Early cretaceous fossil evidence for angiosperm evolution

Morphological, stratigraphic, and sedimentological analyses of Early Cretaceous pollen and leaf sequences, especially from the Potomac Group of the eastern United States, support the concept of a Cretaceous adaptive radiation of the angiosperms and suggest pathways of their initial ecological and systematic diversification. The oldest acceptable records of angiosperms are rare monosulcate pollen grains with columellar exine structure from probable Barremian strata of England, equatorial Africa, and the Potomac Group, and small, simple, pinnately veined leaves with several orders of reticulate venation from the Neocomian of Siberia and the basal Potomac Group. The relatively low diversity and generalized character of these fossils and the subsequent coherent pattern of morphological diversification are consistent with a monophyletic origin of the angiosperms not long before the Barremian. PatuxentArundel floras (Barremian-early Albian?) of the Potomac Group include some pollen and leaves with monocotyledonous features as well as dicotyledonous forms. Patuxent angiosperm pollen is strictly monosulcate and has exine sculpture indicative of insect pollination. Rare Patuxent-Arundel angiosperm leaves are generally small, have disorganized venation, and are largely restricted to sandy stream margin lithofacies; the largest are comparable to and may include ancestors of woody Magnoliidae adapted to understory conditions. Patapsco floras (middle to late Albian?) contain rapidly diversifying tricolpate pollen and several new complexes of locally abundant angiosperm leaves. Ovate-cordate and peltate leaves in clayey pond lithofacies may includeancestors of aquatic Nymphaeales and Nelumbonales. Pinnatifid and later pinnately compound leaves with increasingly regular venation which are abundant just above rapid changes in sedimentation are interpreted as early successional “weed trees” transitional to but more primitive than the modern subclass Rosidae. Apparently related palmately lobed, palinactinodromous leaves which develop rigidly percurrent tertiary venation and become abundant in uppermost Potomac stream margin deposits (latest Albian-early Cenomanian?) are interpreted as riparian trees ancestral to the order Hamamelidales. Comparisons of dated pollen floras of other regions indicate that one major subgroup of angiosperms, tricolpate-producing dicots (i.e., excluding Magnoliidae of Takhtajan) originated in the Aptian of Africa-South America at a time of increasing aridity and migrated poleward into Laurasia and Australasia. However, the earlier (Barremian) monosulcate phase of the angiosperm record is represented equally in Africa-South America and Laurasia before marked climatic differentiation between the two areas. These trends are considered consistent with the hypothesis that the angiosperms originated as small-leafed shrubs of seasonally arid environments, and underwent secondary expansion of leaf area and radiated into consecutively later successional stages and aquatic habitats after entering mesic regions as riparian “weeds,” as opposed to the concept that they arose as trees of mesic forest environments.     

Fossil Nelumbonaceae from the La Colonia Formation (Campanian–Maastrichtian,Upper Cretaceous), Chubut,Patagonia, Argentina

We describe here fossil leaves and fruits assignable to the family Nelumbonaceae Dumortier 1828. Fossils were collected at the Cañadón del Irupé locality, La Colonia Formation (Campanian–Maastrichtian, Upper Cretaceous), Chubut Province, Patagonia, Argentina. The fossil leaves are simple, with symmetrical and peltate lamina, orbicular in shape, and an entire margin. The venation is truly actinodromous with at least 15 primary veins, the secondary veins are poorly developed and intercalated with the primary veins, the third category vein is opposite, and the areoles are well-developed and 4- to 5-sided. These features are characteristic of the extant genus Nelumbo Adamson 1763, and the presence of these characters in the fossils allows their placement within this genus. Reproductive structures, similar to the fruit-receptacle of Nelumbo with fruits in situ, were found associated but not in organic connection with the leaves. These fossils constitute the only and oldest record for the family in the Southern Hemisphere. This record indicates that Nelumbo was more widespread in the past than today.     

