Characterisation of the Xylem of 352 Conifers L
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Invest Agrar: Sist Recur For (2004) 13(3), 452-478 Characterisation of the xylem of 352 conifers L. García Esteban1*, P. de Palacios de Palacios1, A. Guindeo Casasús1 and F. García Fernández2 1 Universidad Politécnica de Madrid. Cátedra de Tecnología de la Madera. ETS Ingenieros de Montes. Ciudad Universitaria. 28040 Madrid. Spain 2 Asociación de Investigación Técnica de las Industrias de Madera y Corcho. C/ Flora, 3. 28013 Madrid. Spain Abstract Following the traditional methods of preparation and description of wood at microscopy level, 352 descriptions of the woods of conifers were made. For the characterisation of each wood a multiple entry key was prepared, with a total of 81 features divided into four groups: tracheids with 29 features, axial parenchyma with 8, wood rays with 37 and resin canals with 7. Key words: anatomy, wood, identification. Resumen Caracterización del xilema de 352 coníferas Siguiendo los métodos tradicionales de preparación y descripción de la madera a nivel microscópico, se han reali- zado 352 descripciones de maderas de coníferas. Para la caracterización de cada madera se ha elaborado una clave de múltiple entrada con un total de 81 caracteres dividida en cuatro grupos: traqueidas con 29 caracteres, parénquima axial 8, radios leñosos 37 y canales resiníferos 7. Palabras clave: anatomía, madera, identificación. Introduction measurements and only uses counting for the number of epithelial cells in the resin canals and the number The uniformity of the xylem of conifers places this of pits per cross field. The last group, containing three vegetal group among those that present most difficulties features, is reserved for the density and hardness of when it comes to making an identification. When the wood. undertaking identification of the wood of conifers, the After this contribution, there have been other first obstacle to overcome is delimiting which large multiple entry keys, which in addition to including the group the wood belongs to, e.g. with or without canals, description of features, also include a data base with with or without ray tracheids, etc. the descriptions of the wood of conifers based on the The tool that best responds to this initial placement particular key (LaPasha, 1986; García Esteban et al., is without a doubt the multiple entry key. Philipps 2002; Heiss, 2003). (1948), proposed the first list of features with which In a manner parallel, or even subsequent to the first any conifer wood could be characterised using a key placement, dichotomic keys provide a fundamental tool of this type. He based it on 36 features divided into for the process of identification, either in terms of 6 groups, bringing about a radical change in the families, genera, species of a specific geographical process of identification. Although the simplicity of region, and so on. (e.g. Castellarnau, 1880; Jacquiot, the features chosen made it difficult for users to 1955; Greguss, 1955; Peraza, 1964; García Esteban and identify conifers at the species level, its use has Guindeo, 1988; Schweingruber, 1990). allowed, and continues to allow, the placement of the Finally, specific studies of comparative anatomy and wood within the large groups of conifers. It lacks the separation of species of conifers anatomically very close to each other can be used to determine species. * Corresponding author: [email protected] (e.g. Castellarnau, 1883; Visscher and Jagels, 2003; Received: 17-03-04; Accepted: 01-06-04. Wiedenhoeft et al., 2003). Xylem of 352 conifers 453 The recent publication of IAWA Committee (2004), AT3. Axial tracheids of circular section. The with its list of the features of the woods of conifers, transverse section of the axial tracheids defines a will unify the dispersion of identification keys and will section with a circular shape. Non-excluding feature. be a compulsory reference document with which all AT4. Axial tracheids of polygonal section. The keys will have to concur. transverse section of the axial tracheids defines a The present work, in addition to characterising the section with a polygonal shape. It must not be xylem of 352 woods of conifers, proposes an open considered an excluding feature in terms of genus but identification key of 81 features. it should be considered so in terms of species, as some genera such as Araucaria have both types of section. AT5. Resinous axial tracheids. IAWA 48. These are Materials and Methods normal tracheids but they have resin inside. Their access is through the cross-field pits. In microscopic slides they The materials used in this study came from samples appear with a reddish or black colour in the cross section. from our own wood collection and from the collections of This feature has been included in the key in spite of the the following centres: Jodrell Kew Botanic Garden; fact that it has no analytical value because of its constant Instituto Nacional de Investigación y Tecnología Agraria presence in genera such as