Shawn Kenaley | Cornell University (original) (raw)

Papers by Shawn Kenaley

AGU Fall Meeting Abstracts, Dec 1, 2018

AGU Fall Meeting Abstracts, Dec 1, 2019

Roughened canker caused by Botryosphaeria dothidea on Salix eriocephala. Note: the location — ter... more Roughened canker caused by Botryosphaeria dothidea on Salix eriocephala. Note: the location — terminated branch or bud — and the small groups of black stromata. Canker caused by a Botryosphaeria spp. on Salix (Tully, NY). Willows (Salix spp.) are susceptible to several canker diseases that cause blighting of new shoots and girdling of branches and stems. Cankers initiated by a complex of fungi in the genus Botryosphaeria appear to be the most common in short rotation willow plantations of NY State. These fungi are opportunistic pathogens that incite cankers on branches, stems, and/or twigs as well as cause dieback on susceptible willows. Infection often occurs when willow shrubs are predisposed by environmental stressors (e.g., drought and frost damage), insect defoliation, or wounding.

Willow rust (Melampsora spp.): Uredinia and exposed urediniospores on the lower-leaf surface of S... more Willow rust (Melampsora spp.): Uredinia and exposed urediniospores on the lower-leaf surface of Salix ericocephala (Tully, NY; August, 2009) Willow rust (Melampsora spp.) life cycle Leaf rust of willow (Salix spp.), a widespread and common disease of native and cultivated Salix, can severely defoliate shrubs and/or trees with up to 100 percent of leaves shed six or more weeks prior to normal autumn leaf drop. The disease is caused by fungi belonging to the genus Melampsora (Uredinales: Melampsoraceae) and is considered the most serious disease affecting intensively managed willow plantations in North America and Europe. Willow-infecting Melampsora species have complex life histories during which they alternate between willow and an unrelated host to complete their life cycles. Two species, M. epitea and M. paradoxa, exist in N. America. Important alternate hosts of M. epitea in New York State are balsam fir, white fir, and saxifrages. Melampsora paradoxa infects willow as well as European larch, western larch and tamarack. Yellow to orange pustules (uredinia) appear on the underside of willow leaves beginning in late spring and continue throughout the summer. These pustules eventually rupture the epidermis to release large numbers of golden-yellow spores (urediniospores). This stage of the rust life cycle, referred to as the "repeating phase", serves to continuously reinfect the initial Salix host as well as to spread the rust to surrounding willows. In mid-autumn, uredinia change to orange-brown or dark brown telia that overwinter on fallen willow leaves and release fragile basidiospores the following spring. Basidiospores are wind-disseminated and infect the foliage of the alternate host (e.g., balsam fir). Spermagonia appear shortly after infection in the late spring and are followed by aecia containing yellow to orange aeciospores, which are dispersed by wind and infect the current growth of willow. Within two-weeks,

Journal of the Botanical Research Institute of Texas, Aug 1, 2013

Fungal Biology, 2015

Sirex noctilio is a woodwasp of Eurasian origin that was inadvertently introduced to the southern... more Sirex noctilio is a woodwasp of Eurasian origin that was inadvertently introduced to the southern hemisphere in the 1900s and to North America over a decade ago. Its larvae bore in Pinus spp. and can cause significant mortality in pine plantations. S noctilio is associated with a symbiotic white rot fungus, Amylostereum areolatum, which females inject into trees when they oviposit and which is required for survival of developing larvae. We compared the genetic diversity of A. areolatum isolated from S. noctilio and other woodwasps collected from Europe and from northeastern North America to determine the origin of introduction(s) into the United States. Multilocus genotyping of nuclear ribosomal regions and protein coding genes revealed two widespread multilocus genotypes (MLGs) among the European samples, one of which is present in the US. The other two MLGs associated with S. noctilio in the US represented unique haplotypes. These latter two haplotypes were likely from unrepresented source populations, and together with the introduced widespread haplotype reveal multiple A. areolatum MLGs introduced by S. noctilio and indicate

