Variation In Leaf Size Research Articles

Are leaf functional traits ‘invariant’ with plant size and what is ‘invariance’ anyway?

Summary Studies of size‐related plant traits have established a suite of mathematical functions describing whole plant investment and allocation. In parallel, studies of plant ‘economic spectra’ have measured the scaling and variance composition of traits related to the major dimensions of both structure and function. Here, we explore the intersection of these two broad areas by exploring the notion that many leaf economic traits are invariant with species differences in adult plant size. Invariant traits are those that do not change with plant size and are invoked as a key simplifying assumption of prominent models that purport to explain the scaling of plant size and metabolism. Unfortunately, leaf trait invariance is neither well defined nor understood and has never been critically evaluated. Using a global plant trait data set, we evaluated whether nine key traits can be considered as effectively invariant as a function of the maximum height of plant species, within and across plant growth forms and within and across broad taxonomic groups. We also examine the influence of habitat, biome and global spatial scales on the size‐relative variance in plant functional traits. We suggest that while invariance is an intuitive concept, an objective statistical definition is elusive. Expanding on ideas drawn from the study of life‐history invariants, we propose five criteria to identify traits that are effectively invariant, depending on the research question. We show that all studied ‘leaf economic spectrum’ (LES) traits approach invariance within and between herbaceous and woody plant groups, angiosperms and gymnosperms, and within most biome and habitat types. Individual leaf area, however, shows a modest increase with plant size, and there are significant shifts in the average LES trait values at a given plant maximum height, among the plant growth forms and taxonomic groups. Our results demonstrate that generally, LES traits show little interspecific variation with maximum plant height, which provides some support for attempts to model plants with ‘average’ leaf properties. Our work also highlights the need for a better understanding of the drivers of leaf size variation within and across individuals, functional groups, clades, biomes and habitats.

Elevational trends in leaf size of Campylotropis polyantha in the arid Minjiang River valley, SW China

Leaf traits are determinants of plant performance in ecosystems. The arid Minjiang River valley offer optimal opportunity to reveal climate-leaf function relationship because steep climatic gradients (e.g., dryness and high temperature decreased with elevation). We investigated the leaf size and structure of Campylotropis polyantha occurring in five 80–100 m elevational bands from 1650 m to 2200 m in this arid valley. Plants growing at higher elevations had larger leaves, epidermal cell and leaf thickness with thicker spongy mesophyll and epidermis, but had lower epidermal cell density and cutin thickness. These variations in leaf size and spongy mesophyll as well as cutin and total leaf thickness were mainly associated with annual precipitation and soil water content, while epidermal cell dimensions were associated with temperature. We conclude that water-related factors are the main mechanisms underlying leaf variations across elevations. High air temperature during the growing season imposes multiple stresses on plants at low elevations. The larger leaf size of high elevation plants is related more to their larger spongy mesophyll and epidermal cell sizes than to their larger palisade cell. These results provide a new understanding of functional ecology and the anatomical plasticity of plants in varying environments with different elevations.

Endopolyploidy as a potential alternative adaptive strategy for Arabidopsis leaf size variation in response to UV-B

The extent of endoreduplication in leaf growth is group- or even species-specific, and its adaptive role is still unclear. A survey of Arabidopsis accessions for variation at the level of endopolyploidy, cell number, and cell size in leaves revealed extensive genetic variation in endopolyploidy level. High endopolyploidy is associated with increased leaf size, both in natural and in genetically unstructured (mapping) populations. The underlying genes were identified as quantitative trait loci that control endopolyploidy in nature by modulating the progression of successive endocycles during organ development. This complex genetic architecture indicates an adaptive mechanism that allows differential organ growth over a broad geographic range and under stressful environmental conditions. UV-B radiation was identified as a significant positive climatic predictor for high endopolyploidy. Arabidopsis accessions carrying the increasing alleles for endopolyploidy also have enhanced tolerance to UV-B radiation. UV-absorbing secondary metabolites provide an additional protective strategy in accessions that display low endopolyploidy. Taken together, these results demonstrate that high constitutive endopolyploidy is a significant predictor for organ size in natural populations and is likely to contribute to sustaining plant growth under high incident UV radiation. Endopolyploidy may therefore form part of the range of UV-B tolerance mechanisms that exist in natural populations.

