Polemonium Foliosissimum Research Articles

Feeding friend and foe: ample pollen mitigates the effects of pollen theft for a gynodioecious plant, Polemonium foliosissimum (Polemoniaceae).

Most angiosperms rely on pollinators to transport pollen and effect fertilization. While some floral visitors are effective pollinators, others act as thieves, consuming pollen but effecting little pollination in return. The importance of pollen theft in male and female reproductive success has received little attention. Here, we examined if pollen consumption by flies altered pollen receipt and exacerbated pollen limitation for a bumblebee-pollinated plant, Polemonium foliosissimum (Polemoniaceae). To examine the effect of pollen-thieving flies, we took a three-pronged approach. First, we used single-visit observations to quantify pollen removal and pollen deposition by flies and bumblebees. Second, we manipulated pollen in the neighbourhood around focal plants in two years to test whether pollen reduction reduced pollen receipt. Third, we combined pollen reduction with hand-pollination to test whether pollen thieving exacerbated pollen limitation. Polemonium foliosissimum is gynodioecious in most populations in the Elk Mountains of central Colorado, USA. Thus, we also tested whether pollen theft affected hermaphrodites and females differently. Flies removed significantly more pollen and deposited less pollen per visit than did bumblebees. Reduction of pollen in the neighbourhood around focal plants reduced pollen receipt in both years but only nearly significantly so in 2015. In 2016, plants were significantly pollen-limited; hand-pollination significantly increased seeds per fruit for both hermaphrodites and females. However, the reduction of pollen around focal plants did not exacerbate pollen limitation for either hermaphrodites or females. Our results suggest that plants tolerate significant consumption of pollen by thieves and pollinators by producing ample pollen to feed both and fertilize available ovules. Our results demonstrate that pollen limitation in P. foliosissimum is driven by lack of effective pollinators rather than lack of pollen. Teasing out these effects elucidates the relative importance of drivers of reproductive success and thus the expected response to selection by different floral visitors.

Direct and indirect effects of episodic frost on plant growth and reproduction in subalpine wildflowers.

Frost is an important episodic event that damages plant tissues through the formation of ice crystals at or below freezing temperatures. In montane regions, where climate change is expected to cause earlier snow melt but may not change the last frost-free day of the year, plants that bud earlier might be directly impacted by frost through damage to flower buds and reproductive structures. However, the indirect effects of frost mediated through changes in plant-pollinator interactions have rarely been explored. We examined the direct and pollinator-mediated indirect effects of frost on three wildflower species in southwestern Colorado, USA, Delphinium barbeyi (Ranunculaceae), Erigeron speciosus (Asteraceae), and Polemonium foliosissimum (Polemoniaceae), by simulating moderate (-1 to -5°C) frost events in early spring in plants insitu. Subsequently, we measured plant growth, and upon flowering measured flower morphology and phenology. Throughout the flowering season, we monitored pollinator visitation and collected seeds to measure plant reproduction. We found that frost had species-specific direct and indirect effects. Frost had direct effects on two of the three species. Frost significantly reduced flower size, total flowers produced, and seed production of Erigeron. Furthermore, frost reduced aboveground plant survival and seed production for Polemonium. However, we found no direct effects of frost on Delphinium. When we considered the indirect impacts of frost mediated through changes in pollinator visitation, one species, Erigeron, incurred indirect, negative effects of frost on plant reproduction through changes in floral traits and pollinator visitation, along with direct effects. Overall, we found that flowering plants exhibited species-specific direct and pollinator-mediated indirect responses to frost, thus suggesting that frost may play an important role in affecting plant communities under climate change.

Wise flies: a pre-dispersal seed predator prefers hermaphrodites over females in the gynodioeciousPolemonium foliosissimum