Madroño, 2015

Abstract The classification of the dwarf mistletoes comprising the Arceuthobium campylopodum-occi... more Abstract The classification of the dwarf mistletoes comprising the Arceuthobium campylopodum-occidentale complex continues to be one of the most difficult taxonomic problems associated with this important group of parasitic flowering plants. The complex consists of four taxa: A. campylopodum Engelmann, A. occidentale Engelmann, A. littorum Hawksworth, Wiens & Nickrent, and A. siskiyouense Hawksworth, Wiens & Nickrent; all of which are morphologically similar, flower and disperse seed in the fall, and parasitize hard pines. We collected morphological measurements for these four taxa from throughout their geographic ranges and used non-parametric and multivariate statistical analyses to compare morphological differences among them. Our analyses demonstrated that male plants of A. littorum and A. siskiyouense can be delimited morphologically; therefore, we recommend that both taxa continue to be recognized as species. Although, our results indicated that A. occidentale is very similar morphologically to A. campylopodum, it can be distinguished from the latter species using morphological characters, particularly for female plants. Furthermore, because A. occidentale flowers and disperses seed nearly one month later than A. campylopodum, we recommend it continue to be treated at the species level pending additional study. Comparative morphological and phenological differences between and among the species studied herein are summarized and can be used for field/laboratory diagnosis of these taxa.

Rust fungi in the genus Melampsora (Pucciniales) are the most important pathogens of shrub willow... more Rust fungi in the genus Melampsora (Pucciniales) are the most important pathogens of shrub willows (Salix spp.) cultivated for biomass in New York State and temperate regions worldwide. The taxonomy and species identification of these fungi historically have been problematic as they are morphologically indistinguishable on willow and often have complex life histories. Melampsora of Salix in North America, therefore, have been circumscribed to the collective species Melampsora epitea Thüm. and further delineated to formae speciales by aecial host. Ribosomal DNA (rDNA) data was obtained from 75 collections/isolates of Melampsora in NY State affecting either native and cultivated Salix spp. or suspected alternate hosts. Maximum likelihood (ML), maximum parsimony (MP), and Bayesian (BI) analyses were conducted on three data partitions (individual and concatenated): complete internal transcribed spacer (ITS) and partial large subunit (LSU) rDNA sequences for all collections. Analyses of the ITS and concatenated ITS-LSU sequences revealed that Melampsora on native and cultivated willows in NY State consisted of three phylogenetically delineable taxa (phylotaxa); monophyly for each phylotaxon was strongly supported by ML, MP, and BI credibility values. Phylotaxa were also delimited phylogenetically by aecial host: Alpine currant (Ribes alpinum), eastern larch (Larix laricina), or balsam fir (Abies balsamea).

Western Journal of Applied Forestry, 2008

Ponderosa pine (Pinus ponderosa Douglas ex C. Lawson var. scopulorum Engelm.) mortality was evalu... more Ponderosa pine (Pinus ponderosa Douglas ex C. Lawson var. scopulorum Engelm.) mortality was evaluated from a 2002 bark beetle outbreak in areas infested with southwestern dwarf mistletoe (Arceuthobium vaginatum [Willd.] Presl subsp. cryptopodum [Engelm.] Hawksw. & Wiens) in a total of nine study sites in northern Arizona. Ponderosa pine mortality attributable to bark beetles (Ips and Dendroctonus spp., Scolytidae) was systematically sampled, and stand attributes, such as basal area, tree density, dwarf mistletoe severity, and site indices were recorded. Ponderosa pine mortality was predominately attributed to Ips spp. Although the prolonged drought likely was the inciting factor responsible for the Ips spp. outbreak, results suggested a strong relationship between ponderosa pine mortality and the interaction between crown class and dwarf mistletoe rating class. Ponderosa pines severely infected with dwarf mistletoe and in the intermediate crown class are at the greatest risk of Ips ...

Willow scab, caused by Venturia saliciperda, on Salix eriocephala (Tully, NY). Note the olive, ve... more Willow scab, caused by Venturia saliciperda, on Salix eriocephala (Tully, NY). Note the olive, velvety-mass of spores (conidia) on the underside of the leaves. Leaf-and shoot-blight of Salix eriocephala caused the willow scab fungus, Venturia saliciperda (Tully, NY). Willow scab, caused by the fungus Venturia saliciperda (Pleosporales: Venturiaceae), affects Salix species throughout Europe and the eastern United States. Common relatives of the willow scab fungus (i.e., Venturia spp.) cause leaf and shoot blight diseases on woody-plants including apple (Malus spp.), pear (Pyrus spp.), or poplar (Populus spp.). However, unlike its relatives, the willow scab fungus frequently interacts with an unrelated pathogen, the black canker fungus (Glomerella miyabeana), to produce a destructive blight of willow. Both fungi, V. saliciperda and G. miyabeana, likely were introduced from Europe by way of Asia prior to or shortly after the turn of the 20 th century.

