Pollination Ecology, Breeding System, and Conservation of Butia lallemantii Deble & Marchiori (Arecaceae): A Useful Dwarf Palm Tree from the Pampa.

The Dwarf Palm, Butia lallemantii Deble & Marchiori, is an endangered species endemic to the Pampa biome and typically grows in sandy and rocky soils. Given its economic, ecological, and cultural relevance, it is crucial to understand the ecology and biology of this species to encourage its preservation and highlight its significance for the Pampa. This study aims to investigate whether this palm relies on animal vectors for pollination, analyze its breeding system, and propose strategies for its conservation and sustainable use. We conducted field observations on pollination ecology, identified floral visitors, and designed six breeding system experiments to test cross-compatibility, self-compatibility, and apomixis. Additionally, we conducted a literature review to propose conservation strategies. Butia lallemantii is pollinator-dependent and self-compatible. The flowers are mostly melittophilous and offer pollen and nectar for floral visitors. The main pollinators are native Meliponinae and Halictinae bees and the introduced Apis mellifera. This study represents the first comprehensive and complete examination of the breeding system and pollination process on Butia palms. This palm can provide materials for industries, but urgent actions are needed to preserve the remaining populations through effective policies and strategies. Furthermore, this palm should be integrated into diversified agroecosystems to evaluate its adaptability to cultivation.

Flower morphology as a predictor of pollination mode in a biotic to abiotic pollination continuum.

BACKGROUND AND AIMS: Wind pollination has evolved repeatedly in flowering plants, yet the identification of a wind pollination syndrome as a set of integrated floral traits can be elusive. Thalictrum (Ranunculaceae) comprises temperate perennial herbs that have transitioned repeatedly from insect to wind pollination while also exhibiting mixed pollination, providing an ideal system to test for evolutionary correlation between floral morphology and pollination mode in a biotic to abiotic continuum. Moreover, the lack of floral organ fusion across this genus allows testing for specialization to pollination vectors in the absence of this feature. METHODS: We expanded phylogenetic sampling in the genus from a previous study using six chloroplast loci, which allowed us to test whether species cluster into distinct pollination syndromes based on floral morphology. We then used multivariate analyses on floral traits followed by ancestral state reconstruction of the emerging flower morphotypes and determined whether these traits are evolutionarily correlated under a Bayesian framework with Brownian motion. KEY RESULTS: Floral traits fell into five distinct clusters, which were reduced to three after considering phylogenetic relatedness and were largely consistent with flower morphotypes and associated pollination vectors. Multivariate evolutionary analyses found a positive correlation between the lengths of floral reproductive structures (styles, stigmas, filaments and anthers). Shorter reproductive structures tracked insect-pollinated species and clades in the phylogeny, whereas longer structures tracked wind-pollinated ones, consistent with selective pressures exerted by biotic vs. abiotic pollination vectors, respectively. CONCLUSIONS: Although detectable suites of integrated floral traits across Thalictrum were correlated with wind or insect pollination at the extremes of the morphospace distribution, a presumed intermediate, mixed pollination mode morphospace was also detected. Thus, our data broadly support the existence of detectable flower morphotypes from convergent evolution underlying the evolution of pollination mode in Thalictrum, presumably via different paths from an ancestral mixed pollination state.

Flowering Biology of Alisma plantago-aquatica (Alismataceae).

Field observations of flowering Alisma plantago-aquatica plants were carried out in Moscow region (Russia). The A. plantago-aquatica flower remains anthetic for a single light day, from 9:00 a.m. to 8:00 p.m. White petals showed a contrast bicolored pattern in UV light, and the pattern probably serves as a nectar clue for pollinators. Flowers were visited by insects in daytime from 11:00 a.m. to 3:00 p.m. Coleopterans (Coccinellidae), dipterans (Drosophilidae, Hybotidae, Muscidae, Sepsidae, and Syrphidae), and hymenopterans (Apidae) were observed as flower visitors. Hoverflies (Syrphidae) and bees (Apidae) were the most frequent visitors. Large amounts of A. plantago-aquatica pollen grains were found on their bodies, and a major role in pollination was consequently assumed for the insects. Based on the original findings and literature data on A. plantago-aquatica reproductive biology in Belgium, Slovakia, and the Czech Republic, hoverflies were identified as the most stable and efficient pollinators of A. plantago-aquatica in various parts of the species range. Bees (Apidae) were recognized as A. plantago-aquatica pollinators for the first time in this work. A flower isolation experiment confirmed that A. plantago-aquatica is a self-compatible plant, but requires insects for the most efficient cross-pollination.

