Pollen grain numbers, ovule numbers and pollen-ovule ratios in Caryophylloideae: correlation with breeding system, pollination, life form, style number, and sexual system

Pollen-ovule ratios (P/O) were measured for 79 species of Caryophylloideae (Agrostemma, Dianthus, Saponaria, Silene, and Vaccaria). We analyzed if these features are best correlated with (1) the breeding system (outcrossing or selfing), (2) diurnal or nocturnal pollination, (3) life form (annual versus perennial), (4) style number, (5) the sexual system (hermaphroditism, gynodioecism, dioecism), or (6) the taxonomy of species. According to the classification of Cruden [(1977) Evolution 31:32-46] most species in the subfamily Caryophylloideae are facultative autogamous or facultative xenogamous. Autogamous or cleistogamous species showed significantly lower P/Os than outcrossing species. We found no differences between night- and day-flowering species; thus from our data diurnal and nocturnal flower visitors may be considered as equally efficient in transferring pollen. However, other factors are also important for the interpretation of P/Os. Pollen grain numbers and ovule numbers were found to correlate with style number, life form, and breeding system. The low P/Os of some dioecious, and therefore obligate outcrossing, species are discussed in relation to morphological traits that improve pollen deposition by pollinators on the stigma, and in relation to different flower numbers of male and female plants.     

Pollen grains: Why so many?

My objective is the examination of selective forces that affect pollen number. Relationships among other floral traits of animalpollinated plants, including pollen size, stigma area and depth, and the pollen-bearing area of the pollinator may affect pollen number and also provide a model to examine how change in one trait may elicit change in other traits. The model provides a conceptual framework for appreciating intra- and inter-specific differences in these traits. An equivalent model is presented for wind-pollinated plants. For these plants the distance between putative mates may be the most important factor affecting pollen number. I briefly consider how many pollen grains must reach a stigma to assure fruit set. I use pollen-ovule ratios (P/Os) to examine how breeding system, sexual system, pollen vector, and dispersal unit influence pollen grain number. I also compare the P/Os of plants with primary and secondary pollen presentation and those that provide only pollen as a reward with those that provide nectar as part or all of the reward. There is a substantial decrease in P/O from xenogamy to facultative xenogamy to autogamy. Relative to homoecious species the P/Os of species with most other sexual systems are higher. This suggests that there is a cost associated with changes in sexual system. The P/Os of wind-pollinated plants are substantially higher than those of animal-pollinated plants, and the available data suggest there is little difference in the pollination efficiency of the various animal vectors. The P/Os of plants whose pollen is dispersed in tetrads, polyads, or pollinia are substantially lower than those of species whose pollen is dispersed as monads. There was no difference in the P/Os of plants with primary and secondary pollen presentation. The P/Os of plants that provide only pollen as a reward were higher than those that provide nectar as a reward. All of these conclusions merit additional testing as they are based on samples that are relatively small and/or systematically biased.     

Isopterofuran,a new 2-arylbenzofuran phytoalexin from Coronilla emerus

Two 2-arylbenzofuran phytoalexins isolated from the fungus-inoculated leaflets of Coronilla emerus (scorpion senna) have been identified as 6-demethylvignafuran and the previously unreported 2-(4-hydroxy-2,3-dimethoxyphenyl)-6-hydroxybenzofuran (isopterofuran). The synthesis of isopterofuran is described.     

Breeding systems in Balsaminaceae in relation to pollen/ovule ratio,pollination syndromes,life history and climate zone

