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SEM photographs of orbicules and pollen grain of Group 4: O. hypsophila (A–D), O. nahuelhuapiensis (E–H), O. pycnophylla (I–L). General view of the orbicules: A, E, I. Scale bar = 5 µm. General views of the pollen grain: B, F, J. Scale bar = 10 µm. Detail of the colpus: C, G, K. Scale bar = 5 µm. Detail of the reticule: D, H, L. Scale bar = 2 µm.
Source publication
Orbicule characteristics and pollen morphology were studied using light microscopy and scanning electron microscopy with 13 species of Oxalis section Alpinae, endemic to South America. Orbicules are either homogeneous or heterogeneous in size; surface smooth or with punctuations; margin smooth, lobed, or wavy; rounded, oblong, or irregular shapes;...
Contexts in source publication
Context 1
... pycnophylla - Figures 3I-3L. Orbicules: Heterogeneous in size; rounded or oblong shape; smooth margin, surface with perforations; sometimes forming linear aggregates or branched in "Y-" to "L-shape"; "doughnut-like" orbicules present. ...
Context 2
... pycnophylla - Figures 3I-3L. Orbicules: Heterogeneous in size; rounded or oblong shape; smooth margin, surface with perforations; sometimes forming linear aggregates or branched in "Y-" to "L-shape"; "doughnut-like" orbicules present. Pollen grain: 18-24 µm in diameter; polygonal brochi; visible lumen content; granules distributed homogeneously on the colpus ...
Citations
... Studies carried out in Gentianaceae (Vinckier and Smets 2003) and Rubiaceae (Huysmans et al. 1997) report a high degree of correlation between orbicule ornamentation and the pollen grain sexine, i.e. the outer, sculptured layer of the exine. Given that the exine ornamentation of pollen grain offers useful characters for systematics, the taxonomic importance of orbicules was also considered for different taxa, such as Apocynaceae (Vinckier and Smets 2002a), Euphorbiaceae (El-Ghazaly and Chaudhary 1993), Gentianaceae (Vinckier and Smets 2003), Loganiaceae (Vinckier and Smets 2002b), Nartheciaceae (Merckx et al. 2008), Oxalidaceae Galati 2005, López andRosenfeldt 2016), and Rubiaceae (e.g. Huysmans et al. 1997, Vinckier et al. 2000, Romero et al. 2017. ...
The orbicules are tiny structures of sporopollenin that occur on the interior wall of anthers in several groups of plants, and they are associated with pollen grains and tapetal cells. Although their function remains still unresolved, they have been widely used in systematics. Rubiaceae is one of the most studied families in this aspect. However, scarce information is available about the orbicules in the tribe Spermacoceae, especially in the Spermacoce clade. The main objectives of this work were to investigate the occurrence, general morphology, evolution, and systematic utility of the orbicular characters in the Spermacoce clade. We investigated the presence/absence, size, abundance, shape, and ornamentation of orbicules in 104 specimens from 84 species in the Spermacoce clade using scanning electron microscopy (SEM). On the basis of these features, the ancestral state reconstruction analyses were performed on a custom-made phylogeny by stochastic character mapping. The orbicules are present in 38 (44%) of 84 analysed species, corresponding to 13 genera (56%) of the Spermacoce clade. Seven genera have orbicules in all analysed species, eight genera lack orbicules in all analysed species, and six genera show both presence and absence of orbicules. The absence of orbicules was estimated to be the ancestral state for the Spermacoce clade and the presence of orbicules evolved several times independently within Clade B. The absence of orbicules in the common ancestor of the Spermacoce clade can be seen as one of the independent losses that occurred during the evolutionary history of the Rubiaceae.
By using light microscopy (LM) and scanning electron microscopy (SEM), the pollen grains and foliar epidermal morphology of four species and two varieties of Egyptian Oxalis Linnaeus, 1753 belonging to three sections of the subgenus Oxalis Linnaeus, 1753 were studied. The objective was to determine the importance of pollen and foliar epidermal characters as taxonomic evidence. The current study revealed that the pollen grains of all taxa examined are monads, radially symmetric, isopolar, and of medium size; the shape varied from sub-spheroidal to subprolate. The pollen apertures were tricolpate with ornamented colpal membranes (rugulate, warty, congregated granules). Exine is semi-tectate, with micro-reticulate to reticulate ornamentation, perforate in O. debilis Kunth, 1822. The study also revealed the presence of four types of stomata: actinocytic, anisocytic, anomocytic, and an unusual 4-celled anisocytic. Both abaxial and adaxial epidermal cells were irregular or polygonal in shape, with undulate or straight anticlinal walls and semi-swollen to swollen periclinal walls with dispersed epicuticular wax. Two forms of non-glandular, unicellular trichomes were observed: short clavate and long with a tapering apex and papillate surface. The study further discussed numerical results based on combined morphological, palynological, and foliar epidermal characters. This study is the first report dealing with anatomical and palynological features of the genus Oxalis in Egypt.
Nitrogen-fixing symbiosis in root nodules is known in only 10 families, which are distributed among a clade of four orders and delimited as the nitrogen-fixing clade. As the seventh in a series that examines pollen morphological distribution and evolution in the angiosperms, this paper focuses on pollen morphological character states of the nitrogen-fixing clade. To illustrate the palynological diversity of the clade, we first examined pollen grains from 26 species with light electron, scanning electron, and transmission electron microscopy. Second, we used a reduced data matrix from Li et al. (2015) to reconstruct a maximum likelihood tree and then optimized 18 pollen character states onto the tree using Fitch parsimony, maximum likelihood, and hierarchical Bayesian inference. Finally, 12 plesiomorphic states for the nitrogen-fixing clade were inferred unambiguously under all methods, and more than 40 clades (or lineages) at or above familial level were characterized by unambiguous pollen character state changes in at least one of the optimizations. We found a number of evolutionary trends for changes in pollen character states. These include increasing grain size, increasing aperture number accompanied by concomitant changes in aperture position (from equatorial to global) and aperture shape (from colpate to colporate), and increasing complexity of tectum ornamentation. There was a strong correlation between some pollen characters (prolate shape class, lobe outline in polar view, colpate ectoaperture, lalongate and lolongate endoaperture, absent supratectal element, reticulate tectum) and insect pollination, while other pollen characters—simple aperture structure, porate ectoaperture, circular endoaperture, present and gemmate or echinate supratectal element, and imperforate tectum—were strongly correlated with wind pollination. In addition, rugulate tectum was significantly correlated with shrub habit while larger pollen size was significantly correlated with vine habit; the helophytic habitat was significantly correlated with having two apertures. Our study provides rich evidence for the phylogenetic significance of pollen morphological diversity in the nitrogen-fixing clade.
