An efficient method for estimating vein density of Glossopteris and its application

Glossopteris-type leaves are the most abundant floristic element from the Gondwanan continent and are recorded throughout the Permian, which was a period of extreme icehouse-to-hothouse climatic global change. Fossil leaf traits can be useful for the reconstruction of palaeoenvironments and identification of climatic changes throughout geological time, but the conservative morphology of Glossopteris leaves has thus far made them difficult to use for this purpose. If the characters of Glossopteris can be better quantified then it should make them useful for tracking environmental changes over a wide geographical area and over a long time interval. Venation density is a highly variable leaf trait that might be useful for this purpose. This trait can be calculated, usually as vein length per centimetre squared, but this can be a time-consuming procedure. In this paper we propose a new rapid method to estimate venation density in a conical sector of Glossopteris leaf lamina using an accurate linear model whose predictors are three linear venation densities, measured as veins per centimetre. In addition to substantially reducing the data collection time, it is less biased and more reproducible than methods applied previously with this leaf type. Using this more robust method, preliminary results significantly distinguish the venation densities of leaves produced in wet and drier ecosystems, matching a pattern similar to modern plants. This is the first survey using a large sample size to reveal that environmental stress controlled the vein architecture of Palaeozoic plants, in a manner similar to plants in modern ecosystems.     

Studies on the leaf anatomy of Euphorbia: II. Venation patterns*

Leaf venation patterns of 150 species of Euphorbia are presented and their value as a diagnostic feature in the genus assessed. Based on the gross venation patterns, the species have been grouped into uni-, bi-, tri-veined and special categories. The majority of the species studied belonged to the tri-veined category, in which ornamentation of the veins and the course of traces in the lamina proved useful additional characters. Features such as the size of the areoles, the number of vein endings, and their further ramifications and composition in each areole varied in the same leaf or in different leaves of a given species. Furthermore, no direct correlation could be established between the areole size and the numbers of vein endings and tips per areole. Forty species possess a parenchymatous vein sheath. Globular chloroplasts showed up conspicuously in the sheath cells of a few species. Dilated tracheidal elements, localized on the venules or at the tips of vein endings, are characteristic of the xerophytic species. In some instances, correlation was apparent between plants grouped according to their venation patterns and their habit.     

贵州小檗属植物(小檗科)叶脉序研究

采用制作叶脉标本和透明叶标本的方法,对贵州产28种2变种小檗属植物叶脉特征进行比较研究。结果表明:贵州小檗属植物的脉序类型有5种:半达缘羽状脉、花环状半达缘羽状脉、简单弓形羽状脉、花环状弓形羽状脉和混合型。叶脉分支一般有五级:1一级脉构架均为羽状脉,粗度有很粗、粗、中等粗细和纤细四种类型,分支方式包括单轴分支和合轴分支;2粗二级脉构架中有分支达缘或分支均不达缘,与中脉夹角变化各异,内二级脉存在或缺失,细二级脉半达缘、真曲行或简单弓形,间二级脉类型复杂多变但频度种间有差异;3三级脉贯串型、结网型或分支型;4四、五级脉网状或自由分支且常混合在一起。脉间区从发育差到良好,小脉从不分支到不均等分支等各种类型均有,叶缘末级脉缺失、不完整、钉状和环状。大部分种类叶缘具齿,每1cm齿数目和齿内腺点的特性等特征在不同种类间有区别,具有鉴定价值,但齿其它特征复杂多变或种间区别较小,同时齿内脉性状也不稳定。此外,齿的有无会对脉序类型产生影响。小檗属植物叶脉类型存在种间差异,具有重要的分类学价值,叶脉类型的变化和复杂程度显示了该属植物的进化特点;叶齿的有无和齿特征具有分类学和系统学意义。基于叶脉特征的研究结果并结合重要的外部形态学特征编制了贵州小檗属植物的分种检索表。研究结果可为小檗属植物分类寻找新的依据并探讨其系统学意义。     

