Large Numbers Of Seeds Research Articles

Productivity and Persistence of Yellow Serradela (Ornithopus compressus L.) and Biserrula (Biserrula pelecinus L.) in the Mediterranean Climate Region of Central Chile

The production and sustainability of non-irrigated pastures in the Mediterranean climate region of central Chile is currently limited by the low diversity of valuable species and cultivars of annual forage legumes, able to persist in zones with highly variable annual rainfall, and low fertility or poorly drained soils. In this work, DM production, seed yield, hardseededness and pasture persistence were evaluated for cultivars of yellow serradella (Ornithopus compressus L.) and biserrula (Biserrula pelecinusL.),�infieldexperimentsconductedinthesubhumidportion� of the Mediterranean climate region of Chile. Burr medic (Medicago polymorpha L.) and sub clover (Trifolium subterraneum L.) were used as a reference plants. A remarkable DM production and seed yield were observed in biserrula (cvs. Mor96 and Casbah), and in some cultivars of yellow serradella (e.g. Madeira, Santorini); biserrula produced by far the largest number of seeds per m 2 . As was expected for species that produce very high levels of hard-seeds, the regeneration of biserrula and serradella was low in second growing season, but plant density and productivity were high in the third growing season. The use of biserrula and serradela in monoculture or in mixture with other annual legumes, either in pasture-crop rotation or permanent pasture, would contribute to the improvement of the prevailing productive systems in the Mediterranean climate region of central Chile.

Caracterização físico-química de progênies de maracujá-roxo e maracujá-azedo cultivados no Distrito Federal

A qualidade de frutos de maracujá para o consumo in natura é um fator de extrema importância na comercialização para o mercado europeu. Diante disso, um experimento foi realizado com o objetivo de avaliar as características físico-químicas de frutos de maracujazeiro nas condições de cerrado. Utilizou-se um delineamento de blocos casualizados, com nove tratamentos e quatro repetições. Os tratamentos constaram de sete progênies de maracujá-roxo provenientes da Austrália e duas progênies de maracujá-azedo. As progênies de maracujazeiro-roxo utilizadas foram: 'Lacey', '14', '25', 'Supersweet 9', '37(1)', '37(2)' e '96A' e os de maracujazeiro-azedo foram 'Marília Seleção Cerrado' e 'Híbrido EC-2-0'. Com base nos resultados, pode-se concluir que o genótipo '37(2)' apresentou o maior teor de sólidos solúveis totais, a progênie 'Lacey' apresentou a menor espessura de casca e formato mais arredondado dos frutos, a progênie 'Marília Seleção Cerrado' obteve o maior peso de polpa e o maior número de sementes por fruto. Entre as progênies de maracujá-roxo, o maior peso da polpa foi da progênie 'S9', que também apresentou maior pH e menor acidez titulável. A cor da polpa predominante foi amarela. A correlação entre peso da polpa e acidez titulável mostrou-se positivamente forte, e a correlação entre pH e acidez titulável foi negativamente forte.

SU-FF-T-65: A Phantom Study to Characterize a Doppler Ultrasound Scanner for Application in Prostate Brachytherapy

Purpose: To characterize the Doppler modes of an ultrasoundscanner, in a phantom, for potential use in prostate brachytherapy.Method and Materials: A flow phantom has been designed and fabricated. The one‐directional flow was generated with the help of peristaltic pump. Images of the phantom were obtained using the color Doppler (CD) and power Doppler (PD) modes. The effect of the instrument's parameters, viz color gain, pulse repetition frequency and wall filter, on flow detection by these Doppler modes has been studied. Results: The Doppler gain has a significant effect on the flow detection in both CD and PD modes. Flow detection in the color Doppler mode is found to be affected by the pulse repetition frequency (PRF). The wall filter shows no effect on flow detection by CD mode, however reducing the wall filter to low value gives aliasing in PD mode. Conclusion: This study can help to identify the optimal setting for acquisition of prostate images using Doppler modes. Inappropriate setting of these parameters can either display incorrect information or can hide useful clinical information. Recognizing the flow in the prostate can help to identify regions of increased blood flow. As an increased flow in prostate vessels may demonstrate the presence of cancer; it can help to recognize the regions within the prostate gland, which could be histopathologically positive for cancer. By delivering a relatively large number of seeds to the areas of hyperflow, dose can be maximized to the cancerous region and possibly be reduced to the surrounding critical organs. This has the potential to improve the treatment outcome and reduce treatment related complications.

