Stomatal Characteristics at Different Ploidy Levels inCoffeaL.

Stomatal frequency, epidermal cell frequency, stomatal guardcell length and stomatal index were examined at different ploidylevels inCoffea. In general, stomatal and epidermal cell frequencyper unit leaf area decreased while stomatal guard cell lengthincreased with an increase in ploidy. The reduction in stomatalfrequency at higher ploidy levels was mainly a result of largerepidermal cells. In the case ofC. canephora(cultivar S.274)a significant reduction in stomatal frequency was noticed fromdiploid to tetraploid level which was due to both larger epidermalcell size and less stomatal differentiation at the tetraploidlevel. Besides the effect of ploidy on stomatal frequency andguard cell length, genotypic differences in stomatal frequencyand stomatal guard cell length were also observed among cultivarsof the same ploidy level. Although variation in stomatal frequencyamong cultivars was found to be associated with the differencein stomatal to epidermal cell ratio, variation in guard celllength was attributed to differential genetic architecture.In the present study a highly significant positive correlation(r=0.82) between stomatal and epidermal cell frequency and highnegative correlations between stomatal frequency and guard celllength (r=-0.91) and epidermal cell frequency and stomatal guardcell length (r=-0.93) were obtained. The study also indicatedthat stomatal frequency can be predicted with 83 and 87% accuracy,respectively, by measuring stomatal guard cell length in coffee.Copyright1997 Annals of Botany Company Coffea; ploidy level; stomatal characteristics     

Crown Spread Patterns for Five Deciduous Broad-leaved Woody Species: Ecological Significance of the Retention Patterns of Larger Branches

Patterns of crown spread and branch retention of two shade-intolerantspecies (Betula platyphyllaandB. maximowicziana) were comparedwith three more tolerant species (Quercus mongolica,Acer sieboldianumandMagnoliaobovata). Branching height (height of the lowest living branch)rose more rapidly with age for the twoBetulaspecies than forthe shade tolerant species. Branching heights ofA. sieboldianumandM.obovatawere similar, irrespective of tree height and age, andlarger trees tended to produce wider crowns than theBetulaspecieswhen trees of similar height were compared. In all species,the branch basal area (cross-sectional area of a branch at itsbase) and the leaf area per branch generally increased as thebranch position on a stem became lower. Therefore, retaininglarger branches contributed significantly to the support ofa larger leaf area per tree. The number of larger branches (branchbasal area >80 cm²) for bothBetulaspecies was significantlysmaller than that of the shade tolerant species. The branchretention pattern ofBetulaspecies was probably a consequenceof intolerance of the leaves to shade. The decline ofBetulaspecieswith forest succession is likely to occur through their inabilityto retain branches with a large base area in closed forests.Copyright1997 Annals of Botany Company Shade tolerance; crown spread; branch retention; branch size; broad-leaved woody species; leaf area index per tree     

Ontogenetic changes in stomatal size and conductance of sunflowers

The ontogenetic changes in stomatal size, frequency and conductance (g_s) on abaxial and adaxial leaf surfaces of sunflower plants (Helianthus annuus L. Russian Mammoth) were examined under controlled environmental conditions. The stomatal frequency on the adaxial and abaxial leaf surfaces decreased with leaf ontogeny and insertion level. The ratio of adaxial to abaxial stomatal frequency did not change with leaf ontogeny and insertion level, and 42–44% of total stomata was apportioned to the adaxial surface. Ontogenetic changes in stomatal pore length were detected and increased with ontogenesis. The stomatal length of both leaf surfaces had linear relationships with leaf area. Ontogenetic changes in g_s were similar between the two surfaces. However the adaxial g_s was lower than abaxial g_s in leaves of higher insertion levels. Conductance had a linear relationship with width x frequency but not with pore area.     

Crown conductance in dwarf, medium, and tall pitch pines in the Long Island Pine Plains

The New York Pine Plains are a unique ecosystem with normal statured and a dwarfed variety of pitch pines (Pinus rigida Mill.). Growing interspersed with the dwarf pines are trees of intermediate height and features. Several hypotheses have been put forward as to why some of the trees are dwarfed, but none have been substantiated. In this study, we tested whether dwarf or medium trees are hydraulically limited compared to normally growing trees. Granier style sap flux sensors were installed in three to six trees of each tree type and sap flux was measured in early August 2004. Sap flux measurements were scaled to crown stomatal conductance using leaf area to sapwood area ratios for each tree. Contrary to expectation, dwarf and medium stature trees had very low leaf area to sapwood area ratios, but high crown stomatal conductances compared to normal trees. Analyses of leaf area, ring widths, and crown stomatal conductance indicate that differences between normal, and dwarf and medium pines are not due to hydraulic limitation, but that stunted growth may be due to other causes.     

