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Article

Reproductive Investment Across Native and Invasive Regions in Pittosporum undulatum Vent., a Range Expanding Gynodioecious Tree

by
Ben O’Leary
1,2,
Martin Burd
1,3,
Susanna Venn
1,4 and
Roslyn M. Gleadow
1,*
1
School of Biological Sciences, Monash University, Clayton, Melbourne, VIC 3800, Australia
2
Yarra Ranges Shire Council, Lilydale, VIC 3140, Australia
3
Royal Botanic Gardens, Melbourne, VIC 3004, Australia
4
School of Life, and Environmental Sciences, Deakin University, Burwood, VIC 3125, Australia
*
Author to whom correspondence should be addressed.
Forests 2026, 17(1), 72; https://doi.org/10.3390/f17010072
Submission received: 26 November 2025 / Revised: 27 December 2025 / Accepted: 31 December 2025 / Published: 5 January 2026
(This article belongs to the Special Issue Advances in Forest Restoration and Applied Conservation: Bridging Science and Practice)
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Abstract

The success of invasive species relies heavily on the production, dispersal and genetic composition of propagules. For range expanding species, breeding strategy and level of reproductive investment will strongly influence their capacity to establish and invade new areas. A hermaphroditic lifestyle provides the advantage of increasing the number of seed bearing individuals within a population while a dioecious habit may enable more rapid adaptation to new environments, improve resource use efficiency, fecundity and dispersal. Pittosporum undulatum, a tree native to coastal areas of southeastern Australia, has many characteristics of an invasive species within and beyond its native range. A previous study detected a male bias within invasive populations, with a high proportion of fruit deriving from female-only trees, leading to recommendations for the removal of ‘matriarch’ trees as a simple management technique. We expanded that study and investigated breeding systems of different populations of P. undulatum by assessing tree density, gender, resource availability and fruit load of 871 individuals in seven native and seven invasive populations. All populations comprised either females (47%) or hermaphrodites. No male-only trees were observed within the study. More females produced more fruit than hermaphrodites, especially in the native site. This could not be attributed to environmental differences between sites. These data support the current management practices of targeting the removal of females as a simple method for containing invasions given the benefits of reducing the workload and spreading limited management resource. Our work highlights the value in understanding the breeding strategy employed by focal invasive species as a means of developing improved and more targeted control methods.

