John F. Gaskin

Molecular Phylogenetic Investigation of U.S. Invasive Tamarix

Abstract Tamarix is a taxonomically difficult Old World genus that has become naturalized and invasive in the Americas and Australia. We examine the morphology and taxonomic history of 12 putative U.S. invasive Tamarix species, and investigate current invasions using chloroplast and nuclear sequence data. We test molecular phylogenetic hypotheses regarding the relationships of putative invasive taxa, and conclude that there are four invasive entities in the U.S., two of which are T. aphylla and T. parviflora. The sequence data also identify an invasive entity consisting of genetically indistinguishable T. ramosissima and T. chinensis, and another consisting of genetically indistinguishable T. gallica and T. canariensis. There is evidence of introgression between T. ramosissima, T. canariensis, and T. gallica, which is a likely source of confusion in the identification of some Tamarix invasions. Communicating Editor: Jeff H. Rettig

Latitudinal variation in cold hardiness in introduced Tamarix and native Populus

To investigate the evolution of clinal variation in an invasive plant, we compared cold hardiness in the introduced saltcedar (Tamarix ramosissima, Tamarix chinensis, and hybrids) and the native plains cottonwood (Populus deltoides subsp. monilifera). In a shadehouse in Colorado (41°N), we grew plants collected along a latitudinal gradient in the central United States (29–48°N). On 17 occasions between September 2005 and June 2006, we determined killing temperatures using freeze‐induced electrolyte leakage and direct observation. In midwinter, cottonwood survived cooling to −70°C, while saltcedar was killed at −33 to −47°C. Frost sensitivity, therefore, may limit northward expansion of saltcedar in North America. Both species demonstrated inherited latitudinal variation in cold hardiness. For example, from September through January killing temperatures for saltcedar from 29.18°N were 5–21°C higher than those for saltcedar from 47.60°N, and on September 26 and October 11, killing temperatures for cottonwood from 33.06°N were >43°C higher than those for cottonwood from 47.60°N. Analysis of nine microsatellite loci showed that southern saltcedars are more closely related to T. chinensis while northern plants are more closely related to T. ramosissima. Hybridization may have introduced the genetic variability necessary for rapid evolution of the cline in saltcedar cold hardiness.

Double trouble for grasshopper molecular systematics: intra-individual heterogeneity of both mitochondrial 12S-valine-16S and nuclear internal transcribed spacer ribosomal DNA sequences in Hesperotettix viridis (Orthoptera: Acrididae)

Abstract Hesperotettix viridis grasshoppers (Orthoptera: Acrididae: Melanoplinae) exhibit intra‐individual variation in both mitochondrial 12S‐valine‐16S and nuclear internal transcribed spacer (ITS) ribosomal DNA sequences. These findings violate core assumptions underlying DNA sequence data obtained via polymerase chain reaction (PCR) amplification for use in molecular systematics investigations. Undetected intra‐individual variation of this sort can confound phylogenetic analyses at a range of taxonomic levels. The use of a DNA extraction protocol designed to enrich mitochondrial DNA as well as an initial long PCR of approximately 40% of the grasshopper mitochondrial genome failed to control for the presence of paralogous mitochondrial DNA‐like sequences within individuals. These findings constitute the first demonstration of intra‐individual heterogeneity in mitochondrial DNA‐like sequences in the grasshopper subfamily, Melanoplinae, and only the second report of intra‐individual variation in nuclear ITS ribosomal DNA sequences in grasshoppers. The fact that intra‐individual variation was detected in two independent DNA marker sets in the same organism strengthens the notion that the orthology of PCR‐derived DNA sequences should be examined thoroughly prior to their use in molecular phylogenetic analyses or as DNA barcodes.