1. Oviposition choices can profoundly affect offspring performance. Oviposition decisions of the dipteran pre-dispersal seed predator, Hylemya sp. (Diptera: Anthomyiidae), when choosing among sex morphs of their host-plant—Polemonium foliosissimum Hook—were evaluated. Polemonium foliosissimum is gynodioecious, with female and hermaphrodite sex morphs that differ in flower size. 2. It was asked: Do female flies preferentially oviposit on hermaphrodite plants and, if so, are oviposition choices correlated with flower size? Is larval survivorship higher on hermaphrodite plants and, if so, is larval success correlated with flower size? Can the differences in oviposition and/or larval success be explained by slight differences in flowering phenology between the sexes? 3. Hermaphrodite flowers received 45% more Hylemya eggs than females. Although hermaphrodites had larger petals and sepals than females, egg loads were not correlated with petal or sepal size. Larval survival was 30% greater on hermaphrodites than females and higher on plants with larger sepals. However, the difference in sepal area between genders did not fully explain larval survival differences. Egg numbers declined over weeks, but differences in egg loads between the sex morphs were not attributable to a slight phenological delay of females. Larval survival declined over the season; however, larval survival differences between sex morphs were consistent. 4. Hylemya preferentially oviposited on hermaphrodites where their larvae had a significantly greater survival rate compared with females. The present results add to the knowledge that intra-specific choices have consequences for phytophagous insects and that the relationship between antagonists and their gynodioecious host plants is complex.

Lack of sex-specific differences in mycorrhizal associations and response to herbivory in the gynodioecious herb, Polemonium foliosissimum

For decades, evolutionary plant biologists have been interested in how females reap a fitness advantage and are thus maintained in gynodioecious plants. Recent attention has focused on the role of multi-species interactions in the maintenance of females, wherein the role of arbuscular mycorrhizal fungi (AMF) is virtually unknown. AMF form symbiotic associations with plants, often resulting in enhanced nutrient acquisition and tolerance to biotic and abiotic stress. Depending on the degree to which females and hermaphrodites rely on their AMF partners, AMF could differentially affect plant tolerance to stress. We conducted a field experiment to examine (1) if females and hermaphrodites of the gynodioecious herb, Polemonium foliosissimum, differentially associate with AMF, and (2) if there was a difference in AMF colonization between the sexes after imposing stress by simulating herbivore damage. First, we compared mycorrhizal colonization between the sexes under ambient (i.e., undamaged) field conditions. Then, for a second set of plants, we simulated herbivory by clipping plants and compared mycorrhizal colonization, leaf phosphorus concentration [P], and fruit and seed production between clipped and control plants. Mycorrhizal colonization did not differ between sexes under ambient field conditions or under the stress imposed by clipping. Clipping did, however, influence both percent root length and vesicle colonization in a plant-size-dependent manner. Overall, colonization and vesicle number increased with plant size for clipped plants, but decreased with size for non-clipped plants. Leaf [P] did not differ between the sexes nor was influenced by clipping, and leaf [P] was not associated with mycorrhizal colonization. Furthermore, neither fruit set nor seed production was associated with mycorrhizal colonization. Our findings suggest that the sexes of P. foliosissimum do not differentially associate with nor differentially garner benefit from mycorrhizal fungi. However, a complete accounting of the costs and benefits of AMF for gynodioecious species must encompass the full life-history of the plant.

Selection of trait combinations through bee and fly visitation to flowers of Polemonium foliosissimum

Pollinators are known to exert natural selection on floral traits, but the extent to which combinations of floral traits are subject to correlational selection (nonadditive effects of two traits on fitness) is not well understood. Over two years, we used phenotypic manipulations of plant traits to test for effects of flower colour, flower shape and their interaction on rates of pollinator visitation to Polemonium foliosissimum. We also tested for correlational selection based on weighting visitation by the amount of conspecific pollen delivered per visit by each category of insect visitor. Although bumblebees were the presumed pollinators, solitary bees and flies contributed substantially (42%) to pollination. In manipulations of one trait at a time, insects visited flowers presenting the natural colour and shape over flowers manipulated to present artificial mutants with either paler colour or a more open or more tubular flower. When both colour and shape were manipulated in combination, selection on both traits arose, with bumblebees responding mainly to colour and flies responding mainly to shape. Despite selection on both floral traits, in a year with many bumblebees, we saw no evidence for correlational selection of these traits. In a year when flies predominated, fly visitation showed a pattern of correlational selection, but not favouring the natural phenotype, and correlational selection was still not detected for expected pollen receipt. These results show that flower colour and shape are subject to pollinator-mediated selection and that correlational selection can be generated based on pollinator visitation alone, but provide no evidence for correlational selection specifically for the current phenotype.