1. Introduction

The success of invasive species relies heavily on the production, dispersal and genetic composition of propagules [1]. Relative to their native range, invasive species commonly show increases in fecundity [2] and self-compatibility [3]. Thus, a focus on the mating systems and reproductive allocations of invasive species may improve our understanding of the processes that promote the establishment and expansion of invasive populations [1,2,4] and potentially guide control strategies [1,5,6,7]. Baker [8] considered the role of self-compatibility in the colonisation of islands. Due to the haphazard nature of long-distance dispersal of propagules to islands, the likelihood of establishing within close proximity to a potential mate is thought to be low. Thus, hermaphroditic species with a self-compatible breeding system should predominate among island colonisers, as they have the capacity for uniparental reproduction through self-pollination [9]. The same concept can be extended to an invasion front, where individuals may be establishing in relative isolation [10]. Baker’s law, as this idea is now called, implies that self-compatible hermaphrodite reproductive systems might predominate among invasive plants, especially at the margins of an invasive range.
Any initial advantage that hermaphrodites may have in founding of new populations need not persist as a population grows [11]. Metapopulation dynamics of an invasion may mean that female plants or hermaphroditic plants that have female-biased sexual allocation are favoured during the initial phase of population expansion, as females will tend to contribute disproportionately more to early population growth [12,13]. Only later in consolidated populations with higher population density and female availability would the selective advantage of males and male allocation increase. Consistent with this, high seed fecundity is also a notable feature of individuals in invasive populations [7,14] be enriched in hermaphrodites with high levels of female investment early in colonisation. Later, as population density (or individual size and thus floral density) increases, increased male investment becomes advantageous due to the abundance of available ovules. These dynamics have been observed at the metapopulation level in Mercurialis annua across southern Europe and northern Africa [15]. In an invasive population, gynodioecy might be advantageous as the hermaphrodites can provide the pollen for selfing and dispersal to the female plants, and the females in the population may produce larger quantities of higher-quality seed since they are not simultaneously allocating resources to pollen production [16].
In large, well established invasive populations, novel resource environments may alter the sex expression of plants or skew flowering sex ratios [17]. Individual plants in many species can often change sex expression according to their size or resource status [18,19], and individuals of monoecious species are known to shift their floral sex ratios in response to resource availability [20]. In these cases, female expression was almost universally favoured by greater moisture, soil nutrients or sunlight. Some degree of segregation of male and females along resource gradients has been noted in dioecious species, with males tending to predominate at the drier, poorer end of the gradient and females at more fertile [21,22]. If invasive ranges offer a more favourable resource environment, for example, through greater resource availability [23], we might expect to find a female bias in sex expression or sex occurrence among plants within those invasive populations. Alternatively, if permissive environments allow small plants to survive, and small size favours male expression, invasive populations may show male-biased sex expression of sex ratios [17].
Suites of morphological and life history traits that promote dispersal are likely to be exaggerated at an invasion front because the best dispersers are most likely to arrive at the front, mate with other recent arrivals, and, to the extent that traits are heritable, pass them to the next generation that itself may extend the front [24,25,26]. This idea, which has been called the ‘Olympic Village effect’ in the context of movement adaptations for animal dispersal [27], suggests that, in invasive plants, traits that affect dispersal and establishment (e.g., of seeds and fruits) might differ between the native and introduced ranges. Such processes seem to account for lower wing loadings (thus, slower descent and more horizontal dispersal) of the winged seeds in more recently derived populations of Pinus contorta following its post-glacial range expansion in North America [28]. For species with animal-dispersed fruits, we might expect selection for dispersal ability to favour greater fruit load and higher probability of fruiting [2,29]. Large seed size, in contrast, is thought to diminish dispersal ability but may enhance competitive ability and stress tolerance during seedling establishment [30,31].
We evaluated the relationship between invasiveness and gender using the Australian tree Pittosporum undulatum Vent. (Sweet Pittosporum). P. undulatum is a long-lived woody invader with many characteristics of an invasive species within and beyond its native range of coastal southeastern Australia [32,33,34] (Figure 1). Within Australia, sites dominated by P. undulatum have reduced biodiversity and species richness of both plants and birds [33,35,36]. There is almost complete suppression ground cover species and total absence of seedlings of the Eucalyptus overstorey in areas dominated by P. undulatum [32,33,37]. This has resulted in calls for its control, despite its ‘native’ status. ‘Native species’ in Australia are typically defined as ones that were present at the time of European invasion, with those that are first recorded after this date regarded as ‘naturalised’ [38,39]. Those whose ranges are still expanding are typically referred to as ‘invasive’. While this simplistic concept ignores the introduction and widespread translocation of plants by First Peoples prior to this date [40,41], we believe the terminology is appropriate for P. undulatum, as there is clear change in distribution since Europeans arrived [35]. It is also invasive in New Zealand, Portugal, Jamaica, Hawaii, and is an emergent weed in South Africa [32,42,43,44,45].
Previous studies indicated that individual P. undulatum trees can be male, female, or hermaphroditic, but how this relates to its environment or invasive status remains unknown [42,46,47]. Here we measured the frequency of sexual types in P. undulatum sampled from populations growing across a spectrum from ‘native’ to ‘non-native’ locations. We also assessed the probability of fruit set, fruit load, and seed size, traits that may affect the ability to reach and establish in novel sites. We hypothesise that P. undulatum from invasive populations will (1) have a higher proportion of females than native populations; (2) produce relatively more fruit; and (3) have a greater number of seeds and/or smaller seeds, relative to native populations. In addition, in order to determine whether seed production was correlated with resource availability, we measured the concentration of total nitrogen, total carbon, and carbon isotope discrimination (δC13) in leaves of trees at each site.

2. Materials and Methods

2.1. Study Species: Pittosporum undulatum Vent. (Sweet Pittosporum)

P. undulatum is found in a range of habitats but is most commonly found marginal to temperate rainforests [31]. Horticultural propagation followed by altered fire regimes and the introduction of new avian vectors such as European blackbirds (Turdus merula L.) and have all contributed to the spread of this species across mainland southeastern Australia [32,33,35,37,48]. P. undulatum is known to establish quickly after disturbance, although it can also become invasive at undisturbed locations [47,49,50]. Once established, mature trees can reach heights of 8–30 m. Individuals form dense canopies, shading out the undergrowth and reducing structural diversity, floristic composition, and the integrity of ecological systems [32,33,51]. Original theories of it being allelopathic are now largely discredited [32,34].

