Molecular evidence for hybridization and introgression in the neotropical coastal desert-endemic Palaua (Malveae, Malvaceae)

Recent years have seen an increasing awareness of the importance of hybridization and introgression in plant evolution. Both processes were also invoked to have had a strong impact in the evolution of Palaua, based on morphological intermediacy. Here, we used nuclear ITS and cellulose synthase DNA sequences to assess previous phylogenetic hypotheses and to uncover previously undescribed reticulate evolution in Palaua. Both nuclear regions recovered largely the same reticulate pattern, showing that interspecific crosses occurred between distantly related species of the Dissecta and Integrifolia clade. Hybridization between species occurred only in a narrow contact zone. Moreover, many sequences of Palaua dissecta were placed in the strongly divergent Integrifolia clade, a pattern that is best explained by introgression. These results support our view that the strong interannual fluctuations of humidity and habitat expansion provide opportunities for the isolation of taxa, establishment of hybrid species, and for introgression between incompletely reproductively isolated taxa following recurrent contact.     

The conserved nature and taxonomic utility of pollen morphology in Cantua (Polemoniaceae)

Pollen exine morphology of nine of the ten species of Cantua (Polemoniaceae) is examined using light and scanning electron microscopy. A total of 28 specimens of C. bicolor, C. buxifolia, C. candelilla, C. cuzcoensis, C. flexuosa, C. pyrifolia, C. quercifolia, C. volcanica, and an as yet undescribed species (Cantua sp. nov.) are examined using either fresh or herbarium material. Pollen grains are found to be spheroidal, pantoporate, and quite large; mean diameter varies from 62 to 87?μm. Mean number of pores varies from 4.5 to 21.2 and mean pore size varies from 4.86 to 12.40?μm. Pollen grains of all species have insulate semitectate sexines. This feature distinguishes the pollen of Cantua species from the remainder of the Polemoniaceae. Insulae are evenly distributed over the surface of the pollen grain, with the exception of C. flexuosa and occasionally C. buxifolia, where insulae are more sparsely and haphazardly distributed. The majority of the species examined have irregularly shaped tectal insulae, with the exception of the large rounded insulae in C. quercifolia and the elongated narrow insulae in C. volcanica. Cantua quercifolia and C. volcanica have supratectal verrucae, a possible synapomorphy. In comparison to close relatives, the pollen grains of Cantua are evolutionarily conserved, and show little variation among species.     

Pollen grain morphology of Nolana L. (Solanaceae: Nolanoideae: Nolaneae) and related genera of southern South American Solanaceae

Nolana comprises 89 species almost entirely restricted to the Atacama and Peruvian deserts. These species are adapted to the arid lomas environment of northern Chile and southern Peru, where they depend on marine fog locally known as garúa or camanchaca for their development. Recent molecular phylogenetic studies provide support for the placement of Nolana in the Solanaceae rather than Nolanaceae. Additionally, a sister relationship with the tribe Lycieae has been suggested. The pollen morphology of 111 species from 18 genera of southern South American Solanaceae was investigated under light and scanning electron microscopes in order to establish the palynological affinities of Nolana within the Solanaceae and to investigate if pollen morphology is congruent with the phylogenetic relationships and former taxonomic classification of the species of Nolana. The following genera were studied: Nolana, Cestrum, Combera, Dunalia, Fabiana, Jaborosa, Latua, Lycium (incl. Grabowskia, Phrodus), Nicandra, Nicotiana, Nierenbergia, Petunia, Physalis, Reyesia, Salpiglossis, Schizanthus, Solanum and Vestia. Two pollen types that differ in exine structure were distinguished within Nolana; these pollen types are congruent with recent phylogenetic studies, thus, we propose to reinstate Nolana sect. Sorema.     

Variation of pollen and ovule parameters among different ploidy levels ofCorydalis (Fumariaceae)

The size and number of pollen grains and ovules are compared between 20 populations of different ploidy levels in two self-incompatible species ofCorydalis (Fumariaceae), to test the presence of ploidy-related variation in these reproductive characters. In both species, higher ploidy levels are associated with larger pollen grains, ovules and corolla, but the number of pollen grains and ovules are not different between ploidy levels. The investment per flower is consequently larger at higher ploidy levels, but the flower number per individual is lower, suggesting that the mode of partition of the investment for sexual reproduction varies between different ploidy levels. InC. orthoceras, sex allocation estimated by pollen:ovule ratios in number and volume is more female-biased in polyploids than in diploids. In spite of these variations, the characters studied can not be used as indicators of ploidy level due to the large overlaps between the ploidy levels.     