(61) Pot-in-pot Production of Intermountain West Native Herbaceous Perennials

Low water landscapes are increasing popular and important in the urban areas of the Intermountain West (IMW). Perennial wildflowers are an essential part of low water landscapes, and are a dominant plant type in IMW native habitats. We compared pot-in-pot (PIP) vs. conventional above-ground (CAG) production of six IMW native wildflower species, Mirabilismultiflora, Aquilegia caerulea, Penstemon palmeri, Polemonium foliosissimum, Sphaeralcea grossularifolia, and Penstemonstrictus in #1 (4-L) containers. Media temperature, container-plant water loss, stomatal conductance, and growth were measured during two production cycles per year over 2 years. Growing medium temperatures in the PIP system averaged 10 °C cooler than in the CAG system. Consistent with cooler growing media, overall water loss of PIP-grown plants averaged 10% lower than plants grown in the CAG production system. Lower growing media temperatures apparently affected transpiration, as stomatal conductance was about 60% higher in the PIP system as compared to the CAG-grown plants. The integrated effect of lower growing media temperatures on plant performance resulted in about one-third greater top and root growth for plants growing in the PIP system compared to those in the CAG system. Pot-in-pot production may be an economically suitable nursery system for producing IMW native perennial wildflowers by reducing water loss and enhancing growth.

Volatile production by buds and corollas of two sympatric, confamilial plants, Ipomopsis aggregata and Polemonium foliosissimum.

We used solid-phase microextraction of headspace samples followed by gas chromatography and mass spectrometry to identify and quantify the major volatile compounds produced by the buds and corollas of Ipomopsis aggregata (Polemoniaceae), and we compared them to a sympatric, confamilial plant species, Polemonium foliosissimum. The two species have distinct floral morphologies and pollinators, but share a common predispersal seed predator that oviposits under the calyces of buds. Ipomopsis aggregata buds emitted fewer compounds than the corollas. The buds of I. aggregata were dominated by alpha-pinene and, to a lesser extent, beta-pinene. The corollas of I. aggregata emitted a mixture of 10 compounds. Like the buds, I. aggregata corollas produced relatively high concentrations of alpha-pinene as well as caryophyllene. In addition, the emission of four terpenoids, three esters, and one ketone added to the volatile bouquet of the corollas. Polemonium foliosissimum buds also emitted fewer compounds than the corollas. The buds of P. foliosissimum were dominated by beta-pinene and, to a lesser extent, alpha-pinene. The corollas of P. foliosissimum were also dominated by beta-pinene along with three terpenoids, three alcohols, one ester, and two aldehydes. Comparing I. aggregata and P. foliosissimum, bud samples from both species produced considerable amounts of alpha- and beta-pinene. Ipomopsis aggregata emitted more alpha-pinene than beta-pinene, while P. foliosissimum emitted more beta-pinene. The corollas of the two species, however, differed in their volatile bouquet. The partition of volatiles between I. aggregata and P. foliosissimum buds and corollas and differences in volatile production between I. aggregata and P. foliosissimum are consistent with selection pressures exerted by organisms interacting with these plants.

Choices and Consequences of Oviposition by Hylemya (Delia) Sp. (Diptera: Anthomyiidae)

Hylema sp.5females oviposit on the undersides of sepals of developing buds of both Ipomopsis aggregata and Polemonium foliosissimum. Eggs deposited on the latter are significantly more likely to be fully protected by the sepal than are eggs deposited on the former. Unexposed eggs have a significantly greater likelihood of successfully developing to the larval stage than do exposed eggs. The difference in frequency of egg exposure on the two plant species can be attributed to differences in sepal morphology: I. aggregata sepals are significantly narrower than those of P. foliosissimum. The hypothesis that females preferentially oviposit on larger flowers was unconfirmed by a manipulative choice experiment. Plants differing in the size of their flowers were potted together and presented to Hylemya in arrays in the field. Flowers of the larger-flowered pair were no more likely to be oviposited on than flowers of the smaller-flowered pair. However, there were significant negative correlations between the corolla length and the percentage of flowers laid on per day at each of two sites. There was also a significant positive correlation between the corolla width and the percentage of flowers laid on at one site. Thus females appear to be using some measure of flower morphology, or a correlated trait, in making oviposition decisions. The degree to which Hylemya is making suboptimal choices between host plant species is discussed and requires further examination.

