Stigmatic Pollen Loads Research Articles

Resource limitation and pollen source (self and outcross) affecting seed production in two louseworts, Pedicularis siphonantha and P. longiflora (Orobanchaceae)

Two animal-pollinated hermaphrodite plants, Pedicularis siphonantha and P. longiflora, have been used to investigate factors limiting seed production in natural populations. To evaluate the potential seed abortion due to resources limitation, seed development has been observed and seed count conducted twice. Seed production per capsule has been compared when flowers have been removed and in a control group. Open pollination has been investigated and pollen supplementation undertaken to estimate the possibility of pollen limitation. Results show that seed abortion is frequent. Stigmatic pollen load is significantly higher than ovule number per ovary under open pollination for both species. Additional self and outcross pollen did not affect seed production. Flower removal significantly increases seed production per capsule, which indicates that seed production of the studied species is limited by available resources. To detect differences in seed production between flowers pollinated by self and outcross pollen, hand pollination of bagged flowers has also been conducted in natural populations of the two Pedicularis species. Compared with open pollination, hand-pollinating self-pollen decreases, while outcross pollen increases seed production per capsule. Such results suggest that inbreeding depression in the two self-compatible species may also result in partial seed abortion under open pollination if mixed pollen is deposited on the stigma. Our results also suggest that pollen interference plays an important role in low female fertility in the two Pedicularis species. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society, 2005, 147, 83–89.

Plant isolation reduces outcross pollen receipt in a partially self‐compatible herb

Summary Few studies of pollination success in fragmented systems measure stigmatic pollen load, and those that do often find it unrelated to plant or population density, size or isolation. Reduced reproductive output, however, is commonly reported, probably because incompatible pollen is contributing substantially to pollen loads of isolated flowers. We used manipulated floral arrays of a bee‐pollinated species (Dianella revoluta) to investigate isolation effects on deposition of outcross pollen, while precluding self‐pollen transfer. Outcross pollen receipt declined significantly over short distances up to approximately 50 m but even the most isolated flowers received some pollen grains. In contrast, heterospecific pollen did not decline, indicating that the outcross‐pollen decline was not due to reduced pollinator visitation. Increased distance of experimental arrays from a nature reserve did not reduce the probability of pollen receipt. Many flowers were damaged by flower feeding beetles in the genus Arsipoda, which would be likely to substantially reduce the efficiency with which flowers are converted to fruits. The probability of flower damage from these predators was significantly lower in arrays that were more distant from the nature reserve. This study indicates that reduced plant density and increased isolation from a source of outcrossed pollen can lead to a substantial decline in the probability of outcrossing, even when pollinator visitation is maintained at a high level. Depending on the mating system, this process will lead to reduced seed set or increased inbreeding for plants in fragmented habitats, even when pollinator abundance and behaviour are unaffected.

Reproductive ecology of distylous Palicourea Padifolia (Rubiaceae) in a tropical montane cloud forest. I. Hummingbirds' effectiveness as pollen vectors

The adaptiveness of distyly has been typically investigated in terms of its female function, specifically pollen receipt. However, pollen loads on stigmas can only provide moderate support for Darwin's hypothesis of the promotion of legitimate crosses. To determine the effectiveness of hummingbirds as pollen vectors between floral morphs and the consequences in terms of male (pollen transfer) and female function (pollen receipt) in Palicourea padifolia (Rubiaceae), floral visitors, their foraging modes, and temporal patterns of floral visitation were observed and documented. Differences in pollen and stigma morphology, pollen flow, rates of pollen deposition, and/or stigmatic pollen loads were then evaluated for their contribution toward differences in reproductive output between floral morphs. A pollination experiment with stuffed hummingbirds that varied in bill size was done to evaluate the contribution of bill variation toward differences between floral morphs in pollen receipt and pollen transfer and female reproductive output. Anthers of long-styled flowers contained significantly more and smaller pollen grains than those of short-styled flowers, independently of corolla and anther lengths. The shape and orientation of the stigma lobes differed between morphs and were significantly longer among short-styled flowers. Hummingbird visitation rates did not differ significantly between floral morphs, and foraging movements from focal plants towards neighboring plants were independent of floral morph. Stigmatic pollen loads under field conditions and those after controlled hummingbird visitation, along with rates of pollen accumulation through the day indicated that stigmas of short-styled flowers receive proportionately more legitimate (intermorph) pollen grains than did those of long-styled flowers. However, the species of hummingbird was marginally significant in explaining variation in pollen deposition on stigmas. Lastly, intermorph pollinations of P. padifolia resulted in significant differences in fruit production between floral morphs, independent of pollination treatment and pollinator species; short-styled flowers proportionately developed almost twice the number of fruits developed by long-styled flowers.