• Pollen/ovule (P/O) ratios are often used as proxy for breeding systems. Here, we investigate the relations between breeding systems and P/O ratios, pollination syndromes, life history and climate zone in Balsaminaceae.
• We conducted controlled breeding system experiments (autonomous and active self‐pollination and outcrossing tests) for 65 Balsaminaceae species, analysed pollen grain and ovule numbers and evaluated the results in combination with data on pollination syndrome, life history and climate zone on a phylogenetic basis.
• Based on fruit set, we assigned three breeding systems: autogamy, self‐compatibility and self‐incompatibility. Self‐pollination led to lower fruit set than outcrossing. We neither found significant P/O differences between breeding systems nor between pollination syndromes. However, the numbers of pollen grains and ovules per flower were significantly lower in autogamous species, but pollen grain and ovule numbers did not differ between most pollination syndromes. Finally, we found no relation between breeding system and climate zone, but a relation between climate zone and life history.
• In Balsaminaceae reproductive traits can change under resource or pollinator limitation, leading to the evolution of autogamy, but are evolutionary rather constant and not under strong selection pressure by pollinator guild and geographic range changes. Colonisation of temperate regions, however, is correlated with transitions towards annual life history. Pollen/ovule‐ratios, commonly accepted as good indicators of breeding system, have a low predictive value in Balsaminaceae. In the absence of experimental data on breeding system, additional floral traits (overall pollen grain and ovule number, traits of floral morphology) may be used as proxies.

     

Two gossypetin methyl ethers as ultraviolet patterning guides in the flowers of Coronilla valentina

The 3′-monomethyl and 8,3′-dimethyl ethers of gossypetin have been identified in the flowers of Coronilla valentine where they occur as the 3-rutinosides. These two yellow flavonols occur specifically in the wings and thus provide both visible yellow colour and UV absorption to bees, which land on the wings and trigger the self-fertilization mechanism. These yellow pigments are absent from the flowers of the related C. emerus, where their role in UV patterning is taken over by colourless kaempferol and quercetin glycosides.     

VARIATION AND COVARIATION AMONG FLORAL TRAITS WITHIN AND AMONG FOUR SPECIES OF NORTHERN EUROPEAN PRIMULA (PRIMULACEAE)

Phenotypic and genetic variation and correlations among floral traits within and among four Primula species were measured to seek evidence for potential constraints on the independent evolution of floral characters, to examine the relationship between mating system, ploidy level, and sex allocation, and to determine whether some traits are more conservative than others within and across these congeners. We measured mean flower diameter, corolla depth, pollen production, modal pollen grain volume, ovule number per flower, and pollen: ovule ratios for 64 field-collected genotypes from northern Europe. These represented one heterostylous (P. farinosa: 2n = 18) and three homostylous (P. scotica: 2n = 54, P. scahdinavica: 2n = 74, and P. stricta: 2n ~ 126) species. All traits differed significantly among species and among the six taxon/morph categories identified (including three morphs of P. farinosa: pin, thrum, and homostylous). Pollen production per flower was significantly higher (and individual pollen grain volume lower) in the outcrossing P. farinosa than in any of the homostylous species; also, pin morphs produced significantly more pollen per flower than thrums in P. farinosa. Among the homostylous species, there were significant differences in all traits except modal pollen grain volume. Ovule number per flower and flower size were less variable among taxa than pollen production and pollen volume. Within species, there were several strong negative correlations among genets between pairs of traits, but each species exhibited a unique set of inverse relationships. We detected only one significant positive genetic correlation; in P. stricta, ovule number and pollen production per flower were positively correlated among genets. Among species means, two pairs of traits were negatively correlated: mean ovule number per flower vs. flower diameter (but P = 0.0587), and mean pollen production per flower vs. modal pollen grain volume. These negative correlations within and among taxa suggest that there may be intrinsic genetic constraints on the independent evolution of these floral characters, but that these constraints differ among species.     

Variations of floral traits among different life forms illustrate the evolution of pollination systems in Potamogeton species from China

Four leaf morpha groups (floating-leaved, submerged broad-leaved, submerged linear-leaved and filiform-leaved) and three inflorescences type groups (erect, facultative floating and floating) can be found in the genus Potamogeton. Life forms in the genus correlate with pollination types (anemophily, epihydrophily and hydroautogamy). Floral traits vary greatly among different life forms and pollination types. Both floating and submerged broad-leaved species produce erect inflorescences that are suited for anemophilous pollination. These flowers also have the highest pollen/ovule (P/O) ratio (25,013) and the smallest pollen grain volume (6046 μm³). On the contrary, submerged filiform-leaved species produce only floating inflorescences and their flowers produce the largest pollen grains (17,567 μm³) and have the lowest P/O ratio (6752), which is typical of the syndromes of hydroautogamy and epihydrophily. The relatively prolific seed production (about 70%) and wide dispersal in the floating and submerged broad-leaved species and the submerged filliform-leaved species indicate that these two groups are well adapted to the aquatic environment. This is in contrast with the less well-adapted complex and unstable pollination system found in linear-leaved species. We propose that the pollination systems and life forms in the Potamogeton, have undergone modification in response to the demands imposed by the aquatic environment during the evolutionary process in the genus.     