Possible long-proboscid insect pollinators from the Early Permian of Russia.

Insect pollination is one of the hallmarks of flowering plants.1 Bees, moths, flies, and some other pollinators evolved elongate siphonate mouthparts for sucking concealed nectar and occasionally other liquids.2 However, it is clear from the fossil record that insects with similar adaptations appeared long before the mid-Cretaceous radiation of angiosperms. These insects most probably used their proboscis to reach pollination drops and other sugary fluids that were hidden in the cones of extinct gymnosperms, pollinating them in the process.3-6 The vast majority of these gymnosperm-associated long-proboscid insects have been reported from the Middle Jurassic to the Early Cretaceous, i.e., the time interval that immediately predated the advent of flowering plants.7 By contrast, the Paleozoic stage of the co-evolution between long-proboscid insect pollinators and plants has remained poorly understood. Here, we report a putative pollination mutualism involving long-proboscid holometabolous insects (Panorpida: Protomeropidae) from the Early Permian of Russia (ca. 283-273 Ma). Their elongate mouthparts have very similar morphology to those of some present-day nectarivorous Coleoptera and Hymenoptera and probably served to imbibe micropylar secretions from the semi-closed ovulate organs of the gymnosperms of a peltaspermalean affinity that have been found in the same locality. This is the earliest record of insects with siphonate-like mouthparts, which could indicate that the complex interactions between pollinators and gymnosperms predate the first flowering plants by over 100 Ma.

Reproductive Biology and Pollination Ecology of Berberis lycium Royle: A Highly Valued Shrub of Immense Medicinal Significance.

Study of reproductive biology and pollination ecology helps in understanding the life history patterns of species. Such a study brings to light the bottlenecks, if any, on account of which the individuals of the species are not able to reproduce in nature and ultimately helps in planning appropriate conservation strategies for the species under threat. The present study was aimed at examining the morphological and reproductive variance in Berberis lycium, a threatened ecological specialist growing within shrubberies and open hillsides of the North-Western Himalayas in India. B. lycium displays three different variants. Flowering period ranges from February to September. Pollen viability as reported on fluorescein diacetate and acetocarmine treatments was highest for variant I, while maximum pollen output was obtained for variant III. Pollen pistil interaction is brought by the movement of anther towards stigma. Fluorescence microscopy of hand pollinated club shaped stigma shows that the germinating pollen form a ring over the receptive adaxial surface. Pollination syndrome is entomophily. Variant II attracts a significantly large number of pollinators from diverse insect families. Breeding experiments reflect that plants are self-compatible and cross fertile. Reproductive output (% fruit set) was highest for variant II followed by III and I, respectively. This investigation helped to understand the effect of different biotic and abiotic constraints on the phenology and reproductive biology of the plant. The information generated so will enable conservationists to design appropriate strategies for its long-term survival and sustenance in nature.

Pollen adaptation to ant pollination: a case study from the Proteaceae.

BACKGROUND AND AIMS: Ant-plant associations are widely diverse and distributed throughout the world, leading to antagonistic and/or mutualistic interactions. Ant pollination is a rare mutualistic association and reports of ants as effective pollinators are limited to a few studies. Conospermum (Proteaceae) is an insect-pollinated genus well represented in the south-western Australia biodiversity hotspot, and here we aimed to evaluate the role of ants as pollinators of C. undulatum. METHODS: Pollen germination after contact with several species of ants and bees was tested for C. undulatum and five co-flowering species for comparison. We then sampled the pollen load of floral visitors of C. undulatum to assess whether ants carried a pollen load sufficient to enable pollination. Lastly, we performed exclusion treatments to assess the relative effect of flying- and non-flying-invertebrate floral visitors on the reproduction of C. undulatum. For this, we measured the seed set under different conditions: ants exclusion, flying-insects exclusion and control. KEY RESULTS: Pollen of C. undulatum, along with the other Conospermum species, had a germination rate after contact with ants of ~80 % which did not differ from the effect of bees; in contrast, the other plant species tested showed a drop in the germination rate to ~10 % following ant treatments. Although ants were generalist visitors, they carried a pollen load with 68-86 % of suitable grains. Moreover, ants significantly contributed to the seed set of C. undulatum. CONCLUSIONS: Our study highlights the complexity of ant-flower interactions and suggests that generalizations neglecting the importance of ants as pollinators cannot be made. Conospermum undulatum has evolved pollen with resistance to the negative effect of ant secretions on pollen grains, with ants providing effective pollination services to this threatened species.

