Structural evolution of nrDNA ITS in Pinaceae and its phylogenetic implications

Nuclear ribosomal DNA (nrDNA) has been considered as an important tool for inferring phylogenetic relationships at many taxonomic levels. In comparison with its fast concerted evolution in angiosperms, nrDNA is symbolized by slow concerted evolution and substantial ITS region length variation in gymnosperms, particularly in Pinaceae. Here we studied structure characteristics, including subrepeat composition, size, GC content and secondary structure, of nrDNA ITS regions of all Pinaceae genera. The results showed that the ITS regions of all taxa studied contained subrepeat units, ranging from 2 to 9 in number, and these units could be divided into two types, longer subrepeat (LSR) without the motif (5'-GGCCACCCTAGTC) and shorter subrepeat (SSR) with the motif. Phylogenetic analyses indicate that the homology of some SSRs still can be recognized, providing important informations for the evolutionary history of nrDNA ITS and phylogeny of Pinaceae. In particular, the adjacent tandem SSRs are not more closely related to one another than they are to remote SSRs in some genera, which may imply that multiple structure variations such as recombination have occurred in the ITS1 region of these groups. This study also found that GC content in the ITS1 region is relevant to its sequence length and subrepeat number, and could provide some phylogenetic information, especially supporting the close relationships among Picea, Pinus, and Cathaya. Moreover, several characteristics of the secondary structure of Pinaceae ITS1 were found as follows: (1) the structure is dominated by several extended hairpins; (2) the configuration complexity is positively correlated with subrepeat number; (3) paired subrepeats often partially overlap at the conserved motif (5'-GGCCACCCTAGTC), and form a long stem, while other subrepeats fold onto itself, leaving part of the conserved motif exposed in hairpin loops.     

Marked Intragenomic Heterogeneity and Geographical Differentiation of nrDNA ITS in <Emphasis Type="BoldItalic">Larix</Emphasis><Emphasis Type="BoldItalic">potaninii</Emphasis> (Pinaceae)

Nuclear ribosomal DNA (nrDNA) of gymnosperms, especially Pinaceae, is characterized by slow concerted evolution and exhibits substantial ITS-region length variation (975–3663 bp), in sharp contrast to the narrow range (565–700 bp) in angiosperms. Here we examined intra- and intergenomic heterogeneity of the nrDNA internal transcribed spacer (ITS) region in four varieties of Larix potaninii, a species from the mountainous areas of western China. Two clones with more than a 100-bp deletion in ITS1 were detected in L. potaninii var. chinensis and L. potaninii var. australis, respectively. The deletion resulted in the loss of most part, including the motif sequence, of subrepeat 1 (SR1). Sequence divergence and phylogenetic analyses showed that some clones would be pseudogenes given their low GC content, high substitution rates, unique positions in the phylogenetic trees, or significant length variation. These clones might represent orphons or paralogues at minor loci resulting from large-scale gene or chromosome reorganization. Some recombinants characterized by chimeric structure and discordant phylogenetic positions in partitioned sequence analyses indicate that unequal crossing-over plays an important role in the process of nrDNA concerted evolution. In addition, some varieties of L. potaninii might have experienced an nrDNA founder effect parallel to their geographical isolation.     

Discovery of Rhizopogon associated with Larix from northeastern Siberia: Insights into host shift of ectomycorrhizal fungi

Rhizopogon (Boletales) is an ectomycorrhizal fungal genus that exhibits a strong specificity to Pinaceae. This strict association occurs almost exclusively with Pinus and Pseudotsuga, while associations with other genera in Pinaceae are inconclusive. Here, we describe Rhizopogon laricinus sp. nov. associated with Larix cajanderi distributed in northeastern Siberia, where forest fires are frequent. We confirmed the host identity by comparing rDNA internal transcribed spacer (ITS) sequences obtained from basidiomata and ectomycorrhizal root tips collected at the same sites. Morphological characteristics and molecular identification revealed that R. laricinus is a new species associated with Larix unequivocally. The molecular phylogeny based on ITS sequences placed this species sister to the subgenus Roseoli, which is specific to Pinus, and not to the Pseudotsuga-specific subgenus Villosuli. Thus, R. laricinus evolution does not correspond to host phylogeny as Larix and Pseudotsuga form a monophyletic clade. Instead, ecological traits of Rhizopogon for adapting to disturbed habitats may have driven the host shift to Larix under high-frequency fire ecosystems.     

