Query: Sextonia

title: Sextonia, a new genus of Lauraceae from South America
abstract: The genus Sextonia is described; it consists of two species, the rather widespread S. rubra and the new species S. pubescens, restricted to eastern Peru. Ocotea is the largest genus of neotropical Lauraceae, including at least 300 species (van der Werff, 1991) It is not surprising that with such a large number of species the genus shows considerable morphological variation, is difficult to delimit, and is in much need of a modern revision. Oftentimes the genus has been used to accommodate species that could not be adequately placed in other, better defined genera. As information from other disciplines, most notably wood and bark anatomy (Richter, 1981) has become available, some of the anomalous species have been removed from Ocotea and recognized as distinct genera. Rohwer et al. (1991) created the genus Chlorocardium for two species previously placed in Ocotea and discussed some other problematical species. I propose to recognize one of those species, until now treated as Ocotea rubra, as belonging to a distinct genus and will describe a new species of this genus as well. Sextonia van der Werff, gen. nov.  Sextonia rubra (Mez) van der Werff.  Inflorescentiae axillares, racemosae vel paniculatae. Tepala 6, inaequalia, 3 exteriora quam 3 interiora minora, erecta; stamina 9, 4 locellata, 6 exteriora locellis in arcu non profundo dispositis, 3 interiora locellis in 2 paribus superpositis; staminodia 3; receptaculum profundum. Fructus cupula insidens, ab ea 13 vel fere omnino obtecta. Large trees, to 45 m tall. Twigs thick, corky, terete. Leaves alternate, clustered near the tips of the branches, pinnately veined, without domatia. Inflorescences axillary, racemose or paniculate, ultimate divisions of inflorescences frequently not strictly cymose, but racemose. Tepals erect, unequal, the outer three smaller than the inner three; stamens 9, 4 celled, the outer 6 with the cells in a shallow arc, the inner 3 with the cells placed in two pairs, the filaments short, as wide as the anthers, staminodia 3; receptacle deep. Fruit initially enclosed in the cupule, at maturity either 2/ exserted or almost completely enclosed in the cupule. The new genus Sextonia is readily recognized by having clustered leaves and flowers with unequal tepals, characters already mentioned by Rohwer et al. (1991) The differences in wood and bark anatomy between Ocotea and Sextonia (as O. rubra) were amply discussed by Richter (1981) and indeed the main reason that Rohwer et al. (1991) did not describe a new genus to accommodate O. rubra was their reluctance to describe another monotypic genus. In a genus as large as Ocotea it is not surprising to find individual species or groups of species that differ in one or more morphological characters from the rest of the species, and finding such differences is not a sufficiently strong argument for describing a new genus. However, when such morphological differences are supported by differences in wood and bark anatomy the argument for a new genus is stronger. Three reasons made me consider the generic status of 0. rubra again. The first is the recent discovery of an undescribed species closely related to O. rubra, sharing with it the clustered leaves and flowers with unequal tepals, but differing in having pubescent flowers and racemose inflorescences. This new species has wood and bark anatomy similar to O. rubra. Describing this species in Ocotea would clearly be incorrect. The second argument is that during a study of the embryology of Lauraceae (Heo et al. in prep. Ocotea rubra was found to differ clearly from the other four investigated species of Ocotea in having the mature embryo sac protruding from the nucellus, a character state otherwise only found in Beilschmiedia, Caryodaphnopsis, Cryptocarya, Endiandra, and Potameia, but lacking in genera considered closely related to Ocotea, such as Aiouea, Aniba, Cinnamomum, Licaria, Mezilaurus, and Nectandra. The third is that the inflorescences of the two species of Sextonia are different from those found in Ocotea. In Ocotea the flowers are arranged in cymes, with the lateral flowers of a cyme strictly opposite. In Sextonia rubra, however, the flowers are not arranged in cymes. Frequently the ultimate branching of the inflorescences appears racemose and flowers are not strictly opposite. The inflorescence types of Lauraceae and their importance for the suprageneric classification are discussed in detail by van NovoN 7: 436 439. 1997. This content downloaded from 157.55.39.151 on Thu, 07 Jul 2016 05:31:01 UTC All use subject to http:/about.jstor.org/terms Volume 7, Number 4 van der Werff 437 1997 New Genus of Lauraceae