Ant pollination of Paepalanthus lundii (Eriocaulaceae) in Brazilian savanna.

BACKGROUND AND AIMS: Ant-plant associations are widely diverse and distributed throughout the world, leading to complex ecological networks. Regarding ant-plant mutualism, ant pollination is a very rare interaction and few studies have shown the role of ants as pollinators. Therefore, we aimed to evaluate the role of ants as effective pollinators of Paepalanthus lundii (Eriocaulaceae) in a Brazilian savanna. METHODS: Fieldwork with experimental manipulation was conducted to evaluate the fitness of P. lundii, considering potential pollinators. For this, we mainly observed the number of seeds produced in different conditions: control, ant exclusion, exclusion of flying insects, and exclusion (entomophily test) of both ants and flying insects. Furthermore, we evaluated all floral visitors throughout the day, stigma receptivity, the numbers of male and female flowers, and patterns of species co-occurrence, which can indicate the presence of different pollinators in the plants at the same time. KEY RESULTS: We observed a relation between seed production and ant visits; Camponotus crassus was the most frequent floral visitor and the most effective pollinator. Also, we observed a statistical difference between the numbers of male and female flowers produced, with a greater number of male flowers. Furthermore, P. lundii presented flowering asynchrony, with 12 different types of maturation sequence, which indicates a cross-pollination system. Lastly, we observed an overlap of the greatest abundance of C. crassus and the time of plant stigmatic receptivity, and a pattern of non co-occurrence of ants, which shows the pollinator role of this ant. CONCLUSIONS: Our data provide evidence that previous generalizations neglecting the importance of ants as pollinators are wrong. Brazilian savanna can reveal a lot about the ant-pollination syndrome, since this environment presents peculiar characteristics related to this association. Thus, this study has great significance for the understanding of the ant-pollination syndrome, and for the understanding of the complex ecological networks present in these dry arid systems.

Nectar trichome structure of aquatic bladderworts from the section Utricularia (Lentibulariaceae) with observation of flower visitors and pollinators.

In Utricularia, the flower spur is a nectary and in this organ, nectar is produced and stored. This study aimed to examine the structure of the nectary trichomes in four Utricularia species (Utricularia vulgaris L., U. australis R.Br., U. bremii Heer and U. foliosa L.) from the generic section Utricularia. We have investigated whether species with different spur morphology had similar spur anatomy and nectary trichome structure. In Utricularia flowers, nectar is produced by spur capitate trichomes (sessile or stalked). Our results showed that regardless of the various spur morphology, trichomes have similar architecture and ultrastructure. Head cells of these trichomes are transfer cells with an eccrine nectar secretion. Examined species differed in the micromorphology of papillae in spurs. The fly Eristalis tenax was found to be a pollinator of U. vulgaris. Small Halictidae bees seem to be pollinators of U. foliosa.

SEX EXPRESSION, BREEDING SYSTEM AND POLLINATORS OF Piper caldense (PIPERACEAE) IN THE BRAZILIAN ATLANTIC FOREST / Expresión sexual, sistema reproductivo y polinizadores de Piper caldense (Piperaceae) en un bosque Atlántico

ABSTRACT Neotropical Piper species have bisexual flowers. Such reproductive trait is considered basal in this pantropical genus. However, neotropical species having unisexual (staminate) flowers along with bisexual ones have also been reported. Dichogamy is common in the genus, associated with either self-compatibility or -incompatibility, as well as with entomophily. We analyzed a natural population of Piper caldense in a Atlantic Forest area (Viçosa municipality, Minas Gerais state, southeastern Brazil). Preliminary observations indicated that the species produces two flower types. We analyzed flower sex in spikes of 50 plants. We obtained additional information through morphological and anatomical studies and scanning electron microscopy analyses. The longevity and exposure dynamics of stigmatic papillae and the pollen release sequence of all four stamens were investigated to verify the degree of dichogamy. Pollination tests were performed, pollinators were identified and their visitation frequency was recorded. Piper caldense has both bisexual and staminate flowers, each flower type being located on separate spikes. These spikes occurred on the same plant, thus indicating andromonoecy; furthermore, plants having only spikes with staminate flowers were also observed. This gender had not yet been reported to the genus. Gradual and sequential exposure of stigmatic papillae associated with asynchronous pollen release (one stamen a day) resulted in incomplete protogyny. Hand pollination tests showed that the species is self-incompatible. Social bees, mainly Apis mellifera and Melipona spp., were the major pollinator group. Our study reinforces the need to associate morphological analysis with floral biology and indicates future changes in studies addressing reproductive traits associated with the phylogeny of the Piper genus.

