Morphological and phylogenetic analyses of Pythium species in South Africa

The genus Pythium is important in agriculture, since it contains many plant pathogenic species, as well as species that can promote plant growth and some that have biocontrol potential. In South Africa, very little is known about the diversity of Pythium species within agricultural soil, irrigation and hydroponic systems. Therefore, the aim of the study was to characterise a selection of 85 Pythium isolates collected in South Africa from 1991 through to 2007. The isolates were characterised morphologically as well as through sequence and phylogenetic analyses of the internal transcribed spacer regions (ITS) and the 5.8S gene of the nuclear ribosomal DNA. Phylogenetic analyses showed that the isolates represented ten of the 11 published Pythium clades [Lévesque & De Cock, 2004. Molecular phylogeny and taxonomy of the genus Pythium. Mycological Research 108: 1363–1383]. Characterisation of isolates in clade D and J suggested that the phylogenetic concept of Pythium acanthicum and Pythium perplexum respectively, needs further investigation in order to enable reliable species identification within these clades. Our phylogenetic analyses of Pythium species in clade B also showed that species with globose sporangia group basal within this clade, and are not dispersed within the clade as previously reported. The 85 South African isolates represented 34 known species, of which 20 species have not been reported previously in South Africa. Additionally, three isolates (PPRI 8428, 8300 and 8418) were identified that may each represent putative new species, Pythium sp. WJB-1 to WJB-3.     

Phylogenetic relationships among Phytopythium species,and re-evaluation of Phytopythium fagopyri comb. nov., recovered from damped-off buckwheat seedlings in Japan

We examined the phylogenetic relationships among Phytopythium species using the rDNA ITS region, the LSU rDNA region, and the mitochondrial coxI and coxII genes. The genus was resolved into three monophyletic clades (1–3). Clade 1 was the largest clade, composed of 12 known species. Clades 2 contained two known and one new species candidate and clade 3 contained two known species. Three isolates in clade 2 (FP1, HonMa, and a strain designated as P. helicoides CBS293.35) formed a monophyletic group with high bootstrap support. This monophyletic group was distinct from P. helicoides sensu stricto. All three isolates came from damped-off buckwheat seedlings. The isolates were morphologically identical with one another and were characterized by globose, sub-globose, or pyriform sporangia with apical papillae; internally or internally nested proliferating sporangia; simple sympodia; coiling antheridial stalks; and wavy, sessile, or clavate antheridial cells. The isolates grew at temperatures between 15 °C and 40 °C, and the optimum temperature was 30 °C, with a radial growth rate of 20 mm/24 h. The phylogenetic and morphological analyses indicated that these isolates belong to a distinct species, which was previously under the genus Pythium, named here Phytopythium fagopyri comb. nov.     

<Emphasis Type="Italic">Pythium montanum</Emphasis> sp. nov., a new species from a spruce stand in the Bavarian Alps

During a study on soilborne Pythiaceae in the Bavarian Alps, 3 isolates of a papillate Pythium species with aplerotic oospores were found in rhizosphere soil from a declining spruce stand. The isolates showed a unique combination of sporangial and gametangial characters, and could not be assigned to any known species of the genus. They were characterised by a relatively low growth rate, internally proliferating sporangia and extremely variable, monoclinous, sessile or shortly stalked antheridia. Direct germination of sporangia frequently occurred in water culture. Internal transcribed spacer (ITS) regions of the ribosomal DNA showed very low levels of similarity to those of all known species of Pythium. This paper describes the isolates as Pythium montanum sp. nov., gives details on its morphology and provides preliminary information on its pathogenicity. Additional molecular evidence for its status as a new species is also provided. Phylogenetic analyses with a set of Pythium spp. showed that P. montanum groups in a clade together with P. vexans, a species whose taxonomical status still remains unclear, and that is considered a ‘border species’ between Pythium and Phytophthora.     

Two new species,Pythium agreste and P. wuhanense,based on morphological characteristics and DNA sequence data

In an investigation of Pythium species in China, two new species, P. agreste and P. wuhanense, were identified based on morphological characteristics and DNA sequence data. Pythium agreste has slightly inflated sporangia, oogonia encompassed by antheridia and antheridial stalks forming a very complicated knot, and plerotic oospores. It differs from the morphologically similar P. volutum which has inflated sporangia, bigger oogonia, and aplerotic oospores; from P. kashmirense which has contiguous inflated sporangia, catenulate oogonia and coiled or bent oogonial stalks; and from P. pectinolyticum which has catenulate oogonia and bigger oogonia and oospores. Pythium wuhanense can be differentiated from morphologically similar P. emineosum and P. paroecandrum by its possession of intercalary cylindrical to elongated sporangia and intercalary oogonia catenulate with sporangia and antheridia. Phylogenetic analyses showed that these two new species were clearly separated from morphologically similar Pythium species, based on the internal transcribed spacer (ITS) region and cytochrome C oxidase subunit I (COI) gene sequences using maximum parsimony and Bayesian methods. The two new species are described and illustrated in detail.     