The metareticulate pollen morphology of Alternanthera Forssk. (Gomphrenoideae,Amaranthaceae) and its taxonomic implications

Alternanthera (Amaranthaceae) is a diverse genus largely restricted to the American Tropics that belongs to the alternantheroid clade containing C₄ and C₃–C₄ intermediate species. This research focuses on the study of pollen characters by studying 13 species, representatives of the two major clades and subclades of Alternanthera. General palynological comparisons were conducted with light microscopy (LM), scanning electron microscopy (SEM) and with confocal laser scanning microscopy (CLSM) for exine ultrastructure. Twenty-five characters were measured and described for Alternanthera and among these, 14 pollen characters were used to discriminate pollen groups using cluster analysis and canonical analysis of principal coordinates (CAP). Pollen form and ornamentation, pores number, spines length, number of ektexinous bodies and nanospines on the ektexinous bodies on pore membranes, arrangement of nanopores and spines on structural elements, and metareticula form were taxonomically important and therefore used to construct the first palynological key to the alternantheroid clade species. Our study indicates that the seemingly subtle morphological variation of pollen is useful for recognising three main pollen types within Alternanthera. The much needed palynological terminology for describing the mesoporium in the metareticulate pollen of Amaranthaceae is provided.     

Unravelling the stylar polymorphism in Melochia (Malvaceae): reciprocity and ancillary characters

Heterostyly is a genetic polymorphism in which plant populations possess two (distyly) or three (tristyly) morphs with flowers differing reciprocally in stigma and anther height. Sex organ deployment has been described as being highly variable among and within species of several distylous taxa belonging to different taxonomic groups. However, the number of studies considering within‐species disparities is still limited. For a better overview of the existing amount of variation that can occur within and between heterostylous species, we sampled 46 populations of six Melochia spp., a style‐polymorphic genus in Cuba. We characterized the floral morphology in all populations and described a set of ancillary characters per species. All of these Melochia spp. are distylous, except for the monomorphic M. nodiflora. The S‐morph produces fewer, larger pollen than L‐morphs, and has verrucose ornamentation. The L‐morph produces reticulate pollen and has larger stigmatic papillae than the S‐morph. The monomorphic M. nodiflora shows ancillary characteristics that are similar to the L‐morph individuals in the related species. As expected, there are differences in ancillary characters among species and also dissimilarities in reciprocity among and within species of Melochia. Our results highlight the importance of considering intraspecific variation in the morphometric characterization of heterostylous taxa. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 176 , 147–158.     

Pollen morphology in the genus Coffea (Rubiaceae) and its taxonomic significance

The pollen morphology of 38 representative species and varieties within the genus Coffea L. is described. Eight pollen types, placed in two major groups, have been identified on the basis of the number of colpi, colpus characteristics, exine morphology and pollen size. Differences in pollen structures of the species studied do not correspond to present taxonomic groupings, but support a current proposal to place some of the species in the genus Paracoffea Leroy. Among the four sections in the genus, the section Eucoffea contains a high degree of pollen polymorphism.     

Phytogeographical data and modern pollen rain of the puna belt in southern Peru (Nevado Coropuna, Western Cordillera)

Aim To improve knowledge of the distribution of species and modern pollen dispersal in the puna vegetation belt (central Andes) for palaeoenvironmental analysis and reconstructions. Location Puna belt, Nevado Coropuna, Western Cordillera, Peru. Methods The vegetation facies and belts of the area were mapped by remote sensing using a March 1998 SPOT4 image. This was complemented by the interpretation of aerial photographs, by field sampling, and by the identification of plants. Data from 1940 to 1994 from the Peruvian meteorological station network were modelled to characterize the relationship between climate and vegetation. Twenty‐four soil‐surface samples were collected in the various vegetation facies identified on the map, and standard palynological techniques were applied to analyse these samples. A principal components analysis was performed on the pollen data set. Results The map shows three bioclimatic belts and seven facies in the puna sensu lato, and identifies the main plants that are characteristic of each bioclimatic area. The pollen results fit the vegetation facies and belts, including the plant species of the distinct facies that are well represented in the pollen assemblages. The mesotropical belt is characterized by the predominance of Asteraceae‐type Ambrosia; the supratropical belt shows significant frequencies of Asteraceae‐type Senecio; the orotropical belt is characterized by high frequencies of Apiaceae and includes Polylepis woodland and peat bogs; and the cryorotropical belt shows significant frequencies of Asteraceae‐type Senecio and Apiaceae. Main conclusions The pollen grains of the plants that grow on the puna sensu lato are generally entomophilous and are therefore not transported far from their plant source. The distinct bioclimatic facies and belts identified by the cartography can thus be well distinguished by their pollen production and deposition. We were therefore able to characterize the relationship between pollen, vegetation and climate that can be used for palaeoenvironmental reconstructions. An altitudinal pollen gradient on the western slopes of the central Andes was revealed by the pollen study, with the succession of Asteraceae‐type Ambrosia (1800–2200 m), Malvaceae (2700–3300 m), Asteraceae‐type Senecio (3500–4100 m) and Apiaceae (above 4600 m).     