RESUMEN Las especies neotropicales de Piper presentan flores bisexuales, condición considerada basal al interior de este género pantropical. Sin embargo, fueron observadas especies neotropicales con flores unisexuales (estaminadas), además de las bisexuales. La dicogamia es común en el género y se encuentra asociada a la autocompatibilidad o incompatibilidad, al igual que la entomofilia. Fue analizada una población natural de Piper caldense en un área de bosque Atlántico (municipio de Viçosa, Minas Gerais, sureste de Brasil). Las observaciones preliminares indicaron que esta especie produce dos tipos florales, para lo cual fue analizada la sexualidad de las flores en 50 espigas a través de estudios morfológicos, anatómicos y análisis con microscopia electrónica de barrido. La longevidad y dinámica de exposición de las papilas estigmáticas y la secuencia de liberación de los granos de polen en los cuatro estambres fueron observados para verificar el grado de dicogamia. El sistema reproductivo se evaluó mediante el test de autopolinización espontánea y polinización abierta. Los visitantes florales fueron identificados y se registró su frecuencia de visita. Piper caldense presenta flores bisexuales y estaminadas, cada tipo floral se encuentra en espigas separadas. Estas espigas se encuentran en la misma planta, lo que indica que es andromonoica; adicionalmente, fueron observadas plantas que solo presentaban espigas con flores estaminadas, lo que se constituye en una combinación sexual inédita para el género. La exposición gradual y secuencial de las papilas estigmáticas asociada con la liberación asincrónica de los granos de polen (un estambre por día) indica una protoginia incompleta. Los test de polinización mostraron que la especie es autoincompatible. Las abejas sociales, principalmente Apis mellifera y Melipona spp., fueron los polinizadores principales. Este estudio refuerza la necesidad de asociar los analisis morfológicos con la funcionalidad de las estructuras florales, además indica los cambios futuros en estudios que abordan características reproductivas asociadas a la filogenia de las especies de Piper.

Insufficient Evidence of Purported Lunar Effect on Pollination in Ephedra.

It has been suggested that the timing of pollination in Ephedra foeminea coincides with the full moon in July. The implication is that the plant can detect the full moon through light or gravity and that this trait is an evolutionary adaptation that aids the navigation by pollinating insects. Here we show that there are insufficient data to make such a claim, and we predict that pollinations of E. foeminea do not in general coincide with the full moon.

Moonlight pollination in the gymnosperm Ephedra (Gnetales).

Most gymnosperms are wind-pollinated, but some are insect-pollinated, and in Ephedra (Gnetales), both wind pollination and insect pollination occur. Little is, however, known about mechanisms and evolution of pollination syndromes in gymnosperms. Based on four seasons of field studies, we show an unexpected correlation between pollination and the phases of the moon in one of our studied species, Ephedra foeminea. It is pollinated by dipterans and lepidopterans, most of them nocturnal, and its pollination coincides with the full moon of July. This may be adaptive in two ways. Many nocturnal insects navigate using the moon. Further, the spectacular reflection of the full-moonlight in the pollination drops is the only apparent means of nocturnal attraction of insects in these plants. In the sympatric but wind-pollinated Ephedra distachya, pollination is not correlated to the full moon but occurs at approximately the same dates every year. The lunar correlation has probably been lost in most species of Ephedra subsequent an evolutionary shift to wind pollination in the clade. When the services of insects are no longer needed for successful pollination, the adaptive value of correlating pollination with the full moon is lost, and conceivably also the trait.

Aerodynamics and pollen ultrastructure in Ephedra.