Journal of the Botanical Research Institute of Texas, 2019

Journal of the Botanical Research Institute of Texas, 2016

Twig rust, caused by the fungus Melampsora farlowii (Arth.) Davis, is a common disease of eastern... more Twig rust, caused by the fungus Melampsora farlowii (Arth.) Davis, is a common disease of eastern (Tsuga canadensis Carr.) and Carolina (T. caroliniana Engelm.) hemlocks throughout eastern North America. Although not generally a problem in forests, hemlock twig rust can cause considerable damage in commercial tree nurseries, where cultural conditions favor the development of disease. Unlike related Melampsora species. (e.g., the poplar rust fungus – M. medusae), M. farlowii produces only two spore stages – teliospores and basidiospores – and does not alternate between hemlock and a taxonomically unrelated plant. Teliospores in dead twigs and fallen needles germinate in spring, producing basidiospores that are wind-dispersed and infect young cones, needles, and stems of T. canadensis and T. caroliniana.

Journal of the Botanical Research Institute of Texas

There have been four subspecies of hemlock dwarf mistletoe (Arceuthobium tsugense: Viscaceae) des... more There have been four subspecies of hemlock dwarf mistletoe (Arceuthobium tsugense: Viscaceae) described by various investigators of this complex group of parasitic flowering plants: subsp. tsugense, subsp. amabilae, subsp. contortae, and subsp. mertensianae. As suggested by their subspecific epithets, these taxa differ in their host affinities; parasitizing different and the same hosts to varying degrees. Although these taxa also have morphological differences, their classifica-tion has been under debate for many years. Therefore, we compared the morphological characteristics of each subspecies using both univariate and multivariate statistical analyses in order to better assess their differences. Because some investigators have grouped hemlock dwarf mistletoe with western dwarf mistletoe (A. campylopodum), we also compared the subspecies of hemlock dwarf mistletoe with western dwarf mistletoe. Our morphometric analyses demonstrated that all of the subspecies are morphologically dis...

The classification of the dwarf mistletoes (Arceuthobium spp., Viscaceae) commonly parasitizing w... more The classification of the dwarf mistletoes (Arceuthobium spp., Viscaceae) commonly parasitizing western hemlock (Tsuga heterophylla) and western larch (Larix occidentalis) in the northwestern United States and Canada has been one of the more difficult taxonomic problems associated with this important group of parasitic flowering plants. We collected new morphological measurements for the dwarf mistletoes parasitizing these commercially valuable conifers, Arceuthobium tsugense and A. laricis, respectively, from throughout most of their geographic ranges and used non-parametric univariate and multivariate statistical analyses to compare the morphological differences between them. In addition, because some investigators consider these taxa to be conspecific with, or subspecies of A. campylopodum, we included this dwarf mistletoe in our statistical analyses. Our analyses demonstrated that A. tsugense and A. laricis can be reliably segregated from each other, as well as from A. campylopo...

Botany

The taxonomic classification of dwarf mistletoes (Arceuthobium spp., Viscaceae) is complicated du... more The taxonomic classification of dwarf mistletoes (Arceuthobium spp., Viscaceae) is complicated due to their reduced morphology, requiring the integration of not only morphology but also phenology, geography, and host relationships. This has been particularly true for the classification of taxa in subgenus Vaginata, section Campylopoda, series Campylopoda. Most of the species in this group have been recently circumscribed in synonymy with or reduced to subspecies of Arceuthobium campylopodum Engelm; however, we contend they deserve separate species recognition. To address this question, we have conducted morphological analyses of the taxa in ser. Campylopoda using univariate and multivariate statistical analyses. Our results have demonstrated that these taxa can be determined to species using morphological data without consideration of geographic location or host specificity; however, the host specialization and geographic distribution exhibited by these taxa also supports their clas...

