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The Transfer of Dolichos junodii to Nesphostylis (Leguminosae)
Abstract
Evidence from gross morphology and pollen morphology is used to show that the anomalous species Dolichos junodii (Harms) Verde, does not belong in Dolichos L. A proposal is made to transfer the species to the genus Nesphostylis Verde., with which it shares many characters. A new combination is proposed: Nesphostylis junodii (Harms) Munyenyembe & F. A. Bisby comb. nov.
... The pollens of Nesphostylis bracteata were triporate, spheroidal and reticulate with diameter ranging from 66-74 µm (Fig. 1d). Reticulate pollen grains are also found in Dolichos, a genus related to Nesphostylis (Munyenyembe and Bisby 1997). ...
Chromosome counts were carried out in root tip cells of Nesphostylis bracteata(Fabaceae),
an endemic legume of Western Ghats, India. A diploid number of 2n =20 is reported here for the first
time. The karyotype was found to be symmetrical with all chromosomes having a median region
centromere. The chromosome length ranged from 1.50 to 2.69 µm.
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.
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