2.2. Site Description

We investigated variations in tree density, sex, resource availability, and fruit load for native and invasive populations of P. undulatum. Seven populations within temperature Eucalyptus forests of East Gippsland in southeastern Victoria, Australia, were selected to represent native populations (Table 1). A further seven populations across peri-urban areas of Melbourne, in southeastern Australia, were selected to represent invasive populations (Table 1).

2.3. Sex Determination and Resource Analysis

Sex expression of individual P. undulatum plants was determined during Spring (September–October 2016; Table 1). At each site a 20 m × 20 m quadrat was established and mature trees growing within the quadrat were examined for the presence or absence of male and female floral structures and labelled. Quadrate size was chosen based on studies in adjacent areas [33,36,46]. Within each quadrat, five leaves from five randomly selected individuals of each sex were sampled for nutrient analysis, specifically leaf nitrogen, carbon, and carbon isotope discrimination (δC13). Leaves were selected from approximately the third stem of a branch. Leaves were dried in an oven for 48 h at 60 degrees before being ground in a homogenising tissue mill. Total elemental nitrogen, carbon, and δC13 were measured on finely ground freeze-dried leaf samples using a LECO CNS2000 analyser (Environmental Analysis Laboratory, Southern Cross University, Lismore, NSW, Australia).

2.4. Fruit Load and Seed Mass Determination

The original sample plots were re-examined six months later (between 1 February and 20 March 2017). True fruit loads were assessed for the same individual plants as above using a ranking system from 0 to 11 where a rank of 0 equated to no capsules observed; 1 equated up to 50 capsules, 2 equated to 50–100, and so on up to 11 which equated to 500–550 capsules (the maximum observed). Capsules were collected and the seeds removed from their fruit casing and cleaned of mucilage using tissue paper. All seeds from each fruit were weighed together and the mean seed mass calculated.

2.5. Statistical Analysis

All analyses were conducted using the R statistical programme [52]. Variation in mature plant density, proportion of females within populations across native and invasive populations, and differences in seed number and weight across populations were analysed through unpaired t-tests. Differences between native and invasive sites were compared using equal variance t-tests. Differences between each reproductive type in the proportion of fruiting trees were examined through a generalised linear model. Comparison of the mean fruit load rank between reproductive types across populations were also examined via a generalised linear model. Linear modelling was also used to investigate variation in the proportion of individuals producing fruit, and the mean rank of fruit production across sex and origin. Data were arcsine square root and cube root transformed, respectively, prior to analysis to meet the conditions of normality. Non-linear modelling was used to analyse the influence of nutrient availability to fruit production. Statistical tables are included in the Supplementary Information.

3. Results

3.1. Reproductive Traits

All populations were gynodioecious (comprising females and hermaphrodites), with no male trees observed within the study. Native and invasive sites did not differ significantly in the mean density (p = 0.719; Table 2) nor in the proportion of females (p = 0.217; Table 2).
No significant difference was detected in the proportion of fruiting individuals between populations of different origins either (p = 0.469; Figure 2; Supplementary Table S2). There were, however, differences at a population level in the presence of capsules, with significantly more fruit set from female than from hermaphrodite flowers (Figure 2A; Supplementary Table S3). Females in native sites were also more likely to fruit comparative to females in invasive populations (p < 0.01; Supplementary Table S3). When examining the quantity of fruit produced by each tree, female individuals appeared more likely to produce higher quantities of fruit (Figure 2B; Supplementary Table S4). The mean mass of seeds produced in invasive populations was approximately twice that of seeds from native populations (Table 2; Supplementary Table S5).

3.2. Resource Availability: Tree Density and Leaf N, C, and δC13

Native and invasive sites did not differ significantly in the mean density of P. undulatum trees (p = 0.718; Table 2 and Table S4). δC13 ranged from −29 to −32‰, consistent with tittle variation among populations regardless of origin (Figure 3A), consistent with the similarity in rainfall at each site (Table 1). No consistent trends were observed in Total C concentration either (Figure 3C). Total leaf nitrogen was low at all sites, with a mean of 1%–1.5% at most sites (Figure 4). A weak correlation was detected between leaf nitrogen and fruit production (slope estimate= 5.540, adjusted r2 = 0.23) (Figure 3B and Figure 4).