Temperature influences stomatal density and maximum potential water loss through stomata of Dodonaea viscosa subsp. angustissima along a latitude gradient in southern Australia

It is well known that physical leaf traits influence leaf functions, and that these traits vary across environmental gradients. Stomata can influence leaf function, with changes in density and size affecting potential water loss, CO2 uptake, and also leaf cooling. Plasticity in stomatal traits occurs in response to environmental factors; however, identifying which factors have the greatest influence is often difficult. We investigated variation in leaf size, stomatal density and size, and potential water loss from open stomata (gwmax), in the Australian native shrub Dodonaea viscosa subsp. angustissima, across a range of environmental factors including temperature, rainfall and CO2. We used herbarium specimens collected across a latitudinal gradient, and also sampled along an elevation gradient in southern Australia. There were significant relationships between mean summer maximum temperature and stomatal density, and gwmax. We found no significant relationships between rainfall or CO2 and the leaf traits we studied. Increased stomatal density at warmer locations may result in an increase in the potential for transpiration, as a means for evaporative cooling. Alternatively, it may enable increased CO2 and nutrient uptake during the short, winter-growing season.

Dynamic scaling in the growth of a non-branching plant, Cardiocrinum cordatum.

We investigated whole-plant leaf area in relation to ontogenetic variation in leaf-size for a forest perennial herb, Cardiocrinum cordatum. The 200-fold ontogenetic variability in C. cordatum leaf area followed a power-law dependence on total leaf number, a measure of developmental stage. When we normalized for plant size, the function describing the size of single leaves along the stem was similar among different-sized plants, implying that the different-sized canopies observed at different times in the growth trajectory were fundamentally similar to each other. We conclude that the growth trajectory of a population of C. cordatum plant leaves obeyed a dynamic scaling law, the first reported for a growth trajectory at the whole-plant level.

Responses of different phytoelements to habitat light level and their dynamic convergence towards crown development of Aucuba japonica Thunb. var. japonica

We analyzed crown development in Aucuba japonica Thunb. var. japonica resulting from the responses of phytoelements to habitat light conditions over a long period of time. Over the years, the degree of extension unit (EU) dimorphism and the degree of anisophylly were higher under shaded conditions than in brighter conditions. An overall temporally increasing pattern in the degree of EU dimorphism was found while no clear-cut trend was found in the case of anisophylly. EU length and number of leaves per EU co-varied in a spatio-temporal context. The number of terminal buds and their sizes acted as the key initiators of morphological differences of phytoelements which were further amplified following bud break. Leaf area density was displayed mostly in the apex peripheral layer of the crown and the apex layer received most of the incident light. There was a tradeoff between annual leaf production and mean leaf size. Depending on the heterogeneity of irradiance level within a crown, correlative growth inhibition caused higher EU mortality at brighter sites. Due to high mortality, shorter EUs had a mere role in the construction of structural framework of the crown except for the formation of some gaps. There was a strong convergence of EU dimorphism, anisophylly, EU extension growth and variations in leaf size towards formation of functional crown to reduce potential self-shading. Depending on the irradiance level, Aucuba japonica Thunb. var. japonica showed two different modes of crown expansion. At the brighter sites, individual crown expansion was progressive while at the darker sites, individual crown expanded in a diminishing manner and maintained a stable size. A plant's "growth diminishing phase" appeared earlier at shaded sites than brighter sites.

