THE PHYLOGENY AND EVOLUTION OF SOME PHACOPID TRILOBITES

Abstract A data matrix of 32 characters, with a total of 132 character states and 48 terminal taxa of phacopid trilobites, was analysed using parsimony. The 108 most parsimonious trees have a length of 301 steps and a consistency index of 0.29. Two major clades were found, one including species referred to Acernaspis and one with species referred to Ananaspis, Paciphacops, Viaphacops , and Phacops . Most homoplasy occurs between the major clades of the trees, rather than within them. The major clades were also analysed separately, resulting in trees with significantly higher consistency indices. We redefine the following supraspecific taxa to make them monophyletic: Acernaspis, Ananaspis , and Paciphacops . In addition, Kainops , new genus, is described for a clade consisting of six taxa previously assigned to Ananaspis and Paciphacops . The evolutionary pattern resulting from our cladogram is compared with the approaches of Campbell and Eldredge, and it is argued that some of the assumptions made by these authors regarding the phylogeny of the group are not valid. The biogeography of the group was also analysed. It is found that phacopids from the Ludlow and older strata are distributed globally, with an emphasis, perhaps due to a large number of suitable localities, on Northern Europe. However, the lineage of phacopines leading up to Phacops is, with some slight exceptions, basically confined to the United States, being entirely absent in Northern Europe. The main phacopine lineage does not re-establish itself geographically until the middle Devonian. Finally, we analysed the evidence for polymorphism in phacopid trilobites, and reject this hypothesis on the basis of stratigraphy and the present cladogram.     

HOMOPLASY AND THE CHOICE AMONG CLADOGRAMS

Abstract Cladistic data are more decisive when the possible trees differ more in tree length. When all the possible dichotomous trees have the same length, no one tree is better supported than the others, and the data are completely undecisive . From a rule for recursively generating undecisive matrices for different numbers of taxa, formulas to calculate consistency, rescaled consistency and retention indices in undecisive matrices are derived. The least decisive matrices are not the matrices with the lowest possible consistency, rescaled consistency or retention indices (on the most parsimonious trees); those statistics do not directly vary with decisiveness. Decisiveness can be measured with a newly proposed statistic, DD = − S )/( − S ) (where S = length of the most parsimonious cladogram, = mean length of all the possible cladograms for the data set and M = observed variation). For any data set, can be calculated exactly with simple formulas; it depends on the types of characters present, and not on their congruence. Despite some recent assertions to the contrary, the consistency index is an appropriate measure of homoplasy (= deviation from hierarchy). The retention index seems more appropriate for comparing the fit of different trees for the same data set.     

PARSIMONY AND THE CHOICE BETWEEN DIFFERENT TRANSFORMATIONS FOR THE SAME CHARACTER SET

Abstract— When phylogeneticists choose among alternative hypotheses, they choose the one that requires the fewest ad hoc assumptions, i.e. the one that is the most parsimonious. For some systematists, choosing among alternative transformation series for the same set of taxa is equivalent to attaining trees with shorter length and minimal homoplasy. Homoplasy is shown to be composed of hierarchical discordance and scattering, which are recognized and described for the first time. Neither the consistency nor retention indices can be used in assessing different theories of multistate character transformation because both are affected by the shape of the transformation series rather than the character state distribution on a tree. Fits of transformations to a tree are better assessed by comparing the transformation to the cladogram character and the nearest neighbor network. Nearest neighbor networks are graphical representations of the nearest neighbor matrix. Transformations with the closest greatest number of matches between cladogram characters and the least complexity in the nearest neighbor network are preferred. These transformations are shown to make the fewest number of ad hoc statements and hence to be the most parsimonious. A means for obtaining cladogram characters and nearest neighbor matrices using a widely distributed microcomputer program is presented.     

SYSTEMATICS AND BIOGEOGRAPHY OF THE AUSTRALIAN "GREEN ASH" EUCALYPTS (MONOCALYPTUS)

Abstract— A cladistic analysis of the "green ash" eucalypts, informal subgenus " Monocalyptus ", is presented- As a first step, ordination methods of principal coordinates analysis and multidimensional scaling delineated some terminal taxa. The cladistic analysis, applying parsimony methods to the unweighted data set, yielded 25 equally parsimonious trees, each with a consistency index of 0.57.
Farris' successive approximations approach to character weighting produced one tree with a consistency index of 0.74.
An informal classification of the group, superseries Eucalyptus , is based on that cladogram. The biogeographic history of superseries Eucalyptus is interpreted from the cladogram as having been caused by lour vicariant events in southeastern Australia, in combination with a suite of ecological features that overlie the biogeographic area-pattern.     