睡莲科的属间关系研究

本文用谱系分支法分析睡莲科的属间关系,３５个衍征中,分析了３１个特征的进化趋势,根据分析将睡莲科提升为睡莲目,分为３个科,莲科、水盾草科、睡莲科。     

Phylogenetic systematics of the nymphaeales

A cladistic analysis was applied to reveal the phylogenetic relationships among the Nymphaeales. Seventeen out of twenty three characters in gross morphology, anatomy and palynology were analyzed, for their evolutionary polarities. From the results of the present analysis, the phylogenetic status of each genus and their relationships were clarified: 1)Nelumbo is a distinct taxon and is presumed to have originated from an ancestral stock of the Nymphaeales; 2)Ceratophyllum has a close phylogenetic relationship withCabomba; and 3) in the Nymphaeaceaesensu stricto, Nuphar and the remaining genral constitute a monophyletic group. A conclusion obtained from the present analysis was that the following three families should be recognized in the Nymphaeales; Nelumbonaceae Nymphaeaceae, and Ceratophyllaceae. The generaBrasenia andCabomba are traditionally classified in the Nymphaeaceae or in the independent family Cabombaceae. However, they should be included in the family Ceratophyllaceae.     

Phylogenetic analysis of Nymphaeales using fast-evolving and noncoding chloroplast markers

The Nymphaeales (water-lilies and relatives) represent one of the earliest branching lineages of angiosperms and comprise about 70 aquatic species. Here, we present a comprehensive study of phylogenetic relationships within the Nymphaeales from a dataset containing 24 representatives of the order, including all currently recognized genera and all subgenera of the genus Nymphaea , plus 5 outgroup taxa. Nine different regions of the chloroplast genome − comprising spacers, group II introns, a group I intron, and a protein coding gene − were analysed. This resulted in a character matrix of 6597 positions and an additional 369 characters obtained from coded length mutations. Maximum parsimony and Bayesian analyses of the complete dataset yielded congruent, fully resolved and well-supported trees. Our data confirm the monophyly of the Cabombaceae but do not provide convincing support for the monophyly of Nymphaeaceae with respect to Nuphar . Moreover, the genus Nymphaea is inferred to be paraphyletic with respect to Ondinea , Victoria and Euryale . In fact, the Australian endemic Ondinea forms a highly supported clade with members of the Australian Nymphaea subgenus Anecphya . In addition, Victoria and Euryale are inferred to be closely related to a clade comprising all night-blooming water-lilies ( Nymphaea subgenera Hydrocallis and Lotos ). An experimental approach showed taxon sampling to be of influence on the nodes reconstructed in core Nymphaeaceae. The results underscore that more diverse genera, if not clearly known to be monophyletic, should be represented by all major lineages.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 154 , 141–163.     

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.     

睡莲科的核型分析及其分类学位置的探讨

本文对睡莲科6属6种代表植物的核型进行了研究,并探讨了它的分类学位置。结果如下：莲2n＝16=9sm+4m+3st;王莲2n＝24=8sm+8m+8T,蓝睡莲2n＝28,可配成14对,染色体小,第l号染色体上有2条随体;萍蓬草2n＝34＝18m+16sm;芡实2n=58,可配成29对,染色体小,第l号染色体有2条随体,莼菜2n＝72,可配成36对,染色体按大小可分成大,中、小三个类别。除莲外,其它5种植物的核型为首次报道。莼菜的体细胞染色体数目2n＝72和国外报道的2n＝80不相一致。莲的染色体以及形态学特征和其它睡莲科分类群显著不同,可将其从睡莲科中独立出来,并成立莲科和莲目。原归属于睡莲科的分类群仍组成睡莲目,并分别置于莼菜科和睡莲科。     

Marsileaceaephyllum, a new genus for marsileaceous macrofossils: leaf remains from the Early Cretaceous (Albian) of southern Gondwana

Three new taxa from Albian, Early Cretaceous assemblages in Gondwana (Australia and Antarctica) and two previously described fossils from the Late Cretaceous and Eocene of North America are attributable to the heterosporous semi-aquatic fern family Marsileaceae. They are assigned to Marsileaceaephyllum, a morphotaxon erected here for sterile remains (whole plants, and isolated leaves and leaflets) of Marsileaceae. The Gondwanan taxa, Marsileaceaephyllum lobatum and Marsileaceaephyllum spp. B-C, have either a cruciform leaflet arrangement or dichotomous and anastomosing venation characteristic of modern Marsileaceae. Two previously established taxa, Marsilea johnhallii and Marsilea sp., which represent sterile Marsileaceae, are also transferred to the new genus (now Marsileaceaephyllum johnhallii and Marsileaceaephyllum sp. A, respectively). Examination of all fossil venation patterns reveals four new venation types not present in extant taxa, suggesting that most fossil Marsileaceae (leaves) are distinct from extant genera, and are likely members of extinct lineages. This is further supported by the absence of modern megaspore types in the Early Cretaceous.     