Effects of European colonization on indigenous ecosystems: post-settlement changes in tree stand structures in Eucalyptus–Callitris woodlands in central New South Wales, Australia

Aim There has been considerable debate about pre‐settlement stand structures in temperate woodlands in south‐eastern Australia. Traditional histories assumed massive tree losses across the region, whereas a number of recent histories propose that woodlands were originally open and trees regenerated densely after settlement. To reconcile these conflicting models, we gathered quantitative data on pre‐settlement stand structures in Eucalyptus–Callitris woodlands in central New South Wales Australia, including: (1) tree density, composition, basal area and canopy cover at the time of European settlement; and (2) post‐settlement changes in these attributes. Location Woodlands dominated by Eucalyptus species and Callitris glaucophylla, which originally occupied approximately 100,000 km² in central New South Wales, Australia. Methods We recorded all evidence of pre‐settlement trees, including stumps, stags and veteran trees, from 39 relatively undisturbed 1‐ha stands within 16 State Forests evenly distributed across the region. Current trees were recorded in a nested 900 m² quadrat at each site. Allometric relationships were used to estimate girth over bark at breast height, tree basal area, and crown diameter from the girth of cut stumps. A post‐settlement disturbance index was developed to assess correlations between post‐settlement disturbance and attributes of pre‐settlement stands. Results The densities of all large trees (> 60 cm girth over bark at breast height) were significantly greater in current stands than at the time of European settlement (198 vs. 39 trees ha^?1). Pre‐settlement and current stands did not differ in basal area. However, the proportional representation of Eucalyptus and Callitris changed completely. At the time of settlement, stands were dominated by Eucalyptus (78% of basal area), whereas current stands are dominated by Callitris (74%). On average, Eucalyptus afforded 83% of crown cover at the time of settlement. Moreover, the estimated density, basal area and crown cover of Eucalyptus at the time of settlement were significantly negatively correlated with post‐settlement disturbance, which suggests that these results underestimate pre‐settlement Eucalyptus representation in the most disturbed stands. Main conclusions These results incorporate elements of traditional and recent vegetation histories. Since European settlement, State Forests have been transformed from Eucalyptus to Callitris dominance as a result of the widespread clearance of pre‐settlement Eucalyptus and dense post‐settlement recruitment of Callitris. Tree densities did increase greatly after European settlement, but most stands were much denser at the time of settlement than recent histories suggest. The original degree of dominance by Eucalyptus was unexpected, and has been consistently underestimated in the past. This study has greatly refined our understanding of post‐settlement changes in woodland stand structures, and will strengthen the foundation for management policies that incorporate historical benchmarks of landscape vegetation changes.     

Stomatal Characteristics, Leaf Waxes, and Transpiration Rates of Theobroma cacao and Hevea brasiliensis Seedlings

Stomatal size and frequency as well as structure and distributionof leaf waxes were compared in seedlings of two varieties ofTheobroma cacao and three families of Hevea brasiliensis. Stomataof both species were located on the abaxial leaf surface only.The stomata of Theobroma averaged 45% shorter and 29% narrowerthan those of Hevea, but stomatal frequency was 44% higher inTheobroma. Stomatal size and frequency differed more among Heveafamilies than between Theobroma varieties. The structure ofthe leaf waxes of Theobroma and Hevea differed appreciably.It also varied greatly between the abaxial and adaxial leafsurfaces of Hevea, but only slightly in Theobroma. The structureof leaf waxes varied little between Theobroma varieties or amongHevea families. Leaf conductances and transpiration rates weremuch higher in Hevea than in Theobroma seedlings. The implicationsof water relations in interplanting of Theobroma and Hevea arediscussed. Cacao, Theobroma cacao, rubber, Hevea brasiliensis, stomatal size, stomatal frequency, leaf waxes, transpiration     

Modification of Drought Resistance by Water Stress Conditioning in Acacia and Eucalyptus