A cladistic analysis of the genus Lopezia (Onagraceae)

Lopezia, a genus of 22 species largely restricted to Mexico, forms a monophyletic group defined by the possession of two stamens in tetramerous flowerS. A cladistic analysis of the genus was performed using 16 characters from morphology, anatomy and embryology. Twenty of the 22 species were considered the terminal taxa. Polarity of the characters was based on the outgroup comparison method, using three alternative outgroups: the genus Fuchsia, Onagraceae excluding Ludwigia, and Epilobieae-Onagreae. Using Fuchsia as outgroup, 29 equally parsimonious cladograms were produced, each with 24 steps and a consistency index of 0.75. A successive weighting procedure was applied, resulting in 15 cladograms with consistency index of 0.85. The strict consensus cladogram defines eight monophyletic groups and supports most of the current sectional classification of Lopezia, with the exception that no synapomorphy defines section Jehlia. The larger sections Lopezia and Pelozia, although well-defined as clades, are not fully resolved internally. All cladograms support section Riesenbachia as monophyletic. The two alternative hypotheses for outgroups produced similar results: 61 most parsimonious trees, reduced after the successive weighting procedure to 15, which are identical to those produced with Fuchsia as outgroup. These results are discussed in the context of data on cytology and pollination biology.     

POLYMORPHIC TAXA, MISSING VALUES AND CLADISTIC ANALYSIS

Abstract Missing values have been used in cladistic analyses when data are unavailable, inapplicable or sometimes when character states are variable within terminal taxa. The practice of scoring taxa as having "missing values" for polymorphic characters introduces errors into the calculation of cladogram lengths and consistency indices because some character change is hidden within terminals. Because these hidden character steps are not counted, the set of most parsimonious cladograms may differ from those that would be found if polymorphic taxa had been broken into monomorphic subunits. In some cases, the trees found when polymorphisms are scored as missing values may not include any of the most parsimonious trees found when the data are scored properly. Additionally, in some cases, polymorphic taxa may be found to be polyphyletic when broken into monomorphic subunits; this is undetected when polymorphisms are treated as missing. Because of these problems, terminal units in cladistic analysis should be based on unique, fixed combinations of characters. Polymorphic taxa should be subdivided into subunits that are monomorphic for each character used in the analysis. Disregarding errors in topology, the additional hidden steps in a cladogram in which polymorphisms are scored as missing can be calculated by a simple formula, based on the observation that if it is assumed that polymorphic terminals include all combinations of character states, 2 ^p − 1 additional steps are required for each taxon in which p polymorphic binary characters are scored as missing values. Thus, when several polymorphisms are scored as missing in the same taxon, very large errors can be introduced into the calculation of tree length.     

THE LIMITS OF AMINO ACID SEQUENCE DATA IN ANGIOSPERM PHYLOGENETIC RECONSTRUCTION

Amino acid sequence data are available for ribulose biphosphate carboxylase, plastocyanin, cytochrome c, and ferredoxin for a number of angiosperm families. Cladistic analysis of the data, including evaluation of all equally or almost equally parsimonious cladograms, shows that much homoplasy (parallelisms and reversals) is present and that few or no well supported monophyletic groups of families can be demonstrated. In one analysis of nine angiosperm families and 40 variable amino acid positions from three proteins, the most parsimonious cladograms were 151 steps long and contained 63 parallelisms and reversals (consistency index = 0.583). In another analysis of six families and 53 variable amino acid positions from four proteins, the most parsimonious cladogram was 161 steps long and contained 50 parallelisms and reversals (consistency index = 0.689). Single changes in both data matrices could yield most parsimonious cladograms with quite different topologies and without common monophyletic groups. Presently, amino acid sequence data are not comprehensive enough for phylogenetic reconstruction among angiosperms. More informative positions are needed, either from sequencing longer parts of the proteins or from sequencing more proteins from the same taxa.     