Comparative ovule and megagametophyte development in Hydatellaceae and water lilies reveal a mosaic of features among the earliest angiosperms

Background and Aims: The embryo sac, nucellus and integuments of the early-divergentangiosperms Hydatellaceae and other Nymphaeales are comparedwith those of other seed plants, in order to evaluate the evolutionaryorigin of these characters in the angiosperms. Methods: Using light microscopy, ovule and embryo sac development aredescribed in five (of 12) species of Trithuria, the sole genusof Hydatellaceae, and compared with those of Cabombaceae andNymphaeaceae. Key Results: The ovule of Trithuria is bitegmic and tenuinucellate, ratherthan bitegmic and crassinucellate as in most other Nymphaeales.The seed is operculate and possesses a perisperm that developsprecociously, which are both key features of Nymphaeales. However,in the Indian species T. konkanensis, perisperm is relativelypoorly developed by the time of fertilization. Perisperm cellsin Trithuria become multinucleate during development, a featureobserved also in other Nymphaeales. The outer integument issemi-annular (‘hood-shaped’), as in Cabombaceaeand some Nymphaeaceae, in contrast to the annular (‘cap-shaped’)outer integument of some other Nymphaeaceae (e.g. Barclaya)and Amborella. The megagametophyte in Trithuria is monosporicand four-nucleate; at the two-nucleate stage both nuclei occurin the micropylar domain. Double megagametophytes were frequentlyobserved, probably developed from different megaspores of thesame tetrad. Indirect, but strong evidence is presented forapomictic embryo development in T. filamentosa. Conclusions: Most features of the ovule and embryo sac of Trithuria are consistentwith a close relationship with other Nymphaeales, especiallyCabombaceae. The frequent occurrence of double megagametophytesin the same ovule indicates a high degree of developmental flexibility,and could provide a clue to the evolutionary origin of the Polygonum-typeof angiosperm embryo sac.     

HIGH-RESOLUTION LEAF X-RADIOGRAPHY IN SYSTEMATICS AND PALEOBOTANY

The foliar vein nets of many seed plants and ferns display systematically informative characters. These venation characters traditionally have been observed by chemically clearing and staining leaves, a process that is slow, involves toxic chemicals, and yields delicate, glass-mounted specimens that require long-term maintenance to prevent or correct bubbling or crystallization of the mounting medium. A technique that uses X-rays and photographic film to produce images of leaf venation consistently shows veins that are 50–100 μm thick. Although the X-ray images are slightly less detailed than the best cleared and stained leaves, the images can be made much more quickly, are more easily stored and reproduced, and do not require permanent alteration of the original herbarium specimen. The technique should facilitate the use of vein characters in systematics, and the identification and systematic analysis of fossil leaves.     

水盾草科系统位置评述

水盾草科（Cabombaceae）是双子叶植物。水盾草科包括2属：水盾草属（Cabomba Aublet．）和莼菜属（Brasenia Schreb．）。形态学研究显示水盾草科具有许多原始性状,而且在其适应水生环境的过程中经历了性状退化。水盾草科又被称为“古草本”。最新的分子系统发育研究显示,水盾草科是现存被子植物系统树基部ANITA类群的成员之一。但有关水盾草科的系统位置存在争议。被子植物的起源与早期分化一直是植物学家关注的热点。本文对该科系统位置的研究历史与现状进行评述。     

Approaches to the identification of angiosperm leaf remains

During the past 125 years the history of early angiosperms, interpreted through the fossil leaf record has been largely an exercise in paleofloristic studies, ignoring evolution. Imprecise identifications of ancient leaves “matched” to extant genera and families have been used as the basis for reconstructions of paleocommunities and paleoclimates. However, as the result of careful morphological studies of leaf form, venation and cuticular features new insights into the evolution of angiosperms are now available. In this paper considerations are given to the usefulness and shortcomings of leaf form, venation and cuticular analysis as diagnostic tools of plant identification. Many techniques for the study of the morphology of modern and fossil leaves are included in this paper as well as tables outlining features of leaf venation and the epidermis. Careful morphological studies of leaf form (such as the venation and epidermal characters emphasized in this paper) will provide better understanding of the relationships of living angiosperms and transform the fossil leaf record into useful data that can be used to study the evolution of the angiosperms.     