Change in nuclear DNA content and pollen size with polyploidisation in the sweet potato (Ipomoea batatas,Convolvulaceae) complex

• Genome size evolution and its relationship with pollen grain size has been investigated in sweet potato (Ipomoea batatas), an economically important crop which is closely related to diploid and tetraploid species, assessing the nuclear DNA content of 22 accessions from five Ipomoea species, ten sweet potato varieties and two outgroup taxa.
• Nuclear DNA amounts were determined using flow cytometry. Pollen grains were studied using scanning and transmission electron microscopy.
• 2C DNA content of hexaploid I. batatas ranged between 3.12–3.29 pg; the mean monoploid genome size being 0.539 pg (527 Mbp), similar to the related diploid accessions. In tetraploid species I. trifida and I. tabascana, 2C DNA content was, respectively, 2.07 and 2.03 pg. In the diploid species closely related to sweet potato e.g. I. ×leucantha, I. tiliacea, I. trifida and I. triloba, 2C DNA content was 1.01–1.12 pg. However, two diploid outgroup species, I. setosa and I. purpurea, were clearly different from the other diploid species, with 2C of 1.47–1.49 pg; they also have larger chromosomes. The I. batatas genome presents 60.0% AT bases.
• DNA content and ploidy level were positively correlated within this complex. In I. batatas and the more closely related species I. trifida, the genome size and ploidy levels were correlated with pollen size. Our results allow us to propose alternative or complementary hypotheses to that currently proposed for the formation of hexaploid Ipomoea batatas.

     

Microsporogenesis, microgametogenesis and pollen morphology of Passiflora spp. (Passifloraceae)

Microsporogenesis, microgametogenesis and pollen morphology of six species of genus Passiflora L. belonging to three subgenera ( Passiflora , Dysosmia , Decaloba ) were studied with light and scanning microscopy; P. caerulea was also examined with transmission microscopy. The tapetum is secretory, microspore tetrads are tetrahedral and pollen grains are two-celled when shed. Small Ubisch bodies are attached to a peritapetal membrane; they are a product of tapetal activity and the rough endoplasmic reticulum (ERr) appears to be involved in their origin. The pollen grains of all the species are subspheroidal, zonocolpate, geminicolpate. Each pair of colpi anastomoses at the poles. The exine is semitectate, reticulate, heterobrochate. The muri are simplibaculate, wavy. The lumina have clavate bacula of varying height. The colpus structure is similar to that of the lumina but generally with fewer and smaller bacula. Lumina size and amount of bacula inside the lumina vary between subgenera. The grains from subgenera Passiflora and Dysosmia differ from those of Decaloba in their size and number of colpi. The pollen and microsporangium morphology of the species of subgenera Passiflora and Dysosmia are more similar than those of subgenus Decaloba . The results are discussed in relation to the current taxonomic classification.  © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society of London , 2002, 139 , 383–394.     

