Southeastern Venezuela Research Articles

Description of Jolyelmis spangleri a new species from Churí-tepui (Chimantá Massif, Venezuela), with a description of the larva of J. spangleri and J. reitmaieri (Insecta: Coleoptera: Elmidae)

Four species have been recognized in the genus Jolyelmis Spangler & Faitoute; all collected at isolated table mountains,mostly in cool stenothermal hypocrenal streams. The known distribution of the genus is confined to Venezuela, and eachspecies is here reported as endemic for the respective table mountain where it has been found. Samples from Churí-tepuiand Mount Roraima in south-eastern Venezuela contained numerous adults and larvae of Elmidae among which is a newspecies, Jolyelmis spangleri, which is here described. The new species is illustrated and keyed with all other Jolyelmis,and new distributional data for J. reitmaieriČiampor, Jr. & Kodada are included. Molecular analysis of partial cytochromeoxidase subunit I (cox1) confirmed conspecific life stages for two species: J. spangleri and J. reitmaieri. The larva of eachspecies is described and illustrated, and the generic diagnosis for Jolyelmis larvae is provided. Among the known larvaeof South American Elmidae, larvae of the genus Xenelmis Hinton appear to be the most similar. Morphological similarities are discussed. Habitats of adults and larvae are briefly described and illustrated by photographs.

A New Ceuthomantis (Anura: Terrarana: Ceuthomantidae) from Sarisariñama Tepui, Southern Venezuela

Abstract A new Ceuthomantis is described from the Sarisarinama tepui in southeastern Venezuela. The new species was collected in 2002 and reported previously as Pristimantis cf. cavernibardus. Herein important differences are highlighted as diagnostic for the new species, fitting the recently described family Ceuthomantidae from the Guianan Shield. The biogeography of the genus and family is discussed.

Aluminum accumulation in nineteen Melastomataceae species from three contrasting plant formations in acid soils

AbstractThis study describes the aluminum (Al) accumulation in relation to macronutrient and micronutrient elements in 19 Melastomataceae species in the Guayana Region in Venezuela. The purpose was to investigate the Al accumulation in four tribes and different life forms. Aluminum accumulation was predicted in the basal tribes Miconieae and Merianieae in contrast to the derived tribes and herbs from any tribe, which generally do not accumulate Al. The survey was done in a vegetation continuum, which includes a savanna shrubland, a palm‐swamp community, and an evergreen forest in the Guayana region in southeastern Venezuela. The highest value of soil Al concentration was found in the savanna shrubland, where ten lignified Miconiae and one Merianeae Al accumulators were present. At the forest, the site with highest soil acidity, four Al‐accumulator tree species from Miconiae were found. Miconia lepidota showed similar Al foliar concentrations in the savanna shrubland and forest, but foliar Ca was lower in the forest, even though it was the site with highest Ca in the soil. At the palm‐swamp community, the Melastomeae shrub Macairea pachyphylla was found with an Al concentration of 0.59 g kg–1 in leaves and 0.16 g kg–1 in bark. At the same site, Al accumulation occurred in one Microlicieae species, one Miconieae species, and in the Melastomeae herbs Pterogastra divaricata (13.25 g [kg dry mass]–1) and Pterolepis trichotoma (17.83 g kg–1). The report of Al hyperaccumulation in P. trichotoma is new for the genus, and Al accumulation in herbs is considered exceptional. The foliar Al concentration was positively correlated (p < 0.005) with Fe (r = 0.64, n = 20) and Zn (r = 0.63). The analysis of the relationships between soil Al, Fe, or Zn and the concentrations of these elements in leaves revealed they were not significantly correlated. The results indicate Al hyperaccumulation in two herbaceous Melastoamataceae species and suggest Al accumulation in this life form deserves future research. However, they also confirm the highest number of Al accumulators in lignified species of the ancient tribe Miconiae (14 out of 19 species studied).