EFFECTS OF POLLINATORS, HERBIVORES, AND SEED PREDATORS ON FLOWERING PHENOLOGY

The evolution of flowering phenology has most often been examined in light of one set of organisms, namely pollinators. However, the patterns of flowering phenology observed in nature are likely to reflect evolutionary compromises in response to a variety of selective forces. Two of the most important potentially opposing selective forces that could elicit such a compromise are pollinators and pre-dispersal seed predators. Using a case study from my own work on the pollinators and pre-dispersal seed predators of two members of the Polemoniaceae, Polemonium foliosissimum and Ipomopsis aggregata, I show that the outcome of selective pressures is not always predictable by examining one group of organisms or another. In addition, the outcome of separate and combined selective pressures is variable among years. Thus I show that only by considering all organisms that affect the fitness of a plant may we gain a complete understanding of the evolution of floral traits. I argue that we must account for both geographical and temporal variation in assessing the ecological and evolutionary importance of interacting organisms.

Effects of Pollinators, Herbivores, and Seed Predators on Flowering Phenology

The evolution of flowering phenology has most often been examined in light of one set of organisms, namely pollinators. However, the patterns of flowering phenology observed in nature are likely to reflect evolutionary compromises in response to a variety of selective forces. Two of the most important potentially opposing selective forces that could elicit such a compromise are pollinators and pre-dispersal seed predators. Using a case study from my own work on the pollinators and pre-dispersal seed predators of two members of the Polemoniaceae, Polemonium foliosissimum and Ipomopsis aggregata, I show that the outcome of selective pressures is not always predictable by examining one group of organisms or another. In addition, the outcome of separate and combined selective pressures is variable among years. Thus I show that only by considering all organisms that affect the fitness of a plant may we gain a complete understanding of the evolution of floral traits. I argue that we must account for both geographical and temporal variation in assessing the ecological and evolutionary importance of interacting organisms.

Oviposition Patterns and Larval Success of a Pre-Dispersal Seed Predator Attacking Two Confamilial Host Plants

Phytophagous insects that deposit eggs directly on hosts confront a plant world of variable quality. Some studies to date provide evidence for positive relationships between the site of oviposition and offspring success, as expected if females choose sites of high quality or if they or their offspring manipulate host physiology. We studied relationships between oviposition site and larval success for the anthomyiid fly Hyle-mya sp., a predispersal seed predator of the confamilial montane plants Polemonium foliosissimum and Ipomopsis aggregata. The intensity of oviposition on a given P. foliosissimum plant was a good predictor of attack in the following year, suggesting choosiness of female flies. However, larval survival did not decline detectably when eggs were transferred among flowers within or between plants, compared to survival where the female fly originally had deposited the eggs. Also, P. foliosissimum flowers with eggs did not have a higher probability of setting fruit than those without. In contrast, I. aggregata flowers on which Hylemya laid eggs had a significantly higher probability of setting fruit than flowers chosen at random ; this probability did not decline if eggs were removed experimentally. These results suggest that female flies are choosing among I. aggregata flowers in an adaptive manner, or manipulating their quality on behalf of offspring.

Partition of Fragrance between Calyx and Corolla in Polemonium foliosissimum

In two populations of Polemonium foliosissimum separated by 500 m elevation in the Colorado Rockies, the floral structures of individual plants produced a succession of fragrances during the reproductive cycle: buds smelled pungent or skunky; most blossoms exuded a pleasant floral fragrance and fruits reverted to a pungent or skunky odor. Dissection of the floral parts revealed that the pungent and skunky volatiles originated in the calyx, whereas the sweet floral scent originated in the corolla. Gas chromatography confirmed that the chemical composition of the corolla differed from that of the calyx and provided tentative identification of some of the compounds responsible for the fragrances.

Experimental Manipulations of Polemonium Foliosissimum: Effects on Subsequent Nectar Production, Seed Production and Growth

(1) The carbon budgets of Polemonium foliosissimum individuals were experimentally manipulated. The amount of available carbon was decreased by defoliating 50% of each plant, while available carbon was enhanced by daily watering and by removing either 50% or 100% of the flower buds. (2) Rates of nectar production per flower were constant across all treatments except for a significant increase observed in the watered individuals. (3) There were no consistent changes in average seed set per flower or per plant across treatment groups. (4) Defoliated and control individuals did not differ significantly from one another with respect to average seed weight, but end-of-season underground biomass was significantly less for defoliated plants relative to controls. (5) In the year following treatment, no differences were observed in nectar production per flower, seed production per flower or seed production per plant, although a significant difference in rate of growth was observed. Defoliated plants grew least during the 2-year period, followed by control individuals. The debudded plants increased in size by the greatest margin. (6) The trade-offs between resources allocated to nectar, flowers, seeds and vegetative growth can apparently be expressed in terms of biomass.