Plants of Acacia and Eucalyptus species were grown under differentlevels of shading, nutrition, and irrigation to assess the effectof these factors on plant water use. Water use per unit of leaf(phyllode) area was affected only by the irrigation treatment,control plants that had received water daily using appreciablymore water than plants that had been repeatedly subjected towater stress. Water stress conditioning had little or no effecton plant height, leaf (phyllode) area, or minimum stomatal resistancein any of the species. Detailed study of the water stress conditioningof Eucalyptus robusta showed that controls used 46% more waterthan conditioned plants. Leaf area and plant height were unaffectedby conditioning. Control of transpiration was not due to stomatalfunctioning, both sets of plants operating with the same leafdiffusive resistance under conditions of ready water availability.Hydraulic conductivity of the intact root system was loweredby conditioning and it is suggested that this was due, at leastin part, to the effect that conditioning had on root xylem conductivity.Specific conductivity of stem sections was lowered by waterstress conditioning. Water stress avoidance was also associatedwith a more pronounced tendency for stomata to close prior towilting and with a higher level of leaf resistance which couldbe maintained at a low leaf water potential. Conditioned plantsexhibited drought tolerance in their ability to control lossof water from the leaf at lower leaf water potentials than thecontrols.     

Size-dependency in hydraulic and photosynthetic properties of three <Emphasis Type="Italic">Acer</Emphasis> species having different maximum sizes

Recent studies suggest that physiological traits can be affected by tree size due to stronger hydraulic limitation in taller trees. As trees vary greatly in size, both within and among species, the adaptive responses to hydraulic limitation may be different among species with different maximum sizes. To investigate this, we explored size-dependency in photosynthetic and hydraulic parameters of three Acer species (Acer mono Maxim., Acer amoenum Carr and Acer japonicum Thunb.) using trees of various sizes under well-lit conditions. Leaf stomatal conductance of the Acer species decreased with tree size, implying that water supply to leaves decreases as trees grow. In contrast, content of nitrogen increased with tree size, which may compensate for the decrease in stomatal conductance to maintain the photosynthetic rate. Although the increase in nitrogen and leaf mass per area were larger in species with larger statures, the size-dependency in stomatal conductance was not different among species, and photosynthetic rate and hydraulic conductance were maintained in the three Acer species. Therefore, we suggest that hydraulic limitation on gas exchange does not necessarily depend on the maximum height of the species and that maintenance of photosynthesis and hydraulic properties is a fundamental physiological process during tree growth.     

Stomatal and Chlorophyll Distribution of Cox's Orange Pippin Apple Flowers Relative to Other Cluster Parts

Surface area, chlorophyll concentration and stomatal size anddensity were measured for all green components of floral clusterson Cox's Orange Pippin apple trees to assess their relativepotential for photosynthesis. Before flower opening, sepalsand receptacles had chlorophyll concentrations similar to thosefound in the laminae of rosette leaves. But, whereas the concentrationin rosette leaves continued to increased until fruit set, thosein the sepals and receptacles decreased. Sepals had a greater mature stomatal density than leaf laminaeshortly after bud burst; although both densities increased,that on the laminae later exceeded that on sepals. Flowers contributed significantly to the green surface are (40%),chlorophyll content (30%) and mature stomatal number (25%) offloral clusters at the green cluster stage, but these contributionsthen decreased. Cox apple flowers appear to have the potentialfor contributing significantly to their carbohydrate requirementat a time when the rosette leaves are not thought to be exportersof photosynthate.Copyright 1993, 1999 Academic Press Malus pumila, apples flowers, chlorophyll, stomata, surface area, flower photosynthesis     

Diurnal change in the relationship between stomatal conductance and abscisic acid in the xylem sap of field-grown peach trees

To evaluate whether abscisic acid (ABA) in the xylem sap playsan important role in controlling stomatal aperture of field-grownPrunus persica trees under drought conditions, stomatal conductance(g) and xylem ABA concentrations were monitored both in irrigatedand non-irrigated trees, on two consecutive summer days (threetimes a day). Stomata1 conductance of non-irrigated trees hada morning maximum and declined afterwards. The changes in gduring the day, rather than resulting from variations in theconcentrations of ABA in the xylem sap or the delivery rateof this compound to the leaves, were associated with changesin the relationship between g and xylem ABA. The stomata ofwater-stressed trees opened during the first hours of the day,despite the occurrence of a high concentration of ABA in thexylem sap. However, stomatal responsiveness to ABA in the xylemwas enhanced throughout the day. As a result, a tight inverserelationship between g and the logarithm of xylem ABA concentrationwas found both at midday and in the afternoon. A similar relationshipbetween g and ABA was found when exogenous ABA was fed to leavesdetached from well-watered trees. These results indicate thatABA derived from the xylem may account for the differences ing observed between field-grown peach trees growing with differentsoil water availabilities. Several possible explanations forthe apparent low stomatal sensitivity to xylem ABA in the morning,are discussed, such as high leaf water potential, low temperatureand high cytokinin activity. Key words: Prunus persica L., stomata, xylem ABA, water deficits, root-to-shoot communication     