Genetic determinants of oil yield in Eucalyptus polybractea R.T. Baker

Eucalyptus polybractea R.T. Baker is the key species used in Australia to produce commercial quantities of pharmaceutical-grade eucalyptus oil. Much of the variability in oil yield observed in coppiced stands of the species is considered genetically determined. Nonetheless it is not known how genetics acts on leaf and secretory cavity morphology to influence oil yield. To examine this, we first chose similar-sized mature leaves of different genotypes and determined that secretory cavity size accounted for 84 % of the variation in oil yield between genotypes. We then examined natural variation in mature leaf size found along branches and observed oil yield to increase in a linear, but non-proportional fashion with increasing leaf size, suggesting leaves of different final sizes on a given tree can have different volumetric oil proportions. From these analyses, we calculated that a minimum of 2.2 μl of photosynthetic tissue is required to service each additional μl of secretory cavities as leaves expand. This suggests there is likely to be a maximum oil concentration obtainable in E. polybractea leaves for a given leaf size increase. Such information helps to understand the factors that underlie oil yields and provides a potential framework for selection strategies aimed at maximising harvestable oil yields.

Fine mapping a major QTL for flag leaf size and yield-related traits in rice

Leaf size is a major determinant of plant architecture and yield potential in crops. A previous study showed that the genomic region of chromosome 1 contains a major quantitative trait locus (QTL) for flag leaf size in a set of backcross recombinant inbred lines derived from two elite parental lines (Zhenshan 97 and 93-11). In the present study, the QTL (qFL1) was shown to explain a large proportion of the variation in flag leaf size (leaf length, width and area) in derived populations (BC(2)F(3) and BC(3)F(2)) in multiple environments. Using a large segregating population, we narrowed the location of qFL1 to a 31kb region containing four predicted genes. Expression of one of these genes, OsFTL1, differed between leaves in near-isogenic lines carrying alleles of Zhenshan 97 and 93-11. qFL1 had a pleiotropic effect on flag leaf size and yield-related traits. Conditional QTL analysis of the derived population (BC(3)F(2)) supports the assertion that qFL1 is the QTL for flag leaf length and exhibits pleiotropy. Pyramiding of qFL1 with two known genes (GS3 and Wx) from 93-11 into Zhenshan 97 enlarged flag leaves, improved grain size and amylose content, and increased yield per plant, but slightly delayed heading date. These results provide a foundation for the functional characterization of the gene underlying the pleiotropic effects of qFL1 and for genetic improvement of the plant architecture and yield potential of rice.

Contrasting leaf characteristics of trees and lianas in secondary and mature forests in southwestern China

We compared variation in sun-canopy leaf anatomy, morphology and photosynthetic rates of coexisting woody species (trees and lianas) in an 8-year-old secondary forest (SF) and mature forest (MF) in the wet season in Xishuangbanna, SW China. Variability of leaf traits of 66 species within growth-form groups in each forest was quantified using coefficients of variation (CV). For the mean values, the woody species in the SF had significantly higher leaf thickness and stomatal density, but lower nonmesophyll/mesophyll ratios than those in the MF. The average leaf area and leaf mass area (LMA) in the studied woody species did not change greatly during the successional process, but differed significantly between the growth forms, with trees having higher values than lianas. The light-saturated photosynthetic rate per unit leaf area (A a) of the woody species in the SF ranged from 11.2 to 34.5 μmol m−2 s−1, similarly to pioneer tree species from literature data in southeast Asia. The A a and photosynthetic nitrogen-use efficiency (PNUE) were significantly higher than those in the MF; whereas A a in the MF ranged between 9 to 21 μmol m−2 s−1, with similar values between lianas and trees. For all woody species in both SF and MF, there were no significant differences in the average values of the CV of all measured variables for both lianas and trees. However, considerable variation in leaf anatomy, morphology, and photosynthetic rates within both growth forms and forests existed, as well as substantial variation in leaf size and stomatal density. We concluded that the tropical woody species formed a heterogeneous functional group in terms of leaf morphology and physiology in both secondary and mature forests.

Leaf structural modifications in Populus × euramericana subjected to Zn excess

In previous experiments elevated but sub-symptomatic applications of Zn (0.1 mM and 1 mM) caused impairments in growth parameters and photosynthetic performance of Populus × euramericana (Dode) Guinier clone I-214. The aim of this work was to evaluate leaf morphological and anatomical traits in this clone in response to the same Zn concentrations. The results showed that Zn treatments induced variations in leaf dry mass, area, mesophyll thickness, intercellular spaces, stomatal density and size. Stronger modifications, especially concerning stomata characteristics induced by 1 mM Zn, were consistent with physiological impairments while those induced by 0.1 mM Zn suggested a compensatory strategy for maintaining functional integrity.