Diversity and evolution of 5S rRNA gene family organization in Pythium

The 5S rRNA gene family organization among 87 species and varieties of Pythium was investigated to assess evolutionary stability of the two patterns detected and to determine which pattern is likely the ancestral state in the genus. Species with filamentous sporangia (Groups A-C according to the ITS phylogenetic tree for Pythium) had 5S genes linked to the rDNA repeat that were predominantly coded for on the DNA strand opposite to the one with the other rRNA genes (‘inverted’ orientation). A small group of species with contiguous sporangia (Group D) is related to Groups A-C but had unlinked 5S genes. The main group of species with spherical zoosporangia (Groups E-J) generally had unlinked 5S genes in tandem arrays. The six species in Group K, although they also have spherical sporangia, had linked genes on the same strand as the other rRNA genes ‘non-inverted’ and most of them had pairs of tandem 5S genes. The evolutionary stability of 5S sequence organization was compared with the stability of morphological characters as interpreted from a phylogeny based on ITS sequence analysis. Features of 5S sequence organization were found to be just as consistent within groups as were the morphological characters. To determine the ancestral type of 5S family organization, a survey of Phytophthora strains was conducted to supply an outgroup reference. The most parsimonious interpretation of the data in this survey yielded the tentative conclusion that the linked condition of the 5S sequences was ancestral.     

Nimbya and Embellisia revisited, with nov. comb for Alternaria celosiae and A. perpunctulata

Previous phylogenetic analyses revealed that species within the genera Nimbya and Embellisia reside within a large monophyletic clade that also includes the genera Alternaria, Ulocladium, Undifilum, Sinomyces, and Crivellia with Stemphylium as the sister taxon. This study expands upon previous work by including many contemporary species of each genus and utilizes molecular and morphological characters to further examine relationships. Maximum parsimony and Bayesian analysis reveals that Nimbya is not a monophyletic genus but is split into two phylogenetically distant clades, which have different and distinct conidial morphologies. One of these clades resides completely within Alternaria. Phylogenetic analyses also reveals that Embellisia does not form a monophyletic genus but is split into four monophyletic lineages. Moreover, several species of Embellisia cluster individually with clades that are predominantly Alternaria, Ulocladium, or Stemphylium, yet these Embellisia spp. possess morphological characters that are diagnostically Embellisia. Thus, these data reveal that both Nimbya and Embellisia are polyphyletic as currently defined and taxonomic restructuring is necessary in order to resolve conflict between historical morphological and contemporary molecular-based phylogenies.     

Phylogenetic position of the southern African members of the tribe Psoraleeae based on molecular and morphological data

The tribe Psoraleeae (Leguminosae subfamily Papilionoideae) comprises 185 species in nine genera that have a nearly worldwide distribution, occurring predominantly in Mediterranean regions. About 60% of the species belong to the genera, Otholobium C.H.Stirt. and Psoralea L., which have a centre of diversity in the Cape Floristic Region of South Africa. Since previous molecular studies have sampled only a few species of the tribe from this region, this study sought to determine the phylogenetic position of the southern African genera and to test whether they are monophyletic. Phylogenetic relationships were reconstructed using DNA sequence data (trnL-F, rpoB-trnC and ITS) and seven morphological characters, which diagnose the two southern African genera. The data were analysed using the parsimony method. There was strong support for the Psoraleeae as a clade, but most of the nodes within the large genera were poorly supported. The southern African species of Psoralea and Otholobium together formed a strongly supported clade. This clade was sister to the genus Hoita Rydb., but without support. However, the Psoralea species were nested within the southern African Otholobium. Additionally, some South American species that are currently recognised as Otholobium were resolved in a clade distinct from the southern African species, making Otholobium polyphyletic. Morphological characters that separate Otholobium and Psoralea are discussed. Finally, the southern African genera as currently circumscribed are not monophyletic. However, further investigations using more informative DNA loci are required to validate this observation. Furthermore, the taxonomic placement of the South American species needs to be reviewed.     