Reproduction in Polemonium: Assessing the Factors Limiting Seed Set

Evidence of pollen and/or resource limitation of seed production in the herbaceous perennial plant Polemonium foliosissimum was investigated. Large numbers of open flowers on selected individuals were hand-pollinated at regular intervals, and seed set was compared with that of control blossoms on those same plants as well as with that of control flowers on control individuals. Experimental and control individuals were monitored and reproductive output measured during the following flowering season as well. Although hand-pollinated flowers set significantly more seeds than did either set of control blossoms, the results suggest that individual reproduction (i.e., the total number of seeds produced by a plant) was limited by resources other than pollen. Pollen availability may also have limited seed production, but to a lesser extent. A proper protocol for examining the limitation of seed set is developed, and the biases inherent in most of the simplified procedures currently in use are discussed.

Reproduction in Polemonium: factors influencing outbreeding potential.

Three measures of potential outbreeding efficiency were quantified throughout two flowering seasons in a population of the mass-flowering Polemonium foliosissimum: 1) the distances flown between plants by bumblebee pollinators; 2) the proximity of visited plants; and 3) the diversity of individuals visited. Results were consistent between years. Individual plants did not function differentially with respect to female (i.e., pollen receipt) and male (i.e., pollen donation) function. Both female and male components of outbreeding, as estimated by all three measures, were positively correlated with the number of flowers per plant. Significantly more outbreeding could occur during the final phase of flowering when most individuals had relatively few blossoms. Although the potential for outbreeding was the same at any time through an individual's blooming regime, individuals for which the peak of blooming occurred after the peak for the population as a whole have significantly more outbreeding potential via both female and male function. These factors may combine such that any pressure to increase outbreeding in this self-incompatible species manifests itself in directional selection for delayed flowering time.

REPRODUCTION IN POLEMONIUM: PATTERNS AND IMPLICATIONS OF FLORAL NECTAR PRODUCTION AND STANDING CROPS

Patterns of floral nectar production and standing crop were measured in four populations of the herbaceous perennial plant species Polemonium foliosissimum. Contrary to prediction (Pleasants, 1983), individual flowers in this mass‐flowering species were found to produce equivalent nectar volumes every day of their lives. Alternative methods of increasing the reward variability presented to pollinators are evaluated for P. foliosissimum and the relationship between that variability and risk‐aversive foraging by pollinators is discussed. Significant spatial and temporal variability in rate of nectar production was found. Populations separated by approximately 200 m exhibited different rates. Nectar production declined significantly as a function of time of the flowering season in two populations but not in a third. In spite of such variability, individual plants showed consistency in production both within a single blooming season and across successive seasons. Because of the variability found in the present study, care should be taken to design appropriate sampling protocols in future nectar studies. Patterns of standing nectar crop were consistent with those expected if pollinators were using an area‐restricted searching pattern.

Reproduction in Polemonium: Patterns and Implications of Floral Nectar Production and Standing Crops

Patterns of floral nectar production and standing crop were measured in four populations of the herbaceous perennial plant species Polemonium foliosissimum. Contrary to prediction (Pleasants, 1983), individual flowers in this mass-flowering species were found to produce equivalent nectar volumes every day of their lives. Alternative methods of increasing the reward variability presented to pollinators are evaluated for P. foliosissimum and the relationship between that variability and risk-aversive foraging by pollinators is discussed. Significant spatial and temporal variability in rate of nectar production was found. Populations separated by approximately 200 m exhibited different rates. Nectar production declined significantly as a function of time of the flowering season in two populations but not in a third. In spite of such variability, individual plants showed consistency in production both within a single blooming season and across successive seasons. Because of the variability found in the present study, care should be taken to design appropriate sampling protocols in future nectar studies. Patterns of standing nectar crop were consistent with those expected if pollinators were using an area-restricted searching pattern.

Oviposition Behavior of Hylemya (Delia) sp. (Diptera: Anthomyiidae): Suboptimal Host Plant Choice?1

Host species preference tests were performed on two groups of the seed predator Hylemya (Della) sp. to determine oviposition choice. One group was captured in the field while ovipositing on Ipomopsis aggregata. The second group came from the confamilial Polemonium foliosissimum. A dimorphism was discovered, with each group preferring the plant species upon which it was originally found. However, egg mortality was greater on I. aggregata, suggesting that P. foliosissimum should always be the preferred host. These results are therefore evolutionarily paradoxical. Selection of a specific individual on which to oviposit is based on similar criteria in both plant species. There is a positive correlation between egg deposition and inflorescence size. There is also a positive association between inflorescence size and pollinator visitation frequency, making it likely that flowers chosen as oviposition sites will set enough seeds to ensure full larval development. Thus, regardless of host species preference, oviposition behavior within a species appears to be adaptive.