水盾草科系统位置评述

水盾草科(Cabombaceae)是双子叶植物。水盾草科包括2属: 水盾草属(Cabomba Aublet.)和莼菜属(Brasenia Schreb.)。形态学研究显示水盾草科具有许多原始性状, 而且在其适应水生环境的过程中经历了性状退化。水盾草科又被称为“古草本”。最新的分子系统发育研究显示, 水盾草科是现存被子植物系统树基部ANITA类群的成员之一。但有关水盾草科的系统位置存在争议。被子植物的起源与早期分化一直是植物学家关注的热点。本文对该科系统位置的研究历史与现状进行评述。     

Gynoecium diversity and systematics of the paleoherbs

Gynoecium and ovule structure was compared in representatives of all families of the paleoherbs, including Nymphaeales (Cabombaceae, Nymphaeaceae), Piperales (Saururaceae, Piperaceae), Aristolochiales (Lactoridaceae, Aristolochiaceae), Rafflesiales (Hydnoraceae, Rafflesiaceae) and, in addition, Ceratophyllaceae and Nelumbonaceae, both of which were earlier included in Nymphaeales, but then segregated and with an unestablished position. In all representatives studied, the carpels are closed at anthesis. Carpel closure is attained in three different ways: (1) postgenital fusion of inner surfaces (Piperales, Aristolochiales); (2) occlusion by secretion or mutual appression of inner surfaces without postgenital fusion (Cabombaceae, Ceratophyllaceae, Nelumbonaceae (?) or (3) strong secretion combined with postgenital fusion at the periphery of the carpel (Nymphaeaceae). In Cytinus (Rafflesiaceae), after an earlier developmental stage with apparent postgenital fusion there is strong internal secretion (within the cell walls). Stigma shape tends to be double-crested in the basal taxa of each order: Cabombaceae (Brasenia), Saururaceae, and Lactoridaceae. In some Aristolochiaceae and Cytinus (Rafflesiaceae) they have two lobes in the transverse symmetry plane (i. e. at right angles to the median plane) or, if the carpels are united, the stigmatic lobes are commissural, accordingly. Stigmas are unicellular papillate and secretory in most taxa, but the papillae are uniseriate-pluricellular in some (not basal) Nymphaeaceae, Asaroideae (Aristolochiaceae) and Cytinus (Rafflesiaceae). Ceratophyllaceae have smooth stigmas. Intrusive oil cells in the carpel epidermis were found in Piperales and Aristolochiaceae. Mature ovules vary in length between 0. 2 mm and 2. 5 mm. Mature nucelli vary in breadth between 0. 03 mm and 1. 6 mm. These differences are larger than in the other major magnoliid groups. The outer integument is fully annular (not semiannular) in all taxa with orthotropous ovules (all Piperales and Barclaya of Nymphaeaceae) and also in some with anatropous ovules (some Nymphaeaceae, some Aristolochiaceae). The integuments are variously lobed or unlobed; both integuments tend to exhibit the same behaviour within a family, either both lobed or both unlobed. The results strongly support three pairs of families in sister group relationships, as suggested by studies based on other characters: Cabombaceae-Nymphaeaceae, Saururaceae-Piperaceae, and Lactoridaceae-Aristolochiaceae, and Hydnoraceae-Rafflesiaceae to some extent. Piperales and Aristolochiales are closer to each other than either is to Nymphaeales. Nelumbonaceae is isolated, as is Ceratophyllaceae, but the status of the latter is more difficult to interpret owing to apparent reduction in morphological, anatomical and histological traits.     