Morphology,reserves and pollen viability of some Solanum Sect. Cyphomandropsis species

The morphology, energy reserves and viability of three species from Solanum Sect. Cyphomandropsis (Solanum adelphum Morton, S. glaucophyllum Desf. and S. stuckertii Bitter), which grow in Argentina were studied. The pollen grains are tricolporate and their characters are homogeneous. The only differences found among the species were the pollen grain size and the sculpture distribution. The surface features of exine were not readily visible under light microscope, but with SEM the sculpture appeared granulate. Analyses of the cytoplasm of pollen grains show the presence of oils. The average viability was high in two of the studied species (S. adelphum and S. glaucophyllum). An interesting difference was observed between the first and second day flowers of S. stuckertii. The second day flowers had high fertility but those from the first day had a very low fertility. In the latter case, an inner placentoid tissue of the anther hinders pollen release until the entire development is completed. The P/O ratio is linked to the breeding system.     

Pollen morphology,ultrastructure and taphonomy of the Neuradaceae with special reference to Neurada procumbens L. and Grielum humifusum E.Mey. ex Harv. et Sond.

Pollen morphology and sporoderm ultrastructure of modern Neurada procumbens L. and Grielum humifusum E.Mey. ex Harv. et Sond. were studied using light (LM) and electron (SEM and TEM) microscopy. Additionally late Holocene pollen of the Grielum-type was studied using LM. Systematic and ecological aspects have been discussed for the family Neuradaceae. The pollen grains of the studied species are characterized by similarities in size, shape, aperture type and differences in exine sculpture (reticulate semitectate exine in Neurada and finely reticulate to foveolate in Grielum) and sporoderm ultrastructure. The cavea in the exine is situated between the ectexine and endexine which are connected near the aperture region only. A combination of the palynological characters of the Neuradaceae (semitectate exine, rather loose columellae, interrupted foot layer, the cavea in the exine) increases the pollen plasticity, allowing considerable changes of the pollen grain volume but still remains insufficient to survive sharp fluctuations in hydration level.     

Decomposition and nutrient dynamics in mixed litter of Mediterranean species

In the last decade a great research effort addressed the effects of litter diversity on ecosystem functions, reporting both synergistic and antagonistic effects for decomposition dynamics. Four coexisting Mediterranean species, representing a range of litter quality, were used to arrange litter mixtures at three diversity levels for a litterbag decomposition experiment. Species identity appeared as the major determinant for litter mass loss (Coronilla emerus～Hedera helix>Festuca drymeia>Quercus ilex) and nutrient release, with rates for all leaf litter types following the sequence K>N>Mg≥Ca>>Fe. Additive diversity effects were prevalent pooling together all data but also for nutrients separately. Antagonistic interactions were more common than synergistic in the cases of mass loss, N and Ca contents, but not for K, Mg and Fe dynamics. The number of species in the litterbag significantly affected the outcome of non-additive interactions, which were mostly antagonistic for two-species mixtures, and synergistic for the combined 4 species. Litter quality appears to be the most important factor affecting mass loss and nutrient dynamics, while litter diversity, influencing the rates of these processes, plays an important role in reducing their variability, thus suggesting a greater stability of ecosystems properties in presence of mixed litter.     

Trisubstituted flavonol glycosides in Coronilla emerus flowers

A novel trisubstituted kaempferol glycoside has been isolated from leaves and flowers of Coronilla emerus and identified as the 3-glucoside-7,4′-dirhamnoside. It co-occurs in the flowers with the 3-glucosides and 3-glucoside-7-rhamnosides of kaempferol and quercetin. A second kaempferol triglycoside based on glucose and xylose is also present. All six glycosides contribute to the UV patterning present in the wings of the flowers. This is the first report of kaempferol triglycosides with monosaccharide units substituting hydroxyl groups at the 3-, 7- and 4′-positions.     