Systematic Botany

— Dwarf mistletoes are a lineage of morphologically-reduced stem parasites inhabiting Pinaceae an... more — Dwarf mistletoes are a lineage of morphologically-reduced stem parasites inhabiting Pinaceae and Cupressaceae throughout the northern hemisphere and equatorial East Africa. Though diagnosable by a suite of morphological traits, phylogenetic knowledge of species relationships has been limited to studies employing either comprehensive taxonomic sampling of one or two genes, or more sequence data from a limited number of individuals. We used data from genome skimming to assemble 3kb of the nuclear ribosomal cistron and up to 45kb of the plastome to clarify the phylogenetic root of the genus, monophyly of species, and relationships among infraspecific taxa. Genomic differentiation among terminal taxa was variable; however, we found strong support for reciprocally monophyletic New World and Old World lineages, congruent nrDNA and plastome topologies at the species level and below, and monophyly of most taxonomic sections and species. Plastome gene content was stable across the genus with minimal pseudogenization or loss, as in other hemiparasites, with the notable exception of cemA. These findings form the basis of our re-evaluation of historical biogeographical hypotheses, species- and subspecies-level taxonomy, and plastome evolution in Arceuthobium. More broadly, this work provides a foundation for future clade-focused comparative and biosystematics studies of Arceuthobium.

Journal of the Botanical Research Institute of Texas

Two new subspecies of fir dwarf mistletoe (Arceuthobium abietinum, Viscaceae) are described herei... more Two new subspecies of fir dwarf mistletoe (Arceuthobium abietinum, Viscaceae) are described herein: Arceuthobium abietinum subsp. mathiasenii (Mathiasen’s dwarf mistletoe) and Arceuthobium abietinum subsp. grandae (grand fir dwarf mistletoe). The former dwarf mistletoe—Mathiasen’s dwarf mistletoe—parasitizes Rocky Mountain white fir in Nevada, Utah, and Arizona and Durango fir in northern Mexico; whereas, grand fir dwarf mistletoe parasitizes grand fir as well grand fir × white fir hybrids in California, Oregon and Washington. The recognition of these subspecies and, hence, their classification is based on morphological discontinuities and host range differences when compared to white fir dwarf mistletoe (Arceuthobium abietinum subsp. abietinum), red fir dwarf mistletoe (A. abietinum subsp. magnificae), and Wiens’ dwarf mistletoe (A. abietinum subsp. wiensii). The combined analyses of plant height, third internode length and width, fruit dimensions, staminate spike and petal dimensi...

Plant Disease, Jul 1, 2018

AGU Fall Meeting Abstracts, Dec 1, 2018

AGU Fall Meeting Abstracts, Dec 1, 2019

Roughened canker caused by Botryosphaeria dothidea on Salix eriocephala. Note: the location — ter... more Roughened canker caused by Botryosphaeria dothidea on Salix eriocephala. Note: the location — terminated branch or bud — and the small groups of black stromata. Canker caused by a Botryosphaeria spp. on Salix (Tully, NY). Willows (Salix spp.) are susceptible to several canker diseases that cause blighting of new shoots and girdling of branches and stems. Cankers initiated by a complex of fungi in the genus Botryosphaeria appear to be the most common in short rotation willow plantations of NY State. These fungi are opportunistic pathogens that incite cankers on branches, stems, and/or twigs as well as cause dieback on susceptible willows. Infection often occurs when willow shrubs are predisposed by environmental stressors (e.g., drought and frost damage), insect defoliation, or wounding.

Willow rust (Melampsora spp.): Uredinia and exposed urediniospores on the lower-leaf surface of S... more Willow rust (Melampsora spp.): Uredinia and exposed urediniospores on the lower-leaf surface of Salix ericocephala (Tully, NY; August, 2009) Willow rust (Melampsora spp.) life cycle Leaf rust of willow (Salix spp.), a widespread and common disease of native and cultivated Salix, can severely defoliate shrubs and/or trees with up to 100 percent of leaves shed six or more weeks prior to normal autumn leaf drop. The disease is caused by fungi belonging to the genus Melampsora (Uredinales: Melampsoraceae) and is considered the most serious disease affecting intensively managed willow plantations in North America and Europe. Willow-infecting Melampsora species have complex life histories during which they alternate between willow and an unrelated host to complete their life cycles. Two species, M. epitea and M. paradoxa, exist in N. America. Important alternate hosts of M. epitea in New York State are balsam fir, white fir, and saxifrages. Melampsora paradoxa infects willow as well as European larch, western larch and tamarack. Yellow to orange pustules (uredinia) appear on the underside of willow leaves beginning in late spring and continue throughout the summer. These pustules eventually rupture the epidermis to release large numbers of golden-yellow spores (urediniospores). This stage of the rust life cycle, referred to as the "repeating phase", serves to continuously reinfect the initial Salix host as well as to spread the rust to surrounding willows. In mid-autumn, uredinia change to orange-brown or dark brown telia that overwinter on fallen willow leaves and release fragile basidiospores the following spring. Basidiospores are wind-disseminated and infect the foliage of the alternate host (e.g., balsam fir). Spermagonia appear shortly after infection in the late spring and are followed by aecia containing yellow to orange aeciospores, which are dispersed by wind and infect the current growth of willow. Within two-weeks,