菝葜科基于形态学证据的系统发育分析

对全世界范围分布的菝葜科Smilacaceae的79个代表种(包括了全部的属和组), 以分布于南美洲的Philesia Comm. ex Juss.和Lapageria Ruiz &; Pav.属为外类群, 选取包括花粉和染色体性状在内的47个广义的形态学性状进行了分支分类系统发育分析, 同时以表征分类的方法构建了距离树(NJ)辅助分析, 首次对世界分布的菝葜科各属间及属内的系统发育关系作了探讨。(1)Ripogonum与菝葜属Smilax +肖菝葜属Heterosmilax互为姐妹群, 但是距离较远, 支持将类菝葜属(新拟中文名)Ripogonum独立为科的观点; (2)肖菝葜属在菝葜科内处于较为进化的分支上, 并与菝葜属土茯苓组sect. Coilanthus的部分种组成一个具较高支持率(88%)的单系分支, 分析表明肖菝葜属并非是一个好属, 应归入菝葜属; (3)菝葜属6个组的划分大都没有得到支持, 只有东亚北美间断分布的草本菝葜组sect. Nemexia的单系得到很好的支持(93%); (4)分布于南美洲巴西的种类聚为一个单系类群, 表明它们可能有共同的起源, 但由于取样局限, 南美洲种类的系统地位有待进一步研究。     

Phylogenetic relationships within the Eurasian cattish family Siluridae (Pisces: Siluriformes), with comments on generic validities and biogeography

A numerical cladistic analysis, based on 23 terminal groups and 63 morphological characters, was done to infer phylogenetic relationships within the Eurasian catfish family Siluridae. Nine hundred and forty-five equally most parsimonious trees (134 steps, consistency index 0.634) were found that differ in their resolutions of four polychotomies. Strict consensus of these trees includes ten internal nodes, does not support monophyly of Silurus, Ompok and Kryptopterus , as usually defined, and offers ambiguous support for monophyly of Wallago. Silurus and Kryptopterus are each composed of two non-sister group clades, and Ompok is composed of at least two such clades. Heuristic searches constrained by monophyly of Silurus, Ompok or Kryptopterus yielded trees five or six steps longer than the shortest trees free of constraints. The strict consensus also infers a basal dichotomy that separates the Siluridae into a temperate Eurasian clade with about 20 nominal species and a subtropical/tropical south and southeast Asian clade with about 75 nominal species. The distributions of these clades overlap in a relatively narrow region of east Asia. A heuristic search for trees 1 step longer than the shortest trees yielded 253890 trees. A strict consensus of these trees also infers a basal dichotomy between the above-mentioned clades. This analysis revealed four additional putative synapomorphies of the Siluridae, pending further resolution of the family's outgroup relationships.     

A CLADISTIC ANALYSIS OF THE FAMILY TRISTIRIDAE (ORTHOPTERA, ACRIDOIDEA)

Abstract— A cladistic analysis of the endemic South American family Tristiridae was performed using 29 characters from external morphology and the genitalia. Polarity of characters was based on the outgroup comparison method. One most parsimonious cladogram of 54 steps was obtained, from which a classification of the family Tristiridae was constructed. The analysis of phylogenetic relationships showed that the different kinds of characters define taxa at different levels in the cladogram. Those mostly from the phallic complex define suprageneric taxa while those from external morphology characterize genera. It is hypothesized that in Tristiridae differentiation of the phallic complex preceded differentiation of external morphology and that characters from the phallic complex arc less conservative than those from the external morphology.     

THE EFFECT OF ORDERED CHARACTERS ON PHYLOGENETIC RECONSTRUCTION

Abstract Morphological structures are likely to undergo more than a single change during the course of evolution. As a result, multistate characters are common in systematic studies and must be dealt with. Particularly interesting is the question of whether or not multistate characters should be treated as ordered (additive) or unordered (non-additive). In accepting a particular hypothesis of order, numerous others are necessarily rejected. We review some of the criteria often used to order character states and the underlying assumptions inherent in these criteria.
The effects that ordered multistate characters can have on phylogenetic reconstruction are examined using 27 data sets. It has been suggested that hypotheses of character state order are more informative then hypotheses of unorder and may restrict the number of equally parsimonious trees as well as increase tree resolution. Our results indicate that ordered characters can produce more, equal or less equally parsimonious trees and can increase, decrease or have no effect on tree resolution. The effect on tree resolution can be a simple gain in resolution or a dramatic change in sister-taxa relationships. In cases where several outgroups are included in the data matrix, hypotheses of order can change character polarities by altering outgroup topology. Ordered characters result in a different topology from unordered characters only when the hierarchy of the cladogram disagrees with the investigator's a priori hypothesis of order. If the best criterion for assessing character evolution is congruence with other characters, the practice of ordering multistate characters is inappropriate.     