On the Use of Paleoecological Evidence to Assess the Role of Humans in the Origin of the Gran Sabana (Venezuela)

In a recent paper published in Human Ecology, Rodriguez (2007) uses paleoecological literature to support some conclusions about the use of fire by the indigenous Pemon people from the Gran Sabana, in southeastern Venezuela. Similar references on past events are used by Sletto (2008) to discuss fire management policies in the region. In both cases, the selected paleoecological evidence is limited, out-of-date, and has not been properly used. This note aims to place the existing paleoecological data in the right context, and to show that there is more useful information pertinent to the discussion. A summary of the past evidence available for the Gran Sabana and its more accurate interpretation is provided to help further work. The origin and maintenance of the huge savanna exten sions in the Gran Sabana are intensely debated. The two main hypotheses are centered on either natural climatic factors or anthropogenic fires. At present, the Gran Sabana is frequently burnt by the Pemon people for a variety of reasons: savanna cleaning and rejuvenation, hunting, aesthetics, magic, cooking, warming, drying firewood, and others (Rodriguez 2007). The fact that this occurs inside the Canaima National Park (a UNESCO World Heritage Site, http://whc.unesco. org/en/list/701) and the headwaters of the Carom river, where reservoirs provide most of the electrical power generated in the country, has extended the controversy beyond the scientific context (Dezzeo et al. 2004, Rodriguez 2004b). The main actors in the debate are the Pemon people, the ecologists and conservationists working in the area, and the electrical company (EDELCA), as well as their individ

Molecular phylogenetics of Reig's short-tailed opossum ( Monodelphis reigi) and its distributional range extension into Guyana

Reig's short-tailed opossum ( Monodelphis reigi) was recently described morphologically, based on a single specimen from southeastern Venezuela. It was considered most similar to M. adusta, which is allopatrically distributed in the Andes and surrounding areas, but there has not been an explicit study of systematic relationships with other species of Monodelphis. We report the first occurrence from Guyana of this rare species that was previously known by only the holotype. In a molecular phylogenetic analysis of mitochondrial cytochrome b sequence variation, it groups within a well-supported monophyletic clade that includes M. adusta, M. handleyi, M. osgoodi, and M. peruviana. M. adusta was found to be the sister taxon to the rest of the adusta-complex. M. reigi is the basal taxon (sister species) of remaining adusta-complex forms. This corroborates earlier morphological studies suggesting close affinity of these taxa. As presently known, M. reigi is endemic to the highland regions (>1,000 m asl) of the Guiana Shield of northern South America, and is the only taxon within the M. adusta species complex that does not occur in the Andes or adjacent lowland regions. Based on previous molecular dating of Didelphidae, this suggests that there was a dispersal event from the Andes to the Guiana Highlands in the Miocene that gave rise to M. reigi.

Characterization of the Mineral Phosphate-Solubilizing Activity of Pantoea aglomerans MMB051 Isolated from an Iron-Rich Soil in Southeastern Venezuela (Bolívar State)

The mineral phosphate-solubilizing (MPS) activity of a Pantoea agglomerans strain, namely MMB051, isolated from an iron-rich, acidic soil near Ciudad Piar (Bolívar State, Venezuela), was characterized on a chemically defined medium (NBRIP). Various insoluble inorganic phosphates, including tri-calcium phosphate [Ca(3)(PO(4))(2)], iron phosphate (FePO(4)), aluminum phosphate (AlPO(4)), and Rock Phosphate (RP) were tested as sole sources of P for bacterial growth. Solubilization of Ca(3)(PO(4))(2) was very efficient and depended on acidification of the external milieu when MMB051 cells were grown in the presence of glucose. This was also the case when RP was used as the sole P source. On the other hand, the solubilization efficiency toward more insoluble mineral phosphates (FePO(4) and AlPO(4)) was shown to be very low. Even though gluconic acid (GA) was detected on culture supernatants of strain MMB051, a consequence of the direct oxidation pathway of glucose, inorganic-P solubilization seemed also to be related to other processes dependent on active cell growth. Among these, proton release by ammonium (NH(4)(+) ) fixation appeared to be of paramount importance to explain inorganic-P solubilization mediated by strain MMB051. On the contrary, the presence of nitrate (NO(3)(-) ) salts as the sole N source affected negatively the ability of MMB051 cells to solubilize inorganic P.

