Open AccessFlower, seed, and fruit development in three Tunisian species of Polygonum: Implications for their taxonomy and evolution of distyly in Polygonaceae
Author(s) -
Maher Mahmoudi,
Fayçal Boughalleb,
Giuseppe Pellegrino,
Raoudha Abdellaoui,
Nizar Nasri
Publication year - 2020
Publication title -
plos one
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.99
H-Index - 332
ISSN - 1932-6203
DOI - 10.1371/journal.pone.0227099
Subject(s) - biology , botany , polygonaceae , stamen , perianth , ovule , bract , receptacle , polygonum , pedicel , tepal , pollen , inflorescence , ecology
Polygonum is the largest genus of Polygonaceae and 5 species are reported in Tunisia. In order to characterized flower, seed, and fruit development in Polygonum , flower and fruit of Polygonium equisetiforme (var. graecum and p eyerinhoffi ), P . aviculare and P . maritimum , collected from Tunisia, were examined. Flowers are composed of five oblong tepals. P . equisetiforme and P . aviculare have whitish-pink distylous flowers with dimorphism of style, filament and anther height, pollen diameter and stigma size. In contrast, P . maritimum shows white homostylous flowers. The floral vasculature showed that the tepals are inserted in one whorl and their traces arise independently in 3+2 manner. The eight stamens are arranged in a 5+3 manner and the staminal bundles arise independently in the two whorls. The epidermis and endothecium cells width were higher in P . maritimum and the lowest endothecium width was observed in P . aviculare . Polygonum aviculare and P . equisetiforme showed circular pollen with shallow colpi and trilobite pollen shape with deep colpi, while P . maritimum rarely showed shallow colpi. The ovule is anatropous with basal placentation in P . equisetiforme and P . aviculare and apical placentation in P . maritimum . The young seed coat was formed by an endotesta with thick-walled cells, a mesotesta and exotesta with thin-walled cells and a tegmen composed of radially elongated cells. The fruits of the studied species are trigonous with ovate-lanceolate shape. In P . aviculare , the exocarp is thicker compared to the two other species, in P . equisetiforme , the mature exocarp consists of smaller rectangular cells with narrow cavities, and in P . maritimum showed a thinner exocarpIn conclusion, P . equisetiforme and P . aviculare are a typically distylous species from the morphological point of view and we discussed the significance of heterostyly in Polygonaceae. From this first morpho-anatomical study of Polygonum species in North Africa, we can conclude mainly that there is no significant difference between P . equisetiforme var. graecum and var. p eyerinhoffi supporting a taxonomic grouping of these two varieties.