Evolution of Angiosperm Pollen: 8. Lamiids

Lamiids, a clade composed of approximately 15% of all flowering plants, contains more than 50,000 species dispersed across 49 families and eight orders (APG IV, 2016). This paper is the eighth in a series that analyzes pollen characters across angiosperms. We reconstructed a maximum likelihood tree based on the most recent phylogenetic studies for the Lamiids, comprising 150 terminal genera (including six outgroups) and covering all eight orders and 49 families within the clade. To illustrate pollen diversity across the Lamiids, pollen grains from 22 species (22 genera in 14 families) were imaged under light, scanning, and transmission electron microscopy. Eighteen pollen characters that were documented from previous publications, websites, and our new observations were coded and optimized onto the reconstructed phylogenetic tree using Fitch parsimony, maximum likelihood, and hierarchical Bayesian analysis. Pollen morphology of the Lamiids is highly diverse, particularly in shape class, pollen size, aperture number, endoaperture shape, supratectal element shape, and tectum sculpture. In addition, some genera show relatively high infrageneric pollen variation within the Lamiids: i.e., Coffea L., Jacquemontia Choisy, Justicia L., Pedicularis L., Psychotria L. nom. cons., Sesamum L., Stachytarpheta Vahl, and Veronica L. The plesiomorphic states for 16 pollen characters were inferred unambiguously, and 10 of them displayed consistent plesiomorphic states under all optimization methods. Seventy-one lineages at or above the family level are characterized by pollen character state transitions. We identified diagnostic character states for monophyletic clades and explored palynological evidence to shed light on unresolved relationships. For example, palynological evidence supports the monophyly of Garryales and Metteniusaceae, and sister relationships between Icacinaceae and Oncothecaceae, as well as between Vahliales and Solanales. The evolutionary patterns of pollen morphology found in this study reconfirm several previously postulated evolutionary trends, which include an increase in aperture number, a transition from equatorially arranged apertures to globally distributed ones, and an increase in exine ornamentation complexity. Furthermore, there is a significant correlation between pollen characters and a number of ecological factors, e.g., pollen size and pollination type, pollen ornamentation and pollination type, and shape class and plant growth form. Our results provide insight into the ecological, environmental, and evolutionary mechanisms driving pollen character state changes in the Lamiids.

Evolution of Angiosperm Pollen. 7. Nitrogen-fixing Clade

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.

Pollen morphology in Lyperia (Scrophulariaceae) and related taxa with a multivariate analysis of the major patterns of pollen character variation in tribe Manuleae

The pollen of all six species of Lyperia (Scrophulariaceae, tribe Manuleae) was investigated by light microscopy and scanning electron microscopy of whole and fractured grains. Pollen grains in Lyperia antirrhinoides (L.f.) Hilliard, Lyperia formosa Hilliard, Lyperia tenuiflora Benth., and Lyperia violacea (Jarosz) Benth. differed from those in Lyperia tristis (L.f.) Benth. and Lyperia lychnidea (L.) Druce in number and length of colpi, sculpturing of the colpus margin, reduction of apocolpial lumina size, reduction of exine thickness toward the colpi, ornamentation of the outer nexine surface, arrangement of columellae beneath the muri, direction of cross-sectional compression in elliptical muri, and relative dimensions of the muri and columellae. Pollen grains from 50 representative species of the putatively related genera Sutera and Jamesbrittenia were also examined. Correlations among quantitative pollen characters of tribe Manuleae and the Sutera complex were investigated by principal components analysis. Morphological similarities in the pollen of Lyperia, genera of the Sutera complex, and other Manuleae were summarized by ordination of the principal components data and (or) cluster analysis. The pollen grains of L. lychnidea and L. tristis differed from those of other Lyperia and stood apart from those of Jamesbrittenia, Sutera, and all other Manuleae. Pollen morphology in Sutera and Jamesbrittenia intergrades with that in tricolporate species of Lyperia.Key words: pollen morphology, Scrophulariaceae, Lyperia, Jamesbrittenia, Sutera.

A biometrie and taxonomic study of pollen character variation in Berendtiella and Hemichaena (Scrophulariaceae)

The pollen grains of Berendtiella and Hemichaena are single, isopolar, and tricolporate with a microreticulate to reticulate sexine 2. Intra- and inter-specific variability in pollen characters are assessed statistically, and preliminary evaluation of the taxonomic utility of these data is presented. The bearing of the pollen evidence on proposed intratribal categories and the transfer of the genera from the tribe Scrophularieae (Cheloneae) to the tribe Mimuleae are discussed. The proposed close relationship between the genera and the transfer of Diplacus rugosa to Berendtiella are consistent with the pollen data, but suggested affinities between Berendtiella and Diplacus clearly are not. The grains of Berendtiella and Hemichaena resemble the type II pollen of Mimulus, and the uniformity of pollen morphology in members of the Mimuleae other than Mimulus lends support to the recognition of segregate genera in the latter palynologically diverse genus.