Recolonization of intertidal Zostera marina L. (eelgrass) following experimental shoot removal

The recovery of eelgrass ( Zostera marina) from physical disturbances is understudied and no attention has been given to the likely differences in damage recovery rates between the continuous lower intertidal perennial meadows and higher intertidal eelgrass patches. In the present study, 4 m 2 plots were treated by removing all eelgrass shoots and followed over a 3 year period until they attained control (untreated) plot shoot densities. The number and types of shoots (vegetative, reproductive, and seedling) were counted semi-monthly with comparisons made between experimental and control plots. In the second year of the study additional plots were denuded and sown with Z. marina seeds to evaluate the importance of seedlings in the recovery process. Our results suggest that recovery in both low and high intertidal plots was due exclusively to rhizome growth from adjacent perennial eelgrass. This recovery began immediately within the permanent eelgrass meadow and was complete within 24 months. Denuded transition zone patches took almost twice as long to recover to control densities. Natural seedling production appeared to play no part in recovery. When larger numbers of seeds were planted into denuded plots in the winter, only a small portion of them produced seedlings in the spring and none appear to survive through the summer. These experimental eelgrass recovery rates were similar to recovery rates determined from aerial photographs of an eelgrass meadow damaged by a boat grounding near the study site. We suggest that transition zone perennial patches are more vulnerable to natural and anthropogenic disturbance events than lower intertidal eelgrass meadows.

Sistema reprodutivo de Sparattosperma leucanthum (Vell.) K. Schum. (Bignoniaceae)

Sparattosperma leucanthum (Vell.) K. Schum. (Bignoniaceae) é uma árvore polinizada por mamangavas, apesar de outros visitantes florais explorarem néctar ou pólen das flores sem exercerem benefício reprodutivo. Neste estudo, focalizaram-se aspectos do sistema de polinização, além de inferir se o espaçamento interplantas encontrado na área amostral e a quantidade de flores produzidas por árvore limitavam ou não a polinização por xenogamia em S. leucanthum. Assim, foram realizados testes reprodutivos, para obtenção da relação fruto-flor, contagens do número de sementes por fruto e das árvores nos transectos amostrados e estimativa da quantidade de flores por árvores. S. leucanthum é autoincompatível e necessita dos visitantes florais para efetuar a polinização, pois se reproduz apenas por xenogamia. A razão fruto-flor obtida foi de 0,0054, indicando alto custo energético, atribuído à baixa eficiência dos visitantes florais em promover a polinização. A distância interplantas foi relativamente menor que a distância máxima percorrida pelas mamangavas, enquanto as árvores produziram poucas flores por inflorescência e em intensidade moderada, auxiliando o processo de polinização por xenogamia, realizada pelas mamangavas. Entretanto, os frutos produziram grande quantidade de sementes, permitindo ampla proliferação de S. leucanthum na área estudada.

Pollen-mediated gene flow from transgenic safflower (CarthamustinctoriusL.) intended for plant molecular farming to conventional safflower

Field experiments were conducted in Chile and western Canada to measure short-distance (0 to 100 m) outcrossing from transgenic safflower (Carthamus tinctorius L.) intended for plant molecular farming to non-transgenic commodity safflower of the same variety. The transgenic safflower used as the pollen source was transformed with a construct for seed-specific expression of a high-value protein and constitutive expression of a gene conferring resistance to the broad-spectrum herbicide glufosinate. Progeny of non-transgenic plants grown in plots adjacent to the transgenic pollen source were screened for glufosinate resistance to measure outcrossing frequency. Outcrossing frequency differed among locations: values closest to the transgenic pollen source (0 to 3 m) ranged from 0.48 to 1.67% and rapidly declined to between 0.0024 to 0.03% at distances of 50 to 100 m. At each location, outcrossing frequency was spatially heterogeneous, indicating insects or wind moved pollen asymmetrically. A power analysis assuming a binomial distribution and a range of alpha values (type 1 error) was conducted to estimate an upper and lower confidence interval for the probable transgenic seed frequency in each sample. This facilitated interpretation when large numbers of seeds were screened from the outcrossing experiments and no transgenic seeds were found. This study should aid regulators and the plant molecular farming industry in developing confinement strategies to mitigate pollen mediated gene flow from transgenic to non-transgenic safflower.