Journal of the Botanical Research Institute of Texas, Aug 1, 2013

Fungal Biology, 2015

Sirex noctilio is a woodwasp of Eurasian origin that was inadvertently introduced to the southern... more Sirex noctilio is a woodwasp of Eurasian origin that was inadvertently introduced to the southern hemisphere in the 1900s and to North America over a decade ago. Its larvae bore in Pinus spp. and can cause significant mortality in pine plantations. S noctilio is associated with a symbiotic white rot fungus, Amylostereum areolatum, which females inject into trees when they oviposit and which is required for survival of developing larvae. We compared the genetic diversity of A. areolatum isolated from S. noctilio and other woodwasps collected from Europe and from northeastern North America to determine the origin of introduction(s) into the United States. Multilocus genotyping of nuclear ribosomal regions and protein coding genes revealed two widespread multilocus genotypes (MLGs) among the European samples, one of which is present in the US. The other two MLGs associated with S. noctilio in the US represented unique haplotypes. These latter two haplotypes were likely from unrepresented source populations, and together with the introduced widespread haplotype reveal multiple A. areolatum MLGs introduced by S. noctilio and indicate

Madroño, 2015

Abstract The classification of the dwarf mistletoes comprising the Arceuthobium campylopodum-occi... more Abstract The classification of the dwarf mistletoes comprising the Arceuthobium campylopodum-occidentale complex continues to be one of the most difficult taxonomic problems associated with this important group of parasitic flowering plants. The complex consists of four taxa: A. campylopodum Engelmann, A. occidentale Engelmann, A. littorum Hawksworth, Wiens & Nickrent, and A. siskiyouense Hawksworth, Wiens & Nickrent; all of which are morphologically similar, flower and disperse seed in the fall, and parasitize hard pines. We collected morphological measurements for these four taxa from throughout their geographic ranges and used non-parametric and multivariate statistical analyses to compare morphological differences among them. Our analyses demonstrated that male plants of A. littorum and A. siskiyouense can be delimited morphologically; therefore, we recommend that both taxa continue to be recognized as species. Although, our results indicated that A. occidentale is very similar morphologically to A. campylopodum, it can be distinguished from the latter species using morphological characters, particularly for female plants. Furthermore, because A. occidentale flowers and disperses seed nearly one month later than A. campylopodum, we recommend it continue to be treated at the species level pending additional study. Comparative morphological and phenological differences between and among the species studied herein are summarized and can be used for field/laboratory diagnosis of these taxa.

Rust fungi in the genus Melampsora (Pucciniales) are the most important pathogens of shrub willow... more Rust fungi in the genus Melampsora (Pucciniales) are the most important pathogens of shrub willows (Salix spp.) cultivated for biomass in New York State and temperate regions worldwide. The taxonomy and species identification of these fungi historically have been problematic as they are morphologically indistinguishable on willow and often have complex life histories. Melampsora of Salix in North America, therefore, have been circumscribed to the collective species Melampsora epitea Thüm. and further delineated to formae speciales by aecial host. Ribosomal DNA (rDNA) data was obtained from 75 collections/isolates of Melampsora in NY State affecting either native and cultivated Salix spp. or suspected alternate hosts. Maximum likelihood (ML), maximum parsimony (MP), and Bayesian (BI) analyses were conducted on three data partitions (individual and concatenated): complete internal transcribed spacer (ITS) and partial large subunit (LSU) rDNA sequences for all collections. Analyses of the ITS and concatenated ITS-LSU sequences revealed that Melampsora on native and cultivated willows in NY State consisted of three phylogenetically delineable taxa (phylotaxa); monophyly for each phylotaxon was strongly supported by ML, MP, and BI credibility values. Phylotaxa were also delimited phylogenetically by aecial host: Alpine currant (Ribes alpinum), eastern larch (Larix laricina), or balsam fir (Abies balsamea).

