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Abstract Pollen, the microgametophyte of seed plants, has an important role in plant reproduction and, therefore, evolution. Pollen is variable in, for example, size, shape, aperture number; these features are particularly diverse in some plant taxa and can be diagnostic. In one family, Boraginaceae, the range of pollen diversity suggests the potential utility of this family as a model for integrative studies of pollen development, evolution and molecular biology. In the present study, a comprehensive survey of the diversity and evolution of pollen from 538 species belonging to 72 genera was made using data from the literature and additional scanning electron microscopy examination. Shifts in diversification rates and the evolution of various quantitative characters were detected, and the results revealed remarkable differences in size, shape and number of apertures. The pollen of one subfamily, Boraginoideae, is larger than that in Cynoglossoideae. The diversity of pollen shapes and aperture numbers in one tribe, Lithospermeae, is greater than that in the other tribes. Ancestral pollen for the family was resolved as small, prolate grains that bear three apertures and are iso‐aperturate. Of all the tribes, the greatest number of changes in pollen size and aperture number were observed in Lithospermeae and Boragineae, and the number of apertures was found to be stable throughout all tribes of Cynoglossoideae. In addition, the present study showed that diversification of Boraginaceae cannot be assigned to a single factor, such as pollen size, and the increased rate of diversification for species‐rich groups (e.g.Cynoglossum) is not correlated with pollen size or shape evolution. The palynological data and patterns of character evolution presented in the study provide better resolution of the roles of geographical and ecological factors in the diversity and evolution of pollen grains of Boraginaceae, and provide suggestions for future palynological research across the family. 

Abstract Monte Carlo simulation is employed using the bond‐fluctuation model (BFM) to explore the role of free‐monomer model on surface‐initiated controlled polymerization from flat substrates. Three free‐monomer models differ in two aspects: 1) their extent of excluded volume interactions between free‐monomer/polymer segments and 2) monomer availability (finite or infinite) during the simulation. In the explicit monomer (EM) model, free‐monomers behave as a single BFM‑type units. In the phantom monomer (PM) model, free‐monomers act analogously to those in the EM model but lack excluded volume interactions with the growing polymers. In the implicit monomer (IM) model, no explicit monomers are included in the simulation box; the polymers can grow as long as space is available near active chain‐ends. It is found that the breadth of the molecular weight distribution of the grown polymers decreases from EM, to PM, to IM models. With the EM model, free‐monomers are excluded from the near‐surface region, while with the PM model they are not. Due to its excluded volume interactions, the EM model tends to compress the brush against the substrate. Finally, the relaxation of the shape of a polydisperse brush after the polymerization reaction ends has been reported. 

PREMISE: Distyly, a plant breeding system characterized by two floral morphs that have reciprocal positioning of anthers and stigmas, is known from at least 27 angiosperm families, making it an excellent example of convergent evolution. The various manners in which patterns of floral development produce the distinct anther and stigma heights in each morph remain largely unexplored from developmental and evolutionary perspectives. METHODS: In 15 species representing at least 12 origins of distyly, heights and lengths of floral organs in each morph throughout development were examined using light microscopy. Patterns of floral organ development were determined and compared among species. Family-level phylogenies of distylous species and relatives were reconstructed, and patterns of ancestral herkogamy were resolved. RESULTS: Differences in floral development between morphs resulted in 12 patterns leading to the anther and stigma positions characterizing distyly. Distylous species evolved from ancestors with different types of herkogamy, with approach herkogamy and lack of herkogamy resolved most frequently. CONCLUSIONS: Seven of the 12 patterns of floral development are known from only one species, with three other patterns described among pairs of close relatives. The most common pattern of floral development, described from at least seven genera, involves for anther heights, distinct intermorph growth rates and for stigma heights, growth rates that differ between morphs only during later development. This pattern is common among subclass Lamiidae, suggesting canalized development within the taxon. Among distylous species, the same type of ancestral herkogamy can give rise to different patterns of floral development. KEY WORDS breeding system; convergent evolution; distyly; herkogamy; heterostyly; phylogenetics. 

The Chihuahuan Desert includes many endemic angiosperm species, some having very restricted geographic ranges. One of these species is Oreocarya crassipes (I. M. Johnst.) Hasenstab & M. G. Simpson, an endangered distylous gypsophile from the Trans-Pecos region in southern Brewster County, Texas, USA. The species is known from 10 populations, and this small number of populations, human development in the area, a distylous breeding system, and edaphic requirements threaten the long-term viability of the species. Using both hundreds of single nucleotide polymorphisms identified via tunable genotyping-by-sequencing (tGBS) and 10 microsatellite loci, patterns of genetic diversity, demography, selection, and migration were examined for 192 individuals from four populations of O. crassipes. From the sampled individuals, two populations (clusters) were identified via multiple methodologies and with both types of data. With SNP data, population substructure was further resolved among one of these populations to identify two distinct groups of individuals. Multiple individuals recognized as having mixed ancestry, along with Fst values and AMOVA results, provide evidence of genetic exchange among populations, which is less common for gypsophiles than non-gypsophiles, and the rate of migration among populations has been increasing recently. The Fst values for O. crassipes are more similar to those of other rare species than to other gypsophiles. Additionally, while distyly specifically does not necessarily impact the population genetics of the species, allogamy, which is facilitated by distyly, seems to have played a role in the genetic structure of O. crassipes.