Nectar robbery by bees Xylocopa virginica and Apis mellifera contributes to the pollination of rabbiteye blueberry.

Honey bees, Apis mellifera L., probe for nectar from robbery slits previously made by male carpenter bees, Xylocopa virginica (L.), at the flowers of rabbiteye blueberry, Vaccinium ashei Reade. This relationship between primary nectar robbers (carpenter bees) and secondary nectar thieves (honey bees) is poorly understood but seemingly unfavorable for V. ashei pollination. We designed two studies to measure the impact of nectar robbers on V. ashei pollination. First, counting the amount of pollen on stigmas (stigmatic pollen loading) showed that nectar robbers delivered fewer blueberry tetrads per stigma after single floral visits than did our benchmark pollinator, the southeastern blueberry bee, Habropoda laboriosa (F.), a recognized effective pollinator of blueberries. Increasing numbers of floral visits by carpenter bee and honey bee robbers yielded larger stigmatic loads. As few as three robbery visits were equivalent to one legitimate visit by a pollen-collecting H. laboriosa female. More than three robbery visits per flower slightly depressed stigmatic pollen loads. In our second study, a survey of 10 commercial blueberry farms demonstrated that corolla slitting by carpenter bees (i.e., robbery) has no appreciable affect on overall V. ashei fruit set. Our observations demonstrate male carpenter bees are benign or even potentially beneficial floral visitors of V ashei. Their robbery of blueberry flowers in the southeast may attract more honey bee pollinators to the crop.

High self-pollen transfer and low fruit set in buzz-pollinated Dianella revoluta (Phormiaceae)

We used pollinator observation, flower manipulation, controlled pollination and pollen-tube analysis to better understand the reproductive ecology of Dianella revoluta R.Br., a common species known to have depressed fruit set at fragmented sites. This buzz-pollinated species was found to receive large quantities of self-pollen even during a single pollinator visit, but is only partially self-compatible. This may be the first direct demonstration of pollinator-facilitated, autogamous self-pollen transfer accounting for a significant proportion of stigmatic pollen load. Frequent high self-pollen transfer may account for the observed low rate of fruit development in open-pollinated flowers. Self-pollen tubes reached the base of the style in comparable numbers and at the same rate as outcross pollen tubes, with no sign of pollen-tube competition favouring outcross pollen. Barriers to greater self-fertility occur late, probably through early abortion of selfed ovules. We also investigated what impact overlapping distribution with D. longifolia may have on D. revoluta pollination and reproduction. Although these species shared pollinators, they differed in terms of frequency of visits. There was also separation of floral phenology within the course of a day.