Growth-unit structure in trees: effects of branch category and position on Nothofagus nervosa, N. obliqua and their hybrids (Nothofagaceae)

In plants with rhythmic growth, a branch segment extended in one event is known as growth unit (GU). GU structure, resulting from the resources allocated to stem length, volume and mass, and to leaf area and mass, is relevant for understanding branch functioning in the context of plant development. This study compares GU structure between main branches and short branches positioned at low and high positions on nursery-grown trees of three closely related genetic entities: Nothofagusnervosa, N. obliqua and natural hybrids between these species. GUs of short branches, compared to those of main branches, had lower length, diameter and number of leaves, and higher specific leaf area (SLA), stem density and proportional mass in leaves than in stems. GUs at high position on the trees had a higher proportion of their mass in stem than in leaves and a lower SLA than those at low position. Stem density was higher for N. nervosa and the hybrid trees than for N. obliqua. Most other GU traits did not differ statistically between the considered genetic entities. The three genetic entities exhibited distinct patterns of variation in leaf size with leaf position along main-branch GUs. The individual tree had a significant effect on most variables. GU structure would have a major ontogenetic component and would play a relevant role in the architecture of Nothofagus species and their adaptation to different environmental conditions.

Ecophysiological significance of leaf size variation in Proteaceae from the Cape Floristic Region

Summary 1. Small leaves of species endemic to Mediterranean‐type climate areas have been associated with both low rainfall and nutrient availability, but the physiological reasons for this association remain unknown. 2. We postulated that small leaves have thin boundary layers that facilitate transpiration in winter and sensible heat loss in summer. High transpiration rates when water is available may facilitate nutrient acquisition in winter, whereas efficient sensible heat loss reduces the requirement for transpirational leaf cooling in summer. 3. The consequences of varying leaf sizes for water and heat loss in Cape Proteaceae were examined at two scales. At the leaf level, gas exchange and thermoregulatory capacities of 15 Proteaceae species with varying leaf size were assessed under controlled conditions using phylogenetically independent contrasts. At an environmental level, leaf attributes of Proteaceae occurring in the winter‐rainfall area of the Cape Floristic Region were correlated with climatic environments derived from distribution data for each species. 4. Leaf temperature was positively correlated with leaf size when wind speed was negligible. However, transpiration decreased significantly with increasing leaf size when measured on individual leaves, detached branches and when expressed on a per stoma basis. 5. From multiple stepwise regression analysis of climatic variables obtained from distribution data, leaf size was negatively correlated with A‐Pan evaporation, mean annual temperatures and water stress in January. We conclude that leaf size is conservative for survival over relatively rare periods of hot dry conditions with low wind speeds. 6. Narrow leaves enable plants to shed heat through sensible heat loss during summer droughts, without the need for transpirational cooling. Additionally, small leaf dimensions confer a capacity for high transpiration when evaporative demand is low and water is abundant (i.e. winter). This may be a particularly important strategy for driving nutrient mass‐flow to the roots of plants that take up most of their nutrients in the wet winter/spring months from nutrient‐poor soils.

Leaf patterns, leaf size and ecologically related traits in high Mediterranean mountain on the Moroccan High Atlas