Otophryne (Anura: Microhylidae) from the highlands of Guyana: redescriptions, vocalisations, tadpoles and new distributions

Recent collections are used to expand existing descriptions of adults of Otophryne robusta and O. steyermarki.The calls of O. pyburni and O. robusta are compared. Tadpoles of O. robusta and O. steyermarki are described. Characters for distinguishing among adults and tadpoles of these two species and O. pyburni are provided. Otophryne is a Guiana shield endemic; O. pyburni is widespread at lower elevations, whereas O. robusta and O. steyermarki occur in southeastern Venezuela and western Guyana, the former at moderate elevations and the latter at higher elevations.

Biogeographic area relationships in Venezuela: A Parsimony analysis of Culicidae—Phytotelmata distribution in National Parks

This study represents the first attempt to understand the current distribution and evolutionary history of Culicidae in Venezuela and adjacent areas using cladistic methods. We studied the association between immature mosquitoes and their aquatic habitats in plants (phytotelmata) in 16 protected natural areas of Venezuela. A total of 68 mosquito species was collected from 47 host-plant species. Parsimony Analysis of Endemicity using localities and mosquito species was used to find the most parsimonious cladograms depicting the biogeographic relationships. Varying degrees of mosquito-plant associations were observed, with the greatest specificity existing at the genus and subgenus levels. Implicit enumeration algorithms obtained one parsimonious tree (L=101 steps) with four well-supported groups named "Amazonas" (southern Venezuela), “Bolivar” (southeastern Venezuela), "Los Andes Cordillera” and "Coastal Cordillera" (northern Caribbean mountain range). These results support the hypothesis that the Guayana Shield was an ancestral center of speciation, followed by the Andean Region, whereas the mosquito fauna from the Central Cordillera was derived from the latter.

Pemon Perspectives of Fire Management in Canaima National Park, Southeastern Venezuela

Recent research on the ecology of fire has challenged the view that the use of fire by indigenous peoples is detrimental to ecosystems and wildlife in protected areas. However, in Canaima National Park and World Heritage Site in southeastern Venezuela, since 1981 managers have employed a costly fire control program to eliminate savanna burning by the Pemon indigenous people. Here I present the results of the first study on Pemon perspectives of fire management in the park. I show that savanna burning is an important tool in indigenous land management and plays a key role in preventing large catastrophic fires. Pemon knowledge of fire also raises questions about conventional interpretations of environmental change in the park. Lastly, I recommend a fire management policy that seeks to integrate local ecological knowledge. This will require: (a) greater openness from scientists and resource managers to understanding Pemon rationale for the use of fire, (b) clarification among the Pemon themselves of their own views of fire, and (c) research partnerships among scientists, resource managers and the Pemon in order to encourage understanding of Pemon ecological knowledge of fire, and to assess its true impact in the Canaima National Park.

AVIAN SPECIATION IN THE PANTEPUI: THE CASE OF THE RORAIMAN ANTBIRD (PERCNOSTOLA [SCHISTOCICHLA] “LEUCOSTIGMA” SATURATA)

Abstract We document the first records for Guyana of Roraiman Antbird (Percnostola [Schistocichla] “leucostigma” saturata), an endemic of the tepui highlands of southeastern Venezuela, northern Brazil and western Guyana. This form is well differentiated from nominate leucostigma (Spot-winged Antbird) of the Guianan lowlands in morphology, vocalizations, and genetics, and replaces it both altitudinally and ecologically. The two taxa are distributed parapatrically on the continuously forested northeastern slopes of the eastern tepuis, and they almost certainly come into contact, yet there is no evidence of intermediacy. We recommend that saturata be treated as a distinct species of Percnostola, and consider its' origin in the light of various models of speciation in the tepuis. Especiacion de Aves en el Pantepui: El Caso de Percnostola (Schistocichla) “leucostigma” saturata Resumen. En este trabajo documentamos los primeros registros para Guyana de Percnostola (Schistocichla) “leucostigma” saturata, un horm...