Junction Complexes between Sieve Tubes in the Secondary Phloem of Myrtaceae

Junction complexes of unusual structure form between neighbouringsieve tubes in the secondary phloem of Eucalyptus species. Thick-walledribs support thin-walled ‘sieve areas’. In longitudinalsections the structures have a ‘concertina’- likeappearance. They are relatively large, up to 0.2 mm in length.Electron micrographs confirmed that the structures consistedof thin-walled areas perforated with pores, supported by muchthicker ribs. The structures provide a vast surface area fortransfer of metabolites between sieve tubes compared with thatof lateral wall sieve areas of other plants. Hydrolysis of parenchymacell walls occurs during the development of the junction complexes.The structures are only found when sieve tubes are in closeproximity and it is the redifferentiation and partitioning ofintervening parenchyma cells which result in junction complexformation. A survey for the presence of the structures in thephloem of other genera in the family Myrtaceae was made andthey were found in Tristania and Angophora but were not observedin Acmena and Metrosideros. Eucalyptus, sieve tubes, lateral walls, ultrastructure     

Stomatal Characteristics of Four Native Herbs Following Exposure to Elevated CO2

Contrasting effects on the stomatal index (SI), stomatal density,epidermal cell size and number were observed in four chalk grasslandherbs (Sanguisorba minor Scop., Lotus corniculatus L., Anthyllisvulneraria L. and Plantago media L.) following exposure to elevatedcarbon dioxide concentrations (CO₂) in controlled environmentgrowth cabinets. SI of S. minor increased for both leaf surfaces,whilst in A. vulneraria and P. media SI decreased on one surfaceonly. In L. corniculatus , no differences in SI were observedas epidermal cell density changed in parallel with stomataldensity. In L. corniculatus and S. minor stomatal density increasedon both surfaces, whereas in P. media it decreased; in A. vulnerariastomatal density decreased on the abaxial leaf surface alonefollowing exposure to elevated CO₂. In the latter three species,SI changed because stomatal density did not change in parallelwith epidermal cell density. The results suggest elevated CO₂is either directly or indirectly affecting cell differentiationand thus stomatal initiation in the meristem. In S. minor and P. media leaf growth increased in elevated CO₂,because of increased cell expansion of epidermal cells, whereasin L. corniculatus, epidermal cell size decreased and greaterleaf growth was because of an increase in epidermal cell divisions.In A. vulneraria, leaf size did not change, but increased cellexpansion on the adaxial surface suggests CO₂ affects leaf surfacesdifferently, either directly or indirectly at the cell differentiationstage or as the leaf grows. These results suggest component species of a plant communitymay differ in their response to elevated CO₂. Predicting theeffect of environmental change is therefore difficult.Copyright1994, 1999 Academic Press Elevated CO₂, Sanguisorba minor (salad burnet), Lotus corniculatus (birdsfoot trefoil), Anthyllis vulneraria (kidney vetch), Plantago media (hoary plantain), stomatal index, stomatal density, epidermal cell size     

Changes in leaf morphology and anatomy with tree age and height in the broadleaved evergreen species, Eucalyptus regnans F. Muell

Relatively little is known about changes in leaf attributes over the lifespan of woody plants. Knowledge of such changes may be useful in interpreting physiological changes with age. This study investigated changes in leaf morphology and anatomy with tree age and height in the broadleaved evergreen species, Eucalyptus regnans. Fully expanded leaves were sampled from the upper canopy of tree ages ranging from 6 to 240 years, and tree heights ranging from about 10–80 m. There were significant changes in leaf form with increasing tree age and height. Leaf size and specific leaf area (SLA; leaf area/leaf mass) decreased, leaf thickness increased, and leaves became narrower relative to their length, with increasing tree age and height. Cuticle thickness and leaf waxiness, including wax occlusion of the stomatal antechamber, increased with increasing age and height. By comparison, there were no clear trends in stomatal frequency or stomatal length with tree age, although there were curvilinear relationships between an index of total stomatal pore area per leaf lamina and both tree age and tree height. The results support the hypothesis that leaves of E. regnans become more xeromorphic with tree age and height. The results are discussed in relation to their significance for changes in water relations in the canopy with age.     