ANASTOMOSES IN THE VENATION OF GINKGO BILOBA

Arnott , Howard J. (Northwestern U., Evanston, Ill.) Anastomoses in the venation of Ginkgo biloba. Amer. Jour. Bot. 46(6): 405–411. Illus. 1959.—Although the vasculature of the lamina of Ginkgo biloba has been described as open dichotomous and devoid of anastomoses, vein unions were found in a survey of 1065 leaves collected from both long and short shoots of 11 trees. When studied by directing a strong light through the lamina and by clearings, 9.9% of the leaves possessed 1 or more anastomoses. Long shoot-leaves showed 13.4% anastomoses while short shoot-leaves showed 8.2% anastomoses. Multiple anastomoses were found in almost half of the leaves bearing anastomoses. In the 105 leaves having vein unions, 163 anastomoses were counted. These anastomoses could be grouped into 4 types which are easily distinguished by the number of dichotomies involved and by the presence or absence of dichotomies above the point of vein union. Other deviations were found from the “normal” venation pattern; these consisted of unconnected veins, veins anastomosed marginally but unconnected basally, and veins ending a considerable distance from the margin. It was speculated that the anastomoses found in Ginkgo biloba are of a simple, archaic type and are apparently analogous to the anastomoses in the leaves of certain ferns and in the leaflets of various cycads. The evolutionary significance of these anastomoses must be assessed by a broad study of venation patterns in the seed-plants.     

滇中半湿润常绿阔叶林主要优势及常见种叶形态结构特征

通过对滇中亚热带半湿润常绿阔叶林８２个主要优势种和常见种进行叶结构分析研究,结果表明这些主要组成树种虽亲缘关系相互较远,但在相同的生态环境条件下叶结构却表现出了相似和相同的特点。主要为：群落中以单叶为主,边缘具齿较全缘为多,缺长渐尖叶,有毛叶和无毛叶所占的比例近于相等;叶脉主要为环结曲行羽状脉,大部分二级脉结环,被三、四级脉环所包围,夹角为锐角且变异多近一致;三级脉多为结网型;网眼发育完善较不完善为多,盲脉多分枝;大部分无包藏脉。并且讨论了其中一些特征如毛被,网眼,包藏脉和边缘脉等可能的生态学意义。该类森林群落主要树种的叶形态结构特征除了是物种自身系统进化的原因外,还是植物长期适应滇中高原偏干旱的季风气候的表现,是生态适应在叶形态结构上的反映     

INVESTIGATIONS OF ANGIOSPERMS FROM THE EOCENE OF SOUTHEASTERN NORTH AMERICA: PHILODENDRON LEAF REMAINS

Large leaves, new to the fossil record, from the Claiborne Formation in western Tennessee have been collected and analyzed. Careful analyses of venation and cuticular anatomy indicate that these fossil leaves contain specific characters found in modern species of the genus Philodendron subgenus Meconostigma. Features of venation were taxonomically more useful than other features. Reports of fossils of the Araceae are scarce and those few fossils assigned to the family frequently have been inadequately studied. This report establishes a reliable and carefully documented occurrence of the Araceae in the fossil record, and provides information concerning the differentiation of the family in time and the distributions of the genus Philodendron.     

中国木犀属植物叶脉形态及其分类学意义

观察了中国木犀属植物4组19种叶脉形态。主要分析木犀属植物叶片脉序走向,脉序为环结曲行或半直行羽状脉。二级脉急转曲行或半直行,叶脉分支一般为4级,少数5级。盲脉1～2次分支,少数3次或不分支。仅柊树叶缘末级脉汇合成边脉.部分叶缘具齿,叶缘齿性状不稳定,因其内主脉不同而在本属种间表现出一个连续的变异过程。圆锥花序组与李榄属和木犀榄属从叶片脉序特征方面表现出较近的亲缘关系。四个组的叶脉形态在演化上关系上与花粉形态表现相一致。编写了叶片脉序特征分种检索表。     

贺兰山岩黄耆及其近缘种的分类学研究

依据植物野外和腊叶标本形态观察以及小叶脉序观察,对贺兰山岩黄耆(豆科)及其近缘种进行了分类学研究。结果表明:贺兰山岩黄耆及其近缘种之间较为稳定的差别体现在花器官的形态方面。贺兰山岩黄耆与短翼岩黄耆的主要区别特征是小苞片长为萼筒的1～2倍,旗瓣与龙骨瓣近等长,而后者的小苞片长为萼筒的0.5～0.8倍,旗瓣长为龙骨瓣的0.8倍。贺兰山岩黄耆与华北岩黄耆和费尔干岩黄耆的主要区别是翼瓣长为龙骨瓣的0.3～0.5倍,而后二者的翼瓣长均为龙骨瓣的0.7～0.8倍。在小叶脉序特征方面,贺兰山岩黄耆与短翼岩黄耆和华北岩黄耆近似,均为小叶一级脉纤细,二级脉不分支,二级脉环外有较多网结三级脉,具少量复合二级间脉或不明显,而费尔干岩黄耆小叶一级脉粗,二级脉多分支,二级脉环外有少量网结三级脉,具明显的简单二级间脉。此外,小叶脉序特征可能在岩黄耆属组间关系的探讨中发挥作用。     

Hydraulic architecture of leaf blades: where is the main resistance?