Variation in the nrDNA ITS of Pinus Subsection Cembroides: Implications for Molecular Systematic Studies of Pine Species Complexes

The pinyon pines (Pinus subsection Cembroides), distributed in semiarid regions of the western United States and Mexico, include a mixture of relictual and more recently evolved taxa. To investigate relationships among the pinyons, we screened and partially sequenced 3000-bp clones of the nuclear ribosomal DNA internal transcribed spacer (ITS) region for 16 taxa from subsect. Cembroides and nine representatives from four other subsections of subgenus Strobus. Restriction digests of clones reveal within-individual heterogeneity, suggesting that concerted evolution is operating slowly on the ITS in pine species. Two ITS clones were identified as pseudogenes. Tandem subrepeats in the ITS1 form stem loops comparable to those in other genera of Pinaceae and may be promoting recombination between rDNA repeats, resulting in ITS1 chimeras. Within the pinyon clade, phylogenetic structure is present, but different clones from the same (or different) individuals of a species are polyphyletic, indicating that coalescence of ITS copies within individual genomes predates evolutionary divergence in the group. At the level of subsection and above, the ITS region corresponds well with morphological and cpDNA evidence. Except for P. nelsonii, the pinyons are monophyletic, with both subsect. Cembroides and P. nelsonii forming a clade with the foxtail and bristlecone pines (subsect. Balfourianae) of western North America.     

Phylogenetic relationships and biogeographic patterns in North American members of Carex section Acrocystis (Cyperaceae) using nrDNA ITS and ETS sequence data

Carex section Acrocystis currently includes 27 taxa in North America. Recent phylogenetic studies have suggested that the North American and some but not all of the Eurasian species form a clade. Relationships and biogeographic patterns among species in this core-Acrocystis group are explored here using nuclear ribosomal (nrDNA) internal transcribed spacer region (ITS) and nrDNA external transcribed spacer region (ETS) sequence data. While maximum parsimony analysis of the ITS and ETS data provides only a moderately resolved branching structure for species relationships within the core-Acrocystis clade, maximum likelihood analysis provides a more resolved hypothesis of relationships in the section. The core-Acrocystis clade consists of a grade of Eurasian and primarily western North American species, with a well-supported clade of only eastern North American species nested within this grade. ITS and ETS types do not coalesce within many species or species complexes. Possible explanations for the non-coalescent nature of ITS and ETS copies in Acrocystis are explored, including lineage sorting, hybridization, and cryptic species.     

Length Variation of the Nuclear Ribosomal DNA Internal Transcribed Spacer in the Genus Abies,with Reference to Its Systematic Utility in Pinaceae

The internal transcribed spacer (1TS) region (1TS1, ITS2 and 5.8S rDNA) of the nuclear ribosomal DNA (nrDNA) was amplified via PCR in 28 taxa of Abies Mill. The amplified fragments showed length polymorphism among species, with species from Central America and two species from North America having a length of approximately 2 500 base pairs (bp) and the remaining taxa having a length of approximately 1 700 bp based on 100 bp and 1 kb ladder standard markers. The complete sequencing of ITS of Abies bracteata showed that the shorter type is 1 697 bp (1TS1 is 1 296 bp, 5.8S + 1TS2 is 401 bp). For the longer one, the partial rrs1 and complete 5.8S + ITS2 sequencing revealed that thelength of 5.8S + ITS2 is the same as that of the shorter type. The length difference of ITS in Abies is mainly due to the length difference in the ITS1 region, a result similar to the previous findings in other genera of Pinaceae. Variation in ITS length seems well correlated with morphological and geographic characters in Abies, suggesting that the length variation may be a phylogenetically informative character within the genus, long ITS was also found in other genera of Pinaceae in the previous studies. The long length of ITS in the family makes the sequencing of the region and subsequent alignment of sequences among species or genera more difficult than in taxa with short ITS, such as angiosperms. Although the length variation of ITS in the genus Abies is significant, the homogenous of ITS sequence between the longer one and the shorter one is obvious if the insertion in the longer ITS is ignored.     

