Pollen Size Research Articles

Pollen morphology in the genus Veronica L. (Plantaginaceae) and its systematic significance

Pollen grains of 30, mainly annual, species from 134 populations of the genus Veronica (Plantaginaceae, formerly Scrophulariaceae) from the Mediterranean Region, have been studied with light and scanning electron microscopy. Three pollen types are defined based on pollen size and exine surface sculpture. In some cases within the study group pollen size can be useful in species determination. Hypothetical relationships of pollen grain size and aperture number with ploidy level, style length and corolla diameter are discussed. The ornamentation of the exine in Veronica, although generally a conservative character within the genus, gives some additional support to the most recent infrageneric classification of Veronica.

Infrageneric variability of pollen morphology in Palaua (Malveae, Malvaceae) and the taxonomic utility of quantitative pollen characters

Palaua (Malvaceae) comprises 15 species endemic to the coastal deserts of Chile and Peru. Previous molecular phylogenetic analyses have shown that this genus is monophyletic and can be subdivided into three clades. In the present study, pollen morphology of all species of Palaua was examined using light and scanning electron microscopy to determine whether it provides additional data in support of the proposed infrageneric groups. The pollen grains are spheroidal, medium to large in diameter, spinose and pantocolporate – the ectocolpi are very short. The tectum is perforate and characterised by granula. In all species the nexine is of a similar thickness in all areas of the pollen grain, while the sexine thickness varies, being notably thicker in the areas where the broad spine bases are sited (‘spine cushions’). Many of the quantitative characters have conspicuous variability, but the variability shows considerable overlap between species. Nonetheless, P. guentheri, P. inconspicua, P. malvifolia and P. modesta are united as a group by having the smallest pollen grains with the smallest apertures, the shortest spines and the shortest interspinal distance. This grouping reflects only partially the suggested infrageneric clades, although it does tend to unite the species with the smallest flowers. A possible link between reproductive resources and pollen size is also considered, as well as the influence of polyploidy. However, the taxonomic utility of these quantitative characters is weakened by species with more than one cytotype.

Especies de plantas visitadas por abejas pecoreadoras durante la inducción de polinización en melón.

El objetivo de la investigación fue determinar, a través de la identificación del polen corbicular, las diferentes especies de plantas que son visitadas por las abejas (Apis mellifera L.) durante la polinización inducida del melón (Cucumis melo L.). El trabajo se llevó a cabo en La Laguna ocalizada en los estados de Coahuila y Durango, México en la primavera del 2003. Durante los primeros 31 días de la floración del melón, un campo de seis hectáreas fue polinizada por 18 colmenas, nueve de las cuales tenía una trampa para captura de polen. El polen fue colectado dos veces por semana, pesado y congelado. Durante el año se colectaron anteras de plantas silvestres y cultivadas en floración alrededor del cultivo y en la región para preservarlas e identificar su polen usando la técnica de acetolisis. El polen corbicular, muestreado los días 5°, 9°, 12°, 20°, 24° y 31° contados a partir del inicio de la aparición de las flores estaminadas, fue procesado y contado en el microscopio óptico. El tamaño del polen fue calculado mediante la fórmula: volumen V=?a2b donde a es el eje mayor y b el eje menor y multiplicado por el número de granos de polen se obtuvo el volumen total. El polen de melón fue el 8.7 %, 9.8%, 17.6 %, 9.3 %, 28.1% y 83.5% del colectado (en base al número de granos) respectivamente en las fechas de muestreo. El porcentaje del polen de melón en base al volumen fue: 51.6%, 85.0%, 66.6 %, 84.4 %, 68.9% y 95.0% respectivamente. Se concluye que el melón fue la principal planta visitada por las abejas como fuente de polen y que las especies de plantas con mayor número de granos de polen presentes en las muestras como mezquite (Prosopis juliflora (Swartz) DC.), alfalfa (Medicago sativa L.), gobernadora (Larrea tridentata (DC) Cov.), pepino (Cucumis sativus L.), mostacilla (Sysimbrium irio L.) y sorgo (Sorghum vulgare L.) fueron especies visitadas como fuentes suplementarias de polen.

Pollen morphology of eight species of Dianthus from Xinjiang.