title: Gene flow and mating system of the tropical tree Sextonia rubra
abstract: In this paper we report a study of the mating system and gene flow of Sextonia rubra, a hermaphroditic, insect pollinated tropical tree species with a geographic distribution in the Guyana Plateau and the Amazon. Using five microsatellites we analysed 428 seeds of 27 open pollinated families at the experimental site "Paracou" in French Guiana. We observed, compared to other tropical tree species, a high level of genetic diversity. We estimated parameters of the mating system and gene flow by using the mixed mating model and the TwoGener approach. The estimated multilocus outcrossing rate, tm, was 0.992 indicating nearly complete outcrossing. A significant level of biparental inbreeding and a small proportion of full sibs were estimated for the 27 seed arrays. The differentiation of allelic frequencies among the pollen pools was PhFT 0.061. We estimated mean pollen dispersal distances between 65 m and 89 m according to the dispersal models used. The joint estimation of pollen dispersal and density of reproductive trees gave an effective density estimate of 2.1 2.2 trees/ha.

title: Oleos essenciais de Sextonia rubra (Mez) van der Werff (Lauraceae)
abstract: The essential oils of the leaves and branches of Sextonia rubra were obtained by hydrodistillation and analyzed by GC FID and GC MS. In the leaves were identified as the major constituents a pinene (21.7% b pinene (15.4% a copaene (12.5% and germacrene D (12.1% In the branches essential oil, a copaene (22.9% b selinene (7.9% and b elemene (7.2% were identified as the most abundant constituents. This paper describes for the first time the composition of these essential oils.

title: Effect of nondestructive testing of laminations on the bending properties of glulam beams made from louro vermelho (Sextonia rubra)
abstract: This work aims to assess the bending properties of glued laminated timber beams (glulam) manufactured with species louro vermelho (Sextonia rubra) Laminations were nondestructively tested using the transverse vibration method (EMlam) Then 10 glulam beams were manufactured and tested in static bending according to ASTM D 198 standard, having modulus of elasticity (EM) modulus of rupture (fM) and bending moment (M) determined. The finished beams were also tested by the transverse vibration method (EMvt) It was noted that the EMvt value was only 2% lower than the EM value. Using laminations with a high modulus of elasticity did allow effective gain in stiffness. Therefore, results indicate that the transverse vibration method is a valid, reliable technique both for testing glulam laminations and for assessing stiffness in finished beams. Bending properties in glulam beams were influenced by the stiffness of constituent laminations.

title: Natural durability of Sextonia rubra, an Amazonian tree species: description and origin
abstract: Sextonia rubra is a tropical tree species belonging to Lauraceae family. In French Guiana, its long lasting heartwood is largely exploited for different purposes including house construction, and furniture making. Decay tests have confirmed S. rubra natural durability, and led us to discover some variability. Rubrynolide and rubrenolide, which are two majors metabolites isolated from the heartwood of S. rubra, exhibit potent antifungal and termiticidal activities that result in the exceptiona l natural durability of this species heartwood. Interestingly, we have also described and isolated acylated precursors of these two secondary metabolites from the sapwood. Although the constitutions and total synthesis of rubrynolide and rubrenolide have been comprehensively described in literature, little is known about their origin and fate in the context of the heartwood formation process. HPLC was thus used to investigate the repartition of rubrenolide and rubrynolide as well as the acylated precursors in sapwood and heartwood of S. rubra, leading to propose that the biotransformation of the precursors into rubrenolide and rubrynolide occurs at the transition zone between sapwood and heartwood. Finally, 13 trees were sampled from natural populations char acterized by different growth dynamics evaluated through dendrometric parameters, tree architecture description and bark desquamation. Our aim was to study the influence of life history traits on S. rubra heartwood formation from a chemical quantitative and qualitative (LC MS analysis) point of view. We observed significant variations concerning sapwood and heartwood extraction yields depending on the trees, as well as a noticeable variability of the heartwood chemical signature.