Nuclear ribosomal DNA internal transcribed spacer 1 (ITS1) in Picea (Pinaceae): sequence divergence and structure

The nrDNA ITS1 of Picea is 2747-3271 bp, the longest known of all plants. We obtained 24 cloned ITS1 sequences from six individuals of Picea glehnii, Picea mariana, Picea orientalis, and Picea rubens. Mean sequence divergence within these individuals (0.018+/-0.009) is more than half that between the species (0.031+/-0.011) and may be maintained against concerted evolution by separation of Picea 18S-26S rDNA repeats on multiple chromosomes. Picea ITS1 contains three subrepeats with a motif (5'-GGCCACCCTAGTC) that is conserved across Pinaceae. Two subrepeats are tandem, remote from the third, and more closely related and significantly more similar to one another than either is to the third subrepeat. This correlation between similarity and proximity may be the result of subrepeat duplication or concerted evolution within rDNA repeats. In inferred secondary structures, subrepeats generally form long hairpins, with a portion of the Pinaceae conserved motif in the terminal loop, and tandem subrepeats pair with one another over most of their length. Coalescence of ITS1 sequences occurs in P. orientalis but not in the other species.     

Molecular phylogenetics of Houstonia (Rubiaceae): descending aneuploidy and breeding system evolution in the radiation of the lineage across North America

Nuclear and chloroplast DNA sequence variation was used to infer evolutionary relationships within and among members of Houstonia (Rubiaceae) and other closely related genera in North America. Sequences from the internal transcribed spacer (ITS) of the nrDNA and a cpDNA intron in the trnL gene were used to reconstruct phylogenetic relationships of 30 species of Houstonia and closely related genera. The data suggest that the North American species of Houstonia are not monophyletic, but belong to the same lineage as Stenaria. The radiation of this lineage has been accompanied by changes in the basic chromosome number of the major clades through descending aneuploidy. This loss of chromosomes was also associated with northward colonization of North America. However, other characters, such as an annual versus perennial habit, heterostylous and homostylous breeding systems, and the evolution of self fertilization, seem to be labile throughout the lineage, originating multiple times throughout the evolutionary history of the lineage.     

Variation in the nrDNA ITS of Pinus subsection Cembroides: implications for molecular systematic studies of pine species complexes.

The pinyon pines (Pinus subsection Cembroides), distributed in semiarid regions of the western United States and Mexico, include a mixture of relictual and more recently evolved taxa. To investigate relationships among the pinyons, we screened and partially sequenced 3000-bp clones of the nuclear ribosomal DNA internal transcribed spacer (ITS) region for 16 taxa from subsect. Cembroides and nine representatives from four other subsections of subgenus Strobus. Restriction digests of clones reveal within-individual heterogeneity, suggesting that concerted evolution is operating slowly on the ITS in pine species. Two ITS clones were identified as pseudogenes. Tandem subrepeats in the ITS1 form stem loops comparable to those in other genera of Pinaceae and may be promoting recombination between rDNA repeats, resulting in ITS1 chimeras. Within the pinyon clade, phylogenetic structure is present, but different clones from the same (or different) individuals of a species are polyphyletic, indicating that coalescence of ITS copies within individual genomes predates evolutionary divergence in the group. At the level of subsection and above, the ITS region corresponds well with morphological and cpDNA evidence. Except for P. nelsonii, the pinyons are monophyletic, with both subsect. Cembroides and P. nelsonii forming a clade with the foxtail and bristlecone pines (subsect. Balfourianae) of western North America.     

长苞铁杉nrDNA内转录间隔区及5.8S的二级结构分析研究

核糖体RNA及相邻区域的二级结构研究,作为一个重要的工具,已在一些分类等级上被应用于系统发育的分析。以长苞铁杉为实验材料,通过克隆、测序,利用最小自由能原理预测nrDNA内转录间隔区及5.8S转录本的二级结构,分析它们的结构特点,探讨假基因化拷贝与功能拷贝结构上的差异。分析结果表明:(1)ITS1区的二级结构主要由几个延展的发夹结构组成,配对的亚重复单位在松科植物特有的保守序列处有部分重叠,未配对的亚重复单位通常能自身折叠,保守序列的部分碱基出现在发夹结构的环中;(2)假基因化拷贝二级结构的自由能比正常拷贝高;(3)与正常拷贝的二级结构相比,假基因化拷贝在进化速率很低的5.8S功能区发生较大的变异,且在5.8 S末端没有和26 S连接配对。     