Characterization,pathogenicity, and fungicide sensitivity of Alternaria isolates associated with preharvest fruit drop in California citrus

Alternaria rot has been recently described as an emerging fungal disease of citrus causing significant damage in California groves. A survey was conducted to determine latent infections on fruits, twigs, and leaves and investigate their seasonal patterns during 2019 and 2020. On fruits, latent infections were more associated with the stem end than with the stylar end, except during spring when a significantly high percentage of flowers (86%) had latent infections. Latent infections on twigs varied markedly between years (28% in 2019 and 9.5% in 2020), while Alternaria spp. were also recovered from citrus leaves. Alternaria isolates collected during the survey were identified based on multigene sequence analysis, confirming that Alternaria alternata and Alternaria arborescens are the two species associated with infections of citrus fruits. Of the 23 isolates, 19 were identified as A. alternata and demonstrated the dominance of this species over A. arborescens. Isolates representing populations of these two species were selected as representative isolates for physiological and morphological studies. A. alternata and A. arborescens showed similar conidial dimensions but differed in the number of conidia produced. Growth rates demonstrated that A. alternata grows faster than A. arborescens at all the temperatures evaluated, except at 25 and 35 °C. The growth patterns were similar for both species. The sporulation rate of the Alternaria isolates was influenced differently by temperature. This parameter also influenced conidial germination and appressorium formation, and no significant differences were observed between Alternaria species. Pathogenicity and aggressiveness tests on detached fruit demonstrated the ability of A. alternata and A. arborescens to cause internal lesions and produce fruit drop in the orchards with no quantitative differences between them (disease severity indexes of 58 and 68%, respectively). The fungicide sensitivity tests showed that DMI fungicides are the most effective fungicides in reducing mycelial growth. The SDHI fungicides had intermediate activity against the mycelial growth but also suppressed spore germination. The spore germination assay suggested that some of the isolates included in this study might have some level of resistance to QoI and SDHI fungicides. The findings of this study provide new information about the pathogens associated with the excessive fruit drop recently observed in some California citrus groves.     

Pollen-ovule ratio,pollen size,and breeding system in Astragalus (Fabaceae) subgenus Epiglottis: a pollen and seed allocation approach

The correlation between pollen/ovule (P/O) ratio and breeding system has generally been accounted for either on the basis that P/O reflects pollination efficiency, or in terms of the sex allocation theory. The following were assessed for taxa belonging to genus Astragalus subgenus Epiglottis: 1) Degree of correlation between P/O and the breeding system, measured by means of autofertility; 2) The absence or existence of correlation between P/O and pollen grain size; and 3) The ability of various theories to account for the results obtained. Results showed a minimal correlation between P/O and autofertility, and between P/O and pollen grain size in the taxa studied. Analysis of these results in terms of the sex allocation theory enabled this correlation to be explained as a function of the variation existing between taxa with respect to the resources invested in each pollen grain and in each ovule. The predictive capacity of this theory, which has moreover proven valuable in explaining the structural peculiarities of the androecium in these taxa, was also highlighted. The type of self-pollination applicable was also discussed, as was the phenotypic model of selection of self-fertilization considered most plausible for these taxa.     