In the present study,the pollen morphology of eight species of Dianthus L. in Xinjiang was observed under the scanning electron microscope(SEM). In these species,the pollen grains are monad,spherical. The size of pollen grains ranges from 30.5 μm to 44.0 μm. The number of round aperture is 12 to 16. The diameter of aperture is from 4.0 μm to 7.0 μm,it has pore membrane with some thorns and exine of pollen with thorn-like and hole-like patterns,the surface with or without perforation. The size of pollen,exine ornamentation and characteristics of aperture are different to some extent among these different species. This shows their important taxonomic significances.

Floral Traits and Seed Production of Sorghum A‐, B‐ and R‐lines under Chilling Field Temperatures

AbstractIn A‐lines of sorghum (Sorghum bicolor L. Moench), seed production under field conditions with manual pollination is generally lower than that in self‐pollinated B‐lines. This may be associated with floral differences. Six pairs of A/B‐lines and four R‐lines were evaluated during 2005 and 2006 at Montecillo, State of México (2240 m altitude). Rachis length, number of primary branches and fertile flowers per panicle, 100‐seed weight, seed number, seed yield and seed set per panicle were evaluated. In the A‐lines, the pistil characteristics were also measured and in the male‐fertile lines, the size of anthers and the amount and size of viable pollen were recorded. Compared with the A‐ and B‐lines, the R‐lines exhibited significantly higher (P ≤ 0.05) numbers of flowers, seed set and seed yield per panicle and they also produced more pollen grains of larger size and with greater viability during their longer flowering period (FP). Between A‐ and B‐lines, there were differences (P ≤ 0.05) in most of the yield traits, which also interacted with year. The proportion of viable pollen in B‐ and R‐lines (75 %) was not considered to be a factor that might account for their low seed production. Chilling temperatures (3.5–8.4 °C) during the FP could have affected stigma receptivity in the three different line types and thus may have reduced seed set in the male‐fertile lines.

Induction of 2n pollen formation in Begonia by trifluralin and N2O treatments

In this study, treatments of both trifluralin (at 10, 100 and 1000 μM) and N2O (in the form of gas under pressure) were applied to Begonia flower buds to induce the formation of 2n pollen. Three male fertile species (B. cucullata, B. subvillosa var. leptotricha and B. fischeri) and two male sterile hybrids (B. schmidtiana × B. cucullata and B. subvillosa var. leptotricha × B. cucullata) were treated. Pollen size, which is related to pollen DNA content, increased after both N2O and trifluralin treatments, but the induction of large pollen was genotype dependent. Trifluralin induced large pollen only in the male fertile species, while N2O treatments induced fertile 2n pollen in the male sterile B. schmidtiana × B. cucullata. Cytological studies showed that trifluralin induced multinuclear monads that resulted in 4n gametes in stead of 2n gametes. In general, large pollen obtained after trifluralin treatments showed low germination capability, while large pollen obtained after N2O treatments retained high germination capability. Seedlings with raised ploidy level could only be obtained after crosses were performed with large pollen obtained from N2O treatments. Hence, N2O treatments are preferable to the use of trifluralin to induce 2n gametes in Begonia.

Genome size variation in Begonia

The genome sizes of a Begonia collection comprising 37 species and 23 hybrids of African, Asiatic, Middle American, and South American origin were screened using flow cytometry. Within the collection, 1C values varied between 0.23 and 1.46 pg DNA. Genome sizes were, in most cases, not positively correlated with chromosome number, but with pollen size. A 12-fold difference in mean chromosome size was found between the genotypes with the largest and smallest chromosomes. In general, chromosomes from South American genotypes were smaller than chromosomes of African, Asian, or Middle American genotypes, except for B. boliviensis and B. pearcei. Cytological chromosome studies in different genotypes showed variable chromosome numbers, length, width, and total chromosome volume, which confirmed the diversity in genome size. Large secondary constrictions were present in several investigated genotypes. These data show that chromosome number and structure exhibit a great deal of variation within the genus Begonia, and likely help to explain the large number of taxa found within the genus.