Aquastella gen. nov.: A new genus of saprolegniaceous oomycete rotifer parasites related to Aphanomyces, with unique sporangial outgrowths

The oomycete genus Aquastella is described to accommodate two new species of parasites of rotifers observed in Brooktrout Lake, New York State, USA. Three rotifer species – Keratella taurocephala, Polyarthra vulgaris, and Ploesoma truncatum – were infected, and this is the first report of oomycete infection in these species. Aquastella attenuata was specific to K. taurocephala and Aquastella acicularis was specific to P. vulgaris and P. truncatum. The occurrence of infections correlated with peak host population densities and rotifers were infected in the upper layers of the water column. Sequencing of 18S rRNA and phylogenetic analysis of both species placed them within the order Saprolegniales, in a clade closely related to Aphanomyces. The Aquastella species were morphologically distinct from other rotifer parasites as the developing sporangia penetrated out through the host body following its death to produce unique tapered outgrowths. Aquastella attenuata produced long, narrow, tapering, finger-like outgrowths, whilst A. acicularis produced shorter, spike-like outgrowths. We hypothesize that the outgrowths serve to deter predation and slow descent in the water column. Spore cleavage was intrasporangial with spore release through exit tubes. Aquastella attenuata produced primary zoospores, whereas A. acicularis released spherical primary aplanospores, more typical of other genera in the Aphanomyces clade.     

Phylogenetic status of Xylaria subgenus Pseudoxylaria among taxa of the subfamily Xylarioideae (Xylariaceae) and phylogeny of the taxa involved in the subfamily

To infer the phylogenetic relationships of Xylaria species associated with termite nests within the genus Xylaria and among genera of the subfamily Xylarioideae, β-tubulin, RPB2, and α-actin sequences of 131 cultures of 114 species from Xylaria and 11 other genera of the subfamily were analyzed. These 11 genera included Astrocystis, Amphirosellinia, Discoxylaria, Entoleuca, Euepixylon, Kretzschmaria, Nemania, Podosordaria, Poronia, Rosellinia, and Stilbohypoxylon. We showed that Xylaria species were distributed among three major clades, TE, HY, and PO, with clade TE—an equivalent of the subgenus Pseudoxylaria—encompassing exclusively those species associated with termite nests and the other two clades containing those associated with substrates other than termite nests. Xylaria appears to be a paraphyletic genus, with most of the 11 genera submerged within it. Podosordaria and Poronia, which formed a distinct clade, apparently diverged from Xylaria and the other genera early. Species of Entoleuca, Euepixylon, Nemania, and Rosellinia constituted clade NR, a major clade sister to clade PO, while those of Kretzschmaria were inserted within clade HY and those of Astrocystis, Amphirosellinia, Discoxylaria, and Stilbohypoxylon were within clade PO.     

<Emphasis Type="Italic">Phylloporia minutipora and P. radiata</Emphasis> spp. nov. (Hymenochaetales,Basidiomycota) from China and a key to worldwide species of <Emphasis Type="Italic">Phylloporia</Emphasis>

Phylloporia is a monophyletic genus within the Hymenochaetaceae as recovered by nuclear large subunit ribosomal DNA (nLSU) sequences. According to the summarization of 38 species accepted in this genus, Phylloporia is characterized by an absence of setae and the presence of abundant thick-walled, colored and tiny basidiospores, although its other morphological characters are highly diverse. Nine herbarium specimens from China, fitting the morphological concept of Phylloporia, were morphologically and phylogenetically studied in detail. The phylogeny inferred from nLSU sequences shows that the nine specimens formed three terminal lineages within the Phylloporia clade. Two lineages being composed of four specimens from Hainan and three from Guizhou were newly described as Phylloporia minutipora and P. radiata, respectively. In Phylloporia, P. minutipora is distinct by a combination of annual, sessile and imbricate basidiocarps, distinctly concentrically sulcate pileal surface with obtuse margin, angular pores of 12–15 per mm, duplex context separated by a black zone, a dimitic hyphal system, and broadly ellipsoid basidiospores of 2.5–3?×?2–2.5 μm, while P. radiata is distinct by a combination of annual, sessile and imbricate basidiocarps, faintly sulcate and radially striate pileal surface, sharp pileal margin, angular pores of 8–10 per mm, duplex context separated by a black zone, a monomitic hyphal system, and broadly ellipsoid basidiospores of 2.5–3.5?×?2–2.5 μm. The third lineage, comprising two specimens from Hainan, was morphologically determined as Phylloporia pulla. This species was recently combined to Phylloporia based on only morphological characters, and the current study for the first time generated its molecular sequences for phylogenetic reference. A key to all 40 species of Phylloporia is provided.     