Is Psammophily an Evolutionary Dead End? A Phylogenetic Test in the Genus Willemia (Collembola: Hypogastruridae)

The law of the unspecialized states that specialized taxa have evolved from more generalized ancestors. Moreover, it is usually assumed that ecological specialization is irreversible and hence leads to extinction. This study aims to test these assumptions using a phylogenetic framework in a case study within the springtail genus Willemia and its diverse life habits. This genus is represented mostly by loam-dwelling species (generalized condition), but some species are psammophilous, living in sandy habitats (specialized condition). Fifty-two morphological characters were examined in 34 of the 36 species of the genus and in three outgroups. The cladistic analysis yielded two most parsimonious trees (tree length 124 steps; consistency index 0.56; retention index 0.86). The evolution of psammophily versus loam-confined life is compared to the cladogram: unexpectedly, psammophily is not an evolutionary innovation that occurred once in a monophyletic group; the evolutionary scenario that parsimoniously fits the phylogeny suggests that psammophily is ancestral to the genus Willemia and reversed twice to loam-confined life. These results demonstrate that habitat generalists can evolve from habitat specialists and therefore that habitat specializations are not necessarily an evolutionary dead end. Many other seemingly specialized characters may be shown to be equally malleable.     

Cladistic analysis of Simulium (Trichodagmia) and Simulium (Thyrsopelma) (Diptera: Simuliidae)

A cladistic analysis of Simulium ( Trichodagmia ) sensu Crosskey and Howard, using 34 morphological characters of larvae (6 characters), pupa (5) and adults (23), yields nine most parsimonious trees under equal weights (length 101 steps CI 0.49 RI 0.73). Successive weighting based on the maximal rescaled consistency index preferred one of the nine (31.37 steps CI 0.62 RI 0.87 total fit_con3= 235.8), which was also one of two trees found under implicit weights with concavity values of 3–6. The cladogram justifies the recognition of two subgenera. Simulium ( Trichodagmia ) sensu stricto (containing S. muiscorum, sumapazense, S. wygodzinskyorum, S. nigrimanum, S. chalcocoma, S. huairayacu and S. lahillei ) is supported by the branchial tip sclerotization and the presence of cibarial teeth, larval body tegument covered with lanceolate hairs, female with simple claw, and gonapophysis size. Simulium ( Thyrsopelma ) (containing S. scutistriatum, S. hirtipupa, S. orbitale, S. guianense, S. perplexum and S. itaunense ) is supported by the hypostomial teeth.     

CLADISTIC AND BIOGEOGRAPHIC ANALYSES OF THE WEEVIL GENUS LISTRODERES SCHOENHERR (COLEOPTERA: CURCULIONIDAE)

Abstract— The weevil genus Listroderes Schoenherr is a monophyletic group defined by the body vestiture consisting of subcircular to suboval scales, and comprises 35 species endemic to southern South America. A cladistic analysis of the genus was carried out using 44 characters from external morphology, body vestiture, and male and female genitalia. The curvipes (three species), nodifer (five species) and robustus (four species) species groups and the 23 species of the costirostris species group were considered terminal taxa. Apomorphic states were identified using the genus Hyperoides Marshall as outgroup. The analysis yielded 122 equally parsimonious cladograms, each with 89 steps and a consistency index of 0.42; a successive weighting procedure resulted in nine cladograms (consistency index of 0.69 and retention index of 0.85). In the general consensus cladogram, nodifer-robustus and curvipes-costirostris are two pairs of sister species groups. The costirostris group comprises the subgroups foveatus, angusticeps, costirostris, delaiguei, bimaculatus and elegans , in phylogenetic order. A distributional analysis of the species of Listroderes led to identification of four areas of endemism, namely central Chile, sub-Antarctic, central Argentina and Chaco. A vicariance biogeographic analysis of these areas, based on area cladograms of Listroderes, Hyperoides, Naupactus taeniatulus species group (Coleoptera: Curculionidae), and Lucilia generic group (Asteraceae) was carried out applying the three-area statements technique. According to the general area cladogram the sequence of area-fragmentation is as follows: (central Chile (sub-Antarctic (central Argentina, Chaco))). This sequence is congruent with the history hypothesized for the region, where the uplift of the Andes (Oligocene-Pliocene) led to a progressive aridification, replacing the ancient subtropical forest by open-country environments.     