The hydraulic architecture of Laurus nobilis L. and Juglans regia L. leaves was studied using three different approaches: (1) hydraulic measurements of both intact leaves and of leaves subjected to treatments aimed at removing the extra‐vascular resistance; (2) direct measurements of the vascular pressure with a pressure probe; and (3) modelling the hydraulic architecture of leaf venation system on the basis of measurements of vein densities and conductivities. The hydraulic resistance of leaves (R_leaf) either cut, boiled or frozen–thawed was reduced by about 60 and 85% with respect to control leaves for laurel and walnut, respectively. Direct pressure drop measurements suggested that 88% of the resistance resided outside the vascular system in walnut. Model simulations were in agreement with these results provided vein hydraulic conductance was 0.12–0.28 that of the conductance predicted by Poiseuille's law. The results suggest that R_leaf is dominated by substantial extra‐vascular resistances and therefore contrast with the conclusions of recent studies dealing with the hydraulic architecture of the leaf. The present study confirms the ‘classical’ view of the hydraulic architecture of leaves as composed by a low‐resistance component (the venation) and a high‐resistance component (the mesophyll).     

Leaf Architecture of Some Monocotyledons with Reticulate Venation

Twelve species belonging to seven monocotyledonous families:Hydrocharitaceae, Taccaceae, Dioscoreaceae, Smilacaceae, Araceae,Alismataceae and Aponogetonaceae show reticulate venation typicalof dicotyledons. A study of the leaves of these species showsthat venation patterns are usually curvipalmate-convergate,occasionally rectipalmate or collimate, and rarely pinnate lyratetype. Number, size and shape of areoles, number of primaries,number of secondaries along one side of the primaries, anglebetween 1 and 2° veins and number of vein endings per areoleare given for each species. Intesecondary veins, isolated tracheids,loops, extension cells, raphide and raphide idioblasts and terminaltracheids were observed. Marginal ultimate venation is mostlyarcuate. Major and minor veins are jacketed by parenchymatousbundle sheath cells. The lamina of Tacca leontopetaloides, Colocasiaesculenta and Scindapsus aureus show a single midrib-like centralregion similar to that of dicotyledonous leaves, and it is multistrandedin Aponogeton natans, Limnophyton obtusifolium and Ottelia alismoides.The degree of vein order is most commonly up to fourth or fifthand rarely up to sixth in Dioscorea hispida. Monocotyledons, leaf architecture, vein endings, venation, areoles     

中国花楸属单叶类群叶脉序特征研究

中国花楸属单叶类群(24种)包含落萼组与冠萼组,亦有学者将其分为两个属(白花楸属和水榆属)或合并成为一个属(白花楸属).由于其花序和果实的高度相似性,长期以来分类地位具有争议,而叶脉序特征在花楸属单叶类群中的分类作用尚不明确.因此,该研究以国产花楸属落萼组的13个物种和冠萼组的7个物种作为研究对象,以清净法制作标本对叶...     

Foliar architecture and anatomy of <Emphasis Type="Italic">Bernardia</Emphasis> and other genera of Acalyphoideae (Euphorbiaceae)

A comparative study of leaf architecture and anatomy of 42 species of Bernardia and other genera related of Acalyphoideae was undertaken to identify characters that support infrageneric and specific delimitation. Thirty variable foliar architectural and anatomical characters were studied. Some characters are consistent (e.g., venation pattern, secondary and tertiary vein arrangement, presence or absence of agrophic veins, type of areoles, bundle sheath cell type, presence or absence of fibers in the mesophyll, trichome type, stomata location, and type of crystals), and characterize genera. In addition, foliar character distribution within Bernardia supports the most recent infrageneric classification.     

Leaf architecture of the genus Didymaea Hook. f. (Rubiaceae)

We examined 532 specimens representing eight species of Didymaea (Rubiaceae) to describe their leaf architecture. Characters observed in the herbarium specimens and cleared leaves were leaf base, apex, and margin; trichome type and distribution; vein orders from primary to higher order veins, veinlets, and ultimate marginal vein. Six morphometric variables were analyzed using variance and principal component analysis to identify which characters are useful to distinguish species. Most of the species present brochidodromous venation pattern, except D. hispidula, which has eucamptodromous venation pattern; Didymaea floribunda is unique in having cylindrical and bicellular trichomes. Principal component analysis revealed that 78% of the total variation is mainly related to leaf maximum width. Variance analysis showed significant differences between D. microflosculosa and the other species. Architectural features were useful for differentiating all the species, and an identification key for the species of Didymaea based only on leaf characters is presented.     