<Emphasis Type="Italic">Pythium apinafurcum</Emphasis>: its morphology,molecular phylogeny,and infectivity for plants

During a survey of Pythium species in soils of Japan, Pythium isolates growing at high temperatures were obtained from an uncultivated field soil in Wakayama Prefecture. All six isolates showed similar morphology to each other and had complexly branched secondary hyphae, globose nonproliferating sporangia, and smooth-surfaced oogonia that have one or two oospores per oogonium. The combination of these characteristics differentiated these isolates from other Pythium species reported. Phylogenetic analyses based on sequences of the ribosomal DNA ITS and D1/D2 region of the large subunit showed that all Pythium isolates were clustered in a single clade that was distantly related to other known clades of the genus. We described these isolates as a new Pythium species, Pythium apinafurcum, based on morphology and molecular phylogeny. The P. apinafurcum isolates nonsymptomatically infected the roots of seedlings of bermudagrass, cabbage, and cucumber in a pot inoculation test.     

Phylogenetic Classification at Generic Level in the Absence of Distinct Phylogenetic Patterns of Phenotypical Variation: A Case Study in Graphidaceae (Ascomycota)

Molecular phylogenies often reveal that taxa circumscribed by phenotypical characters are not monophyletic. While re-examination of phenotypical characters often identifies the presence of characters characterizing clades, there is a growing number of studies that fail to identify diagnostic characters, especially in organismal groups lacking complex morphologies. Taxonomists then can either merge the groups or split taxa into smaller entities. Due to the nature of binomial nomenclature, this decision is of special importance at the generic level. Here we propose a new approach to choose among classification alternatives using a combination of morphology-based phylogenetic binning and a multiresponse permutation procedure to test for morphological differences among clades. We illustrate the use of this method in the tribe Thelotremateae focusing on the genus Chapsa, a group of lichenized fungi in which our phylogenetic estimate is in conflict with traditional classification and the morphological and chemical characters do not show a clear phylogenetic pattern. We generated 75 new DNA sequences of mitochondrial SSU rDNA, nuclear LSU rDNA and the protein-coding RPB2. This data set was used to infer phylogenetic estimates using maximum likelihood and Bayesian approaches. The genus Chapsa was found to be polyphyletic, forming four well-supported clades, three of which clustering into one unsupported clade, and the other, supported clade forming two supported subclades. While these clades cannot be readily separated morphologically, the combined binning/multiresponse permutation procedure showed that accepting the four clades as different genera each reflects the phenotypical pattern significantly better than accepting two genera (or five genera if splitting the first clade). Another species within the Thelotremateae, Thelotrema petractoides, a unique taxon with carbonized excipulum resembling Schizotrema, was shown to fall outside Thelotrema. Consequently, the new genera Astrochapsa, Crutarndina, Pseudochapsa, and Pseudotopeliopsis are described here and 39 new combinations are proposed.     

A New Notosuchian from the Late Cretaceous of Brazil and the Phylogeny of Advanced Notosuchians

A new notosuchian crocodyliform from the Late Cretaceous Bauru Group found in the southeastern State of São Paulo (Brazil) is described here. The new taxon, Caipirasuchus stenognathus, is referred as a new species of the recently erected genus Caipirasuchus within the clade Sphagesauridae based on a phylogenetic analysis of basal mesoeucrocodylians. Caipirasuchus stenognathus is represented by an almost complete skull and lower jaw that has autapomorphic characters that distinguish it from other species of Sphagesauridae. These autapomorphies include: maxilla forming part of the orbital margin (absence of lacrimal-jugal contact), nasal with smooth depressions on the posterior region close to the contact with the maxilla and lacrimal, postorbital with posterior palpebral facet that extends posteriorly underneath the ear-flap groove, and a distinct anterior process of the medial flange of the retroarticular process. Additionally, the new taxon lacks autapomorphic features described in other sphagesaurids. The phylogenetic analysis results in a monophyletic genus Caipirasuchus, that is the sister group of a clade fomed by Sphagesaurus huenei, Caryonosuchus pricei, and Armadillosuchus arrudai. Sphagesaurids also include a basal clade formed by Adamantinasuchus navae and Yacarerani boliviensis. Other notosuchian taxa, such as Mariliasuchus amarali, Labidiosuchus amicum, Notosuchus terrestris, and Morrinhosuchus luziae are successive sister taxa of Sphagesauridae, forming a clade of advanced notosuchians that are restricted to the Late Cretaceous of South America. These results contrast with most previous phylogenetic hypotheses of the group that depicted some members of Sphagesauridae as more closely related to baurusuchids, or found Asian (e.g., Chimaerasuchus) or African (Malawisuchus, Pakasuchus) forms nested within advanced notosuchians that are, according to our analysis, endemic of the Late Cretaceous of South America.     