Study on Floral and Pollen Characters of Tetraploid Rice

Polyploidization is the evolution trend of many crops, and the yield increased obviously after polyploidization. The polyploidization of rice often brings “gigas” of both vegetative organs and seeds. Howevere, in rice breeding, it is required for restoring lines to have not only big anthers but also abundant pollens. People often doubt that the enlargement of the floral organ may just be enlargement of cell size in polyploid rice. So, it is of significance to study characteristics of floral organs and pollens of several tetraploid rice varieties or lines. Floral organ and pollen characteristics of Sg99012 and HN2026 were studied comparatively by stages and different ploidy levels, with the materials 9311, HD9802S, and PA64S as the control. The results showed that chromosome doubling had much more influence on floral characteristics of every lines than seeding by stages, and the tetraploids of every lines displayed “gigas”. In correlation analysis, spikelet length, spikelet width, and anther length had significant correlation; spikelet width and anther width had significant correlation, too. Both seeding by stages and chromosome doubling made the correlations of characters between every floral organ changed to some extent. Seeding by stages had little effect on pollen diameter and fertility of HN2026-4X and Sg99012-4X. But chromosome doubling increased pollen size of every lines remarkably, and also increased the pollen quantity of PMeS (polyploid meiosis stability) restoring line HN2026-4X and gene map restoring line 9311-4X remarkably, whereas only had little effect on that of sterile lines. Moreover, chromosome doubling changed pollen fertility and made the number of fertility pollen of 9311 reduced significantly, but the pollen fertility of HN2026 (PMeS restoring line) and PA64S (sterile line) almost had no change after chromosome doubling. The results showed that tetraploid restoring lines had advantage of abundant and big size pollens, and tetraploid sterile lines had the characters of big size pollens, few change of pollen quantity and stable sterile character. These results provided evidence in reproductive biology for utilizing heterosis of polyploid rice by two-line method.

Karyotypic, palynological, and RAPD study on 12 taxa from two subsections of section Idaeobatus in Rubus L. and taxonomic treatment of R. ellipticus, R. pinfaensis, and R. ellipticus var. obcordatus

Twelve taxa belonging to two subsections of section Idaeobatus in Rubus L. from southwestern China were characterized by karyotypic, palynological, and random amplified polymorphic DNA (RAPD) data as follows: (1) The 12 taxa were all diploid species (2n = 2x = 14), among which the chromosome counts for R. mesogaeus var. oxycomus, R. subtibetanus, R. ellipticus var. obcordatus, R. inopertus var. echinocalyx, and R. stans were reported for the first time; (2) All taxa except for R. ellipticus and R. pinfaensis could be distinguished from each other by karyotype, pollen morphology, and RAPD markers. Karyotypes were mainly characterized by the difference in numbers and positions of submetacentric chromosomes and chromosomes with satellited pair, the index of the karyotypic asymmetry, and the ratio of the longest to the shortest chromosome. Pollen morphology were mainly characterized by the discrepancy in specific pollen size, P/E ratio, colpi width, distance between the apices of two ectocolpi, and exine ornamentation characters. The cluster results based on RAPD markers were consistent with morphology classification except for R. pinfaensis; (3) Based on the general data of karyotypic, palynological, and RAPD, R. ellipticus var. obcordatus should be treated as a species R. obcordatus, R. ellipticus and R. pinfaensis should be combined as R. ellipticus, and it was more reasonable to place the combinants and R. obcordatus into subsection Stimulantes rather than into subsection Pungentes.

Pollen studies in Bauhinia variegata L.

Pollen grains have helped the species of plants to adapt to life on land, be able to disperse its pollen, and fertilize the female eggs to produce new seeds that would give rise to new plants. Pollen morphology is closely related to its function. Pollen grains of Bauhinia variegata were found triangular in shape with three germ pores and remained viable at 4+1oC for more than six months. Pollen size varied from 47.61-95.22 µm. Maximum pollen germination occurred in 15.0 per cent sucrose solution.

Pollen morphology supports the reinstatement of Bergera (Rutaceae)

Pollen morphology of 11 species of Murraya and Micromelum (Clauseneae: Rutaceae) was investigated using scanning electron microscopy (SEM) and palynological characters including pollen size, aperture number and exine ornamentation were evaluated. The results indicate that species in M. sect. Bergera and sect. Murraya have very distinct pollen morphology. Species in section Bergera have rugulate to foveolate exine, whereas the tectum in section Murraya is cross‐striate. This supports the redefinition of the genus Murraya, retaining only the species of section Murraya, while M. sect. Bergera is better treated as a separate genus. From the palynological point of view, it is suggested that Bergera and Murraya s.s. are not closely related, with the latter being more close to Micromelum and Merrillia, a result in accordance with phytochemical, chromosomal and molecular evidence, thus supporting the reinstatement of the generic name Bergera L.

Detailed characterization of Mirafiori lettuce virus-resistant transgenic lettuce.