UNLABELLED: • PREMISE OF THE STUDY: Pollen dispersal is affected by the terminal settling velocity (Ut) of the grains, which is determined by their size, bulk density, and by atmospheric conditions. The likelihood that wind-dispersed pollen is captured by ovulate organs is influenced by the aerodynamic environment created around and by ovulate organs. We investigated pollen ultrastructure and Ut of Ephedra foeminea (purported to be entomophilous), and simulated the capture efficiency of its ovules. Results were compared with those from previously studied anemophilous Ephedra species.• METHODS: Ut was determined using stroboscopic photography of pollen in free fall. The acceleration field around an "average" ovule was calculated, and inflight behavior of pollen grains was predicted using computer simulations. Pollen morphology and ultrastructure were investigated using SEM and STEM.• KEY RESULTS: Pollen wall ultrastructure was correlated with Ut in Ephedra. The relative proportion and amount of granules in the infratectum determine pollen bulk densities, and (together with overall size) determine Ut and thus dispersal capability. Computer simulations failed to reveal any functional traits favoring anemophilous pollen capture in E. foeminea.• CONCLUSION: The fast Ut and dense ultrastructure of E. foeminea pollen are consistent with functional traits that distinguish entomophilous species from anemophilous species. In anemophilous Ephedra species, ovulate organs create an aerodynamic microenvironment that directs airborne pollen to the pollination drops. In E. foeminea, no such microenvironment is created. Ephedroid palynomorphs from the Cretaceous share the ultrastructural characteristics of E. foeminea, and at least some may, therefore, have been produced by insect-pollinated plants.

Fenologia e síndromes de polinização e dispersão de espécies de sub-bosque em um remanescente florestal urbano no Brasil central / Phenology and pollination and dispersal syndromes of understory species in an urban forest remnant in central Brazil

O objetivo foi avaliar a fenologia reprodutiva e as síndromes de polinização e dispersão de um subbosque de Mata Seca Semidecídua. O estudo foi realizado na cidade de Catalão-GO, de maio de 2010 a maio de 2011, no Parque Municipal do Setor Santa Cruz, um fragmento de 29 hectares. A coleta dos dados fenológicos foi semanal utilizando um transecto de 1000 m. Para as síndromes, foi observado à morfologia de flores e frutos, e estes dados foram relacionados aos de fenologia. A floração teve maior índice (43,13%) em dezembro de 2010 (chuva) e a frutificação manteve índices de 25 a 30% na maior parte do ano. Acanthaceae apresentou o maior índice de floração em maio de 2010 e fevereiro de 2011; Piperaceae em outubro de 2010 e Rubiaceae em dezembro 2010. A frutificação em Acanthaceae ocorreu durante a seca e inicio das chuvas, com maior índice em outubro de 2010, Piperaceae na estação das chuvas e inicio da seca, com pico em maio de 2011, e em Rubiaceae ocorreu durante 11 meses, com pico em março de 2011. Duas espécies de Acanthaceae e uma de Piperaceae não apresentaram frutificação, já a fenofase de floração foi observada nessas espécies. Foram identificadas três síndromes de polinização, sendo estas melitofilia (pico de intensidade em outubro de 2010), psicofilia (janeiro de 2011) e ornitofilia (maio de 2010). As síndromes de dispersão foram ornitocoria (dois picos, um em julho de 2010 e outro em maio de 2011) e anemocoria (pico em outubro de 2010). A presença de espécies em floração e/ou frutificação ao longo do ano pode contribuir para a dinâmica e permanência da comunidade estudada, pois essas espécies auxiliam na manutenção de abelhas e aves no fragmento, importantes vetores de polinização e dispersão. Levando em consideração que o Cerrado vem sofrendo um intenso impacto ambiental e a área de estudo ser um fragmento localizado dentro de um perímetro urbano, a sua conservação torna-se de grande importância, apesar de sua pequena área, devido os importantes processos ecológicos que ali existem.