Patterns and sources of variation in pollen deposition and pollen tube formation in flowers of the endemic monoecious shrub Cnidoscolus souzae (Euphorbiaceae)

Pollen deposition and pollen tube formation are key components of angiosperm reproduction but intraspecific variation in these has rarely been quantified. Documenting and partitioning (populations, plants and flowers) natural variation in these two aspects of plant reproduction can help uncover spatial mosaics of reproductive success and underlying causes. In this study, we assess variation in pollen deposition and pollen tube formation for the endemic monoecious shrub Cnidoscolus souzae throughout its distribution range in Mexico, and determine how this variation is structured among populations, plants and flowers. We also infer the relative importance of pollen quantity and quality in determining pollination success in this species. While we found no evidence suggesting that pollen receipt limits C. souzae reproduction across 19 populations, we did find extensive variation in pollen load size and pollen tube number per flower. Total variation in pollen receipt and pollen tube number was mostly explained by intra‐individual and among‐population variance. Furthermore, pollen load size had a stronger effect on the number of pollen tubes at the base of the style than pollen germination rate, suggesting that pollen quantity may be more important than quality for pollen tube success in C. souzae. Our results suggest that both small within‐plant flower differences and broad‐scale differences in community attributes can play an important role in determining pollination success. We emphasise the need to evaluate patterns and sources of variation in pollen deposition and pollen tube formation as a first step in understanding the causes of variation in pollination success over broad spatial scales.     

A taxonomic revision and pollen morphology of the genus Dendrokingstonia (Annonaceae)

The genus Dendrokingstonia (Annonaceae) is taxonomically revised and palynologically studied. Three species are recognized, one of which, D. gardneri , is described as new to science. One new combination, D. acuminata , is made. The genus occurs from southern Thailand to Peninsular Malaysia and Sumatra. On the basis of macromorphology and pollen characters, it is considered to be related to Monocarpia. Both genera show a combination of macromorphological characters that is rare in the family, i.e. considerably enlarged stigmas, leaves with percurrent tertiary veins, a highly reduced number of carpels per flower and relatively large monocarps with a thick, hard wall. Scanning and transmission electron microscopy show that the pollen grains of Dendrokingstonia and Monocarpia are monosulcate monads with a columellate infratectum and a more or less bulging intine at the sulcus. © 2011 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 168 , 76–90.     

Systematic relevance of pollen and orbicule characters in the tribe Hillieae (Rubiaceae)

Pollen and orbicule morphology of 26 species in the tribe Hillieae is described based on observations by light, scanning and transmission electron microscopy. Pollen and orbicule characters are critically evaluated and discussed in the context of existing hypotheses of systematic relationships within the tribe. Pollen is 3-zonocolporate with a perforate, microreticulate, reticulate or eutectate sexine. In the two species of Blepharidium , however, the pollen has one, four or five apertures. These pollen morphological data were incorporated into an existing macromorphological matrix of the group and cladistically analysed. The resulting phylogenies indicate that it may be appropriate to reduce Cosmibuena to a subgenus of the genus Hillia , while Blepharidium should be removed from Hillieae because of the deviating pollen type that is unique to the Rubiaceae. All species investigated produce orbicules, which are mostly spherical and possess an electron-lucent core that is sometimes characteristically flattened.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 146 , 303−321.     

Pollen morphology of Adenandra (Rutaceae: Diosminae) and its taxonomic implications

The pollen morphology of Adenandra Willd. (Rutaceae: Diosminae) was investigated to determine its taxonomic significance. Pollen of 27 of the 30 infrageneric taxa (representing 16 of the 18 species) was investigated by LM, SEM and TEM. Adenandra differs from all other Diosminae in having 4-colporate rather than 3-colporate pollen grains. This supports the alleged monophyletic status of the genus. Exine morphology and structure, however, is extremely diverse considering the size of the genus, with eight distinct pollen types and four subtypes being discerned. In some members the grains have uniform macroreticulate, striate or striato-reticulate sculpturing, whereas in others the poles have striate, striato-reticulate or reticulate-perforate sculpturing with various types of reticulate or rugulate sculpturing at the mesocolpia. Taxonomic groupings revealed by the pollen characters suggest elationships between taxa that were not previously apparent. It is suggested that evolutionary diversification among species of Adenandra is often more strikingly reflected by pollen morphology than by macromorphology, hence the eurypalynous state of the genus.     