Araucaria and Agathis. y Alimentaria Madrid. Spain; U.S. Forest Products AT6. Intercellular spaces present. IAWA 53. This Laboratory, Madison Wisconsin. USA; Wood Research is the space between two or more axial tracheids. It is Institute Kyoto University, Kyoto. Japan; National a feature associated to circular section tracheids, although Museum of Natural History. Smithsonian Institution. it is also present in polygonal section tracheids Botany Department, Washington. USA; Landbouw- (Juniperus, Tetraclinis, etc). At least 12 genera present universiteit. Department of Forestry, Wagenigen. Holland; abundant intercellular spaces. Excluding feature. Papua New Guinea Forest Research Institute, Papua New AT7. Spiral thickenings present in all the axial Guinea; Universiteit Utrecht. Department of Plant Ecology tracheids. IAWA 62. This is a very important analytical and Evolutionary Biology, Utrecht. Holland. feature as its origin is genetic. It is a thickening The preparation of the microscopic slides followed produced in the secondary wall of the tracheids which the traditional methods of softening, cutting, staining develops in the form of a spiral. All the genera of the and mounting. Taxaceae family (Taxus, Torreya, Amentotaxus and The descriptions were made according to the Nothotaxus), with the exception of the Austrotaxus following multiple entry key. For features that correspond genus, have spiral thickenings. Other genera such as to the IAWA Committee (2004), a code has been Pseudotsuga, Cephalotaxus, Acmopyle and Austrocedrus included below. also have them. Excluding feature. AT8. Spiral thickenings present, but not in all the Axial tracheids axial tracheids. IAWA 63-64. Some genera such as Larix or Pseudotsuga do not present these thickenings AT1. Well-defined growth rings. IAWA 40. The in all the tracheids, but thickenings may appear in a structural differences between earlywood cells, which random manner in the whole ring or be confined to show thin walls and wide lumen, and latewood either earlywood or latewood. Excluding feature. cells, of thick walls and small lumen, establish the AT9. Bordered pits present on the tangential walls differentiation between the growth rings. This is a of the axial tracheids. This is an important analytical common feature in Araucariaceae, Cupressaceae and feature, as some species do not have it. Its presence Podocarpaceae. It is not an excluding feature as its indicates a greater degree of evolution of the species. presence only determines the location of the species in a Excluding feature. zone with marked periods of vegetative activity and rest. AT10. Uniseriate bordered pits on the radial walls AT2. Slightly-defined growth rings. IAWA 41. The of the axial tracheids. IAWA 44. The pits are arranged similarity between earlywood and latewood cells on the radial walls of the tracheids, in both earlywood makes differentiation between growth rings very and latewood, in rows of one series. Excluding feature. difficult. As with the previous feature, its presence AT11. Biseriate bordered pits on the radial walls conforms to the location of the species in sites where of the axial tracheids. IAWA 45. The pits are located in the vegetative period is not interrupted abruptly. pairs on the radial walls along the tracheids, normally in 454 L. García Esteban et al. / Invest Agrar: Sist Recur For (2004) 13(3), 452-478 earlywood, and may also be present simultaneously in the radial wall of the axial tracheids. It is a thickening uniseriate rows on the tracheids of both earlywood and of the secondary wall associated with the bordered pits, latewood. This feature only exists in tracheids of large located on the external face of the pit chamber. lumen in earlywood, and is not found in the wood near Excluding feature. the pith. It is a useful feature for differentiating the AT19. Bars of Sanio. Unlike the callitroid thickening, sapwood of alerce from that of picea. Excluding feature. the bars of Sanio or crassulae are thickenings in the AT12. Triseriate or multiseriate bordered pits on primary wall and the middle lamella. They are the radial walls of the axial tracheids. IAWA 45. These associated with the bordered pits and they must be only appear on the radial face of the axial tracheids observed on the radial wall of the axial tracheids. They and are normally found in the tracheids of earlywood, have the appearance of bars surrounding the pits. They while the pits form uniseriate rows simultaneously on are located on both uniseriate and biseriate pits, latewood. For some genera this feature has a fundamental although they are more numerous on biseriate pits. analytical value as it is always present, as is the case They are considered a differentiating analytical feature of the Araucaria, Agathis, Taxodium and Sequoia of the genera which have them. genera, among others. Excluding feature. AT20. Trabecula. Structure with the shape of a AT13. Polygonal bordered pits on the radial walls cylindrical bar crossing the lumen of the tracheids from of the axial tracheids. IAWA 47.