Lettuce big-vein disease is caused by Mirafiori lettuce virus (MiLV), which is vectored by the soil-borne fungus Olpidium brassicae. A MiLV-resistant transgenic lettuce line was developed through introducing inverted repeats of the MiLV coat protein (CP) gene. Here, a detailed characterization study of this lettuce line was conducted by comparing it with the parental, non-transformed 'Kaiser' cultivar. There were no significant differences between transgenic and non-transgenic lettuce in terms of pollen fertility, pollen dispersal, seed production, seed dispersal, dormancy, germination, growth of seedlings under low or high temperature, chromatographic patterns of leaf extracts, or effects of lettuce on the growth of broccoli or soil microflora. A significant difference in pollen size was noted, but the difference was small. The length of the cotyledons of the transgenic lettuce was shorter than that of 'Kaiser,' but there were no differences in other morphological characteristics. Agrobacterium tumefaciens used for the production of transgenic lettuce was not detected in transgenic seeds. The transgenic T(3), T(4), and T(5) generations showed higher resistance to MiLV and big-vein symptoms expression than the resistant 'Pacific' cultivar, indicating that high resistance to lettuce big-vein disease is stably inherited. PCR analysis showed that segregation of the CP gene was nearly 3:1 in the T(1) and T(2) generations, and that the transgenic T(3) generation was homozygous for the CP gene. Segregation of the neomycin phosphotransferase II (npt II) gene was about 3:1 in the T(1) generation, but the full length npt II gene was not detected in the T(2) or T(3) generation. The segregation pattern of the CP and npt II genes in the T(1) generation showed the expected 9:3:3:1 ratio. These results suggest that the fragment including the CP gene and that including the npt II gene have been integrated into two unlinked loci, and that the T(1) plant selected in our study did not have the npt II gene. DNA sequences flanking T-DNA insertions in the T(2) generation were determined using inverse PCR, and showed that the right side of the T-DNA including the npt II gene had been truncated in the transgenic lettuce.

Influence of flower functionality and pollination system on the pollen size-pistil length relationship

Twenty-five biotically pollinated plants of the Chaco Serrano Forest (Córdoba, Argentina) were studied in order to analyze whether ‘flower functionality’ is related to the relationship between pollen size and pistil length. Because flower functionality may act on the respective mean values of pollen size and pistil length rather than on intraspecific variation in these traits, we expected (1) a high positive correlation between pollen size and pistil length in a set of sympatric species, independent of their degree of pollination specialization or generalization; and (2) no interspecific correlation between the coefficients of variation (CVs) of those traits. On the other hand, on the assumption that pollinators are influencing the variation in floral traits (e.g. in pistil length) we expected lower mean phenotypic variation of pollen size and pistil length in pollination-specialist plants than in pollination-generalist ones. A positive correlation between pollen size and pistil length was found for the set of species, but not between the CVs of these traits. This trend was maintained when pollination-specialist plants were analyzed separately, but no statistical significance was obtained for the correlation in pollination-generalist plants. Contrary to our expectations, pollination-specialist plants did not show less mean intraspecific variation in floral traits than pollination-generalist plants. Therefore, the relationship between pollen size and pistil length among species suggests that the pollination system may be of less importance as a selective force than flower functionality.

Production and Identification of Colchicine-derived Tetraploid Vaccinium darrowii and Its Use in Breeding

In Vaccinium L., most tetraploid hybrids between tetraploid cultivated highbush blueberry (V. corymbosum L.) and diploid darrow's evergreen blueberry (V. darrowii Camp) have been produced by exploiting V. darrowii's tendency to produce 2n gametes and a strong triploid block, which greatly reduces the number of triploid hybrids produced. Colchicine-derived tetraploids offer an alternative method of producing V. darrowii plants that will easily cross with tetraploid Vaccinium species. V. darrowii (2n = 2x = 24) seeds were imbibed in 0.2% aqueous colchicine solution for 24 h. The seeds were germinated and seedlings whose morphology suggested colchicine effects were selected at various stages of development. No macromorphological changes were consistently associated with chromosome doubling. However, stomatal guard cells and pollen size increased substantially as a result of chromosome doubling. Several types of plants were identified after colchicine treatment: 1) plants with a doubled LI (epidermal tissues) and LII (internal tissues) plant layers; 2) periclinal chimeras with a doubled LI layer and a normal LII; and 3) periclinal chimeras with a doubled LII layer and a normal LI. Of ≈4000 seedlings that emerged from colchicine-treated seeds, 200 were selected for further examination based on leaf and stem morphology. Of the 200, five appeared to be tetraploid in LI, LII, or both layers based on stomatal guard cell size and pollen size. Crosses between colchicine-derived V. darrowii (4x) plants and southern highbush blueberry (V. corymbosum) cultivars (4x) were successful compared with 4x–2x and 2x–4x crosses using diploid V. darrowii and tetraploid southern highbush blueberry. Stomatal guard cells and pollen screening of the colchicine-treated plants were used as indicators of doubled V. darrowii plants and periclinal chimeras. The results from the crosses between colchicine-treated V. darrowii plants and tetraploid highbush blueberry cultivars confirmed the information obtained by stomata and pollen screening.