4. Discussion

Investigating how the breeding system and sexual expression of invasive species differs between native and novel environments may improve our understanding of pest species and their management [27,53,54,55,56]. Furthermore, contrasting the performance of species within and beyond their native ranges can be use useful in testing ecological theory [4,57,58,59]. This study explored the breeding strategy and reproductive ecology of a range expanding invasive tree and considered how these factors varied between native and invasive populations. We expected to find a high level of female sex expression among plants in invasive populations, because higher numbers of females are likely to enhance population expansion at the invasion front through seed production [12]. We also anticipated a higher investment in reproductive traits for invasive populations, as these traits are likely to both extend the dispersal capacity of seeds and improve their chance of survival to maturity within novel environments. However, populations present a mosaic of both sex ratio and female traits, and our expectations could be met in different ways.

4.1. The Proportion of Female and Hermaphrodite Trees Was Similar Across All Sites

The most striking observation in this study was the lack of male trees within any population regardless of its native or invasive origin. Populations were comprised of either females or hermaphroditic individuals. This is surprising as male bias is more common in trees and in plants that depend on biotic seed dispersal [60]. A hermaphroditic bias has been observed within an invasive population of P. undulatum in Jamaica [42]. Of the 60 trees sampled in their study, Goodland and Healey [42] found 78.4% of individuals to be hermaphroditic, with the remainder female. The lack of male trees is in stark contrast to previous studies that showed a male bias within invasive population [46,47]. Previous work in Victoria has suggested females make up between 30% and 40% of invasive P. undulatum populations, with the remainder being male [47]. Mullet [46] found approximately 9% of male flowering plants at one site had fruit remnants from the previous reproductive episode and may indicate that either some of the flowers had been hermaphrodites. These distinct results suggest that the proportion of males, females, and hermaphrodites making up P. undulatum populations may be highly variable among sites and certainly less consistent across reproductive seasons than previously proposed. The sexual composition of invasive populations of P. undulatum is unlikely to be at equilibrium given the relatively recent colonisation of many sites. A geographic mosaic of sexual composition across is not uncommon in other species [12,15].
Theory suggests hermaphroditism should be more common in populations with younger age cohorts and in lower densities [11,15]. This theory could imply that as invasive populations of our study are relatively younger (approximately 10–30 years) they should be less dense and therefore support higher proportions of hermaphrodites relative to older aged native populations. Instead, our sample populations showed an approximate even proportion of female and hermaphroditic individuals, and though variable, a similar density of individuals across populations, in both cases regardless of their native or invasive origin. Our prediction of greater female representation in invasive populations has therefore not been met. One possibility is that despite the younger age of invasive P. undulatum populations, the equivalent density of trees at native and invasive sites means that the selective pressure for a higher proportion of females may not be as strong for the established invasive populations of this study, comparative to a population at the very early stages of invasion/range expansion, where tree density is lower.

4.2. Fruit Production Was Higher in Female Trees in the Native Range

Female trees were far more likely to produce fruit than hermaphrodites, with significantly higher fruit loads, suggesting that hermaphrodites are predominately filling the role of males as pollen producers. Baker’s law postulates the selective advantage that hermaphrodites may have due to their capacity to self-pollinate in environments where mates are sparse [8]. The strong persistence of females within all populations together with observations of hermaphrodites generally fulfilling the male role within P. undulatum populations suggest there is no strong pressure for self-fertilisation. Given the high stand density that P. undulatum populations can reach along with the consistent and ongoing introduction of P. undulatum to invasion sites [32,33,48], mate proximity may not be an issue, which would therefore reduce selective pressure for self-fertilisation. In this instance, enhanced reproductive and growth traits may present a stronger selective advantage, improving the capacity to establish, develop, and reproduce within varied and disturbed environments.
Contrary to expectations, females from native populations were more likely to fruit relative to those from the invasive range. Higher fruit set in females in native populations may indicate that individuals within invasive populations might not be reaching their full fruiting capacity. A variety of factors, such as the level of disturbance, reduced pollination services or presence of facilitator species could contribute to this [61,62]. Regardless, the result may be of concern for land managers, as the ongoing naturalisation of invasive populations may potentially reduce this fruiting constraint and therefore the expansion of invasive populations.