Floral visitors of Trillium camschatcense (Trilliaceae) in fragmented forests

Plant–pollinator interactions are of particular interest in conservation biology because of their ecological and agricultural importance (Bachmann & Nabhan 1996; AllenWardell et al . 1998; Kearns et al . 1998). Pollinator deficits may result in shortfalls in fruit or seed production, and ultimately, plant extinction (Rathcke & Jules 1993; Olesen & Jain 1994; Kearns & Inouye 1997). Many recent studies have shown that seed production is reduced in small, fragmented plant populations due to pollen limitation (e.g. Jennersten 1988; Aizen & Feinsinger 1994a). However, the effects of habitat fragmentation on pollinator assemblages have been rarely examined directly (Didham et al . 1996; Kearns et al . 1998). Further understanding of the pollinator dynamics in a fragmented landscape, for example, what kinds of pollinators are likely to be lost from fragmented habitats, is required to obtain useful implications for conservation of plant–pollinator interactions. In the Tokachi region of eastern Hokkaido, Japan, intensive agricultural development since the 1880s has resulted in a highly fragmented landscape with a large number of small forest remnants. Trillium camschatcense Ker Gawler (Trilliaceae), a representative woodland spring herb in this region, once often formed large ( > 5 ha), continuous populations, but is now mostly found in the understory of small remnant forests surrounded by pastureland or agricultural fields. In a previous study (Tomimatsu & Ohara 2002), we demonstrated that small, fragmented T. camschatcense populations generally produced fewer seeds than large, continuous populations and that the low stigmatic pollen load was largely responsible for the reduced seed production. The aim of the present study was to describe floral visitors of T. camschatcense in fragmented forests, where the availability of pollinators was hypothesized to be reduced (Tomimatsu & Ohara 2002). We observed floral visitors at five different-sized populations and examined the differences in species composition and visitation frequency among the populations. We also discuss the relationship between floral visitors and outcross pollen load, which was measured in our previous study (Tomimatsu & Ohara 2002).

Dose‐response relationships between pollination and fruiting refine pollinator comparisons for cranberry (Vaccinium macrocarpon [Ericaceae

Comparisons of pollinator efficacy using pollen received on stigmas can be refined by incorporating experimental dose-response relationships for pollen deposition and fruiting responses. A range of discrete pollen doses applied to cranberry stigmas resulted in decelerating curvilinear responses for fruiting, berry size, and seed set. Minimum thresholds and maximum asymptotes bounded reproductive responses to incremental stigmatic pollen loads. Four bee species were compared for their pollination efficacies on commercial cranberries, using counts of pollen received by stigmas during single bee visits to previously virgin flowers. Differences between these bee species were found to be exaggerated when raw pollen counts were used for comparison because foragers of some species often delivered pollen in excess of that needed to maximize fruit and seed production. Sixfold differences between species in mean pollen deposition translated into 1.5-2-fold differences in predicted cranberry fruit set and size. Implications for pollen tube competition and agricultural production are discussed.

Pollination ecology and breeding system of the very narrow coastal endemic Seseli farrenyi (Apiaceae). Effects of population fragmentation

The reproductive biology of Seseli farrenyi (Apiaceae), a very narrow endemic to Cape Creus (Catalonia, Spain), including flowering timing patterns, quantity and quality of pollination services (type and frequency of pollinators, pollen carryover, pollen deposition on stigmas and reproductive success measured as fruit set), and breeding system was studied. Given the decline of population size detected in the last twenty years, we also analyzed the effects of fragmentation on pollination mechanisms. Protandry along with strong synchrony of floral development within umbels and sequential inflorescence emission within individual stalks, produces sexual phase alternation that promotes a strong outcrossing despite its non‐specific pollination system and its (at least partial) self‐compatibility. This pronounced xenogamy is supported by results of the insect exclusion test, hand‐pollination experiments, and high P/O ratio. S. farrenyi flowers received visits from at least 28 species of insects, including wasps, small bees, ants, flies, syrphid flies, beetles and stink bugs, with different pollen carry‐overs. Heterospecific pollen on stigmas decreased notably during the season (50% to 2.5%), averaging 12%. In the small population the stigmatic pollen loads and seed set decreased, but there was no effect of pollinator visitation rates. It was more affected by the composition of pollinators and their efficiency. The wind had a considerable effect on the plant. Some conservation measures are proposed.

Variation in stigma morphology – How does it contribute¶to pollination adaptation in Pedicularis (Orobanchaceae)?