HYBRIDIZATION OF TAMARIX RAMOSISSIMA AND T. CHINENSIS (SALTCEDARS) WITH T. APHYLLA (ATHEL) (TAMARICACEAE) IN THE SOUTHWESTERN USA DETERMINED FROM DNA SEQUENCE DATA

ABSTRACT Morphological intermediates between Tamarix ramosissima or T. chinensis (saltcedars) and T. aphylla (athel) were found recently in three locations in the southwestern USA, and were assumed to be hybrids or a previously unreported species. We sequenced chloroplast and nuclear DNA from putative parental and hybrid morphotypes and hybrid status of morphological intermediates was supported. Chloroplast data suggest that the seed source for these hybrids is T. aphylla. Invasive T. aphylla genotypes found in Australia match those found in the USA. Seed was collected from one of the hybrids, and a low percentage of it was viable. This hybrid combination has not been previously reported in the USA or the native ranges of the species. Although populations of this novel Tamarix hybrid appear to be uncommon at present, both parental species are considered invasive (saltcedars in North America; athel in Australia), and it is possible that more aggressive hybrid genotypes could be produced. Therefore, natural resource managers concerned with the potential spread of non-native species should be aware of the existence of these plants and monitor their future spread.

Phylogenetic Relationships Among Native and Naturalized Hieracium (Asteraceae) in Canada and the United States Based on Plastid DNA Sequences

Abstract We used parsimony and maximum likelihood analyses of chloroplast DNA to examine the relationships of native North American Hieracium (hawkweeds; Asteraceae) with non-native Hieracium species being studied for classical biological control. Thirty-six taxa were included; these representing the three morphologically-based subgenera: Pilosella from Eurasia, the circumboreal Hieracium, and Chionoracium from North and South America. Results from the trnT-F and petN-psbM sequence data strongly support the morphologically based classifications. An exception is the placement of H. canadense within subgenus Chionoracium, rather than subgenus Hieracium, which may be due to chloroplast capture. Placement of the genus Andryala within Hieracium subgenus Pilosella is also supported. Additionally, species in subgenus Pilosella targeted for classical biological control are still supported as being in a separate subgenus from native North American taxa.

GENOTYPE DIVERSITY OF SALSOLA TRAGUS AND POTENTIAL ORIGINS OF A PREVIOUSLY UNIDENTIFIED INVASIVE SALSOLA FROM CALIFORNIA AND ARIZONA

ABSTRACT Various Salsola spp. have been introduced to the USA, and some of these are considered noxious or invasive in certain regions. The genus is taxonomically challenging, and recent morphological, cytological, and molecular work has shown that an unknown taxon, previously identified as S. tragus, but recently temporarily designated as Type B, with unknown origins, exists in California and Arizona. Type Bs origins and identity are a point of concern for biological control efforts, as it is much less affected by fungal biological control agents than the sympatric invasive S. tragus. Initial studies in 2005 indicated that Type B is morphologically very similar to S. kali subsp. austroafricana which has been collected in southern Africa. Here we use DNA sequence data from a PEPC intron to compare USA and Old World specimens, and results indicate that S. kali subsp. austroafricana is genetically identical to Type B and distinct from S. tragus. It is unclear if S. kali subsp. austroafricana is native to southern Africa or to the northern hemisphere of the Old World, and further investigations in both regions are needed.

Stem anatomy is congruent with molecular phylogenies placing Hypericopsis persica in Frankenia (Frankeniaceae): comments on vasicentric tracheids