4.3. Seed Size Was Greater in the Invasive Range

Seeds produced in the invasive range were significantly larger than in the native range. Seed mass reflects maternal investment, with larger mass representing a potential establishment advantage through greater stored resources. Findings of greater seed mass within invasive populations throughout the literature is mixed, with data supporting [63,64,65] and failing to support [66,67] the hypothesis. Large seed typically do not disperse as far as smaller seeds [30]. This may explain, at least in part, the nucleation-style pattern of invasion seen in P. undulatum [35]. Heavier seeds are considered to be advantageous to populations expanding into new sites as a larger seed mass may improve the capacity for a plant to withstand the unpredictable environments found at novel and disturbed sites [68,69]. Avian seed dispersal may be important to P. undulatum colonisation of new sites [45], but ultimate persistence and population growth may benefit enhanced establishment traits over dispersal characteristics [35,48]. Because humans have assisted the introduction of P. undulatum to novel environments, there may not have been as high a selection on dispersal traits that we expected based on studies of other invasive plants. However, traits that enhance seedling establishment and thus population growth may be favoured in young populations [12,13]. Moreover, the high levels of specialised metabolites may enhance tolerance to abiotic and biotic stresses [34].

4.4. Influence of Resources on Seed and Fruit Production

Leaf nitrogen is typically limiting in most terrestrial environments, reflected in below optimal leaf N concentrations in many trees; plants in environments with high resource availability generally have higher Leaf N concentrations, and thus more resources available for reproduction. Production of fleshy fruits is resource intensive; thus females within dioecious populations are likely to incur higher reproductive costs [70]. However, pollen production may also require high nitrogen resources which may in part explain why both females and hermaphrodites in the present study had similar levels of nitrogen [71]. Female trees with higher leaf N concentrations did not have larger seeds, as has been observed in studies of other trees [72] but, in the present study, female trees did tend to have an overall higher fruit load. The scaling exponent of 5.54 is much higher than unity, and indicates the dramatic benefits increased nitrogen availability may have on fruit production (Supplementary Table S4). Exponent values of this magnitude have been found in other plant species [73]. The scaling factor of nitrogen availability on fruit production has implications on management of the species, as populations downstream from agricultural areas may be more prone to range expansion. Population density was similar in all sites and cannot be considered a factor in affecting flowering, sex, or fruit production. All trees had carbon isotope discrimination ranged from 29.5%–32.0‰, indicative of well-watered environments.

5. Conclusions: Management and Control of P. undulatum

Our work highlights the value in understanding the breeding strategy employed by a focal invasive species as a means of developing improved and more targeted control methods. Current management practises focus on removing females from populations where the range is expanding, with a focus on trees that have large fruit loads, as these are the individuals that promote further colonising spread via seed dispersal [47]. This action has the benefit of reducing the workload and spreading limited management resources, although the potential variability in sex expression should be monitored from year to year. Though our work has observed evidence of hermaphroditic individuals producing fruit, a general trend for significantly greater fruit production and seed size in females would support their targeted removal, as proposed by Gleadow and Walker [47]. However, this policy assumes sex ratios are consistent across all populations, and that the breeding system displayed by individuals remains fixed, regardless of fluctuations in resources, time, and stochastic factors. Anecdotal reports suggest sexual labiality in P. undulatum may present a factor in the species control, with the removal of all females from a population in one season, followed by the production of fruit by trees previously considered ‘male’. This study was conducted in Victoria, which has a clear demarcation between native and invasive ranges. Further study using larger sample sizes is advocated as a means of improving management efforts more broadly, paying particular attention to invasive area in regions that have different soils and climatic conditions.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/f17010072/s1. Supplementary Table S1: t-test comparing differences in total tree density, the proportion of females, and proportion of fruiting individuals among native and invasive populations of Pittosporum undulatum sampled across Victoria. Supplementary Table S2: Generalised linear model comparing variation in the proportion of fruit producing individuals between female and hermaphroditic trees from native and invasive populations. Supplementary Table S3: Linear model comparing variation in ranked fruit production between female and hermaphrodite trees from native and invasive populations. Supplementary Table S4: Linear model examining the relationship between female fruit rank and total leaf nitrogen. Supplementary Table S5: t-test on variation in mean seed number and seed, weight between native and invasive populations.

Author Contributions

Conceptualization, B.O., R.M.G., M.B. and S.V.; methodology, B.O., M.B. and S.V.; software, B.O.; validation, B.O. and M.B.; formal analysis, B.O.; investigation, B.O.; resources, R.M.G.; data curation, B.O.; writing—original draft preparation, B.O.; writing—review and editing, R.M.G., M.B. and S.V.; visualisation, B.O. and R.M.G.; supervision, R.M.G., M.B. and S.V.; project administration, R.M.G.; funding acquisition, R.M.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded in part through the Parks Victoria Research Partners Program. O’Leary was supported through an Australian Government Research Training Program (RTP).