Recognising angiosperm clades in the Early Cretaceous fossil record

Studies of the earliest Cretaceous angiosperms in the 1970s made only broad comparisons with living taxa, but discoveries of fossil flowers and increasingly robust molecular phylogenies of living angiosperms allow more secure recognition of extant clades. The middle to late Albian rise of tricolpate pollen and the first local dominance of angiosperm leaves mark the influx of near-basal lines of eudicots. Associated flowers indicate that palmately lobed ‘platanoids’ and Sapindopsis are both stem relatives of Platanus, while Nelumbites was related to Nelumbo (also Proteales) and Spanomera to Buxaceae. Monocots are attested by Aptian Liliacidites pollen and Acaciaephyllum leaves and Albian araceous inflorescences. Several Albian–Cenomanian fossils belong to Magnoliidae in the revised monophyletic sense, including Archaeanthus in Magnoliales and Virginianthus and Mauldinia in Laurales, while late Barremian pollen tetrads (Walkeripollis) are related to Winteraceae. In the basal ANITA grade, Nymphaeales are represented by Aptian and Albian flowers and whole plants (Monetianthus, Carpestella and Pluricarpellatia). Epidermal similarities of lower Potomac leaves to woody members of the ANITA grade are consistent with Albian flowers assignable to Austrobaileyales (Anacostia). Aptian to Cenomanian mesofossils represent both crown group Chloranthaceae (Asteropollis plant) and stem relatives of Chloranthaceae and/or Ceratophyllum (Canrightia, Zlatkocarpus, Pennipollis plant and possibly Appomattoxia).     

Miocene honey bees from the Randeck Maar of southwestern Germany (Hymenoptera, Apidae)

The Miocene Randeck Maar (southwestern Germany) is one of the only sites with abundant material of fossil honey bees. The fauna has been the focus of much scrutiny by early authors who recognized multiple species or subspecies within the fauna. The history of work on the Randeck Maar is briefly reviewed and these fossils placed into context with other Tertiary and living species of the genus Apis Linnaeus (Apinae: Apini). Previously unrecorded specimens from Randeck Maar were compared with earlier series in an attempt to evaluate the observed variation. A morphometric analysis of forewing venation angles across representative Recent and Tertiary species of Apis as well as various non-Apini controls was undertaken to evaluate the distribution of variation in fossil honey bees. The resulting dendrogram shows considerable variation concerning the wing venation of Miocene Apini, but intergradation of other morphological characters reveals no clear pattern of separate species. This suggests that a single, highly variable species was present in Europe during the Miocene. The pattern also supports the notion that the multiple species and subspecies proposed by earlier authors for the Randeck Maar honey bee fauna are not valid, and all are accordingly recognized as Apis armbrusteri Zeuner.     

Xylem of early angiosperms: Novel microstructure in stem tracheids of Barclaya (Nymphaeaceae)

Pit membranes of stem tracheids of all recognized species of Barclaya, an Indomalaysian genus of Nymphaeaceae, were studied with scanning electron microscopy (SEM). Pit membranes of the tracheids are composed of two thick layers, both constructed of fibrils much larger than those of tracheary elements of angiosperms other than Nymphaeaceae. The outer (distal) layer, which comprises the continuous primary wall around the tracheids, is spongiform, perforated by porosities of relatively uniform size, and confined to or most prominent on end walls of stem tracheids. The second layer consists of thick widely spaced fibrils that are oriented axially and are laid down proximally (facing the cell lumen) to the first (outer) layer, although continuous with it. These axial fibrils are attached at their ends to the pit cavities. This peculiar microstructure is not known outside Nymphaeaceae except in Brasenia and Cabomba (Cabombaceae, Nymphaeales), and has not been previously described for Barclaya. The longitudinally oriented threads and strands in perforation plates of secondary xylem of wood and stems of a variety of primitive woody angiosperms (e.g., Illicium) are not homologous to the pit membrane structure observed in stem tracheids of Barclaya, which, like other Nymphaeaceae, has only primary xylem and no perforation plates. The tracheid microstructure reported here is different from pit structures observed in any other group of vascular plants, living or fossil. The tracheid stem microstructures of Barclaya and other Nymphaeaceae appear to be a synapomorphy of Nymphaeaceae and Cabombaceae, and need further study with respect to ultrastructure and function.     