Comparative pollen morphology of Glechoma and Marmoritis (Nepetinae,Lamiaceae)

Abstract The pollen morphology of 13 taxa (34 specimens) of the genera Glechoma L., and Marmoritis Benth. was investigated in detail using light, scanning electron, and transmission electron microscopy. Pollen grains of all studied taxa are small to large in size (P= 32.5–60.4 μm, E= 20.2–50.5 μm), prolate‐spheroidal to prolate in shape and mostly hexacolpate (the amb more or less circular or rarely ellipsoid) with granular membranes. The sexine ornamentation of Glechoma is bireticulate; the muri of the primary reticulum are irregularly circled, and lumen size is short. In contrast, the sexine surfaces of the Marmoritis pollen tend to more elongate or wider at the muri of the primary reticulum than those of the Glechoma. The pollen wall stratification of selected taxa (three from Glechoma and one from Marmoritis) is characterized by unbranched columellae, and continuous or distinctly discontinuous endexine based on transmission electron microscopy observation. The results of Glechoma and Marmoritis reveal rather similar pollen morphological features, however, fine details of sexine ornamentation are characteristic to differentiate the pollen taxa. Although these differences may be useful in establishing the taxonomic boundary between two genera, they are too weak to segregate diagnostic characters.     

Comparative pollen morphology of Glechoma and Marmoritis(Nepetinae,Lamiaceae)

The pollen morphology of 13 taxa(34 specimens)of the genera Glechoma L.,and Marmoritis Benth.was investigated in detail using light,scanning electron,and transmission electron microscopy.Pollen grains of all studied taxa are small to large in size(P = 32.5-60.4μm,E = 20.2-50.5μm),prolate-spheroidal to prolate in shape and mostly hexacolpate(the amb more or less circular or rarely ellipsoid)with granular membranes.The sexine ornamentation of Glechoma is bireticulate; the muri of the primary reticulum are irregularly circled,and lumen size is short.In contrast,the sexine surfaces of the Marmoritis pollen tend to more elongate or wider at the muri of the primary reticulum than those of the Glechoma.The pollen wall stratification of selected taxa(three from Glechoma and one from Marmoritis)is characterized by unbranched columellae,and continuous or distinctly discontinuous endexine based on transmission electron microscopy observation.The results of Glechoma and Marmoritis reveal rather similar pollen morphological features,however,fine details of sexine ornamentation are characteristic to differentiate the pollen taxa.Although these differences may be useful in establishing the taxonomic boundary between two genera,they are too weak to segregate diagnostic characters.     

Effects of sequential pollination on the success of "fast" and "slow" pollen donors in Hibiscus moscheutos (Malvaceae)

Competition among pollen grains for the chance to fertilize ovules typically involves two stages: arrival times on stigmas and/or the growth of pollen tubes through styles. In a previous study of Hibiscus moscheutos, we found that individual pollen donors often differed in pollen tube competitive ability. Here we determined whether short delays in pollen arrival time altered the average success of "fast" and "slow" pollen donors when both types of pollen experienced the same delays. Hand-pollination experiments were carried out using four pairs of pollen donors that differed in competitive ability. We allowed delays of 15 or 30 min between the first and second pollen donor and then determined seed paternity using allozyme markers. The second donor typically sired fewer seeds than pollen that arrived earlier, but, contrary to expectation, "faster" pollen did not always sire significantly more seeds than "slower" pollen when each was applied after delays of the same duration. In two of the four pairs of donors, differences that were seen following simultaneous pollinations disappeared when each type of pollen was applied following identical delays of 15 or 30 min. This unexpected response suggests that the dynamics of pollen tube competition are more complex than anticipated.     

Pollen grain morphology supports the taxonomical discrimination of Mediterranean oaks (Quercus,Fagaceae)

The exine architecture and some quantitative parameters (polar and equatorial axes and their ratio) of pollen grains allow a clear discrimination between groups of Mediterranean oak species. For the differentiation of species within groups only the quoted parameters prove useful.     

Effects of soil phosphorus on pollen production,pollen size,pollen phosphorus content,and the ability to sire seeds in Cucurbita pepo (Cucurbitaceae)

To determine the effects of soil phosphorus on pollen production, pollen grain size, phosphate concentration per pollen grain, and the siring ability of pollen, two cultivars of the common zucchini (Cucurbita pepo) were grown under two soil phosphorus conditions in an experimental garden. Overall, soil phosphorus availability had a significant effect on reproductive output through the female function and on traits affecting the male function of plants (staminate flower production, pollen production per flower, and pollen grain size). In addition, pollen produced by plants in the high phosphorus soils had a higher phosphate concentration than pollen produced by plants in the low phosphorus soils. A pollen mixture experiment revealed that pollen produced by plants in the high phosphorus treatment sired significantly more seeds than pollen produced by plants in the low phosphorus treatment. This study showed that growing conditions such as soil phosphorus can influence the size of a pollen grain and its chemical composition, which, in turn, can affect its ability to sire mature seeds.