ANALYSIS OF PETAL VENATION IN RANUNCULUS. I. ANASTOMOSES IN R. REPENS V. PLENIFLORUS

Arnott , Howard J., and Shirley C. Tucker . (Northwestern U., Evanston, Ill.) Analysis of petal venation in Ranunculus. I. Anastomoses in R. repens v. pleniflorus. Amer. Jour. Bot. 50(8): 821–830. Illus. 1963.—The venation patterns of 1218 petals of Ranunculus repens v. pleniflorus were analyzed, with particular attention to the number and position of vein anastomoses. The essentially open dichotomous vascular pattern is complicated by the presence of vein fusions in 69.4% of the petals. The anastomosis ratio (number of anastomoses/number of appendages) is, therefore, high (1.37), compared to a maximal 0.61 for Ginkgo leaves. Of the petals having such fusions, 55.3% have more than 1 anastomosis; the maximal number of fusions found per petal is 8. The presence of anastomoses shows a high degree of correlation with petal size and petal lobing. The types of fusions (types A, B, C, D) are identical with those found in Ginkgo leaves, with the addition of 2 modifications of type C. Curiously, types C and D account for 98.7% of the total anastomoses, while types A and B are rare. An analysis of the location of each type within the petal shows that type C's are disproportionately numerous along the distal periphery, and that type-D fusions are unusually numerous in the central and basal regions. Such evidence suggests that the occurrence of a vein fusion is no “accident,” but rather that it is one manifestation of morphogenetic control.     

Decline of leaf hydraulic conductance with dehydration: relationship to leaf size and venation architecture

Across plant species, leaves vary enormously in their size and their venation architecture, of which one major function is to replace water lost to transpiration. The leaf hydraulic conductance (K(leaf)) represents the capacity of the transport system to deliver water, allowing stomata to remain open for photosynthesis. Previous studies showed that K(leaf) relates to vein density (vein length per area). Additionally, venation architecture determines the sensitivity of K(leaf) to damage; severing the midrib caused K(leaf) and gas exchange to decline, with lesser impacts in leaves with higher major vein density that provided more numerous water flow pathways around the damaged vein. Because xylem embolism during dehydration also reduces K(leaf), we hypothesized that higher major vein density would also reduce hydraulic vulnerability. Smaller leaves, which generally have higher major vein density, would thus have lower hydraulic vulnerability. Tests using simulations with a spatially explicit model confirmed that smaller leaves with higher major vein density were more tolerant of major vein embolism. Additionally, for 10 species ranging strongly in drought tolerance, hydraulic vulnerability, determined as the leaf water potential at 50% and 80% loss of K(leaf), was lower with greater major vein density and smaller leaf size (|r| = 0.85-0.90; P < 0.01). These relationships were independent of other aspects of physiological and morphological drought tolerance. These findings point to a new functional role of venation architecture and small leaf size in drought tolerance, potentially contributing to well-known biogeographic trends in leaf size.     

中国云实属植物叶脉形态学

对中国云实属植物小叶叶片脉序的观察表明,该属植物小叶叶片脉序类型非常一致,均为环结曲行羽状脉,二级脉急转曲行.叶脉分支一般为四级,少数达五级.盲脉不分支或分支较少,最多两次分支.见血飞亚属与云实亚属叶片脉序特征相似,属于同一自然类群.编写了中国云实属植物叶片脉序特征分种检索表.     

Leaf architecture of some acanthaceae

Leaf architectural pattern has been studied in 27 genera and 35 species of the Acanthaceae. The major venation pattern conforms to pinnate camptodromous with eucamptodromous or festooned brochidodromous secondaries, pinnate craspedodromous inAcanthus ilicifolius and acrodromous inLepidagathis trinervis. Intersecondary veins are common. The marginal ultimate venation is looped. The areoles are variable in size. The vein endings are usually simple, linear or cuved or divide once or twice dichotomously. Isolated vein endings, tracheids, isolated free vein endings and extension cells are observed. Transfusion tracheids are seen inDicliptera verticillata. Miniature vessel elements with simple perforation plates are noticed lying free in the areole or at the end of tracheids inSeriocalyx scaber andThunbergia grandiflora.Elytraria acaulis, Nelsonia canescens andStaurogynae zeylanica exhibit venation pattern shown by majority of the taxa studied, of the Acanthaceae.     