Synchronized protandry and hermaphroditism in a tropical secondary forest tree, Schefflera heptaphylla (Araliaceae)

Selection favoring avoidance of stigma clogging, pollen discounting, self-fertilization, and other negative effects of self-pollination can produce intricate patterns of intra- and interfloral dichogamy in plants bearing numerous flowers. Here we report an extensive study of the relationships among dichogamy, floral sex allocation (pollen-to-ovule ratios), nectar production, floral visitors, mating system, and fruit set in natural populations of Schefflera heptaphylla, a widespread paleotropical secondary forest tree that produces thousands of flowers in a blooming season. Each tree produces 15?C30 sequentially blooming, paniculate, compound inflorescences. Each compound inflorescence has up to three orders of umbellets, which also bloom sequentially. While hand-pollinations showed that S. heptaphylla was capable of self-fertilization, our observations of thousands of flowers showed that strong intra- and interfloral protandry severely restricts both autogamous and geitonogamous self-pollination. All flowers were bisexual, thus the sexual system of the populations we studied was hermaphroditism. The pollen-to-ovule (P/O) ratios were characteristic of outcrossing species, and P/O ratios of flowers in the last-maturing (third order) umbellets were significantly higher than those in earlier-maturing (first and second order) umbellets. Floral visitors were primarily flies (Chrysomya sp. and Syrphinae sp.) and wasps (Vespula sp. and Eumenes sp.). Flowers produced nectar during both the male (pollen presentation) and female (stigma receptivity) stages of their development, and the volume of nectar production was higher in the female stage. Nevertheless, flowers received fewer visits in the female stage than they did in the male stage, and natural fruit set was low, especially in first and third order umbellets. Fruit set from hand cross- and self-pollinations was significantly higher than natural fruit set, indicating pollen limitation of fruit set. Schefflera heptaphylla has also been reported to be andromonoecious. Both hermaphroditism and andromonoecy are consistent with theoretical predictions for variation in sex allocation among sequentially maturing flowers in protandrous species. Further studies comparing hermaphroditic and andromonoecious populations of S. heptaphylla could elucidate the selective factors affecting sex expression, nectar production, and fruit set in species with numerous flowers displaying both intra- and interfloral dichogamy.     

Purification and properties of d-galactose-binding lectins from some erythrina species: Comparison of properties of lectins from E. indica,E. arborescens,E. suberosa, and E. lithosperma

The lectins of the seeds of four species of the genus Erythrina, namely E. indica, E. arborescens, E. lithosperma, and E. suberosa were isolated by affinity chromatography on acid-treated ECD-Sepharose 6B. The lectins were found homogeneous in polyacrylamide gel electrophoresis and immunochemical tests. In SDS-gel electrophoresis, E. indica and E. lithosperma lectins each gave two bands with subunit molecular weights of 30,000 and 33,000 in the case of the former and 26,000 and 28,000 in the case of the latter. E. arborescens and E. suberosa gave single bands corresponding to polypetide chain molecular weight of 28,000. The lectins were found to be glycoproteins with their neutral sugar contents ranging from 4–9%. In carbohydrate specificity all the lectins were d-galactose specific. Their close similarity was also demonstrated by their homologous cross-reaction against the antiserum to E. indica lectin. In hemagglutinating activity toward human erythrocytes, E. indica and E. suberosa lectins showed higher activity toward the O group and E. arborescens toward the B group. The results show the similarity of the lectins derived from different species of the same genus in respect of immunochemical properties and carbohydrate specificity. In studies on E. indica lectin, the protein was found homogeneous by electrophoretic, immunochemical, and sedimentation experiments. Its molecular weight of 68,000 determined from sedimentation and diffusion data indicated that the molecule was a dimer of two noncovalently bound unequal subunits whose SDS-gel electrophoretic molecular weights are noted above. The lectin was devoid of cysteine and methionine and contained valine as its N-terminal amino acid. It had 9% neutral sugars and 1.5% glucosamine. Equilibrium dialysis studies with lactose showed that the values of the association constant K at different temperatures were of similar orders of magnitude to other lectins and the dimeric molecule possessed two noninteracting binding sites.     