Stigma morphology in Pedicularis and its role in pollination have not been evaluated. This paper reports for the first time the relationship between stigma morphology and other aspects of floral design. 17 species of Pedicularis representing all the different types of corolla structure in the genus were studied in the field and in the labora- tory. Results indicate that the stigmatic surface morphology of Pedicularis species is related to the type of corolla structure occurring in the species. Pollination studies in eight Pedicularis species demonstrated adaptation between stigmatic surface morphology and other aspects of floral biology. Species with larger, more corrugated stigmatic surfaces always possess a subsidiary construction (''tooth'' or ''beak'') on the galea. In addition, they have relatively longer flower tubes, higher stigmatic pollen loads, bigger pollen size and a shorter blooming period for individual flowers. Finally, the authors discuss the evolutionary significance of floral design in genus Pedicularis. Pedicularis Linn. (Orobanchaceae) has about 700 species all occurring in subalpine-alpine areas. More than 350 Pedicularis species have been recorded from China, with most being restricted to the southwest of the country (Hong 1983). The task of studying floral

Pollen transfer patterns in a distylous plant with overlapping pollen‐size distributions

In this study we quantify the relative rates and amounts of between‐morph (legitimate) cross‐pollination, within‐morph (illegitimate) cross‐pollination and self‐pollination in a natural population of distylous Gaertnera vaginata (Rubiaceae) endemic to the oceanic island of La Réunion in the Indian Ocean. Since pollen size distributions of each morph overlap we develop a method, based on chi‐squared comparisons of observed to expected pollen size distributions, to quantify pollen transfer proficiencies. This method, unlike previous methods, does not assume an equal chance of pollen transfer for pollen grains in the region of overlap. The probability that a single pollen grain from a short‐styled plant undergoes legitimate pollen transfer to long‐styled flowers (4.19×10−2) was more than twice that for illegitimate transfer to other short‐styled plants (1.56×10−2). In contrast, the probability that a single pollen grain from a long‐styled flower undergoes legitimate pollen transfer to short‐styled flowers (1.65×10−2) was no greater than that of illegitimate pollen transfer to other long‐styled plants (2.15×10−2). The transfer proficiencies of individual pollen grains are thus highly asymmetric. However, because long‐styled flowers produce significantly more pollen, the ratio of legitimate to illegitimate pollen on the stigmas of short‐styled flowers (1.85) markedly exceeded that for long‐styled flowers (1.11). Short‐styled flowers incurred significantly higher levels of self‐pollination than long‐styled plants, emphasizing the importance for self‐pollination to be removed before comparing stigmatic pollen loads. The method we propose could be applied to other distylous species with pollen size overlap between morphs and thus allow for a more widespread study of the pollination ecology of heterostylous species.

Effects of Forest Fragmentation on Seed Production of the Understory Herb Trillium camschatcense

Abstract: We investigated the effects of forest fragmentation on reproduction of a common understory perennial, Trillium camschatcense, in Hokkaido, Japan. We measured seed production of 12 (1998) and 14 (1999) populations, and we explored the relationships of seed production to the number of flowering plants ( population size) and to the surrounding landscape condition ( landscape type). We discriminated between two landscape types, isolated and continuous, to describe the quantity and distribution of forests around T. camschatcense populations. Population size may be correlated with attractiveness to pollinators and the availability of compatible mates, whereas landscape condition can affect the abundance of pollinators. The number of seeds per flower was related to population size in 1999, but not in 1998. In both years, small populations of <50 flowering plants produced few seeds. Although the effect of landscape type was not significant, continuous populations with abundant forest series in their neighborhood tended to produce a higher number of seeds than isolated populations located in small, isolated forest. We attribute the decrease in seed production to pollen limitation because the stigmatic pollen load had a positive relationship to seed production and addition of pollen by hand increased seed production. Variation in population structure ( four stage classes) among populations was better explained by population size than number of seeds produced, suggesting the relative importance of population size for the demography of T. camschatcense. Larger populations had a higher proportion of seedlings, possibly because large populations had fewer edge effects, which reduce seedling recruitment and survival. Small populations with 220 flowering plants or less showed almost no seedling recruitment. The data on seed production and population structure suggest that continuous populations with at least 1000 flowering plants may be required to avoid the effects of fragmentation.