Western Journal of Applied Forestry, 2008

Ponderosa pine (Pinus ponderosa Douglas ex C. Lawson var. scopulorum Engelm.) mortality was evalu... more Ponderosa pine (Pinus ponderosa Douglas ex C. Lawson var. scopulorum Engelm.) mortality was evaluated from a 2002 bark beetle outbreak in areas infested with southwestern dwarf mistletoe (Arceuthobium vaginatum [Willd.] Presl subsp. cryptopodum [Engelm.] Hawksw. & Wiens) in a total of nine study sites in northern Arizona. Ponderosa pine mortality attributable to bark beetles (Ips and Dendroctonus spp., Scolytidae) was systematically sampled, and stand attributes, such as basal area, tree density, dwarf mistletoe severity, and site indices were recorded. Ponderosa pine mortality was predominately attributed to Ips spp. Although the prolonged drought likely was the inciting factor responsible for the Ips spp. outbreak, results suggested a strong relationship between ponderosa pine mortality and the interaction between crown class and dwarf mistletoe rating class. Ponderosa pines severely infected with dwarf mistletoe and in the intermediate crown class are at the greatest risk of Ips ...

Willow scab, caused by Venturia saliciperda, on Salix eriocephala (Tully, NY). Note the olive, ve... more Willow scab, caused by Venturia saliciperda, on Salix eriocephala (Tully, NY). Note the olive, velvety-mass of spores (conidia) on the underside of the leaves. Leaf-and shoot-blight of Salix eriocephala caused the willow scab fungus, Venturia saliciperda (Tully, NY). Willow scab, caused by the fungus Venturia saliciperda (Pleosporales: Venturiaceae), affects Salix species throughout Europe and the eastern United States. Common relatives of the willow scab fungus (i.e., Venturia spp.) cause leaf and shoot blight diseases on woody-plants including apple (Malus spp.), pear (Pyrus spp.), or poplar (Populus spp.). However, unlike its relatives, the willow scab fungus frequently interacts with an unrelated pathogen, the black canker fungus (Glomerella miyabeana), to produce a destructive blight of willow. Both fungi, V. saliciperda and G. miyabeana, likely were introduced from Europe by way of Asia prior to or shortly after the turn of the 20 th century.

Journal of the Botanical Research Institute of Texas, 2019

Journal of the Botanical Research Institute of Texas, 2016

Twig rust, caused by the fungus Melampsora farlowii (Arth.) Davis, is a common disease of eastern... more Twig rust, caused by the fungus Melampsora farlowii (Arth.) Davis, is a common disease of eastern (Tsuga canadensis Carr.) and Carolina (T. caroliniana Engelm.) hemlocks throughout eastern North America. Although not generally a problem in forests, hemlock twig rust can cause considerable damage in commercial tree nurseries, where cultural conditions favor the development of disease. Unlike related Melampsora species. (e.g., the poplar rust fungus – M. medusae), M. farlowii produces only two spore stages – teliospores and basidiospores – and does not alternate between hemlock and a taxonomically unrelated plant. Teliospores in dead twigs and fallen needles germinate in spring, producing basidiospores that are wind-dispersed and infect young cones, needles, and stems of T. canadensis and T. caroliniana.

Journal of the Botanical Research Institute of Texas

There have been four subspecies of hemlock dwarf mistletoe (Arceuthobium tsugense: Viscaceae) des... more There have been four subspecies of hemlock dwarf mistletoe (Arceuthobium tsugense: Viscaceae) described by various investigators of this complex group of parasitic flowering plants: subsp. tsugense, subsp. amabilae, subsp. contortae, and subsp. mertensianae. As suggested by their subspecific epithets, these taxa differ in their host affinities; parasitizing different and the same hosts to varying degrees. Although these taxa also have morphological differences, their classifica-tion has been under debate for many years. Therefore, we compared the morphological characteristics of each subspecies using both univariate and multivariate statistical analyses in order to better assess their differences. Because some investigators have grouped hemlock dwarf mistletoe with western dwarf mistletoe (A. campylopodum), we also compared the subspecies of hemlock dwarf mistletoe with western dwarf mistletoe. Our morphometric analyses demonstrated that all of the subspecies are morphologically dis...