The objective was to identify the reproductive phenology and the pollination and dispersal syndromes of understory species of Semi-deciduous Dry Forest. The work was carried out from May 2010 to May 2011 in a forest fragment, about 29 hectares, localized in Catalão city, Goiás State, Brazil. The phenological phases were observed weekly along a transect at 1000m. Pollination and dispersion syndromes were determined through literature data, and theses data were linked to phenology. The flowering proportion reached the peak (43,13%) in December 2010 (rainy) and fruiting (30%) in September 2010 (dry). Acanthaceae flowering peak in May 2010 and February 2011; Piperaceae peaked in October 2010 and Rubiaceae in December 2010. Fruiting in the Acanthaceae occurred during the dry period and the beginning of the rainy season, with the highest incidence in October 2010, Piperaceae reached their peak in May 2011, while in the Rubiaceae, it went on for 11 months, with the highest incidence being in March 2011. Two Acanthaceae and one Piperaceae species not fruited, but all species presented flowering. Pollination syndromes found were Ornithophily, peaking in May 2010, Melittophily, in October 2010, and Psycophily, in January 2011. Dispersal syndromes found were Anemochoric, with a higher incidence in October 2010, and Ornithocoric with two peaks, one in July 2010 and other in May 2011. The year-long presence of flowering and/or fruiting species contributes to the survival and dynamics of the community studied, because these species play an important role maintaining bees and birds in the fragment, which are important vectors of pollination and dispersal, respectively. Considering the rapid loss of the Cerrado vegetation in recent times and the study site to be a fragment localized inside the urban environment, the conservation of the green area becomes important, regardless of its small size, due to the important ecological processes that lie therein, as portrayed in this study.

Dispersión polínica y éxito reproductivo de cuatro especies arbóreas de un bosque xerófito de Argentina

Pollen dispersion and reproductive success of four tree species of a xerophytic forest from Argentina. The "talares" in eastern Buenos Aires province, Argentina, are coastal xerophitic forests structured by few arboreal species surrounded by a lower and moister soil matrix. We studied the reproductive parameters of the most representative arboreal species (Celtis tala, Scutia buxifolia, Jodina rhombifolia,and Schinus longifolia). Pollen dispersion was studied through floral visitor traps (biotic dispersion) and using gravimetric pollen collectors (abiotic dispersion). The reproductive success (fruit formation rate) of the focal species was studied by enclosing flowers with different mesh bags. The reproductive system varied among the different species. C. tala was anemophilous and selfcompatible. S. buxifolia was entomophilous and floral visitors dependant. J. rhombifolia was entomophylous, although spontaneous autogamy could favor reproduction in the absence of pollinators. Lastly, S. longifolia could be an ambophilous species (pollinated by insects and by the wind). This dual system may be the result of system flexibility mechanism or an evolutionary transition. Rev. Biol. Trop. 57 (1-2): 283-292. Epub 2009 June 30.

Los "talares" del E de la provincia de Buenos Aires son bosques xerófitos costeros estructurados por pocas especies arbóreas rodeados de una matriz de suelos más bajos y húmedos. Estudiamos los parámetros reproductivos de las especies arbóreas más representativas (Celtis tala, Scutia buxifolia, Jodina rhombifolia y Schinus longifolia). La dispersión polínica fue estudiada a través de trampas para visitantes florales (dispersión biótica) y utilizando recolectores gravimétricos de polen (dispersión abiótica). El éxito reproductivo (tasa de formación de frutos) de las especies focales fue estudiado a través de embolsado de flores con bolsas de distintos tipos de malla. El sistema reproductivo varió entre las especies. C. tala resultó anemófila y autocompatible, S. buxifolia fue entomófila y dependiente de los visitantes florales. J. rhombifolia fue una especie entomófila, aunque la autogamia espontánea podría favorecer al aseguramiento reproductivo en caso de falta de polinizadores. Finalmente, S. longifolia podría ser una especie ambófila (polinizada por insectos y por el viento). Este sistema dual podría ser el resultado de un mecanismo de flexibilidad del sistema de polinización o una transición evolutiva.

Pollen limitation of reproductive effort in willows.

Pollen limitation of seed set differs from resource limitation in its implications for the evolution of floral traits. Willow flowers attract insects, but also abundantly produce wind-dispersed pollen. I demonstrated pollen limitation in single branches bearing 2-4 inflorescences (catkins) in a field experiment with five species by artificially increasing or decreasing the pollen load. Because the responses by single branches might be explained by diversion of resources to better-pollinated branches within a plant, a second experiment with one species tested both pollen limitation of whole plants and the autonomy of catkins. Seed set of single willow catkins is unaffected by experimental alterations of seed set in other catkins on the same plant. Hand-pollination of single catkins and of whole plants increased seed set to the same degree, suggesting there is little or no competition for resources between catkins only 5-10 cm apart. Thus, seed set in willows appears to be pollen limited, favoring insect pollination and the evolution of entomophilous traits. The data support previous views that willows have a dual pollination system utilizing wind and insects.