Composition and seasonal dynamics of seed rain in broad-leaved Korean pine ( Pinus koraiensis) mixed forest in Changbai Mountain, China

To explore the composition and spatio-temporal dynamics of seed rain in broad-leaved Korean pine ( Pinus koraiensis) mixed forest, 150 seed traps were set up in a 25 hm 2 plot in Changbai Mountain. Seeds, fruits, anthotaxy and others in seed traps were collected, identified and divided into 4 types. From 2005 to 2006, we collected 47 different types. Total number of seeds and fruits was 121291, including 23147 mature seeds and fruits (19.1% of the total). Tilia amurensis and Fraxinus mandshurica, with the most seeds and fruits, accounted for 90% of the total. The analysis on seasonal dynamics of seed rain showed that there were the largest number of seeds and fruits between July and October, which were composed of immature seeds and fruits. In mid-October, mature seeds and fruits reached their peak, but immature seeds and fruits still accounted for high proportion. There were 91 traps that contained 100–200 mature seeds and fruits, and one trap without any mature seed or fruit. The largest number of species found in a trap was 7, and usually 3 or 4 species were found in most of the traps. There were obvious relationships between spatial patterns of mature seeds and fruits and their parent trees, indicating that their mature seeds and fruits were not dispersed far from their parent trees.

Dissecting components of flowering pattern: size effects on female fitness

Flowering synchrony is essential for plant reproductive success, especially in the case of small-sized populations of self-incompatible species. Closely related to synchrony, flowering intensity influences pollinator attraction and pollinator movements. Thus, a high flowering intensity may increase pollinator attraction but, at the same time, may also increase the probability of geitonogamous pollinations. Depending on the mating system, the female fitness of plants in small populations may be affected by both the positive effects of higher flowering synchrony and pollinator attraction and the negative effects of geitonogamous pollinations induced by a high flowering intensity. It was hypothesized that different-sized plants in a population would show contrasting flowering patterns, resulting in differences in pollinator behaviour. These influences could result in differences in mating and female reproductive success. This hypothesis was tested by studying the flowering pattern of Erodium paularense (Geraniaceae), a rare and endangered endemic of central Spain. The temporal distribution of flower production was explored throughout the reproductive season, and the probability of xenogamy and geitonogamy and their relationship to plant size and fitness components were calculated. The analysis of this partially self-compatible species showed diverse flowering patterns related to different plant sizes. Small plants produced a larger number of seeds per fruit in spite of having lower values of flowering synchrony. By contrast, large plants produced a larger number of seeds from geitonogamous pollinations. The effect of different flower displays and outcrossing rates on seed set varied throughout the season in the different groups. Our findings highlight the relevance of individual plant size-dependent phenology on female reproductive success and, in particular, on the relationship between flowering synchrony and fitness. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 156, 227–236.

Flowering, capsule and seed characteristics in Cuphea

We modeled the flowering and capsule set dynamics, quantified the level of variation in seed characteristics, elucidated the inter-relationships between seed and capsule physical dimensions, and quantified their impact on single seed weight in the cuphea germplasm line PSR23. Temporal patterns of flowering and capsule set were largely time-dependent and highly auto-correlated, with significant autoregressive parameters of number of flowers (0.76) and number of capsules (0.74). Large numbers of seeds per capsule were associated with large coefficient of variation in single seed weight. Seed number and seed weight per capsule, when log-transformed, exhibited a slope of −0.65 indicating that cuphea plants have only a limited capacity to maintain seed weight by adjusting seed number if resources vary. Capsule tissue/seed weight ratio and number of seeds per capsule have the largest potential impact on single seed weight. Sensitivity analyses indicated that capsule perimeter (>76 mm), capsule major (>23 mm) and minor axes (>7.0 mm), capsule circularity (between 0.350 and 0.375), capsule area (<85 mm2), capsule tissue/seed weight ratio (<0.40), and number of seeds per capsule (∼9.0) would optimize single seed weight. This information would help plant breeders exploit genotypic variability in seed and capsule characteristics and agronomists identify optimum trait combinations to produce high yields of this potential oilseed crop.