Phylogeny of the genus Pythium and description of new genera

Phylogeny of the genus Pythium is analyzed based on sequences of the large subunit ribosomal DNA D1/D2 region and cytochrome oxidase II gene region of Pythium isolates and comprehensive species of related taxa belonging to the Oomycetes. The phylogenetic trees show that the genus Pythium is a highly divergent group and divided into five well- or moderately supported monophyletic clades. Each clade is characterized by sporangial morphology such as globose, ovoid, elongated, or filamentous shapes. Based on phylogeny and morphology, the genus Pythium (s. str.) is emended, and four new genera, Ovatisporangium, Globisporangium, Elongisporangium, and Pilasporangium, are described and segregated from Pythium s. lato.     

The phylogenetic placement of hypocrealean insect pathogens in the genus Polycephalomyces: An application of One Fungus One Name

Understanding the systematics and evolution of clavicipitoid fungi has been greatly aided by the application of molecular phylogenetics. They are now classified in three families, largely driven by reevaluation of the morphologically and ecologically diverse genus Cordyceps. Although reevaluation of morphological features of both sexual and asexual states were often found to reflect the structure of phylogenies based on molecular data, many species remain of uncertain placement due to a lack of reliable data or conflicting morphological characters. A rigid, darkly pigmented stipe and the production of a Hirsutella-like anamorph in culture were taken as evidence for the transfer of the species Cordyceps cuboidea, Cordyceps prolifica, and Cordyceps ryogamiensis to the genus Ophiocordyceps. Data from ribosomal DNA supported these species as a single group, but were unable to infer deeper relationships in Hypocreales. Here, molecular data for ribosomal and protein coding DNA from specimens of Ophiocordyceps cuboidea, Ophiocordyceps ryogamiensis, Ophiocordyceps paracuboidea, Ophiocordyceps prolifica, Cordyceps ramosopulvinata, Cordyceps nipponica, and isolates of Polycephalomyces were combined with a broadly sampled dataset of Hypocreales. Phylogenetic analyses of these data revealed that these species represent a clade distinct from the other clavicipitoid genera. Applying the recently adopted single system of nomenclature, new taxonomic combinations are proposed for these species in the genus Polycephalomyces, which has been historically reserved for asexual or anamorphic taxa.     

Using multilocus approach to uncover cryptic diversity within Pseudotrapelus lizards from Saudi Arabia

The agamid Pseudotrapelus lizards inhabit the mountainous areas of the Arabian Peninsula and eastern North Africa. Currently six Pseudotrapelus species are recognised, though diagnostic morphological characters are still lacking, creating great difficulty in describing new species. Recently, two specimens of Pseudotrapelus were collected from the vicinity of Riyadh in central Saudi Arabia, an area that was not sampled in previous phylogenetic studies. In here we used both mitochondrial and nuclear data to investigate the phylogenetic position of the new samples, and assess their phylogenetic relationships with the other recognised species of Pseudotrapelus from across the distribution range of the genus. We used a multilocus approach of haplotype networks, concatenated datasets and species trees, performed mitochondrial and nuclear species delimitation analyses, and estimated divergence times. In general, our results support previous molecular studies and uncover the presence of cryptic diversity within Pseudotrapelus. The phylogenetic structure of the genus is of two major clades and within them seven distinct, delimited phylogenetic groups belonging to the six recognised species and the seventh to the individuals from Riyadh. The Riyadh specimens were distinct in all analyses performed. We suggest that the new specimens from the Riyadh area are a distinct lineage, forming a clade with their phylogenetic relatives, P. sinaitus and P. chlodnickii. The clade formed by these three species diverged during the Late Miocene around 6.4 Ma, with cladogenesis possibly facilitated by vicariance and isolation caused due to climatic fluctuations and the progression of sandy areas. Our results suggest further morphological research is necessary to revise the taxonomic status of this lineage and of the entire genus.     