Comparative anatomy of resin ducts of the Pinaceae

 Resin ducts are common in the Pinaceae. The comparative anatomy of stems and leaves of 50 species and two varieties from ten genera has been investigated. The structure and distribution of resin ducts differ among genera. Resin ducts occur in foliage leaves of ten genera of Pinaceae. Cortical resin ducts are absent in the stems of Pseudolarix and Larix. Resin ducts only occur in the secondary xylem of stems of Pinus, Picea, Cathaya, Larix, Pseudotsuga and some Keteleeria species. All of the epithelial and sheath cells are alive and thin-walled in the resin ducts of stem cortex and mesophyll. Except for Pinus the epithelial cells of resin ducts in the secondary xylem of stems have thick, lignified walls. Comparative study shows there are obvious differences in the resin ducts of different genera; apparent differences do not exist, however, in the resin ducts of different species of the same genus. According to the structure and distribution of the resin ducts in ten genera of Pinaceae, a synoptical arrangement of the genera is given and generic relationships of the Pinaceae are discussed. Received: 12 September 1995 / Accepted: 14 March 1996     

Comparisons of phylogenetic hypotheses among different data sets in dwarf dandelions (Krigia,Asteraceae): Additional information from internal transcribed spacer sequences of nuclear ribosomal DNA

The internal transcribed spacer (ITS) region of the 18 S–25 S nuclear ribosomal DNA repeat was sequenced from 19 populations of the tribeLactuceae, including all species of dwarf dandelion (Krigia) and five outgroup genera. The incidence of length changes and base substitutions was at least two times higher for ITS 1 than ITS 2. Interspecific sequence divergence withinKrigia averaged 9.62% (1.61%–15.19%) and 4.26% (0%–6.64%) in ITS 1 and ITS 2, respectively. Intergeneric sequence divergence ranged from 15.6% to 44.5% in ITS 1 and from 8.0% to 28.6% in ITS 2. High sequence divergence and homoplasy among genera of tribeLactuceae suggest that the phylogenetic utility of ITS sequence data is limited to interspecific studies or comparisons among closely related genera. Trees generated from ITS sequences are essentially identical to those from restriction site comparisons of the entire nuclear ribosomal (nr) DNA region. The degree of tree resolution differed depending on how gaps were treated in phylogenetic analyses. The ITS trees were congruent with the chloroplast DNA and morphological phylogenies in three major ways: 1) the sister group relationship betweenKrigia andPyrrhopappus; 2) the recognition of two monophyletic sections,Krigia andCymbia, in genusKrigia; and 3) the monophyly of theK. occidentalis-K. cespitosa clade in sect.Cymbia. However, the two nrDNA-based trees are not congruent with morphology/chloroplast DNA-based trees for the interspecific relationships in sect.Krigia. An average of 22.5% incongruence was observed among fourKrigia data sets. The relatively high degree of incongruence among data sets is due primarily to conflict between trees based on nrDNA and morphological/cpDNA data. The incongruence is probably due to the concerted evolution of nrDNA repeating units. The results fromKrigia and theLactuceae suggest that nrDNA data may have limited utility in phylogenetic studies of plants, especially in groups which exhibit high levels of sequence divergence. Our combined phylogenetic analysis as a total evidence shows the least conflict to each of the individual data sets.     

Russula velenovskyi new to Japan,with phylogenetic implications of Russula species between Japanese subalpine forests and Northern Europe

To compare morphological characters and phylogenetic placement between Japanese and European Russula, 32 specimens of 12 species were collected from Japanese subalpine forests and Northern Europe. Several sequences of nrDNA ITS region (ITS) of these Russula species were obtained. High homological similarities were shown between ITS sequences of several Russula samples collected from Japanese subalpine forests, Europe and North America. These facts show distribution of the same Russula species among these areas. From morphological observations and phylogenetic analyses, two same Russula species, R. velenovskyi, and R. decolorans are found in Japan, Europe and North America. Of these, R. velenovskyi collected from Mt. Fuji, Mt. Nyukasa and Mt. Tateshina in mountainous area of central Honshu is reported as a new Japanese record.     

Morphological evolution and ecological diversification of the forest-dwelling poppies (Papaveraceae: Chelidonioideae) as deduced from a molecular phylogeny of the ITS region

Sequences of the ITS region of nrDNA were analyzed for the seven genera of Papaveraceae subf. Chelidonioideae s.str. Three major clades can be recognized. These are 1.Chelidonium/Hylomecon/Stylophorum, 2.Eomecon/Sanguinaria, and 3.Bocconia/Macleaya. The monophyly of genera in the first of these three clades is doubtful, and clades two and three are sister to each other. Use of the ITS phylogeny of the subfamily to trace its morphological and ecological evolution shows that morphological change is concentrated in theBocconia/Macleaya clade, and probably related to the evolution of wind-pollination from insect-pollination in these two genera after habitat shift.     