Effects of seed migration on post‐implant dosimetry of prostate brachytherapy

Brachytherapy using permanent seed implants has been an effective treatment for prostate cancer. However, seeds will migrate after implant, thus making the evaluation of post-implant dosimetry difficult. In this study, we developed a computer program to simulate seed migration and analyzed dosimetric changes due to seed migration at various migration amounts. The study was based on 14 patients treated with Pd-103 at the James Cancer Hospital. Modeling of seed migration, including direction, distance as well as day of migration, was based on clinical observations. Changes of commonly used dosimetric parameters as a function of migration amount (2, 4, 6 mm respectively), prostate size (from 20 to 90 cc), and prostate region (central vs peripheral) were studied. Change of biological outcome (tumor control probability) due to migration was also estimated. Migration reduced prostate D90 to 99+/-2% of original value in 2 mm migration, and the reduction increased to 94+/-6% in 6 mm migration. The reduction of prostate dose led to a 14% (40%) drop in the tumor control probability for 2 mm (6 mm) migration, assuming radiosensitive tumors. However, migration has less effect on a prostate implanted with a larger number of seeds. Prostate V100 was less sensitive to migration than D90 since its mean value was still 99% of original value even in 6 mm migration. Migration also showed a different effect in the peripheral region vs the central region of the prostate, where the peripheral mean dose tended to drop more significantly. Therefore, extra activity implanted in the peripheral region during pre-plan can be considered. The detrimental effects of migration were more severe in terms of increasing the dose to normal structures, as rectum V50 may be 70% higher and urethra V100 may be 50% higher in the case of 6 mm migration. Quantitative knowledge of these effects is helpful in treatment planning and post-implant evaluation.

Extreme long-distance seed dispersal via sheep

Extremely long seed dispersal distances occur as a result of processes such as ocean drift and tornadoes. However, we have found that large numbers of seeds with different morphologies (Trifolium angustifolium, Daucus carota, Hordeum murinum, and Plantago lagopus) are frequently dispersed equivalent distances while attached to migrating ungulates. We determined experimentally that seeds attached to the fleece of traditional nomadic (“transhumant”) sheep are transported distances of up to several hundred kilometers in substantial numbers (ranging from 5–47% of the initial seed population). Given the current and historical importance of migrating herds of sheep (wild and domestic) on different continents, the results of this study highlight the role of adhesion in long-distance dispersal and support the inclusion of migrating ungulates among forces responsible rapid plant migrations (eg following glaciations, invasion events, or in a future global change scenario). Our results also highlight an unexplored ecological consequence of abandoning nomadism.

Commercial Bumble Bee Bombus impatiens (Hymenoptera: Apidae) as a Pollinator in Lowbush Blueberry (Ericale: Ericaceae) Fields

Here, we evaluate the potential of the bumble bee Bombus impatiens Cresson, obtained from commercial colonies, as a pollen vector for lowbush blueberry, Vaccinium augustifolium Aiton. We wanted to gain insight into the relationships between pollination by introduced bumble bees, the categories of seeds produced, and the weight and the maturity of the blueberries. The effect of B. impatiens foraging in blueberry stands was measured quantitatively through fruit set and seed set analysis. We created a density gradient of B. impatiens by clustering 72 small hives at the southern extremity of blueberry fields located in Girardville (49° 00′ N, 72° 33′ W), Quebec, Canada. Observers recorded plant and insect data in 52 plots of 1 by 10 m, distributed at distances ranging from 25 to 1,500 m from the hives. From these data, we evaluated the fruit set rate, the weight and maturity of the berries, and the number of seed structures per berry, including true seeds of large, medium, and small size, pseudo-seeds, and ovules. Positive correlations were found between the density of B. impatiens and fruit set as well as the number of large seeds per berry. Large seeds influenced the weight and maturity of berries. B. impatiens acted as a “near-nest central forager” and increased fruit set and seed production up to 100 and 150 m respectively, from the hives.

Commercial Bumble Bee &lt;I&gt;Bombus impatiens&lt;/I&gt; (Hymenoptera: Apidae) as a Pollinator in Lowbush Blueberry (Ericale: Ericaceae) Fields

Here, we evaluate the potential of the bumble bee Bombus impatiens Cresson, obtained from commercial colonies, as a pollen vector for lowbush blueberry, Vaccinium augustifolium Aiton. We wanted to gain insight into the relationships between pollination by introduced bumble bees, the categories of seeds produced, and the weight and the maturity of the blueberries. The effect of B. impatiens foraging in blueberry stands was measured quantitatively through fruit set and seed set analysis. We created a density gradient of B. impatiens by clustering 72 small hives at the southern extremity of blueberry fields located in Girardville (49 degrees 00' N, 72 degrees 33' W), Quebec, Canada. Observers recorded plant and insect data in 52 plots of 1 by 10 m, distributed at distances ranging from 25 to 1,500 m from the hives. From these data, we evaluated the fruit set rate, the weight and maturity of the berries, and the number of seed structures per berry, including true seeds of large, medium, and small size, pseudo-seeds, and ovules. Positive correlations were found between the density of B. impatiens and fruit set as well as the number of large seeds per berry. Large seeds influenced the weight and maturity of berries. B. impatiens acted as a "near-nest central forager" and increased fruit set and seed production up to 100 and 150 m respectively, from the hives.