On the phylogeny of Euryteinae (Crustacea,Copepoda, Cyclopoida), with description of one new species from Korea

Euryte koreana sp. nov. is described from the shallow littoral on the East Coast of South Korea, and represents the first record of the subfamily Euryteinae Monchenko, 1974 in the Pacific Ocean north of the tropics. It belongs to a group of species that have the caudal rami length/width ratio of around four, but differs from all congeners by a number of morphological features. Detailed drawings and extensive scanning electron micrographs of many characters of ornamentation provided for this species should serve as a benchmark for distinguishing closely related species in this subfamily with conservative macro-morphology. A morphologically distinct population from anchialine caves in Mallorca, identified previously as Euryte longicauda Philippi, 1843, is described as another new species: Euryte jaumei sp. nov. To test the phylogenetic relationships of its members and previous hypotheses about generic placement of two species associated with scleractinian corals, several cladistic analyses are performed on all 16 currently recognized species of Euryteinae and two outgroups, Neocyclops australiensis Karanovic, 2008 and Troglocyclops janstocki Rocha and Iliffe, 1994, using 25 morphological characters. All resulting trees suggest a close relationship between the two commensal species and them as a sister clade to all other Euryteinae. They are transferred into a newly erected genus Coraleuryte gen. nov., as C. bellatula (Humes, 1991) comb. nov. and C. verecunda (Humes, 1992) comb. nov., and a revised diagnoses is provided for the genus Euryte Philippi, 1843. Obtained cladograms also show that Ancheuryte Herbst, 1989 is nested deeply within the Euryte clade, so the genus is synonymized and its only species is transferred, as E. notabilis (Herbst, 1989) comb. nov. A key to species of Euryteinae is also provided.     

A polyphasic approach to the study of the genus Nitzschia (Bacillariophyta): three new planktonic species from the Adriatic Sea

The paraphyletic diatom genus Nitzschia comprises over 1000 morphologically distinct pennate taxa, known from the benthos and plankton of freshwater, brackish, and marine environments. The principal diagnostic characters for delimitation of Nitzschia species include valve shape, the position and structure of the raphe, presence/absence and shape of the proximal raphe endings and terminal raphe fissures, areola structure, and specific morphometric features such as cell size, and stria and fibula density. In this study, we isolated 12 diatom strains into culture from samples collected at the surface or greater depths of the southeastern Adriatic Sea. Morphological analyses included LM, SEM, and TEM observations, which, along with specific morphometric features, allowed us to distinguish three new Nitzschia species. These findings were congruent with the results of phylogenetic analyses performed on nuclear‐encoded SSU (18S) rDNA and chloroplast‐encoded rbcL and psbC genes. One of the new species (Nitzschia dalmatica sp. nov.) formed a lineage within a clade of Bacillariaceae containing members of the Nitzschia sect. Dubiae, which was sister to Psammodictyon. A second lineage was part of a novel clade that is significantly distinct from other Nitzschia species sequenced so far and includes Nitzschia adhaerens sp. nov. and N. cf. adhaerens. A further new species was found, Nitzschia inordinata sp. nov., which appeared as the sister group to the N. adhaerens clade and the conopeoid Nitzschia species in our phylogenetic trees. Our findings contribute to the overall diversity of genus Nitzschia, especially in identifying some deep branches within the Bacillariaceae, and highlight under‐scoring of this genus in marine plankton.     

Stem anatomy of Philodendron Schott (Araceae) and its contribution to the systematics of the genus

Previous morphological analysis has indicated that subgenus Meconostigma was the basal group of the genus and sister group of a clade formed by subgenera Philodendron and Pteromischum. However, recent molecular analysis suggests Pteromischum is the sister group of the clade Philodendron and Meconostigma. The objective of this work was to anatomically describe the stem of Philodendron, searching for possible synapomorphies for the three currently accepted subgenera, and thus give support to one of the two phylogenetic hypotheses, and to contribute new and updated information about characters relevant to the taxonomy of the group. Anatomical data were obtained from 14 species of Philodendron. The main conclusions of our study were recognition of a sclerified hypodermis and storied cork in Philodendron and verification of the absence of amphivasal bundles, the presence of which was previously suggested for the genus by French and Tomlinson. The presence of a branched root vascular plexus in Meconostigma and Philodendron gives support to the phylogenetic hypothesis in which those two subgenera form a monophyletic clade. The unistratified and sclerified hypodermis, only simple vascular bundles within the periphery of the central cylinder, and a connection through a fibrous sheath between them were considered apomorphic characters of Pteromischum.