Stress tolerance,genetic analysis and symbiotic properties of root-nodulating bacteria isolated from Mediterranean leguminous shrubs in Central Spain

Nine root-nodulating bacterial isolates were obtained from the leguminous shrubs Spartium junceum, Adenocarpus hispanicus, Cytisus purgans, Cytisus laburnuum, Retama sphaerocarpa and Colutea arborescens in areas of Central Spain. A poliphasic approach analyzing phenotypic, symbiotic and genetic properties was used to study their diversity and characterize them in relation to Mediterranean conditions. Stress tolerance assays revealed marked variations in salinity, extreme pH and cadmium tolerance compared with reference strains, with the majority showing salinity, alkalinity and Cd tolerance and three of them growing at acid pH. Variation within the 16S rRNA gene was examined by amplified 16S rDNA restriction analysis (ARDRA) and direct sequencing to show genetic diversity. Phylogeny confirmed the close relationship of four isolates with Bradyrhizobium canariense, three with Phylobacterium myrsinacearum, one with Rhizobium rhizogenes and another with Mesorhizobium huakuii. The cross inoculation tests revealed wide spectra of nodulation. This is the first report of P. myrsinacearum being able to nodulate these leguminous shrubs, and also the first time reported the association between B.canariense, R. rhizogenes and M. huakuii and C. laburnuum, C. purgans and C. arborescens, respectively. These results suggested that native rhizobia could be suitable candidates as biofertilizers and/or inoculants of leguminous shrubs with restoration or revegetation purposes in Mediterranean areas.     

灌溉对三种荒漠植物蒸腾耗水特性的影响

利用热平衡式茎流计和压力室对塔里木沙漠公路防护林不同灌溉量条件下3种荒漠植物多枝柽柳(Tamarix ramosissima)、梭梭(Haloxylon ammodendron)和乔木状沙拐枣(Calligonum arborescens)的液流变化、水势进行了测定。研究结果表明:(1)茎干液流速率因灌溉量和物种的不同而异,同一灌溉量条件下不同物种间表现为多枝柽柳>乔木状沙拐枣>梭梭,不同灌溉量条件下3种荒漠植物的茎干液流速率均随灌溉量的减少而显著降低。3种荒漠植物的夜间蒸腾占有一定比例,表现为梭梭(18.68%)>乔木状沙拐枣(17.48%)>多枝柽柳(12.82%),表明3种灌木均可通过夜间液流以补充植物体白天的水分消耗,表现出较强的抗旱性,但梭梭形成的叶片-冠-根的水势差相对较大,夜间补偿流较多,表现出更强的抗旱性。多枝柽柳和乔木状沙拐枣茎干液流日变化趋势基本相同,在灌溉量为35 kg·株-1.次-1和28 kg·株-1.次-1时均呈单峰曲线,液流速率较高且变化幅度较大,而灌溉量为17.5 kg·株-1.次-1时呈双峰曲线,液流速率较低;梭梭在不同灌溉量条件下其变化均呈单峰曲线,即当灌溉量降低到17.5 kg·株-1.次-1时多枝柽柳和乔木状沙拐枣可能出现了水分亏缺,通过调节气孔张开度或部分关闭降低蒸腾来适应其胁迫条件,但该灌溉条件下梭梭并没有出现水分亏缺,表明出较强的抗旱性。(2)相同时间不同灌溉量条件下,3种荒漠植物的清晨水势和午后水势均随着灌溉量的减少而降低;整个生长季相同时间同一灌溉量条件下,3种防护林植物的清晨、午后水势表现为乔木状沙拐枣>多枝柽柳>梭梭,表明3种荒漠植物在相同的灌溉条件下梭梭因保持较低的水势表现出较强的抗旱性。(3)相同时间不同灌溉量条件下,3种荒漠植物单株日耗水量均随着灌溉量的减少而减少,整个生长季各处理日平均耗水量的动态变化趋势均为单峰型,7月份耗水量最大,表明在塔克拉玛干沙漠腹地最炎热的7月份,3种防护林植物可以通过增加其蒸腾耗水量来适应干旱的环境条件。     

Comparative pollen morphology of the Iberian species of Pulicaria (Asteraceae, Inuleae, Inulinae) and its taxonomic significance