Variation of pollination and resource limitation in a low seed-set tree, Liriodendron chinense (Magnoliaceae)

Pollen limitation and resource limitation have been documented as the major factors responsible for plants commonly producing more ovules than seeds, but few studies have examined pollen deposition directly in natural populations at different sites and times. We investigated the causes of low seed set in four populations of Liriodendron chinense (Magnoliaceae), an insect-pollinated endangered tree endemic to southern China, over 2–3 years. One pistil potentially produces two ovules. The number of pistils per flower varies among populations, but in three of the four populations the variation in a given population was not significantly different among years. Overall, populations with higher pistil numbers tend to set more seeds per flower, but a positive correlation between pistil numbers and seed production per flower was observed in only one of the four populations. The numbers of pollen grains deposited per stigma varied from 0 to 60. The proportion of pollinated stigmas per flower ranged from 44% to 88% among populations and years. The numbers of pollen grains deposited per stigma and the percentages of pollinated stigmas were significantly different between populations, and two populations showed significant differences between years. A positive correlation between stigmatic pollen load and seed set was sought in ten population-by-year combinations but, in a given population, high stigmatic pollen loads did not always result in high seed set. Examination of pollen deposition, pistil and seed production over several sites and years showed that in addition to pollination, other factors such as resource or genetic loads were likely to limit the (lower than 10%) seed set in L. chinense. It appears that small, isolated populations experience severe pollination limitation; one population studied had seed/ovule ratios of 0.84% and 1.88% in 1995 and 1996.

Pollination ecology of the pre-Pyrenean endemic Petrocoptis montsicciana (Caryophyllaceae): effects of population size

Petrocoptis montsicciana (Caryophyllaceae) is a threatened pre-Pyrenean endemic that grows exclusively on caves and walls of limestone. We studied its pollination ecology by monitoring phenology and by evaluating pollen and nectar production, pollinator activity (frequency and behaviour of visitors), quantity and quality of pollination services, pollen/ovule ratio, and seed set in response to insect exclusion and self-compatibility tests. We also analysed the effect of population size on reproductive mechanisms by comparing a large and a small population. Flowers of P. montsicciana produced nectar and were visited by Hymenoptera (79.7%), Diptera (11.5%), and Lepidoptera (8.8%). The most frequent pollinators (60.6% of total visits) were long-tongued bees of the genus Anthophora. Both populations had a similar range of pollinators. We found a correlation between the number of visited flowers and the number of open flowers per census; 88.7% of pollen grains deposited on the stigmas were conspecific and the main competitor was another chasmophyte plant, Antirrhinum molle. Bagged flowers set seeds but significantly less so than hand-self-pollinated and control flowers. Thus, although self-compatible and self-pollinated, entomophilous pollination of P. montsicciana is required in order to explain c. 10–40% of total seed set, in accordance with P/O ratio estimations. Bagged flowers from the small population set significantly more seeds than the large one. Visitation rates were lower in the small population, but, unexpectedly, showed higher stigmatic pollen loads and similar or higher seed set. These results suggest an increase of spontaneous selfing rates in the small population, probably favoured by a smaller flower size, which can not only assure reproductive success when pollinators are scarce, but also provide additional potential to adapt to climatic changes. © 2002 The Linnean Society of London, Biological Journal of the Linnean Society, 2002, 76, 79–90.

Biologie de la reproduction de Aloe mayottensis (Liliaceae), une espèce endémique de l'île Mayotte (Océan Indien)

A particularly interesting aspect of the study of organisms in insular environments is plant reproduction and the interaction of plants with their pollinators. Differences in composition between the fauna and flora of continental and island populations, combined with their geographical isolation, have frequently driven rapid evolution in colonizing populations. In particular, floral traits and compatibility systems tend to favour autogamy in response to a paucity of pollinators in the environment. In this context we investigate the origins of the reproductive biology of Aloe mayottensis Berger, a lily endemic to the island of Mayotte. We show that this species is pollinated by the island's endemic sunbird species, and has floral traits and a reproduction system that favour allogamy. Our results show that A. mayottensis is a protandrous and partially self-compatible species. Analysis of stigmatic pollen load shows that stigma received a mean of 56 crossed pollen grains and 62.2 selfed pollen grains per stigma. Study of visitation rates of plants and flowers by the sunbird showed that there is daily variation in the activity of this pollinator, and that males are more active than females.Key words: Aloe mayottensis, floral biology, Lomatophyllum, Nectarinia, bird pollinization, sunbirds, Oceanic islands, Mayotte.