Intestinal parasitic infections in human immunodeficiency virus (HIV) positive individuals in Southeastern Venezuela

Un estudio fue realizado en relacion a establecer la presencia de parasitos intestinales en 35 pacientes infectados con el virus de la inmunodeficiencia humana (VIH), desde julio 1997 a octubre 1998, admitidos en el Hospital Universitario Ruiz y Paez de Ciudad Bolivar, Venezuela. Parasitos fueron detectados en heces usando diversos metodos para la investigacion de protozoos y hemintos, concentracion eter-formalina, tincion de Kinyoung y tricromico. Edad, sexo, estado clinico de la infeccion de VIH fueron registrados para cada participante del estudio. Todos los pacientes presentaron diarrea cronica. En 20 pacientes infectados con VIH (57%), uno o mas parasitos intestinales fueron encontrados. Los protozoos mas frecuentemente encontrados fueron: Blastocystis hominis (28,6%), Cryptosporidium sp. (22,8%) e Isospora belli (2,9%). Microsporidia no fueron detectados. Estos datos enfatizan la importancia de los portozoos oportunistas en pacientes infectados con VIH.

Holocene paleoceanography in the southeast Venezuela Basin, Caribbean Sea

Abundance variations of benthic foraminifera in four box cores (3775–4447 m water depth) from the southeastern Venezuela Basin reflect the Holocene paleoclimatic history of the basin. There are no significant but some subtle paleoclimaticl changes during the Holocene. Overall, the following nine dominant calcareous benthic foraminifera species fluctuate down-core but display no obvious stratigraphic trends:Cibicides wuellerstorfi, Nuttallides decorata, Eponides polius, E. turgidus, E. tumidulus, Pullenia quinqueloba, P. bulloides, Melonis pompilioides, andOridorsalis tener. Primitive species of arenaceous foraminifera are abundant, while more complex forms are rare. Arenaceous foraminifera disappear at 16–18 cm depth in all four cores suggesting that below 16–18 cm the sediment is affected by diagenesis. Significant down-core dissolution of carbonate is seen in the deepest core 68-8 (4447 m). Except core 68-8, the late Holocene is characterized by a higher abundance of theGloborotalia menardii complex, a higher percentage of calcium carbonate, and a greater coarse fraction. Relatively large values for both calcium carbonate and coarse fraction percentages are caused by high productivity in warm surface waters. The late Holocene record of the foraminifera shows greater calcium carbonate dissolution, higher productivity (fertility), and more efficient water mixing during deposition than the early Holocene record. Corrosive bottom water masses are also indicated in the late Holocene by brown color and a high degree of broken planktonic foraminifera. The homogeneity of the southeastern Venezuela basin water mass is responsible for the small variations of S, H(S), and E.

Two polyisoprenylated benzophenones from the trunk latex of Clusia grandiflora (Clusiaceae)

The polyisoprenylated benzophenones, chamones I and II, were isolated from the trunk latex of Clusia grandiflora (Clusiaceae) growing in southeastern Venezuela. A third benzophenone, nemorosone II, was isolated from the pollinator reward resin of the female flowers of the same plant. Chamone I and nemorosone II are structurally similar, differing only in the degree of prenylation. Bioassays of chamone I and nemorosone II using the honeybee pathogens, Paenibacillus larvae and Paenibacillus alvei, demonstrate that both have potent antibacterial activity, and that their structural differences affect both their bactericidal efficacies and their aqueous mobilities.