Stem and root anatomy of Hypericopsis persica is evaluated in light of molecular data reconstructing Hypericopsis within a clade of Asian Frankenia. No anatomical information contradicts the idea that Hypericopsis should be subsum ed within Frankenia. Anatomy in the two genera is comparable, taking into account the unusual habit of Hypericopsis , which consists of slender, short-lived shoots from a long-lived caudex, whereas most species of Frankenia are small shrubs with long-lived shoots. Wood of the slender stem s of Hypericopsis is similar to twig wood of the related Frankenia hirsuta in qualitative and quantitative features but differs from mature wood of other species of Frankenia described in previous studies in having smaller cells and little storying. Wood of Hypericopsis is rayless and is made up mostly of libriform fibers and vessel elements associated with vasicentric tracheids. Axial parenchyma is occasional at the margins of growth rings. We briefly evaluate wood characters in the context of Caryophyllales s.l. and suggest characters that may be synapomorphies of clades within this group, e.g., minute lateral wall pits apparently characterize the clade comprising Plum baginaceae, Polygonaceae, Frankeniaceae, and Tamaricaceae. That vasicentric tracheids elongate considerably beyond the lengths of the vessel elements with which they are associated is cited as a distinct ontogenetic difference between these cell types. Likewise, num erous vessel elem ents comparable in diameter to vasicentric tracheids were observed. These observations are offered as reasons to reject the concept of vasicentric tracheids as simply vessel elements that are too narrow for the formation of perforation plates.

Clonal structure of invasive hoary cress (Lepidium draba) infestations.

Abstract Hoary cress is a perennial herbaceous weed that has invaded agricultural and natural areas of western North America. Invasions are often composed of dense patches, and it is unclear whether clonal growth via lateral rhizomes or seedling recruitment is the dominant method of patch expansion. To study the clonal structure of this invasive, six patches from three USA populations (194 ramets) were analyzed with the use of Amplified Fragment Length Polymorphisms (AFLPs). Known siblings and clones were also included to ensure sufficient variation for discrimination between clonal and nonclonal ramets. Patches had low genet/ramet ratios (mean G/N = 0.25) and low diversity levels (mean D = 0.49) compared to similar clonal studies. Single genets represented 55–85% of the ramets sampled in a patch, and the largest genet was 38 m across. Hoary cress exhibits a strong bias toward patch-size increase from clonal reproduction rather than from seedling recruitment. Results indicate that biological control methods that focus on reducing or eliminating seed production would do little to stop expansion of a patch. Despite the domination of a patch by one or a few large genets, other smaller genets are able to persist or are occasionally recruited into dense areas of a patch. Nomenclature: Hoary cress, Lepidium draba L. [= Cardaria draba (L.) Desv.], CADDR.

Comparison of ornamental and wild saltcedar (Tamarix spp.) along Eastern Montana, USA riverways using chloroplast and nuclear DNA sequence markers

Saltcedars (Tamarix ramosissima, T. chinensis, and their hybrids) have invaded riverways and lakeshores across the western USA and northern Mexico. In Montana, ornamental plantings of saltcedar have been hypothesized, to varying degrees, to be the origin of nearby, wild populations. To examine this hypothesis, we compared chloroplast and nuclear DNA sequences from 36 ornamental and 182 wild saltcedars from Montana, North Dakota, and Wyoming, USA. We found that ornamental and wild population genotype frequencies were highly dissimilar. Also, genotype frequencies of hypothetical propagule populations under scenarios of random mating, self-fertilization, and clonal reproduction in the ornamental population were highly dissimilar to the genotype frequencies of the wild populations. Assignment tests indicated that the majority of wild genotypes originated from other wild plants, not from ornamental plants. However, ornamental plants could not be excluded as contributors to wild populations because all chloroplast and nuclear haplotypes found in the ornamental plants were found at some frequency in the wild. These findings suggest that while ornamental saltcedars are not the sole source of wild saltcedar, they do have potential to contribute genetic material to an invasion or re-establish a population after existing wild saltcedars are removed.

Geographic population structure in an outcrossing plant invasion after centuries of cultivation and recent founding events

We investigated the genetic diversity and origins of a long-term cultivar. Dyer’s woad has been used as a dye source for at least eight centuries in Eurasia. It was introduced to eastern USA in the 1600s, and is now considered invasive in the western USA. Our analysis of plants from the USA and Eurasia suggests that there are two distinct invasions in western USA that most likely originate from Switzerland, Ukraine and Germany. This information assists in finding effective biological control agents, and continued combination of ecological and molecular data helps bring us closer to sustainable management of plant invasions.