Effects of seed predation by ants on Mediterranean grassland related to seed size

Abstract Questions: 1. Do harvester ants (Messor barbarus) promote seed mortality in Mediterranean grassland?; 2. Is this effect greater in large-seeded species? Location: Central Spain. Methods: We established an ant-exclusion experiment of five circular (1.5 m diameter) plots from where ants were excluded during one year, along with ten control plots. We recorded the seed bank of all species in the plots both before and after the treatment. The effect of seed length and weight was analysed after transforming data into phylogenetically independent contrasts, and alternatively by dividing the species data set into morphological groups. Results: Longer and heavier seeded species significantly increased in the seed banks under the exclusion treatment, although ants did not significantly modify overall seed densities. Conclusions: Although the ants do not collect large numbers of seeds, they differentially affect the composition of the seed banks by selecting the longest or heaviest seeds, or both. The persi...

BENEFITS OF SMALL-SIZED CACHES FOR SCATTER-HOARDING RODENTS: INFLUENCE OF CACHE SIZE, DEPTH, AND SOIL MOISTURE

Some granivorous rodents scatter hoard; they bury seeds in shallow pits throughout their territory. These buried caches can represent food stores for the hoarders, food for competitors, or a means of seed dispersal and propagation for plants. Large numbers of seeds may be buried in many caches throughout an area; thus, fate of caches has important consequences for granivores, other animals, and plants. This study examined the ability of Ord’s kangaroo rat (Dipodomys ordii) to exploit artificial caches of different sizes, at 2 depths, and in substrates of differing moisture content. Kangaroo rats harvested significantly more caches in moist substrates and at shallower depths; however, small caches containing � 5 seeds were removed infrequently by individuals regardless of substrate moisture and depth. As cache size was increased in moist sand, a threshold existed at each depth where caches were greatly exploited by kangaroo rats. Results suggest that pilferage of caches under natural conditions is not linear with respect to cache size in moist substrates. As cache size was increased in dry sand, no threshold of increased exploitation was observed for cache sizes used in this experiment. Results also suggest that pilferage of caches under natural conditions is not strongly influenced by size in dry substrates for relatively small caches. Overall, size and depth of caches greatly influence their fate. Perturbations, such as rainfall, also alter detection of caches. To reduce detection of caches by competitors, scatter hoarders should distribute relatively small caches, especially during wet conditions.

Interspecific hybridization between diploid Fagopyrum esculentum and tetraploid F. homotropicum

The wild diploid species Fagopyrum homotropicum (2n = 2x = 16) has been used for buckwheat improvement, but, prior to this study, the tetraploid form (2n = 4x = 32) had not been hybridized with the cultivated species F. esculentum. The objective of this study was to hybridize F. esculentum with tetraploid F. homotropicum to increase the genetic variability. Forty-one interspecific F1 hybrids were obtained through ovule rescue in vitro, with hybridity confirmed using morphological characters, chromosome numbers (2n = 3x = 24) and DNA analysis. The F1 plants were mainly sterile. However, seven seeds were set spontaneously on two hybrid plants, and a large number of seeds were obtained after colchicine treatment. The F2 plants were divided into two groups based on chromosome numbers and morphology. The first group was hexaploid plants (2n = 6x = 48) or hypohexaploid plants (2n = 44–46), partially fertile with “gigas” features including increased height, dark green leaves, and large seeds with thick seed hulls. The second group of plants was diploid (2n = 2x = 16) (one plant had 17 chromosomes), with normal growth and fertility, and a combination of characters from both parents, indicating that genetic recombination had occurred during chromosome elimination. The diploid group was superior to the hexaploid group for use in buckwheat breeding programs due to the desirable characters and the ease of crossing. This is the first report of interspecific hybridization using different ploidy levels in the Fagopyrum genus. Key words: Buckwheat (F. esculentum; F. homotropicum), interspecific hybridization, breeding, tetraploid, diploid, hexaploid, fertility