Seimatoantlerium tepuiense gen. nov., a Unique Epiphytic Fungus Producing Taxol from the Venezuelan Guyana

Seimatoantlerium gen. nov., type species, S. tepuiense sp. nov. is proposed for an acervular fungus producing 4-septate, holoblastic conidia with 6-8 unbranched, apical appendages that dehisce as an appendage apparatus and also commonly possessing one or two exogenous basal appendages as well as a pedicel. It is compared with Seimatosporium, Seimatosporiopsis, and other genera. It is epiphytic on Maguireothamnus speciosus, a rubiaceous plant endemic to the tepuis of southeastern Venezuela. It produces the anti-oomycetous anticancer compound, taxol, as shown by immunological and spectroscopic methods. Taxol production is discussed relative to the ability of this fungus to exist in an extremely moist ecosystem, as well as to its relationship to other plant associated fungi.

Anti-bacterial function in the sexually dimorphic pollinator rewards of Clusia grandiflora (Clusiaceae).

Many species of the dioecious, neo-tropical plant genus Clusia secrete a viscous, hydrophobic resin from glandular tissues in both male and female flowers. This substance is readily gathered by meliponine and euglossine bees for whom it most often serves as the sole pollinator reward. Bees use Clusia resin as a nest-building material. As such, resin clearly serves an indispensable mechanical function. However, resins with antimicrobial properties may also serve to reduce the risk of pathogenesis in the nest. If resin-gathering apids benefit from antimicrobial properties in nesting materials and are able to discern these characteristics in the forage they gather, one might predict that the resin reward presented in Clusia could have evolved under selection for both mechanical and antimicrobial properties. In dioecious species, where females and males each present a resin reward, selection regimes may differ between the sexes with the result that resin form and function diverge. We investigated both the form and function of the male and female pollinator reward resins of Clusia grandiflora. Using thin-layer chromatography (TLC), we compared the chemical compositions of floral resins from five widely separated populations of this species growing in southeastern Venezuela. We found that male and female resins exhibited a marked chemical dimorphism, with females having two major TLC-resolvable fractions and males having seven. This dimorphism was stable: there were no component differences between populations in either sex. Using a disk-diffusion technique, we surveyed the same resins for antimicrobial activity using assay microorganisms isolated from eusocial meliponine bees. Both male and female Clusia grandiflora resins had pronounced but relatively directed antimicrobial activity: both were toxic to 10 of 11 Gram-positive bacteria, 7 of 15 Gram-negative or variably-staining bacteria, 0 of 3 yeasts, and 0 of 3 filamentous fungi. Again with the disk-diffusion technique, we performed more detailed tests of resin bioactivity using two Gram-positive honeybee associates, Paenibacillus larvae and P. alvei, as model pathogens. Both male and female C. grandiflora resins were highly toxic to these honeybee pathogens. Female resin, however, produced zones of inhibition with more than twice the mean diameter of those produced by the male resin. This divergence in form and function of the C. grandiflora pollinator reward resins could be in response to different selective regimes as mediated by the pollinating insects.

Malaria diagnosis by the polymerase chain reaction: a field study in southeastern Venezuela

A polymerase chain reaction (PCR) method that amplifies genus- and species-specific sequences present within the small subunit of ribosomal ribonucleic acid (ssRNA) genes of the human malaria parasites was used for the diagnosis of malaria in south-eastern Venezuela. One hundred blood samples were submitted to deoxyribonucleic acid extraction, PCR amplification and electrophoretic analysis of the PCR products, and the results were compared to those of routine microscopical diagnosis. The sensitivity of PCR for detection of Plasmodium vivax and P. falciparum malaria was 99% and 100%, respectively. However, 6 patients (6%) harboured parasites undetected by microscopy. The PCR assay detected a high proportion of mixed infections: 29% ( 17 59 ) of the infections microscopically diagnosed as P. vivax were shown to be mixed infections of P. vivax and P. falciparum. Forty per cent ( 7 17 ) of the individuals with a missed P. falciparum infection had received chloroquine in the previous 30 d. These results suggest that, in places where transmission of both P. vivax and P. falciparum occurs, PCR detection of malaria parasites can be a very useful complement to microscopical diagnosis in order to ascertain the true incidence of each species and for the follow-up of patients after specific treatment.