Leaf traits functional relationship is particularly important in plant ecological strategies, but few data are available from Mediterranean high-altitude environments. We analysed leaf general patterns and leaf trait relationships in 84 perennial species on the High Atlas, Morocco. We examined the correlation amongst leaf size, leaf width and length, plant height and seed size, analysed multi-trait relationships using Structural Equation Models and tested leaf size variation amongst growth forms (functional groups). Species spanned 103 range of leaf size (sub-lepto- to microphylls). Nanophylls (48.8%) were dominant and over-represented in half-shrubs. Tree and rosette herbs were more likely to have large leaf size (nano-micro- and microphylls), whereas shrubs have medium leaf size (nano-micro- and nanophylls) and cushion and half-shrubs have small (sub-lepto- to nanophylls) and narrow leaves. Small-leaved species synchronized their leaf phenological activity with the dry summer months (May–August), and large-leaved species extended throughout the spring until the end of summer following the similar patterns found in lowland Mediterranean environments. Regarding woody species, our results showed a positive and significant relationship between leaf size and plant height and a non-significant relationship between leaf size and seed size. Structural Equation Models showed that variation in leaf size was triggered chiefly by changes in leaf form (leaf width) and plant height, seed size being of no relevance. In our study area, large-seeded species have a relatively wide range of leaf size. The hypothesis that the combination of large seeds and small leaves is allometrically unlikely (except for leptophyll Conifers) was supported in this study.

Size-dependent leaf area ratio in plant twigs: implication for leaf size optimization

Although many hypotheses have been proposed to explain variation in leaf size, the mechanism underlying the variation remains not fully understood. To help understand leaf size variation, the cost/benefit of twig size was analysed, since, according to Corner's rule, twig size is positively correlated with the size of appendages the twig bears. An extensive survey of twig functional traits, including twig (current-year shoots including one stem and few leaves) and leaf size (individual leaf area and mass), was conducted for 234 species from four broadleaved forests. The scaling relationship between twig mass and leaf area was determined using standardized major axis regression and phylogenetic independent comparative analyses. Leaf area was found to scale positively and allometrically with both stem and twig mass (stem mass plus leaf mass) with slopes significantly smaller than 1.0, independent of life form and habitat type. Thus, the leaf area ratio (the ratio of total leaf area to stem or twig mass) decreases with increasing twig size. Moreover, the leaf area ratio correlated negatively with individual leaf mass. The results of phylogenetic independent comparativeanalyses were consistent with the correlations. Based on the above results, a simple model for twig size optimization was constructed, from which it is postulated that large leaf size-twig size may be favoured when leaf photosynthetic capacity is high and/or when leaf life span and/or stem longevity are long. The model's predictions are consistent with leaf size variation among habitats, in which leaf size tends to be small in poor habitats with a low primary productivity. The model also explains large variations in leaf size within habitats for which leaf longevity and stem longevity serve as important determinants. The diminishing returns in the scaling of total leaf area with twig size can be explained in terms of a very simple model on twig siz

Testing the generality of the ‘leafing intensity premium’ hypothesis in temperate broad-leaved forests: a survey of variation in leaf size within and between habitats

Because leaf size scales negatively and isometrically with leaf number per shoot size (leafing intensity) in woody species, and because most tree and shrub species have small leaves, Kleiman and Aarssen (J Ecol 95:376–382, 2007) recently proposed that natural selection favors high leafing intensity resulting in small leaves, i.e., the leafing-intensity-premium hypothesis. However, empirical evidence for or against this hypothesis is still lacking. In addition, this hypothesis has not been examined in the context of how leaf size varies among habitats. To fill this void, we investigated leaf size frequency distributions of woody species from temperate China and explored the relationships among leaf mass, leaf number, and stem mass of current-year shoots of 133 woody species at low and high altitudes of three mountain ranges. The scaling relationships between leaf size and leafing intensity (leaf number per stem mass) were determined using both standardized major axis regression analyses and phylogenetically independent comparative techniques. In light of the leafing-intensity-premium hypothesis, we made three predictions: (1) leaf size frequency distributions should be right-skewed for each local study area and for the entire study region, (2) leafing intensities at different altitudes at different sites should differ while leafing intensities at comparable altitudes should be similar baring large taxonomic differences among sites, and (3) that leafing intensity should be higher for any given leaf size in habitats with small-leaved species. Significant negative and isometric scaling relationships between leaf size and leafing intensity were found to be consistently conserved independent of habitat type, both across species and across correlated evolutionary divergences. Within each mountain range or across the entire study region, leaf size frequency distributions were right-skewed, in accordance with our prediction. However, leafing intensity was smaller for any given leaf size at the altitude with smaller leafed species than for altitudes characterized by large leafed species, i.e., altitudes characterized by species with small leaves did not have consistently higher leafing intensities than other altitudes on each mountain range. Our analyses therefore indicate the direct adaptive value of leaf size but not the selective advantage in high leafing intensity as posited by the leafing-intensity-premium hypothesis. We suggest that this hypothesis explains less about the variation of leaf size among different habitats as it does about variation within habitats, i.e., the relative importance of the adaptive significance of leafing intensity and leaf size can and does vary with habitats.