MORPHOLOGY AND DICHOTOMOUS VASCULATURE OF THE LEAF OF KINGDONIA UNIFLORA

Foster , Adriance S. (U. California, Berkeley), and Howard J. Arnott . Morphology and dichotomous vasculature of the leaf of Kingdonia uniflora. Amer. Jour. Bot. 47 (8): 684–698. Illus. 1960.—An intensive study of the nodal anatomy, petiolar vasculature and open dichotomous venation of the leaf of Kingdonia has revealed a type of foliar vascular system of unusual morphological and phylogenetic interest. The vascular supply at the nodal level consists of 4 collateral traces which diverge from a single gap into the sheathing leaf base. This type of nodal anatomy is perhaps primitive, and comparisons are made with the unilacunar nodes and the 2- and 4-parted leaf trace systems characteristic of many angiospermous cotyledons and the foliage leaves of certain woody ranalian genera. The petiole of Kingdonia is vascularized by 2 pairs of bundles which represent the upward continuation of the 4 leaf traces. A transition from an even (4) to an odd (3) number of strands occurs near the point of attachment of the 5, lobed, cuneiform lamina segments to the petiole. Each of the 2 abaxial bundles dichotomizes and the central derivative branches fuse to form a double bundle which enters the base of the median lamina segment. The 2 adaxial petiolar bundles diverge right and left into the bases of the paired lateral segments of the lamina. An analogous type of transition from an even to an odd number of veins occurs in many angiospermous cotyledons which develop a definable mid-vein. But, in Kingdonia, the bundles which enter the bases of the lamina segments give rise to systems of dichotomizing veinlets devoid of “mid-veins.” Although the majority of the terminal veinlets enter the marginal teeth of the lamina segments, “blind” endings, unrelated to the dentations, occur in all the leaves studied. Typically, all of the vein endings in a given lobule of a lamina segment are derived from the same dichotomous vein system. However, in some leaves, a veinlet dichotomizes directly below a sinus and the branches diverge into the marginal regions of 2 separate lobules. The phylogenetic significance of the occurrence of open dichotomous venation in such an herbaceous angiosperm as Kingdonia is briefly discussed. From a purely morphological viewpoint, the Kingdonia type of venation invites direct comparison with the venation of Sphenophyllum, certain ferns or Ginkgo rather than with any of the known reticulate venation patterns of modern angiosperms. Although the foliar venation of Kingdonia may represent the result of evolutionary reversion, the very rare anastomoses which occur seem primitive in type rather than “vestiges” of a former system of closed venation.     

The FORKED genes are essential for distal vein meeting in Arabidopsis

As in most dicotyledonous plants, the leaves and cotyledons of Arabidopsis have a closed, reticulate venation pattern. This pattern is proposed to be generated through canalization of the hormone auxin. We have identified two genes, FORKED 1 (FKD1) and FORKED 2 (FKD2), that are necessary for the closed venation pattern: mutations in either gene result in an open venation pattern that lacks distal meeting. In fkd1 leaves and cotyledons, the defect is first evident in the provascular tissue, such that the distal end of the newly forming vein does not connect to the previously formed, more distal vein. Plants doubly mutant for both genes have widespread defects in leaf venation, suggesting that the genes function in an overlapping manner at the distal junctions, but act redundantly throughout leaf veins. Expression of an auxin responsive reporter gene is reduced in fkd1 leaves, suggesting that FKD1 is necessary for the auxin response that directs vascular tissue development. The reduction in reporter gene expression and the fkd1 phenotype are relieved in the presence of auxin transport inhibition. The restoration of vein junctions in situations where auxin concentrations are increased indicates that distal vein junctions are sites of low auxin concentration and are particularly sensitive to reduced FKD1 and FKD2 activity.     

Leaf architecture and ecophysiology of an early basal eudicot from the Early Cretaceous of Spain

Iterophyllum lobatum gen. et sp. nov. is reported from the late Barremian lithographic limestones of Las Hoyas, Spain. It consists of a simple, petiolate leaf, with a pinnately lobed lamina. The dentate thickened margin bears chloranthoid‐like glands at lobe apices and sinuses. The venation is pinnate and craspedodromous, with three discernible vein orders. Based on the low regularity of vein course and angles and the low leaf rank, such a venation pattern may represent an early evolved leaf archetype in early basal eudicots. An acropetal leaf development mode in I. lobatum is similar to that in several living Papaveraceae. The leaf architecture and ecophysiology, particularly the vein widths and the glands, indicate that I. lobatum leaves were aerial. The plant grew close to water in the wetland terrestrial ecosystem of Las Hoyas. Iterophyllum lobatum might have been an opportunist species in early ecological succession stages after wildfires. © 2013 The Linnean Society of London, Botanical Journal of the Linnean Society, 2013, 173 , 594–605.