Fuels and fire at savanna-gallery forest boundaries in southeastern Venezuela

ABSTRACT. Factors contributing to the resistance of gallery forests in savannas to the entry of fire were investigated using field observations and manipulation experiments. Mass of savanna fuels did not decrease close to forest boundaries, and in some instances increased, while savanna fuels adjacent to forests were moister than in the savanna beyond for only 1 d after rainfall. A fuel drying experiment conducted in both forest and savanna microclimates indicated that both fuel type and microclimate contributed to the resistance of forests to fire entry, although the former played a larger role. While savanna fuels in a savanna microclimate became ignitable in c. 1 d after rain, forest fuels in a forest microclimate required 4 wk to achieve ignitability. A further experiment juxtaposing forest fuels to burning savanna indicated that fire entry into forests was faciliated by deep root mats and the presence of a superficial litter layer, both of which become attenuated at the forest/savanna contact. It is concluded that fuels in these forests can reach an ignitable state late in the dry season, but that frequent fire entry is probably precluded by the tendency of savanna fires to occur earlier in the dry season and by discontinuities in fuels at the savanna/forest contact.RESUMEN. Se investigaron los factores que contribuyen a la resistencia de la entrada del fuego a los bosques en galería de las savanas mediante observaciones de campo y experimentos de manipulación. La masa de los combustibles de la savana no decrecieron cerca de los bordes del bosque; por el contrario, en algunos casos se incrementaron, mientras que los combustibles de la savana cercanos al bosque eran mas húmedos que en la savana restante, solamente por un día despues de un evento de lluvia. Un experimento de secado de combustible, que fue conducido en los microclimas de bosque y de savana, indica que tanto el tipo de combustible como el microclima contribuyen a la resistencia de los bosques a la entrada del fuego, aunque el primer factor tuvo un papel de mayor importancia. Mientras que los combustibles de la savana en el microclima de la savana se volvieron ‘encendibles’ cerca de un día despues de lluvia, los combustibles del bosque dentro del microlima del bosque tomaron cuatro semanas para llegar a dicho estado. Un experimento que sobrepuso combustibles del bosque a la savana ardiente indicó que la entrada del fuego a los bosques se facilitó por la presencia de mantillos orgánicos profundos y de una capa superficial de hojarasca, presencia que se ve atenuada en la zona de contacto bosque/savana. Se concluye que los combustibles en estos bosques pueden alcanzar un estado de ignición tarde en la estación de sequía, pero que la entrada frecuente del fuego es probablemente evitada por la tendencia que tienen los fuegos de savana a presentarse temprano en la estación seca y por las discontinuidades de combustibles en la zona de contacto savana/bosque.

Palynology and Chronostratigraphy of the Upper Cretaceous in the Subsurface of the Barinas Area, Western Venezuela

Palynological and well-log analyses of Cretaceous strata from southeastern Venezuela allow the recognition of third-order eustatic cycles and are the basis for a chronostratigraphic framework with a datum approximately every 0.8 m.y. This definition permits the correlation of events in the local geologic evolution with regionally important sedimentological and tectonic events. An Early Cretaceous marine transgression reached areas north of the Andes before 113 Ma; however, according to our framework, the transgression extended into the Barinas area shortly after 98 Ma. An interval of relatively low sea level, from 95.5 Ma to 91.5 Ma, is represented by oil-bearing sandstones and dolomitic limestones. A second marine transgression reached the area at approximately 91.5 Ma and resulted in the deposition of organic-rich clastics that are correlatable with source rocks from areas to the north. A major hiatus (Santonian-Campanian) encompasses approximately 11 m.y. and probably is related to the emplacement of oceanic rocks in western Colombia. A younger major hiatus (Maastrichtian-Eocene) encompasses approximately 26 m.y. and probably is related to the emplacement of the Lara nappes in northern Venezuela. Two other minor intra-Turonian and intra-Maastrichtian hiatuses are recognized and encompass approximately 1.5 m.y. each.