The Relationship Between Flowering Phenology and Seed Set in an Herbaceous Perennial Plant, Polemonium foliosissimum Gray

To assess the potential for evolutionary change in blooming time within a population of Polemonium foliosissimum Gray (Polemoniaceae), flowering phenology, seed set and seed predation frequencies of individual plants were monitored from 1977-1981 in the Colorado Rocky Mountains. In only 1 of 4 years was there a significant correlation between flowering rank and average seed set per flower. In contrast, there was a significant (or nearly significant, p<.06) positive correlation between blooming time and total plant seed set in 3 of 4 years. These positive correlations resulted from greater flower production by later-blooming plants. Thus, total seed set varied independently of seed production on a per blossom basis, indicating that seed set per flower'should be used only with caution as a measure of the maternal component of plant fitness. The fairly consistent positive relationship between blooming time and totat seed set indicates that directional selection for later flowering may be occurring in P:folioszssimum. Seed predation by Hylemya sp. (Anthomyiidae, Diptera) increases selection pressure more often than it offsets it. Significant, positive between-year correlations of flowering ranks of individuals, along with other inferential evidence, suggest that flowering time is likely to be heritable in P. foliosissimum.

Pollination, Predation and Seed Set in Linaria vulgaris (Scrophulariaceae)

Linaria vulgaris, a self-incompatible perennial herb, has a complex of adaptations related to insect-pollination. These include: (a) the production of conspicuous yellow flowers, each with a bright orange palate, arranged in vertical inflorescences of 15-20 flowers; (b) the production of multiple inflorescences by individuals. These flower in a staggered, but temporally overlapping, sequence suggesting a trade-off between maximum showiness and maximum blooming period; (c) the production of nectar containing 37% sugar, as sucrose equivalents. Despite these adaptations, however, Linaria vulgaris has low seed set when compared to most other self-incompatible perennials that have been studied. The success of ovules declined from ca. 1.6%o in early August (the height of the season for this species) to ca. 0.3% in early September, although individuals continued to produce new flowers until the end of September. The declining seed set occurred at a time when pollinator activity was declining. It is clear that predispersal seed predation by insect larvae was important in limiting seed set. Heavy predation of ovaries, however, made it difficult to assess the relative importance of pollinator availability as an additional limiting factor. INTRODUCTION Recently, there has been considerable interest in the features of flowering plants that make them attractive to pollinators. One of the questions investigated has been the extent to which seed set in self-incompatible plant species is pollinatoror predatorlimited. Schemske et al. (1978) showed that such limitation is a factor in six selfincompatible spring woodland herbs, which set fewer seeds under natural conditions that when hand-pollinated. Barkham (1980) suggested that seed set in Narcissus pseudonarcissus is severely pollinator-limited. Silander and Primack (1978), however, concluded that pollinator service was adequate to achieve complete seed set in Oenothera fruticosa. Zimmerman (1980a) reported that pollinator service was adequate to achieve a high level of seed set in Polemonium foliosissimum in the early part of its flowering season, but that pollinators were a limiting resource later in the season. Zimmerman (1980b) also reported that the seed predator, Hylemya sp., of P. foliosissimum caused high seed mortality in ovaries of flowers that had received a large number of pollinator visits and, as a result, set many seeds. This paper describes the pollination ecology of Linaria vulgaris Mill. (Scrophulariaceae). The research was designed to answer four questions: (1) How attractive are flowers of this species to pollinators; (2) What is the success rate for ovules of this species; (3) How available and effective are the pollinators; and (4) Is predation an important factor in limiting seed set? Linaria vulgaris is a rhizomatous perennial which is widespread along roads, railroad tracks and waste places throughout the United States. It is believed to have been deliberately introduced into eastern North America as an ornamental soon after the arrival of European settlers and has become a serious weed in some places, especially W of the Rocky Mountains. The flowers are strongly zygomorphic, yellow with a bright orange palate, and arranged in racemose inflorescences of 15-20 flowers. Each flower has a spur 15-20 mm long in which nectar collects. MATERIALS AND METHODS