Number and weight of seeds and reproductive strategies of herbaceous plants

The paper brings data set of seed reproduction of about 500 wild herbaceous species of Central Europe and presents a number of produced seeds in a new way. Number of seeds — reproductive capacity of a population (RCP) was defined as a number of seeds produced by one species per 1 m2 at its one-hundred-per-cent cover per one season. About 23% of seed weight variability and about 26% of variability in RCP were explainable on a family level. The trade-off between RCP and seed weight was confirmed both within families and also among families. Both characteristics had higher variability on a family level and on lower taxonomic levels than on subclass and class levels. Species with an annual life cycle have a larger number of seeds than perennials. Geophytes and species without lateral spread have a tendency to produce a large amount of relatively weighty seeds in comparison to other life forms, and to species with vegetative lateral spread. Species with seeds dispersed by wind usually have a large number of lightweight seeds. Multivariate analyses confirmed some tendencies of reproductive traits which correspond to the definition of C-, S-, R- strategies by Grime — “verification” of the RCP as ecological trait. The R- strategy was well distinguished from the C- and S- strategies by reproductive traits, whereas C- and S- strategies are very similar to each other. Species with insect pollination agent often correspond to C- strategy, wind agent to S- strategy, and species with self-pollination to R- strategy.

The Biology of Invasive Alien Plants in Canada. 1. Eriochloa villosa (Thunb.) Kunth

The annual grass weed Eriochloa villosa, woolly cup grass, was reported for the first time in Canada in 2000, in southwestern Quebec. It is a serious agricultural pest of field crops in the Midwest United States where it has been difficult and expensive to control. The production of stolons early in the growing season and the extensive branching of stems later in the season mean that single plants occupy and disperse seed over a large area. Cleistogamous flowers ensure good seed set, and plants produce large numbers of seeds. After an initial spring germination flush, seeds continue to germinate throughout the growing season resulting in escapes from early control measures. The large seeds can germinate and emerge under a wide range of soil temperatures and soil depths. Woolly cup grass is tolerant of many herbicides and effective control in agro-ecosystems usually depends on integrated strategies of multiple herbicide applications, cultural and mechanical methods. The above biological features and its presence in a number of bordering States suggest that the species is a potential weed hazard in southern Canada, particularly in areas of corn and soybean production in Quebec and Ontario. Key words: Eriochloa villosa, woolly cup grass, ERBVI, weed biology, invasive alien

High levels of genetic diversity in populations of Iris aphylla L. (Iridaceae), an endangered species in Poland

We used RAPDs (Random Amplified Polymorphic DNAs) to investigate genetic diversity and its partition within and between three populations of Iris aphylla in Poland. Analysis of Molecular Variance (AMOVA) of 84 distinct RAPD multiband genotypes revealed higher variation within populations (77.2%) than genetic differentiation between them (22.8%, P < 0.002). Values of genetic diversity indices (H) were similar in all three sites (0.21–0.24). The differentiation of the populations corresponded to low average gene flow (Nm = 0.81). Our results indicated that genetic diversity was independent of population size. We concluded that although sexual reproduction and gene flow between populations of I. aphylla were very limited, they preserved high levels of genetic diversity. Relatively large number of seeds, which migrated in the past to populations, as well as patterns of reproduction and life history of I. aphylla may explain this situation.

Phenotypic trade‐offs in the sexual reproduction of Salicaceae from flood plains

We studied the relationship of seed mass to seed longevity (controlled conditions) and to seed number in six species of Salicaceae (Populus nigra, Salix alba, S. daphnoides, S. elaeagnos, S. purpurea, and S. triandra) that frequently co-occur on European flood plains. These species regenerate sexually in the same habitat but differ in seed mass. Half-viability periods, i.e., the time after which 50% of the initially viable seeds no longer germinate, were short (between 6.5 ± 0.1 and 23.3 ± 0.3 d), and large numbers of seeds were produced (between 10 000 and 1 × 10(6) per plant). Mean seed mass ranged from 0.02 ± 0.001 mg in S. triandra to 0.80 ± 0.05 mg in P. nigra. Whereas seed mass was, against expectation, positively related to half-viability periods, seed number generally decreased with increasing seed mass. Thus, a phenotypic trade-off between seed mass and seed number appears to be accentuated by an increase in seed longevity with increasing seed mass.