Data Availability Statement

Data in addition to that contained within the article or Supplementary Material are available on request.

Acknowledgments

This research was supported by an Australian Government Research Training Program (RTP) Scholarship. The authors acknowledge Parks Victoria, Melbourne Water, Yarra Ranges Council, and Mornington Peninsula Council for their support and site access. The authors also thank all field volunteers and StopPitt for assistance and guidance. The authors have reviewed and edited the output and take full responsibility for the content of this publication.

Conflicts of Interest

The authors declare no conflicts of interest.

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Forests 17 00072 g001
Figure 1. (A) Map of Australia showing current distribution of Pittosporum undulatum (Atlas of Living Australia http://www.ala.org.au). The dotted line indicates the native distribution [32]. State borders are defined by the solid lines. (B) Location of the 14 sampling sites across Victoria that span native and expanded ranges: Morwell, Lakes Entrance, Lake Tyres, Marlo, and Mallacoota are all considered native populations. Remaining locations represent invasive populations.
Figure 1. (A) Map of Australia showing current distribution of Pittosporum undulatum (Atlas of Living Australia http://www.ala.org.au). The dotted line indicates the native distribution [32]. State borders are defined by the solid lines. (B) Location of the 14 sampling sites across Victoria that span native and expanded ranges: Morwell, Lakes Entrance, Lake Tyres, Marlo, and Mallacoota are all considered native populations. Remaining locations represent invasive populations.
Forests 17 00072 g001
Forests 17 00072 g002aForests 17 00072 g002b
Figure 2. (A) Proportion of female and hermaphrodite individuals fruiting in native and invasive populations of P. undulatum. (B) Mean fruit rank (an index of numbers of fruit) for individual females and hermaphrodites within native and invasive populations. Closed circles represent trees from native populations and open circles those from invaded populations. For full statistical analysis see Supplementary Tables S2 and S3.
Figure 2. (A) Proportion of female and hermaphrodite individuals fruiting in native and invasive populations of P. undulatum. (B) Mean fruit rank (an index of numbers of fruit) for individual females and hermaphrodites within native and invasive populations. Closed circles represent trees from native populations and open circles those from invaded populations. For full statistical analysis see Supplementary Tables S2 and S3.
Forests 17 00072 g002aForests 17 00072 g002b
Forests 17 00072 g003aForests 17 00072 g003b
Figure 3. Mean fruit rank at each site relative to leaf chemical traits of P. undulatum. (A) δC13 ‰; (B) total nitrogen (% dw); (C) total carbon (% dw). Females are represented by closed circles and hermaphrodites by open circles. No significant correlations were detected overall between traits and fruit rank.
Figure 3. Mean fruit rank at each site relative to leaf chemical traits of P. undulatum. (A) δC13 ‰; (B) total nitrogen (% dw); (C) total carbon (% dw). Females are represented by closed circles and hermaphrodites by open circles. No significant correlations were detected overall between traits and fruit rank.
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Figure 4. Leaf nitrogen concentration (% dw) for P. undulatum trees collected from 14 different populations. Bars represent means ± 1 SE. Grey bars = Female; white bars = Hermaphrodite. Statistical analysis can be found in Supplementary Table S5.
Figure 4. Leaf nitrogen concentration (% dw) for P. undulatum trees collected from 14 different populations. Bars represent means ± 1 SE. Grey bars = Female; white bars = Hermaphrodite. Statistical analysis can be found in Supplementary Table S5.
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Table 1. Location (latitude and longitude), elevation and climatic data * for 14 sites sampled across Victoria, Australia. Seven populations are considered to be within the ‘native’ range and seven where P. undulatum was only more recently recorded (see Figure 1).