title: Durabilite naturelle et couleur des bois de Guyane mesure, variabilite, determinisme chimique applications a Dicorynia guianensis (Angelique) Sextonia rubra (Grignon) Eperua falcata (Wapa) et Eperua grandiflora (Wapa courbaril)
abstract: Il existe une grande variabilite de la resistance des bois aux agents de degradation chez les especes tropicales, qu'il faut maitriser pour augmenter leur potentiel d'utilisation, notamment en Guyane. La these aborde deux problematiques: comment caracteriser les structures de la variabilite intra specifique (inter et intra arbre) de la resistance aux champignons basidiomycetes chez des especes durables et surtout tres variables? Quel est le role des differentes familles chimiques d'extraits dans la durabilite naturelle en comparant des especes botaniquement proches (Eperua falcata et Eperua grandiflora) tres durable d'une part, durable et variable d'autre part. La durabilite naturelle a ete etudiee au travers de differents types d'essais. Elle est peu influencee par la hauteur de prelevement, mais elle diminue du duramen externe vers le duramen interne. Il existe une correlation significative mais peu etroite entre la couleur du bois et sa durabilite naturelle. La resistance de l'Angelique est liee au parametre <a* (axe rouge vert du systeme CIELAB) De meme pour le Wapa courbaril, les arbres presentant les valeurs de <a* les plus elevees sont les plus resistants. Enfin, pour ce qui concerne determinisme chimique de la durabilite naturelle, les essais realises en conditions in vivo ont montre que seuls les composes diterpenoiques issus d' Eperua falcata presentent une activite antifongique. Tandis que les composes polyphenoliques, participent activement au mecanisme de la durabilite naturelle pour les deux especes de Wapa. Les resultats des analyses chimiques expliquent en partie les structures de variabilite observees pour la durabilite et la couleur d'Eperua grandiflora. (Resume d'auteur)

title: Genetic variation for growth, morphological, and physiological traits in a wild population of the Neotropical shadetolerant rainforest tree Sextonia rubra (Mez) van der Werff (Lauraceae)
abstract: Quantitative genetic diversity is a fundamental component of the interaction between natural populations and their environment. In breeding programmes, quantitative genetic studies on tropical trees have so far focused on fast growing, light demanding species, but no information exists on shade tolerant, slow growing species. For this study, 27 3 year old open pollinated families of the Neotropical shade tolerant rainforest tree Sextonia rubra were measured in semicontrolled conditions for 20 morphological, growth, and photosynthesis traits; the effect of genetic relatedness, habitat of provenance, and mother tree status on seedling traits was analysed. Nine traits displayed significant genetic effects, while mother tree status and habitat effects were not significant (P 0.05) for an y trait. Estimated heritability varied between 0.14 and 0.28, with growth related traits having the highest values. Additive genetic variation correlated positively with nonheritable variation, suggesting that ecological evolutionary factors increasing or decreasing additive genetic variance may also affect nonheritable variation in the same direction. Our results suggest that quantitative genetic variability should be taken into account in ecological studies on, and in the management of, natural tropical rainforests; further research is needed to investigate genetic x environment interactions, in particular from the point of view of the genetic response of shade tolerant plant species to variations in light availability.

title: The termiticidal activity of Sextonia rubra (Mez) van der Werff (Lauraceae) extract and its active constituent rubrynolide.
abstract: Termites are degradation agents that inflict severe damage on wood. Some long lasting Amazonian trees can resist these insects by producing toxic secondary metabolites. These metabolites could potentially replace synthetic termiticidal products which are becoming more restricted to use.  Sextonia rubra is resistant to termite induced degradation. It has been demonstrated that this species naturally produces an ethyl acetate soluble termiticidal metabolite, rubrynolide, to protect its wood. Assays in the presence of tropical and invasive termites established that both rubrynolide and crude ethyl acetate extract from S. rubra wood can be used as a treatment for the protection of sensitive woods against termites.  Rubrynolide and S. rubra extract are promising candidates for the replacement of synthetic termiticides.

title: Tandem Mass Spectrometry Imaging and in Situ Characterization of Bioactive Wood Metabolites in Amazonian Tree Species Sextonia rubra.
abstract: Driven by a necessity for confident molecular identification at high spatial resolution, a new time of flight secondary ion mass spectrometry (TOF SIMS) tandem mass spectrometry (tandem MS) imaging instrument has been recently developed. In this paper, the superior MS/MS spectrometry and imaging capability of this new tool is shown for natural product study. For the first time, via in situ analysis of the bioactive metabolites rubrynolide and rubrenolide in Amazonian tree species Sextonia rubra (Lauraceae) we were able both to analyze and to image by tandem MS the molecular products of natural biosynthesis. Despite the low abundance of the metabolites in the wood sample(s) efficient MS/MS analysis of these g lactone compounds was achieved, providing high confidence in the identification and localization. In addition, tandem MS imaging minimized the mass interferences and revealed specific localization of these metabolites primarily in the ray parenchyma cells but also in certain oil cells and, further, revealed the presence of previously unidentified g lactone, paving the way for future studies in biosynthesis.

title: A new species of Sextonia Chevreux, 1920 (Crustacea: Amphipoda: Liljeborgiidae) from the Okhotsk Sea.
abstract: A new amphipod species, Sextonia caecus sp. nov. from the shelf of northern Sakhalin Island (Russian Far East) is described. A key to the amphipod species of the genus Sextonia is given.