Synthetic polyploids of Tragopogon miscellus and T. mirus (Asteraceae): 60 Years after Ownbey's discovery

In plants, polyploidy has been a significant evolutionary force on both recent and ancient time scales. In 1950, Ownbey reported two newly formed Tragopogon allopolyploids in the northwestern United States. We have made the first synthetic lines of T. mirus and T. miscellus using T. dubius, T. porrifolius, and T. pratensis as parents and colchicine treatment of F(1) hybrids. We also produced allotetraploids between T. porrifolius and T. pratensis, which are not known from nature. We report on the crossability between the diploids, as well as the inflorescence morphology, pollen size, meiotic behavior, and fertility of the synthetic polyploids. Morphologically, the synthetics resemble the natural polyploids with short- and long-liguled forms of T. miscellus resulting when T. pratensis and T. dubius are reciprocally crossed. Synthetic T. mirus was also formed reciprocally, but without any obvious morphological differences resulting from the direction of the cross. Of the 27 original crosses that yielded 171 hybrid individuals, 18 of these lineages have persisted to produce 386 S(1) progeny; each of these lineages has produced S(2) seed that are viable. The successful generation of these synthetic polyploids offers the opportunity for detailed comparative studies of natural and synthetic polyploids within a nonmodel system.

Pollination biology of a night-flowering Galápagos endemic,Ipomoea habeliana(Convolvulaceae)

Ipomoea habeliana is an endemic, night-flowering member of the Galápagos flora. Pollination experiments, flower-visitor observations, nectar sampling, pollen transfer, and pollen to ovule ratio and pollen size studies were included in this project. The large, white flowers of this species set fruit via open pollination (55%), autonomous autogamy (51%), facilitated autogamy (91%), cross-pollination (80%), diurnal open pollination (60%) and nocturnal open pollination (60%). Fruit set is pollen-limited. Ants, beetles, crickets and hawk moths regularly visit the flowers. Ants are the most frequent visitors, but hawk moths are the only effective pollinators. Nectar is available throughout the night, but is most abundant early in the evening when hawk moth visits are most frequent. Experiments with fluorescent dust demonstrate intra- and inter-plant pollen movement by hawk moths. Although this species is adapted for hawk moth pollination, it readily sets fruit via autonomous autogamy when no visits are made. Thus, it is concluded that it is facultatively xenogamous. Additional support for this conclusion is provided by the pollen to ovule ratio of 1407 and by the fact that the plants grow in a region that has few or no faithful pollinators. Conservation efforts for I. habeliana should include hand pollinations, which could significantly increase seed set.

Pollen morphology ofRhododendronsubgen.Tsutsusiand its systematic implications

Eighty-four pollen samples were obtained for 80 taxa, of which, 13 species and one variety are from sect. Brachycalyx Sweet, 58 species and two varieties from sect. Tsutsusi Sweet, and six species from subgen. Pentanthera (G. Don) Pojarkova, respectively. Pollen morphology of all samples was observed using LM and SEM. Pollen grains are revealed to be spheroidal and tetrahedral with tricolporate apertures. Pollen sizes of subgen. Tsutsusi (Sweet) Pojarkova range from 37.67 μm to 61.06 μm, and the exine sculptures are more or less compactly granulated. Pollen sizes are significantly different between sect. Brachycalyx and sect. Tsutsusi of subgen. Tsutsusi. Rhododendron tashiroi Maxim. of sect. Tsusiopsis Sleumer shows a close affinity to sect. Brachycalyx. Pollen size and exine are consistent with general morphology in differentiating species in sect. Tsutsusi. Rhododendron huadingense B. Y. Ding & Y. Y. Fang, once placed as a member of sect. Brachycalyx, should be considered as a species in subgen. Pentanthera.