The leaf size/number trade-off in herbaceous angiosperms

Aims In this study, we examined the extent to which between-species leaf size variation relates to variation in the intensity of leaf production in herbaceous angiosperms. Leaf size variation has been most commonly interpreted in terms of biomechanical constraints (e.g. affected by plant size limitations) or in terms of direct adaptation associated with leaf size effects in optimizing important physiological functions of individual leaves along environmental gradients (e.g. involving temperature and moisture). An additional interpretation is explored here, where adaptation may be more directly associated with the number of leaves produced and where relatively small leaf size then results as a trade-off of high ‘leafing intensity’—i.e. number of leaves produced per unit plant body size. Methods The relationships between mean individual leaf mass, number of leaves and plant body size were examined for 127 species of herbaceous angiosperms collected from natural populations in southern Ontario, Canada. Important Findings In all, 88% of the variation in mean individual leaf mass across species, spanning four orders of magnitude, is accounted for by a negative isometric (proportional) trade-off relationship with leafing intensity. These results parallel those reported in recent studies of woody species. Because each leaf is normally associated with an axillary bud or meristem, having a high leafing intensity is equivalent to having a greater number of meristems per unit body size—i.e. a larger ‘bud bank’. According to the ‘leafing intensity premium’ hypothesis, because an axillary meristem represents the potential to produce either a new shoot or a reproductive structure, high leafing intensity should confer greater architectural and/or reproductive plasticity (with relatively small leaf size required as a trade-off). This greater plasticity, we suggest, should be especially important for smaller species since they are likely to suffer greater suppression of growth and reproduction from competition within multi-species vegetation. Accordingly, we tested and found support for the prediction that smaller species have not just smaller leaves generally but also higher leafing intensities, thus conferring larger bud banks, i.e. more meristems per unit plant body size.

Leaf traits variation during leaf expansion in Quercus ilex L.

The morphological, anatomical and physiological variations of leaf traits were analysed during Quercus ilex L. leaf expansion. The leaf water content (LWC), leaf area relative growth rate (RGRl) and leaf dry mass relative growth rate (RGRm) were the highest (76±2 %, 0.413 cm2 cm−2 d−1, 0.709 mg mg−1 d−1, respectively) at the beginning of the leaf expansion process (7 days after bud break). Leaf expansion lasted 84±2 days when air temperature ranged from 13.3±0.8 to 27.6±0.9 °C. The net photosynthetic rate (PN), stomatal conductance (gs), and chlorophyll content per fresh mass (Chl) increased during leaf expansion, having the highest values [12.62±1.64 µmol (CO2) m−2 s−1, 0.090 mol (H2O) m−2 s−1, and 1.03±0.08 mg g−1, respectively] 56 days after bud break. Chl was directly correlated with leaf dry mass (DM) and PN. The thickness of palisade parenchyma contributed to the total leaf thickness (263.1±1.5 µm) by 47 %, spongy layer thickness 38 %, adaxial epidermis and cuticle thickness 9 %, and abaxial epidermis and cuticle thickness 6 %. Variation in leaf size during leaf expansion might be attributed to a combination of cells density and length, and it is confirmed by the significant (p<0.001) correlations among these traits. Q. ilex leaves reached 90 % of their definitive structure before the most severe drought period (beginning of June — end of August). The high leaf mass area (LMA, 15.1±0.6 mg cm−2) at full leaf expansion was indicative of compact leaves (2028±100 cells mm−2). Air temperature increasing might shorten the favourable period for leaf expansion, thus changing the final amount of biomass per unit leaf area of Q. ilex.