Reproductive biology of Colletia spinosissima (Rhamnaceae) in Argentina

We studied the reproductive behavior of Colletia spinosissima Gmel. at six sites in two regions of Argentina during the 1998–2000 flowering seasons. Flowering takes place in winter. The flowers are homogamous, fragrant, and entomophilous. There was evidence of self-incompatibility and cross-incompatibility between nearby partners. Fruit set of open-pollinated flowers (13.3%) seemed pollen-limited, since low fecundity was consistently associated with small stigmatic pollen loads and with low numbers of successful pollen tubes, and fecundity increased with abundance of efficient pollinators. Reproductive success (percent ovules becoming viable seeds) was 3.6. It is hypothesized that homogamy was established in Colletia because in an impoverished pollination environment – such as the one likely prevailing when this lineage evolved – achieving pollen export and receipt in a single pollinator visit has selective advantages. A large stigma and an extragynoecial compitum would compensate for the homogamy-driven, increased pollen-stigma interference.

Effect of bumble bee (Hymenoptera: Apidae) pollination intensity on the quality of greenhouse tomatoes.

Laboratory studies were conducted to assess tomato, Lycopersicon esculentum Mill. (Solanaceae), quality in relation to the level of buzz-pollination by bumble bees. Studies were conducted in commercial tomato greenhouses in the Leamington, Ontario, area to categorize bruising of tomato anther cones by bumble bees into five levels of bruising. The number of pollen grains per stigma was determined for each bruising level, and the bruising level was found to be a good predictor of stigmatic pollen load. Experimental flowers were pollinated by bumble bees and assigned to bruising levels based on the degree of anther cone discoloration. Fruit set, tomato weight, minimum diameter, the number of days until ripe, roundness, weight, percentage sugars, and number of seeds were assessed and compared among bruising level. Fruit set in flowers receiving no pollination visits was 30.2%, whereas, 83.3, 84.4, 81.2, and 100% of the flowers set fruit in bruising levels 1, 2, 3, and 4, respectively. Minimum diameter, number of seeds, and tomato weight all increased from no bruising to different levels of bruising. There was no increase in weight or diameter above a bruising level of 1, and no increase in the number of seeds per fruit after a bruising level of 2. We found that pollination of tomato flowers greater than a bruising level of 2 (corresponding to approximately one to two bee visits) did not result in a significant increase in quality.

Absence of conspecific pollen advantage in the dynamics of anIpomopsis(Polemoniaceae) hybrid zone

The frequency of hybrid formation in angiosperms depends on how often heterospecific pollen is transferred to the stigma and on the success of that heterospecific pollen at fertilizing ovules. Even if heterospecific pollen is capable of effecting fertilization it may perform poorly when conspecific pollen is also available on the stigma. We applied pollen mixtures to stigmas to determine how pollen interactions affect siring success and the frequency of hybrid formation between two species of Ipomopsis (Polemoniaceae) in Colorado. Plants of both parental species and natural hybrids were pollinated with I. aggregata and I. tenuituba pollen in ratios of 100:0, 80:20, 50:50, 20:80, and 0:100 by mass. Plants were homozygous for different alleles at an isozyme marker, allowing us to distinguish the type of pollen parent for 2166 viable seeds from 273 fruits. In contrast to studies of many other hybridizing taxa, there was no evidence of an advantage to conspecific pollen, nor did composition of the stigmatic pollen load affect seed set. Instead, the frequency of seeds sired by a given species was proportional to its representation in the pollen load. In this hybrid zone, both the frequency of first-generation hybrid formation and the relative male fitness of the two parental species should be predictable from the rates of pollen transfer to stigmas.