RECONSTRUCTING CHARACTER EVOLUTION ON POLYTOMOUS CLADOGRAMS

Abstract— Algorithms to reconstruct character evolution on polytomous cladograms or phylogenetic trees have to date interpreted each polytomy literally, as if it were an event of multiple speciation, with multiple daughter species descending independently from a mother species, thus requiring any similarities shared by only some of these daughters to be accounted for by convergence. These algorithms are not appropriate when the polytomy is interpreted in the usual way, namely as representing uncertainty in the cladogram's resolution. New algorithms for both ordered and unordered characters are presented to reconstruct character evolution under the uncertain-resolution interpretation of polytomies. These algorithms allow the cladogram to resolve itself so as to be favourable for the character whose evolution is being reconstructed. Because different characters may have different favourable resolutions, it is not possible in general to use these algorithms to determine the total parsimony of a polytomous cladogram (the number of evolutionary steps required over all characters by the cladogram), for which the only adequate approach is to find a most parsimonious dichotomous resolution of the cladogram.     

A cladistic approach to relationships in pentastomida.

The positioning of the Pentastomida among the Metazoa has provoked many debates up to the present. On the other hand, the internal relationships among the pentastomid subgroups have received much less attention in the past. We provide the first phylogenetic analyses under Hennigian principles. Thirty-two morphological characters were selected from the primary literature, analyzed manually, and then with the program Hennig86. Four most parsimonious trees were obtained; these were analyzed by successive weighting and reduced to 1 consensus cladogram 380 steps long, with a consistency index of 0.98 and a retention index of 0.99. Characters were also analyzed as unordered, producing results that were congruent with the previous analyses. The internal groups were ordered according to the following system: (Heymnonsicambria + Haffnericambria + Backlericambria (Cephalobaenida (Railietiellida nov. (Reighardiida nov. (Porocephalida (Linguatuloidea (Linguatulidae + Subtriquetridae) + Porocephaloidea (Sebekidae + Porocephalidae))))))). This phylogenetic system is largely congruent with the first modern taxonomic arrangement proposed for the Pentastomida.     

A phylogenetic hypothesis for species of the genus Taenia (Eucestoda : Taeniidae)

Cladistic analysis of a numerical data matrix describing 27 characters for species of Taenia resulted in 4 most parsimonious phylogenetic trees (174 steps; consistency index = 0.28; homoplasy index = 0.72; retention index = 0.48). Monophyly for Taenia is diagnosed by the metacestode that is either a cysticercus or a form derived from a bladder-like larva; no other unequivocal synapomorphies are evident. Tree structure provides no support for recognition of a diversity of tribes or genera within the Taeniinae: Fimbriotaeniini and Taeniini have no phylogenetic basis. Hydatigera, Fimbriotaenia, Fossor, Monordotaenia, Multiceps, Taeniarhynchus, Tetratirotaenia must be subsumed within Taenia as synonyms. Taenia saginata and Taenia asiatica are sister species and distantly related to Taenia solium. Cospeciation with respect to carnivorous definitive hosts and Taenia appears to be limited. Although felids are putative ancestral hosts, contemporary associations appear to have resulted from extensive host-switching among felids, canids, hyaenids, and others. In contrast, relationships with herbivorous intermediate hosts are indicative of more pervasive coevolution; rodents as intermediate hosts are postulated as ancestral for the Taeniidae, Taenia + Echinococcus. Patterns appear consistent with rapid shifts between phylogenetically unrelated carnivores but among those that historically exploited a common prey resource within communities in specific biogeographic regions.     

