Authors: Gama, Thália S. S., Cordeiro, Inês, Demarco, Diego
• Format: Journal Article
• Language: English
• Published: Chicago University of Chicago Press 01-11-2016; University of Chicago, acting through its Press
• Subjects: Breynia; Flowers & plants; Genetics; Morphology; Phyllanthus; Phyllanthus urinaria; flower development; Phyllanthaceae; perianth; corolla; ontogeny
• ISSN: 1058-5893; 1537-5315
• DOI: 10.1086/688639

Premise of research. Phyllanthus is a pantropical genus and the largest in Phyllanthaceae with a wide diversity of habits and floral morphologies. The flowers are considered monochlamydeous, but some divergences are found in the literature. The aim of this study was to investigate the floral structure of Phyllanthus urinaria based on ontogenetic, structural, and vascular analyses.
Methodology. Flowers and buds of P. urinaria were embedded in Paraplast and sectioned using a rotatory microtome for analysis under LM. SEM was performed for additional structural and ontogenetic data.
Pivotal results. The primordia of the sepals are the first structures to be formed in a counterclockwise direction, followed by the petals, which arise in a clockwise direction. Nectaries are formed on the base of the corolla in the staminate and pistillate flowers; then, the two perianth whorls merge, fusing at the base of the adult flowers. The three stamens have filaments postgenitally fused and free anthers. The ovary has three carpels congenitally connate with two ovules hemitropous with one long nucellar beak per locule and styles partially fused.
Conclusions. Our results demonstrate for the first time the petaliferous nature of the inner whorl of the perianth in Phyllanthus, based on ontogenetic and anatomical evidence. The presence of a perianth with sepals and petals is a possible synapomorphy of the clade formed by Phyllanthus sect. Emblica + Phyllanthus sect. Urinaria and Breynia, Glochidion, and Sauropus, now under Phyllanthus in the current phylogenetic circumscription of the tribe Phyllantheae.