Effects of Photoperiodic Induction and Debudding in Xanthium pennsylvanicum and of Partial Defoliation in Phaseolus vulgaris on Rates of Net Photosynthesis and Stomatal Conductances

Xanthium pennsylvanicum plants received four treatments in thefactorial experiment (a) debudded v. not debudded, and (b) longdays . photoinductive short days. Rates of net photosynthesis,carbon dioxide compensation points (), and stomatal conductanceswere assessed after 8 days and before leaf growth or stomatalsize were appreciably affected. Leaf size, stomatal frequencies,and lengths of guard cells were estimated at this time and again22 flays after treatment. Debudding alone slightly Increased stomatal conductance; inductionalone had a similar but larger effect. Debudding and inductiontogether caused a more than additive increase in net photosynthesisat 8 days, with marked decreases in . At 22 days this combinationcaused more than additive increases in leaf size and guard-celllengths while stomatal frequencies had decreased. Induction alone directly increased stomatal conductance andthis may be responsible for the increase in photosynthesis;but debudding alone may directly affect photosynthesis by increasingthe supply of cytokinins to the leaves. The positive interactionof these factors in photosynthesis could not be explained interms of stomatal conductance and a synergism between cytokininsand a photoperiodically induced hormone is suggested. In Phaseolus vulgaris plants, 4 days after partial defoliation,stomatal conductances and rates of net photosynthesis increasedgreatly in the remaining leaflets.     

The effect of elevated atmospheric CO2 and drought onstomatal frequency in groundnut (Arachis hypogaea (L.))

The effects of elevated atmospheric CO₂, alone or in combinationwith water stress, on stomatal frequency in groundnut (Arachishypogaea (L.) cv. Kadiri-3) were investigated. CO₂ exerted significanteffects on stomatal frequency only in irrigated plants. Theeffects of drought on leaf development out weighed the smallereffects of CO₂ concentration, although reductions in stomatalfrequency induced by elevated atmo-spheric CO₂ were still observed.When stands of groundnut were grown under irrigated conditionswith unrestricted root systems, an increase in atmospheric CO₂from 375 to 700 ppmv decreased stomatal frequency on both leafsurfaces by up to 16% in droughted plants, stomatal frequencywas reduced by 8% on the adaxial leaf surface only. Elevatedatmospheric CO₂ promoted larger reductions in leaf conductancethan the changes in stomatal frequency, indicating partial stomatalclosure. As a result, the groundnut stands grown at elevatedCO₂ utilized the available soil moisture more slowly than thosegrown under ambient CO₂, there by extending the growing period.Despite the large variations in cell frequencies induced bydrought, there was no treatment effect on either stomatal indexor the adaxial/abaxial stomatalfrequency ratio. The data suggestthat the effects of future increases in atmospheric CO₂ concentrationon stomatal frequency in groundnut are likely to be small, especiallyunder conditions of water stress, but that the combination ofassociated reductions in leaf con-ductance and enhanced assimilationat elevated CO₂ will be important in semi-arid regions Key words: Arachis hypogaea L, Leguminosae, groundnu, stomatal frequency, CO₂, drought     

Comparison of Palaeobotanical Observations with Experimental Data on the Leaf Anatomy of Durmast Oak [Quercus petraea(Fagaceae)] in Response to Environmental Change

To test whether stomatal density measurements on oak leaf remainsare reliable tools for assessing palaeoatmospheric carbon dioxideconcentration [CO₂], under changing Late Miocene palaeoenvironmentalconditions, young seedings of oak (Quercus petraea,Liebl.) weregrown at elevatedvs.ambient atmospheric [CO₂] and at high humiditycombined with an increased air temperature. The leaf anatomyof the young oaks was compared with that of fossil leaves ofthe same species. In the experiments, stomatal density and stomatalindex were significantly decreased at elevated [CO₂] in comparisonto ambient [CO₂]. Elevated [CO₂] induced leaf cell expansionand reduced the intercellular air space by 35%. Leaf cell sizeor length were also stimulated at high air humidity and temperature.Regardless of a temperate or subtropical palaeoclimate, leafcell size in fossil oak was not enhanced, since neither epidermalcell density nor length of the stomatal apparatus changed. Theabsence of these effects may be attributed to the phenologicalresponse of trees to climatic changes that balanced temporalchanges in environmental variables to maintain leaf growth underoptimal and stable conditions.Quercus petraea,which evolvedunder recurring depletions in the palaeoatmospheric [CO₂], maypossess sufficient phenotypic plasticity to alter stomatal frequencyin hypostomatous leaves allowing high maximum stomatal conductanceand high assimilation rates during these phases of low [CO₂].Copyright1998 Annals of Botany Company Atmospheric CO₂, high humidity, elevated temperature,Quercus petraea,durmast oak, Late Miocene, palaeoclimates, leaf anatomy, stomatal density, stomatal index     