To better understand the taxonomy of Pulicaria, the pollen wall architecture of the six Iberian species were investigated using light (LM) and scanning electron microscopy (SEM). The exine structure of Pulicaria odora was also investigated using transmission electron microscopy (TEM). Statistical analysis was performed to distinguish taxonomically significant morphometric information from all the measured parameters of pollen grains. It was found that the exine sculpture characters, with special importance paid to the spines, were the most useful of all characters to define Pulicaria pollen types and separate the species. Three pollen types distinguishable through the spines morphology and the inter-spinular sculpture are described: P. microcephala pollen type (incl. P. microcephala), P. vulgaris pollen type (incl. P. vulgaris), and P. dysenterica pollen type (incl. P. dysenterica, P. odora, P. paludosa and P. sicula). A dichotomous key to these Pulicaria pollen types is proposed. The distribution of P. dysenterica, P. odora, P. paludosa and P. sicula in more than one leaf node in the classification tree reveals that the pollen grains of these species are difficult to segregate. Therefore, the construction of a satisfactory dichotomous key to the P. dysenterica pollen type species is not feasible. Yet, the different spines apex morphology between P. microcephala and P. paludosa and the existence of significant differences in five of the eight studied quantitative pollen characters of these two taxa, supports the opinion that the Berlengas Islands endemic P. microcephala should be accepted as a separate species. In addition, the differences among the spines morphology of P. vulgaris, P. microcephala, and the other four Iberian (and European) species, strengthen the conclusion that the section Pulicaria is non-monophyletic.     

Pollen and ovule production in wind-pollinated species with special reference to Juncus

The reproductive biology of wind-pollinated species in terms of pollen and ovule production is rarely studied compared with zoophilous species, despite available hypotheses on the effect of growth form and life-history traits on reproductive investment. Here, we use published data and new data for species of Juncus and Luzula (Juncaceae) to test the hypotheses that, in wind-pollinated species, woody perennials should exhibit larger pollen–ovule (P/O) ratios than herbaceous species and that species with separate sexes have larger P/O ratios than homoecious species. In total, we report pollen and ovule production for 291 wind-pollinated species, including 19 Juncus and 5 Luzula species. Compared with other wind-pollinated species, Juncus exhibits unusually low P/O ratios (log P/O = 2.06 ± 0.46) because of high ovule production. We argue that the high ovule and seed production in Juncus, associated with frequent self-fertilization, may be beneficial in habitats preferred by the genus. In general, we found higher P/O ratios in woody perennials (log P/O = 4.37 ± 1.18) or in species with separate sexes (log P/O = 4.28 ± 1.12) than in herbaceous (log P/O = 3.51 ± 0.77) or homoecious (log P/O = 3.52 ± 0.80) species, respectively. However, when we analyzed woody perennials separately, we found no significant difference in P/O ratios between homoecious and nonhomoecious species. We argue that woody perennials, independent of dicliny, may be preferentially outcrossed and therefore exhibit decreased variation in mating systems compared with herbs. Because the degree of outcrossing correlates with P/O ratios, differences between homoecious and nonhomoecious woody perennials could be less pronounced.     

Pollen morphology of the aquatic Brazilian endemic genus Castelnavia Tul. & Wedd. (Podostemaceae)

The utility of pollen characteristics for taxonomic and phylogenetic analysis of most genera of Podostemaceae has barely been examined. Herein we report on the diversity of pollen structure in Castelnavia (Podostemaceae), a genus of six species endemic to central and southern Brazil. Pollen grain was shed as three-colpate, planaperturate monads and ranged from 12.5 to 22.5?μm for the polar axis and from 12.5 to 20.0?μm for the equatorial axis. All species examined had polar and radially symmetrical pollen grains. Grains from Castelnavia fluitans, Castelnavia multipartita, and Castelnavia noveloi had an oblate spheroidal shape (PD/ED), those from Castelnavia monandra and Castelnavia pendulosa were subprolate, and those from Castelnavia princeps were prolate spheroidal. The polar view was subcircular for C. monandra and subtriangular for the other species. A fastigium was observed in C. fluitans and C. pendulosa whereas a costa was present in C. multipartita and C. princeps, with the colpus margin not thickened in the former species but prominently thickened in the latter. Castelnavia monandra and C. noveloi did not have a fastigium or costa. For all species spicules occurred on the exine (microechinate sexine) and were most conspicuous on the colpus membrane. There was little correspondence between variation in pollen structure and species relationships supported by phylogenetic analysis.