Pollen ontogeny in Brasenia (Cabombaceae, Nymphaeales)

Brasenia is a monotypic genus sporadically distributed throughout the Americas, Asia, Australia, and Africa. It is one of eight genera that comprise the two families of Nymphaeales, or water lilies: Cabombaceae (Brasenia, Cabomba) and Nymphaeaceae (Victoria, Euryale, Nymphaea, Ondinea, Barclaya, Nuphar). Evidence from a range of studies indicates that Nymphaeales are among the most primitive angiosperms. Despite their phylogenetic utility, pollen developmental characters are not well known in Brasenia. This paper is the first to describe the complete pollen developmental sequence in Brasenia schreberi. Anthers at the microspore mother cell, tetrad, free microspore, and mature pollen grain stages were studied using combined scanning electron, transmission electron, and light microscopy. Both tetragonal and decussate tetrads have been identified in Brasenia, indicating successive microsporogenesis. The exine is tectate-columellate. The tetrad stage proceeds rapidly, and the infratectal columellae are the first exine elements to form. Development of the tectum and the foot layer is initiated later during the tetrad stage, with the tectum forming discontinuously. The endexine lamellae form during the free microspore stage, and their development varies in the apertural and non-apertural regions of the pollen wall. Degradation of the secretory tapetum also occurs during the free microspore stage. Unlike other water lilies, Brasenia is wind-pollinated, and several pollen characters appear to be correlated with this pollination syndrome. The adaptive significance of these characters, in contrast to those of the fly-pollinated genus Cabomba, has been considered. Brasenia does not produce pollenkitt nor develop tectal microchannels as does Cabomba. Instead, the discontinuity of the tectum reduces the amount of sporopollenin in the wall, which may allow for more effective wind dispersal. The importance of reassessing palynological characters in light of new ontogenetic data and the phylogenetic implications of this reevaluation are also discussed.     

Analysis of monoterpenoids in glandular trichomes of the catmint Nepeta racemosa

Plants within the Lamiaceae are characterized by their production of essential oils, largely composed of monoterpenoids. They also possess on their aerial surfaces different types of trichomes, including relatively large peltate glandular trichomes. Observation of leaves of the catmint Nepeta racemosa , using cryogenic scanning electron microscopy, showed that around 3000 peltate trichomes are present on a single expanded leaf. An approach has been developed for sampling directly from the subcuticular cavity of such trichomes, in order to characterize qualitatively and quantitatively their contents. Gland samples from Nepeta spp. were analysed by combined gas chromatography-mass spectrometry. These analyses have confirmed that the monoterpenoids characteristic of these species (nepetalactones) accumulate within the subcuticular cavity of peltate glandular trichomes. Qualitative analysis showed that three different nepetalactone stereoisomers were accumulated in different proportions in peltate glands from individual N. racemosa plants. Quantitative analysis showed that individual peltate glands accumulate around 30 ng of nepetalactone by maturity, and that accumulation of nepetalactone probably occurs exclusively within this gland type.     

Phylogeny of the Sympetrinae (Odonata: Libellulidae): further evidence of the homoplasious nature of wing venation

Abstract.  Sympetrinae is the largest subfamily of the diverse dragonfly family Libellulidae. This subfamily, like most libellulid subfamilies, is defined currently by a few wing venation characters, none of which are synapomorphies for the taxon. In this study, we used DNA sequence data from the nuclear locus elongation factor-1α and the mitochondrial loci 16S and 12S rRNA, together with 38 wing venation characters, to test the monophyly of the Sympetrinae and several other libellulid subfamilies. No analysis recovered Sympetrinae as monophyletic, partly because of the position of Leucorrhinia (of the subfamily Leucorrhininae) as a strongly supported sister to Sympetrum (of Sympetrinae) in all analyses. The subfamilies Brachydiplactinae, Leucorrhininae, Trameinae and Trithemistinae were also found not to be monophyletic. Libellulinae was the only subfamily supported strongly as monophyletic. Consistency indices and retention indices of wing venation characters used to define various subfamilies were closer to zero than unity, showing that many of these characters were homoplasious, and therefore not useful for a classification scheme within Libellulidae.