New approaches to the systematics of the ancyrocephalid Monogenea from Nearctic freshwater fishes

A total of 133 ancyrocephalid species found on Nearctic freshwater fishes have been named. Of these, 103 are now considered valid; 14 and 16 have been declared previously as synonyms or species inquirendae, respectively, and Urocleidus rarus Mizelle, 1940, is designated as a species inquirenda in the present work. A cladistic analysis, based on 13 binary and 4 multistate characters and 32 apomorphic character states was carried out. Generalized forms of Entobdella, Gyrodactylus, and Tetraonchus were used to generate a hypothetical outgroup taxon. Thirteen terminal taxa emerged. Of these, 3 (the articulating bar group, Ligictaluridus, and Onchocleidus sensu Wheeler and Beverley-Burton, 1989) have been recognized previously as monophyletic; 3 (Aethycteron, Lyrodiscus, and Salsuginus) were shown to be monophyletic in the present study; 3 (Leptocleidus, Macrohaptor, and Tetracleidus) are monotypic genera; and 4 were identified as unresolved assemblages that contain a number of species considered to be incertae sedis as well as those assigned to the following genera: Aristocleidus Mueller, 1936, Urocleidus sensu Suriano and Beverley-Burton, 1981, Cleidodiscoides Mayes and Miller, 1973, and Cleidodiscus sensu Beverley-Burton and Suriano, 1980. The resultant cladogram was 40 steps long with a consistency index of 0.80. The monophyly of the ingroup is supported by 5 synapomorphies. Comparison and mapping of the parasite cladogram with/onto a family-level cladogram of hosts indicated that the present data provided no unequivocal evidence of cospeciation. Some possible origins for the Nearctic ancyrocephalids are discussed, and the need for further taxonomic studies on the Holarctic ancyrocephalids to explore the possible sister-group relationship between the Nearctic and Eurasian faunas is emphasized.     

Sophisticated falsification and research cycles: Consequences for differential character weighting in phylogenetic systematics

Practicing phylogenetic systematics as a sophisticated falsification research program provides a basis for claiming increased knowledge of sister species relationships and synapomorphies as evidence for those cladistic propositions. Research in phylogenetic systematics is necessarily cyclic, and the place where the positive shift in understanding occurs is subsequent to discovering the most parsimonious cladogram(s). A priori differential character weighting is inconsistent with seeking the maximally corroborated cladogram (sensu Popper), because weighting adds to background knowledge, the evidence being then less improbable than it would be otherwise. Also, estimating weights from character state frequencies on a cladogram is inconsistent with the view that history is unique. Sophisticated falsification provides the place in the cycle of phylogenetic systematic research where weight of evidence can be evaluated and these inconsistencies do not apply. On balance, phylogenetic systematics appears to achieve greater coherence and generality as a result of focusing on the foundations for claiming increased knowledge and avoiding efforts to differentially weight characters.     

PHYLOGENY OF THE RUBIACEAE AND THE LOGANIACEAE: CONGRUENCE OR CONFLICT BETWEEN MORPHOLOGICAL AND MOLECULAR DATA?

Phylogenetic analyses of 33 genera of Rubiaceae were performed using morphological and a few chemical characters. Parsimony analysis based on 29 characters resulted in eight equally parsimonious trees, with a consistency index of 0.40 and a retention index of 0.69. These results were compared to a phylogenetic analysis of the same genera based on chloroplast DNA restriction site data. There are discrepancies between the two analyses, but if we consider groupings reflected in the present classification there is much congruency. With the exception of four genera, all the genera are positioned in the same group of taxa in the two analyses. Clades of taxa representing three of the four subfamilies (~the Antirheoideae, ~the Rubioideae, and the ~Ixoroideae) are monophyletic, while the fourth subfamily Cinchonoideae is shown to be paraphyletic. Both analyses support a widened tribe Chiococceae, including the former subtribe Portlandiinae (Condamineeae). Furthermore, in both analyses the tribe Hamelieae is placed outside the subfamily Rubioideae where it is now housed. In search for the most plausible sister group to the Rubiaceae, the genus Cinchona (Rubiaceae) was analyzed together with 13 genera of the Loganiaceae, Nerium (Apocynaceae), and Exacum (Gentianaceae). Cornus (Comaceae), Olea (Oleaceae), and these two genera together were used as outgroups. The analysis, including 25 characters, 16 taxa, and with Cornus and Olea together as an outgroup, resulted in four equally parsimonious trees, with a consistency index of 0.53 and a retention index of 0.62. The non-Loganiaceae taxa Cinchona (Rubiaceae), Nerium (Apocynaceae), and Exacum (Gentianaceae) were all found to have their closest relatives within the Loganiaceae indicating that the Loganiaceae are paraphyletic and ought to be reclassified. As a result of the morphological data the most plausible sister group to the Rubiaceae is the tribe Gelsemieae of the Loganiaceae.