The leafing intensity premium hypothesis tested across clades, growth forms and altitudes

Summary 1. Recent reports provide empirical evidence for a negative isometric scaling of (log)leaf number per unit shoot volume (i.e. leafing intensity) to (log)leaf size in woody plants. In this context, a theory of leaf size variation was anticipated, stating that natural selection should have favoured high leafing intensity, given that most tree and shrub species are small‐leaved. Leaf size is thus proposed to be a mere correlate of leafing intensity. This was coined the leafing intensity premium hypothesis. 2. I investigated the generality of the leaf size–number trade‐off by testing its extension to a set of 60 small‐stature species, growing along an altitude gradient. Also, I compiled data from 224 species and re‐analysed their leaf size and leafing intensity. Finally, I explored the validity of the leafing intensity premium hypothesis to account for the leaf size–number trade‐off, if the latter was sustained, and examined patterns of coordinated evolution of leaf size and leafing intensity across seed plant lineages. 3. Negative isometric scaling was supported in all analyses, except when evergreens were considered in isolation. Frequency distribution of both leaf size and leafing intensity was severely right‐skewed in the 224‐species data set, which provided no evidence in support of the view that natural selection favoured species with high leafing intensity. 4. Node divergences in the phylogenetic tree showed a tendency for inverse coordinated evolution of leafing intensity and leaf size. However, interactions between environments and divergence patterns, and also node‐wise peculiarities, were detected. 5. Synthesis. The leaf size–number trade‐off is of general scope, although scaling exponents differ among evergreen and deciduous species. In addition, signals of coordinated evolution of both traits across the seed plant tree were detected. Still, the leafing intensity premium hypothesis cannot be supported, since leafing intensity of present‐day species is not particularly biased towards high scores.

Morphological characteristics of leaf epidermis and size variation of leaf, flower and fruit in different ploidy levels in Buddleja macrostachya (Buddlejaceae)

Abstract Buddleja macrostachya (Buddlejaceae) is a widespread shrub native to the Sino‐Himalayan mountains and beyond. It has been found to occur at two ploidy levels, hexaploid, 2n=6x=114 and dodecaploid, 2n=12x=228. To determine if morphological characters might be used as indicators of ploidy levels, we measured floral and fruit length, relative and absolute leaf size, trichome density on both leaf surfaces, and stomatal density and length in different populations of B. macrostachya. In general, flower and fruit length, absolute leaf size, and stomatal length increased with an increase at ploidy level (P&lt;0.01), whereas adaxial cell and stomatal density decreased with an increase at ploidy level (P&lt;0.01). We found no conspicuous differences in relative leaf size (P&gt;0.05) in different populations. Other characters studied such as trichome type, cuticular membrane and ornamentation of stomata, cell and stomatal shape, and anticlinal wall pattern were quite constant in this species. Thus it appears that flower and fruit length, absolute leaf size, and stomatal frequency and length can be used to distinguish hexaploid from dodecaploid cytotypes either in the field or in herbarium specimens.

LibocedrusMacrofossils from Tasmania (Australia)

Fossilized Libocedrus (Cupressaceae) foliage from three Tasmanian fossil sites—Regatta Point (∼52–51 Ma), Lea River (∼32–30 Ma), and Balfour (∼29–21 Ma)—is described, and three new species are recognized. Brief descriptions of extant Libocedrus precede the fossil descriptions. Libocedrus leaf morphology has remained much the same for 30 Myr. Variations in leaf size, stomatal frequency, size, and distribution are indicative of prevailing climatic conditions. Although Libocedrus appears to have had a quite widespread distribution in southeastern Australia in the past, the genus is now found only in New Zealand and New Caledonia. Its disappearance from Tasmania and the Australian mainland is linked to continental rearrangement and global climate change. A single specimen from Balfour shares features common to extant Libocedrus and the closely related monotypic cupressaceous genus Diselma.