The efficiency of insect pollination of the neophyte Impatiens glandulifera (Balsaminaceae)

To comprehend the reproductional success of Impatiens glandulifera in Central Europe, the pollination system was analyzed under field conditions. Impatiens glandulifera attracts a lot of visitors because of its abundant amount of nectar with its high sugar content. The range of visitors, their composition and their changes during the blooming time and their pollen loading capacity were investigated as well as plant and flower morphology, the nectar production, the quantity and viability of pollen, the stigmatic pollen load, the pollen/ovule ratio and the seed production of the neophyte. The visitors, which in Central Europe almost exclusively utilize the nectar, are passively covered with pollen because of the morphology and the mobile suspension of the flowers. Consequently the next landing results in a pollination of I. glandulifera during the female blooming phase. Although the germination rate of the pollen deposited on the stigma is very low, a 100% seed set is readily obtained during the initial visit to a flower in female stage.

Floral biology and breeding system of pohutukawa (Metrosideros excelsa, Myrtaceae)

The floral biology and breeding system of pohutukawa (Metrosideros excelsa, Myrtaceae), a mass‐flowering tree of northern New Zealand coastlines, were examined. Trees flower over a peak period of 2 weeks, and compound inflorescences contain an average of 14.3 showy, hermaphrodite, red brush flowers that remain open for 7 days. A brief female flower stage (mean duration 1.3 d) is followed by the main hermaphrodite phase that lasts for 4 days. Neither dichogamy nor herkogamy is important in preventing pollen and stigma interference. Pollen is highly viable (93.6%), and stigma receptivity extends for at least 9 days, as indicated by peroxidase activity, pollen germination, pollen tube length 24 h after pollination, and seed set. Stigmatic exudate production appears to increase up to 5 days post‐anthesis. On average, flowers produce 46 p1 nectar per day, containing 18% (w/v) sucrose. Floral design and display of pohutukawa are consistent with high levels of autogamous and geitonogamous self‐pollination. Controlled pollination experiments were used to assess the effect of self‐ and cross‐pollen and a pollen mixture from five unrelated parents on capsule and seed production, and on pollen tube growth in seven trees. Three trees in the experiment were self‐incompatible, as quantified by the index of self‐incompatibility (ISI), indicating that natural populations may consist of a mosaic of self‐compatible and incompatible individuals. Self‐in‐compatibility is late‐acting as pollen tubes from selfs and crosses reached the ovary simultaneously at 10–15 d after pollination. In common with other Myrtaceae, the seed/ovule ratio in pohutukawa is low and this is likely to be genetically determined rather than limited by stigmatic pollen load. Germination of fertile seeds from all pollination treatments was equally high (98.4%), indicating that no inbreeding depression is acting at this stage of the life cycle. The pollen/ovule ratio of 462.5 (s.e. ±43.3) places the breeding system of pohutukawa between facultative selfing and facultative outcrossing.

Fecundity above the Species Level: Ovule Number and Brood Size in the Genisteae (Fabaceae: Papilionoideae).

Per-fruit components of fecundity (ovules per ovary, seeds per fruit, seed : ovule ratio, and patterns of seed maturation within pods) were studied in 33 species of the Genisteae, a legume tribe of mostly Mediterranean shrubs, e.g., Cytisus, Ulex, that also includes more widespread herbs such as Lupinus. Species identity explained most variance in both potential (ovules) and realized (seeds per fruit and seed : ovule ratio) fecundity, and although significant population-specific effects existed, these were relatively small, indicating that estimates of fecundity were not particularly prone to environment-induced changes. Average seed : ovule ratios varied between 20% (for a few species in which fixed rates of embryo abortion result into single seeded pods) and 100% (annuals), but most taxa were in the 40%-60% range. The probability that an ovule near the base of the ovary matured into a seed was significantly lower than the pod average in the majority of species. As indicated by the large size of stigmatic pollen loads, this was unlikely to result from insufficient pollination but rather from preferential embryo abortion. High abortion rates next to pod base occurred in both presumed selfers and obligate outcrossers. Evidence points to relatively stereotyped reproductive ways and high reproductive coherence in the tribe, with major departures from the norm being high seed : ovule ratios exhibited by annual Lupinus (associated with selfing), and low ratios shown by species with single seeded pods (associated with fixed rates of embryo abortion).