Phylogenetic diversity of true morels (Morchella), the main edible non-timber product from native Patagonian forests of Argentina

Morchella species are edible fungi in high demand and therefore command high prices in world markets. Phenotypic-based identification at the species-level remains inadequate because of their complex life cycles, minor differences and plasticity of morphological characteristics between species, and the lack of agreement between scientific and common names. In Patagonia–Argentina, morels are associated with native forests of Austrocedrus chilensis (Cordilleran or Chilean cypress) and Nothofagus antarctica (ñire) and several exotic conifers that were introduced from western North America. Little is known about their taxonomy and phylogenetic relationships with other species in the genus. This work focused on the identification of collections of Morchella from Patagonia and their phylogenetic relationships with other species from the Northern Hemisphere. The comparison was made by analysis of DNA sequences obtained from four loci: the nuclear ribosomal internal transcribed spacer region (ITS) and the partial RNA polymerase I gene (RPB1) for the complete collection; and ITS, RPB1, RNA polymerase II gene (RPB2), and translation elongation factor (EF1-α) for the species-rich Elata Subclade. Analyses of individual and combined data sets revealed that Patagonian morels belong to the Elata Clade and comprised three strongly supported species-level lineages from both Patagonian native forest, and exotic trees introduced from western North America. One lineage was identified as Morchella frustrata phylogenetic species Mel-2, which is known from the USA and Canada. The second lineage, which appeared to be ‘fire-adapted’, was identified as Morchella septimelata phylogenetic species (Mel-7), which is also known from the USA. This species was collected from burned native forests mainly composed of A. chilensis and N. antarctica but also Pseudotsuga menziesii (Mirb.) Blanco, which is native to western North America. The phylogenetic analyses suggested that the third species from Patagonia was nested within the species-rich Elata Subclade and represents a new species-level lineage (informally designated Mel-37) within Elata Clade. The present collections from Patagonia constitute the southernmost latitude from which Morchella has been reported to date. The identification of two Argentine morels as North American taxa is therefore a remarkable biogeographic pattern. In view of the hypothesis that the Elata Clade originated in western North America, we speculate that at least two of the lineages colonized South America from North America via long distance dispersal, migration or, more likely, they were introduced with the exotic tree species that they were collected near.     

The complete external transcribed spacer of 18S-26S rDNA: amplification and phylogenetic utility at low taxonomic levels in asteraceae and closely allied families

For molecular phylogenetic reconstruction of some intrageneric groups of plants, a DNA region is needed that evolves more rapidly than the internal transcribed spacer (ITS) of the 18S-26S nuclear ribosomal DNA (nrDNA) repeat. If the region identified is nuclear, it would also be desirable for it to undergo rapid concerted evolution to eliminate problems with coalescence. The external transcribed spacer (ETS) of the nrDNA repeat has shown promise for intrageneric phylogenetic reconstruction, but only the 3' end of the region has been utilized for phylogenetic reconstruction and "universal" primers for PCR amplification have been elusive. We present a method for reliably amplifying and sequencing the entire ETS throughout Asteraceae and some closely allied families. We also show that the ETS is more variable and phylogenetically informative than the ITS in three disparate genera of Asteraceae-Argyranthemum (tribe Anthemideae), Asteriscus (tribe Inuleae), and Helianthus (tribe Heliantheae). The full ETS was amplified using a primer (ETS1f) within the intergenic spacer in combination with a primer (18S-2L) in the 5' end of the highly conserved 18S gene. ETS1f was designed to correspond to a highly conserved region found in Helianthus and Crepis, which are in separate subfamilies of Asteraceae. ETS1f/18S-2L primed in all of the tribes of Asteraceae as well as exemplar taxa from Campanulaceae, Goodeniaceae, and Calyceraceae. For both Argyranthemum and Asteriscus, we were able to directly sequence the ETS PCR products when a single band was produced. When multiple bands were produced, we gel-purified and occasionally cloned the band of interest before sequencing. Although PCR produced single bands for Helianthus species, it was necessary to clone Helianthus amplifications prior to sequencing due to multiple intragenomic ETS repeat types. Alignment of ETS sequences for Argyranthemum and Asteriscus was straightforward and unambiguous despite some subrepeat structure in the 5' end. For Helianthus, different numbers of large tandem subrepeats in different species required analysis of the orthology of the subrepeats prior to alignment. In all three genera, the ETS provided more informative variation for phylogenetic reconstruction and allowed better resolution of relationships than the ITS. Although cloned sequences from Helianthus differed, intragenomic clones consistently formed clades. This result indicated that concerted evolution was proceeding rapidly enough in ETS that species-specific phylogenetic signal was retained. It should be now be possible to use the entire ETS for phylogenetic reconstruction of recently diverged lineages in Asteraceae and at least three other families (approximately 26,000 species or about 8% of all angiosperms).     