Occurrence of viable unreduced pollen in a Begonia collection

Polyploidy is widespread in plants and has played a major role in the evolution and diversification of the plant kingdom. Unreduced (2n) gametes are an interesting tool for polyploidisation and the creation of genetic variation in plant breeding. Especially in ornamentals, polyploidisation can broaden attractive features within a species. A Begonia collection was screened on the occurrence of 2n pollen with the aid of four different techniques: pollen size measurement, flow cytometric analysis of nuclei isolated from germinated and non germinated pollen, investigation of the microsporogenesis and analysis of progeny. In ten of the 70 screened genotypes (B. dregei, B. pearcei, B. ‘Anna Christina’, B. ‘Bubbles’, B. ‘Florence Rita’, B. ‘Orococo’, B. ‘Rubaiyat’, B. ‘Spatflacier’, B. ‘Tamo’ and B276), large pollen were observed with a rather spherical than normal ellipsoidal shape. Flow cytometric data proved that these aberrantly shaped pollen were associated with 2n ploidy levels, although they were not always viable. Meiotic aberrations in these large pollen producers resulted mainly in dyads although also monads, triads and polyads were observed. Successful crosses were obtained with B. dregei, B. ‘Orococo’, and B276 as pollinators; DNA content had increased in all or a part of the progeny. The results show that the occurrence of 2n pollen is not a rare phenomenon in Begonia.

The pollen metamorphosis phenomenon in Panax ginseng, Aralia elata and Oplopanax elatus; an addition to discussion concerning the Panax affinity in Araliaceae

To find more morphological characteristics useful for discussion on aralian or non-aralian Panax affinity, pollen morphological diversity was comparatively analysed in P. ginseng, Aralia elata and Oplopanax elatus collected during their pollination periods. In the anthers of both the buds and open flowers, the pollen average diameter varied between some species-specific maximum and minimal measurement. However, the larger pollen grains were typically found in the buds whereas the smaller pollen prevailed in the open flowers, testifying to the pollen size diminution during anther maturation. Based on this finding, the subsequent examination of pollen according to size decrease was put into operation as a method of pollen modification for the study. The structural mechanisms of pollen metamorphosis were identified as not being species specific but rather universal. These mechanisms are suggested to be the shrinkage of the pollen vegetative cytoplasm, the intine enlargement, the deepening of three colporate apertures provided by exine sunken into enlarged intine areas, the aperture accretion as well as the transformation of the exine from thick/sculptured into thin/less sculptured. During 'size-reducing metamorphosis', the pollen grains changed dramatically, going through a species-specific set of intermediate morphs to the final species-specific morphotype. In P. ginseng this morphotype is round (diameter is about 16 microm), in A. elata it is round with a single projection (diameter is about 15 microm) and in O. elatus it is ovoid with a single projection (average diameter is about 18 microm). In addition, every species is peculiar in having the unique vegetative cytoplasm inclusions and individual construction of the largest pollen exine. From a phylogenetic perspective, these findings presumably add support to the option of equal remoteness of P. ginseng from A. elata and O. elatus. The characteristics found seem to be suitable for examination of Panax affinity, by the subsequent study of more Araliaceae representatives.

Pollen morphology of Gaultheria L. and related genera of subfamily Vaccinioideae: Taxonomic and evolutionary significance

The pollen morphology of 86 samples from 84 species of Gaultheria and the closely related genera Chamaedaphne, Craibiodendron, Diplycosia, Eubotrys, Gaylussacia, Leucothoe, Lyonia, Oxydendrum, Pieris, Satyria, and Vaccinium (subfamily Vaccinioideae) was investigated with light and scanning electron microscopy. The tetrahedral tetrads are tri-zonocolporate and range from 22.9 to 51.5 μm in diameter. Exine ornamentation (apocolpia and mesocolpia) of pollen grains is highly variable. Six exine types of apocolpia and five exine types of mesocolpia are distinguished. Viscin threads on the pollen grains of members of Gaultheria are first reported in the study. Colpus length is correlated with both pollen size and colpus maximum width. There is a weak correlation between corolla length and pollen size when the length of the corolla is less than 6 mm. Infrageneric relationships of taxa in Gaultheria are discussed on the basis of pollen data. Pollen morphology is ubiquitously variable at both the species and genus levels. Pollen data support the sister relationships between Satyria and Vaccinium and between Chamaedaphne and Eubotrys of a previously reported molecular phylogenetic analysis. The evolution of pollen characters is traced by character optimization and results discussed. An evolutionary trend of mesocolpium ornamentation within Vaccinioideae from granulate through granulate–rugulate to rugulate is apparent.