The classification of the dwarf mistletoes (Arceuthobium spp., Viscaceae) commonly parasitizing w... more The classification of the dwarf mistletoes (Arceuthobium spp., Viscaceae) commonly parasitizing western hemlock (Tsuga heterophylla) and western larch (Larix occidentalis) in the northwestern United States and Canada has been one of the more difficult taxonomic problems associated with this important group of parasitic flowering plants. We collected new morphological measurements for the dwarf mistletoes parasitizing these commercially valuable conifers, Arceuthobium tsugense and A. laricis, respectively, from throughout most of their geographic ranges and used non-parametric univariate and multivariate statistical analyses to compare the morphological differences between them. In addition, because some investigators consider these taxa to be conspecific with, or subspecies of A. campylopodum, we included this dwarf mistletoe in our statistical analyses. Our analyses demonstrated that A. tsugense and A. laricis can be reliably segregated from each other, as well as from A. campylopo...

Botany

The taxonomic classification of dwarf mistletoes (Arceuthobium spp., Viscaceae) is complicated du... more The taxonomic classification of dwarf mistletoes (Arceuthobium spp., Viscaceae) is complicated due to their reduced morphology, requiring the integration of not only morphology but also phenology, geography, and host relationships. This has been particularly true for the classification of taxa in subgenus Vaginata, section Campylopoda, series Campylopoda. Most of the species in this group have been recently circumscribed in synonymy with or reduced to subspecies of Arceuthobium campylopodum Engelm; however, we contend they deserve separate species recognition. To address this question, we have conducted morphological analyses of the taxa in ser. Campylopoda using univariate and multivariate statistical analyses. Our results have demonstrated that these taxa can be determined to species using morphological data without consideration of geographic location or host specificity; however, the host specialization and geographic distribution exhibited by these taxa also supports their clas...

Systematic Botany

— Dwarf mistletoes are a lineage of morphologically-reduced stem parasites inhabiting Pinaceae an... more — Dwarf mistletoes are a lineage of morphologically-reduced stem parasites inhabiting Pinaceae and Cupressaceae throughout the northern hemisphere and equatorial East Africa. Though diagnosable by a suite of morphological traits, phylogenetic knowledge of species relationships has been limited to studies employing either comprehensive taxonomic sampling of one or two genes, or more sequence data from a limited number of individuals. We used data from genome skimming to assemble 3kb of the nuclear ribosomal cistron and up to 45kb of the plastome to clarify the phylogenetic root of the genus, monophyly of species, and relationships among infraspecific taxa. Genomic differentiation among terminal taxa was variable; however, we found strong support for reciprocally monophyletic New World and Old World lineages, congruent nrDNA and plastome topologies at the species level and below, and monophyly of most taxonomic sections and species. Plastome gene content was stable across the genus with minimal pseudogenization or loss, as in other hemiparasites, with the notable exception of cemA. These findings form the basis of our re-evaluation of historical biogeographical hypotheses, species- and subspecies-level taxonomy, and plastome evolution in Arceuthobium. More broadly, this work provides a foundation for future clade-focused comparative and biosystematics studies of Arceuthobium.

Journal of the Botanical Research Institute of Texas

Two new subspecies of fir dwarf mistletoe (Arceuthobium abietinum, Viscaceae) are described herei... more Two new subspecies of fir dwarf mistletoe (Arceuthobium abietinum, Viscaceae) are described herein: Arceuthobium abietinum subsp. mathiasenii (Mathiasen’s dwarf mistletoe) and Arceuthobium abietinum subsp. grandae (grand fir dwarf mistletoe). The former dwarf mistletoe—Mathiasen’s dwarf mistletoe—parasitizes Rocky Mountain white fir in Nevada, Utah, and Arizona and Durango fir in northern Mexico; whereas, grand fir dwarf mistletoe parasitizes grand fir as well grand fir × white fir hybrids in California, Oregon and Washington. The recognition of these subspecies and, hence, their classification is based on morphological discontinuities and host range differences when compared to white fir dwarf mistletoe (Arceuthobium abietinum subsp. abietinum), red fir dwarf mistletoe (A. abietinum subsp. magnificae), and Wiens’ dwarf mistletoe (A. abietinum subsp. wiensii). The combined analyses of plant height, third internode length and width, fruit dimensions, staminate spike and petal dimensi...

Plant Disease, Jul 1, 2018