Biogeographical and evolutionary insights onErigeron and allies (Asteraceae) from ITS sequence data

Complex geographical distribution patterns and agamospermy have united to obscure systematic relationships in the genusErigeron (400+ species). Sequence data were analyzed from the internal transcribed spacer region of nrDNA (ITS) and 5.8S cistron for 77 taxa including 63Erigeron species. Results support the North American origin ofErigeron and document thatAphanostephus, Conyza, and three small genera restricted to South America (Apopyros, Hysterionica, Neja) are all derived from withinErigeron. Phylogenetic data indicate that agamospermy has arisen at least three times inErigeron and that autogamy has evolved independently inConyza and inE. sect.Trimorpha.     

Evolution of Lycopodiaceae Inferred from Spacer Sequencing of Chloroplast rRNA Genes

Nucleotide sequences of a chloroplast rDNA region including 8 bp from the 3" end of 23S rDNA–ITS2–4.5S rDNA–ITS3–5S rDNA–ITS4 (approximately 800 bp) were determined in 25 species of Lycopodiaceae and two species of the genus Isoetes. The rate of molecular evolution of spacers significantly varied in different Lycopsida taxa. A phylogenetic analysis by the neighbor-joining (NJ) method revealed that the family Lycopodiaceae is monophyletic. The topology of phylogenetic trees suggests the isolation of four or probably five genera in family Lycopodiaceae. For these genera, synapomorphic indels were detected. The obtained data were compared with the results of phylogenetic analysis of Lycopsida with regard to other sequences. The relationships of taxa within the family Lycopodiaceae is discussed.     

Phylogenetic relationship of China Dendrobium species based on the sequence of the internal transcribed spacer of ribosomal DNA

The genetic relationship of 36 Dendrobium species in China was determined based on sequence analysis of the internal transcribed spacer (ITS) region of ribosomal DNA. Aligned sequences of the complete ITS region obtained from the 36 Dendrobium species and 2 outgroup species (Epigeneium amplum and Epigeneium nakaharaei) by using PCR amplification and direct DNA sequencing. The nrDNA ITS1 of Dendrobium was 225–234 bp and ITS2 was 239–248 bp. Phylogenetic tree was constructed, and seven main clusters were generated among the 36 Dendrobium species. From the results, D. moulmeinense was not grouped in the classification of Dendrobium and E. amplum and E. nakaharaei were shown to be divergent from Dendrobium species. The phylogenetic relationships revealed by ITS DNA analysis partially supported previously published morphological data.     

Chemotaxonomic differentiation of conifer families and genera based on the seed oil fatty acid compositions: multivariate analyses

 The fatty acid compositions of seed oils from 34 conifer species, mainly Pinaceae and secondarily Cupressaceae, have been determined by gas-liquid chromatography of the methyl esters. As noted in earlier studies, these oils were characterized by the presence of several Δ5-olefinic acids, i.e., 5,9-18:2, 5,9,12-18:3, 5,9,12,15-18:4, 5,11-20:2, 5,11,14-20:3, and 5,11,14,17-20:4 acids, in addition to the more common saturated, oleic, linoleic and α-linolenic acids. Based on these fatty acid compositions, and on those established in earlier systematic studies (totalling 82 species), we established a chemotaxonomic grouping of the main conifer families, i.e., of the Pinaceae, Taxodiaceae, Cupressaceae, and Taxaceae. This was achieved using multivariate analyses (principal component analysis and discriminant analysis). The fatty acids that discriminate best in this classification are the 5,11,14,17-20:4, 9,12,15-18:3 and 5,9,12-18:3 acids. Moreover, it was possible to differentiate between several genera of the Pinaceae: Pinus (including Tsuga and Pseudotsuga), Abies, Cedrus, and Picea plus Larix, represented quite distinct groups. Other fatty acids such as oleic, linoleic, and 5,9-18:2 acids were also important for this purpose. The fatty acid compositions, and particularly the Δ5-olefinic acid contents of conifer seed oils, may thus be applied to the chemosystematic distinction among conifer families as well as genera of the Pinaceae. Received: 3 January 1997 / Accepted: 17 April 1997