New Synonymy and Useful Taxonomic Characters in Smilax (Smilacaceae) from the Venezuelan Guayana

In conjunction with a treatment of Smilax (Smilacaceae) for the Flora of the Venezuelan Guayana, a number of taxonomic changes are proposed for previously described taxa from southern Venezuela. A discussion of morphological characters used in the revision and a key to the species in the Venezuelan Guayana are also presented. Smilax is a genus of approximately 300 species of dioecious vines inhabiting tropical and temperate areas of both hemispheres, with most species concentrated in tropical Asia and the Neotropics. The genus has a well deserved reputation for being taxonomically difficult. Problems arise from the paucity of fertile collections of both sexes or even a single sex from particular localities (Huft, 1994), the use of characters that are not reliable for species delimitation (Howard, 1979), and conflicting treatment of species across flora boundaries (Sipman, 1979). For future collections of Smilax, collectors should strive to obtain samples from both sexes and, even more importantly, include a section or a description of the lower portion of the stem (where larger spines may be found) as well as an upper, fertile portion of the plant. We recently completed a treatment of the Smilacaceae for the Flora of the Venezuelan Guayana, which includes the states of Amazonas, Bolivar, and Delta Amacuro in southeastern Venezuela. At the onset of our project, there were 37 different species names in Smilax that had been used to identify herbarium specimens from the flora area. Currently, we recognize only 9 species. We dealt with synonymy of names whose types are from the flora area, but we did not attempt this with species described from other countries. The next logical step in the taxonomic study of South American Smilax would be a comprehensive treatment which would include examination of type material and the identification of the many synonyms that undoubtedly exist across national and floristic boundaries. The following discussion addresses our choice of characters, which should prove useful for future work in other areas. Due to the paucity of comparable fertile collections, we focused on vegetative characters more than reproductive ones. Among the type specimens examined for the nine species currently recognized in the Venezuelan Guayana, only three have flowers, and one has fruit. Also missing from these type specimens (and from most other collections in the flora area as well) is a sample of the lower stem and lower leaves of the plant, which are frequently quite different from the younger, higher stems (Killip & Morton, 1936). Stem. The presence of stem spines can be a useful character, but young growth is often unarmed, while the base of the stem can be heavily armed. In Smilax poeppigii Kunth, spines may be absent on most of the stem, while the base, which may be 20 m away, has dense spines (Berry et al. 6239, MO). A character that is more important outside the flora area is the shape of the spines, which can range from terete and needle-like to flattened and triangular. The texture of the stem has been used in many treatments, and Steyermark and Maguire (1972) used the verruculose-tuberculate texture of the stem in S. jauaensis Steyermark & Maguire as virtually the sole character to differentiate it from S. staminea Grisebach. Stem texture has been shown to be a variable character, and verruculose-tuberculate stems also appear in occasional specimens of S. staminea. Another species, S. lappacea Humboldt & Bonpland ex Willdenow, which Steyermark and Maguire (1972) noted as having smooth stems, has some specimens with tuberculate stems, although the bumps are typically not darkned and thus not readily visible (Huber 581, VEN). Only in the case of S. schomburgkiana Kunth did we use stem texture as a diagnostic character. The stem of this species is consistently NovoN 8: 364-370. 1998. This content downloaded from 157.55.39.163 on Fri, 18 Nov 2016 04:22:17 UTC All use subject to http://about.jstor.org/terms Volume 8, Number 4 Gaskin & Berry 365 1998 Smilax from Venezuelan Guayana

Root mat depths and surface soil chemistry in Southeastern Venezuela

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