Table 1. Location (latitude and longitude), elevation and climatic data * for 14 sites sampled across Victoria, Australia. Seven populations are considered to be within the ‘native’ range and seven where P. undulatum was only more recently recorded (see Figure 1).
SiteOriginLatitudeLongitudeElevation (m)Ave Min Temp °CAve Max Temp °CAve Rainfall (mm)
Morwell National Park 1 aNativeLat: −38.36Lon: 146.401848.020.2736.7
Morwell National Park 2 aNativeLat: −38.36Lon: 146.401848.020.2736.7
Lakes Entrance 1 bNativeLat: −37.88Lon: 147.964010.419.7733.6
Lakes Entrance 2 bNativeLat: −37.88Lon: 147.964010.419.7733.6
Lake Tyers State park bNativeLat: −37.76Lon: 148.07898.320.1729.9
Marlo cNativeLat: −37.79Lon: 148.55228.820.2845.5
Mallacoota dNativeLat: −37.56Lon: 149.761911.019.6943.7
Red Hill eInvadedLat: −38.39Lon: 145.021319.919.9708.4
Bittern 1 eInvadedLat: −38.30Lon: 145.12819.919.9708.4
Bittern 2 eInvadedLat: −38.30Lon: 145.12819.919.9708.4
Upwey 1 fInvadedLat: −37.90Lon: 145.312919.619.7855.4
Upwey 2 fInvadedLat: −37.90Lon: 145.312919.619.7855.4
Montrose fInvadedLat: −37.84Lon: 145.332229.619.7855.4
Silvan fInvadedLat: −37.83 Lon: 145.422939.619.7855.4
* Climate data Australian Bureau of Meteorology long term records for: a Morwell 085280; b Lakes Entrance 084150; c Orbost 084145 (Marlo); d Mallacoota 84084; e Cerberus 086361 (Red Hill/Bittern); f Ferny Creek 086266 (Montrose/Upwey/Silvan). https://www.bom.gov.au/climate/data/index.shtml (accessed on 22 December 2025).
Table 2. Number of trees per 20 m × 20 m plot (tree density), number of females per plot, mean number of seeds per fruit capsule (±1 SD) and mean seed mass (g dw) (±1 SD) across all sampled populations. Fruit availability limited sampling for the sites at Silvan and Bittern. Differences between native and invaded sites are not significantly different (p < 0.05, Supplementary Table S1).
Table 2. Number of trees per 20 m × 20 m plot (tree density), number of females per plot, mean number of seeds per fruit capsule (±1 SD) and mean seed mass (g dw) (±1 SD) across all sampled populations. Fruit availability limited sampling for the sites at Silvan and Bittern. Differences between native and invaded sites are not significantly different (p < 0.05, Supplementary Table S1).
TreesFemalesSeed NumberSeed Mass (g)
Native populations
Morwell 1301032.0 ± 1.80.0023 ± 0.0003
Morwell 28528.0 ± 3.60.0020 ± 0.0001
Lakes Entrance 11034633.8 ± 1.30.0036 ± 0.0003
Lakes Entrance 2341627.1 ± 3.60.0038 ± 0.0001
Lake Tyers22825.0 ± 1.40.0029 ± 0.0026
Marlo623427.3 ± 4.90.0040 ± 0.0014
Mallacoota1437128.7 ± 5.70.0027 ± 0.0006
Invasive populations
Red Hill1597227.6 ± 4.00.0082 ± 0.0026
Bittern 15115N/A
Bittern 28944N/A
Upwey 1301426.8 ± 4.20.0071 ± 0.0017
Upwey 2291228.7 ± 5.40.0066 ± 0.0016
Montrose843127.9 ± 4.70.0028 ± 0.0009
Silvan2710N/A
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O’Leary, B.; Burd, M.; Venn, S.; Gleadow, R.M. Reproductive Investment Across Native and Invasive Regions in Pittosporum undulatum Vent., a Range Expanding Gynodioecious Tree. Forests 2026, 17, 72. https://doi.org/10.3390/f17010072

AMA Style

O’Leary B, Burd M, Venn S, Gleadow RM. Reproductive Investment Across Native and Invasive Regions in Pittosporum undulatum Vent., a Range Expanding Gynodioecious Tree. Forests. 2026; 17(1):72. https://doi.org/10.3390/f17010072

Chicago/Turabian Style

O’Leary, Ben, Martin Burd, Susanna Venn, and Roslyn M. Gleadow. 2026. "Reproductive Investment Across Native and Invasive Regions in Pittosporum undulatum Vent., a Range Expanding Gynodioecious Tree" Forests 17, no. 1: 72. https://doi.org/10.3390/f17010072

APA Style

O’Leary, B., Burd, M., Venn, S., & Gleadow, R. M. (2026). Reproductive Investment Across Native and Invasive Regions in Pittosporum undulatum Vent., a Range Expanding Gynodioecious Tree. Forests, 17(1), 72. https://doi.org/10.3390/f17010072

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