Effect of Evaporative Demand on Water Relations of Citrus limon

Conductance, transpirational flux and xylem pressure potentialwere measured in leaves of well-watered 5-year-old lemon trees(Citrus limon (L.) Burm. f.) subjected to different levels ofevaporative demand. Increased leaf-to-air absolute humiditydifference generally decreased stomatal conductance and increasedxylem pressure potential, with a good correlation between thelast two parameters; but this trend was reversed on days withvery high evaporative demand, when stomata opened in spite ofthe low humidity. Citrus limon (L.) Burm. f., lemon, water stress, stomatal conductance, leaf water potential, transpiration, air humidity     

Stem hydraulic conductance of European beech (Fagus sylvatica L.) and pedunculate oak (Quercus robur L.) grown in elevated CO2

Over two seasons in c. 600 ppm CO₂, oak had lower stomatal conductancein CO₂-enriched compared to amblent air. Beech showed no responseto CO₂ concentration on sunny days. Mirroring this pattern,exposure to elevated CO₂ reduced whole-shoot hydraulic conductanceper unit leaf area in oak, but not in beech. Key words: Climate change, Fagaceae, gas exchange, trees, water relations     

Converging patterns of vertical variability in leaf morphology and nitrogen across seven Eucalyptus plantations in Brazil and Hawaii,USA

Key message

Across sites in Brazil and Hawaii, LMA and N _mass were strongly correlated with height and shade index, respectively, which may help simplify canopy function modeling of Eucalyptus plantations.

Abstract

Within tree canopies, leaf mass per area (LMA) and leaf nitrogen per unit area (N _area) commonly increase with height. Previous research has suggested that these patterns occur as a strategy to optimize carbon gain by allocating available resources to upper canopy leaves that are exposed to greater light availability. We tested three hypotheses about the influences of height, shade index (a proxy for light), and stand age on LMA and leaf nitrogen for even-aged Eucalyptus saligna and Eucalyptus grandis × urophylla plantations in Brazil and Hawaii, USA, spanning most of the environmental conditions found across 19.6 million ha of Eucalyptus spp. plantations around the world. Shade index was developed by incorporating canopy depth (inner-crown shading) and a tree height ratio relative to neighbor trees (shading from other trees). Across all sites and ages, leaf height accounted for 45 % of the variation in LMA, whereas shade index accounted for only 6 %. A combination of both factors was slightly better in accounting for LMA variation than height alone. LMA–height relationships among sites were strongest under greater light availability and in older stands. Leaf nitrogen per unit mass (N _mass) consistently decreased with shade index, whereas N _area showed no consistent pattern with height or shade index. These relationships indicate that N _mass is primarily driven by light, while height is the primary driver for LMA. The general relationships between LMA and leaf N _mass across all sites may simplify canopy function modeling of E. saligna and E. grandis × urophylla plantations.     

An Unusual Feature of Stomatal Microanatomy in Certain Taxonomically- related Eucalyptus spp

The line of closure in the stoma in fully grown adult leavesof certain eucalypts is formed by special ridges of cuticlecalled ‘stomatal bars’ developed at the line ofclosure itself or from upgrowth of the cuticle of the lowersurface of the guard cells. Stomatal bars, previously discoveredin three members of the informal group ‘Bisectae’are shown to be restricted to certain species in that group.Possession of stomatal bars may affect stomatal performancebut does not appear to be a general adaptive response to thehabitats of the species which possess them. More probably, thepossession of stomatal bars is an inherited character with taxonomicvalue. The presence of stomatal bars in other genera is discussed. Eucalyptus spp, stomata, microanatomy, guard cells, stomatal bars