-common reed, is a perennial, emergent aquatic plant with annual cane-like stems developed from an extensive rhizome system. It grows in low-lying wet areas such as fresh and salt-water marshes, drainage ditches, shallow lake edges, sandy banks, roadsides, woodlands and rocky places. Stems can reach up to 6.0 m in height, vary in diameter from 4 to10 mm and have 10 to 25 cm long hollow internodes. Clones are extended by perennial rhizomes with extensive aerenchymatous tissue that supplies oxygen. Roots develop from rhizomes and other submerged parts of shoots. Leaves are smooth, alternate with narrow-lanceolate laminae, 20 to 70 cm long and 1 to 5 cm broad, and tapering to long slender points. The inflorescence is a terminal panicle, often 30 cm long, dull purple to yellow, with main branches bearing many spikelets. Seed production and germination are extremely variable and comparatively rare in many populations. Phragmites australis carries out photosynthesis through the C 3 pathway (or a variation thereof). Studies of genetic variation through isozyme and other molecular methods suggest that the populations are very closely related, and that variation in the metapopulation is small. Chloroplast DNA sequences of two non-coding regions indicate that non-native introduced genotypes of P. australis have displaced native genotypes in parts of North America. Phragmites australis often forms extensive monocultures in North America. As a consequence, habitat quality and species diversity have been documented to decline. However, in roadside populations it is effective in taking up many typical heavy metals that originate from nearby highways and buildings. Phragmites australis is found in all Canadian provinces and the Northwest Territories, but not in the Yukon Territory or Nunavut. The infestation of P. australis is most severe in the Great Lakes region and its migration is primarily mediated through rivers, canals and waterways but roadways are increasingly becoming important. Changes in the water regime have been linked to its success and could ultimately result in changes to the floristic composition of a habitat. Rodeo™, an aqueous solution of the isopropylamine salt of glyphosate, is most frequently used to control P. australis populations. Other methods of control include cutting, burning, and drainage of the species' habitat. As P. australis is considered to be invasive in North America, introduction of biological control agents is now being investigated. Can. J. Plant Sci. 84: 365-396. Le roseau commun Phragmites australis (Cav.) Trin. ex Steud. est une vivace aquatique dont le vaste système de rhizomes donne chaque année des tiges ressemblant à des cannes. L'espèce pousse dans les dépressions humides comme les marais d'eau douce et salants, les fossés de drainage, la rive des lacs peu profonds, les berges sablonneuses, le bord des routes, les boisés et les endroits rocailleux. Les tiges atteignent parfois jusqu'à 6,0 m de hauteur et leur diamètre varie de 4 à 10 mm, avec de longues sections creuses de 10 à ...

In colonizing species, high phenotypic plasticity can contribute to survival and propagation in heterogenous adventive environments, and it has been suggested as a predictor of invasiveness. Observation of natural populations of an invasive species, Lythrum salicaria salicaria, indicated extensive variation in its growth and reproductive traits. Phenotypic plasticity of different life history traits of L. salicaria was investigated using vegetative clones of each of 12 genotypes from one population in Ontario, Canada. We chose soil moisture as the treatment factor because of its importance in wetland species and raised all 12 genotypes in each of four soil moisture treatments. We examined an array of vegetative and reproductive traits, including root and shoot mass, shoot and inflorescence length, total seed set, floral mass, and morphometric variables. All observed vegetative as well as reproductive traits demonstrated significant phenotypic plasticity in response to soil moisture treatment. Even the stigma-anther separation involved significant genotype by environment interactions, suggesting that soil moisture may modify the relative positions of anthers and stigma. Compared to vegetative traits, most reproductive traits demonstrated crossing reaction norms, implying that the average differences in those traits among genotypes vary with the environment maintaining the genetic variation in a population.

No abstract

Management of invasive species depends on developing prevention and control strategies through comprehensive risk assessment frameworks that need a thorough analysis of exposure to invasive species. However, accurate exposure analysis of invasive species can be a daunting task because of the inherent uncertainty in invasion processes. Risk assessment of invasive species under uncertainty requires potential integration of expert judgment with empirical information, which often can be incomplete, imprecise, and fragmentary. The representation of knowledge in classical risk models depends on the formulation of a precise probabilistic value or well-defined joint distribution of unknown parameters. However, expert knowledge and judgments are often represented in value-laden terms or preference-ordered criteria. We offer a novel approach to risk assessment by using a dominance-based rough set approach to account for preference order in the domains of attributes in the set of risk classes. The model is illustrated with an example showing how a knowledge-centric risk model can be integrated with the dominance-based principle of rough set to derive minimal covering "if ... , then...," decision rules to reason over a set of possible invasion scenarios. The inconsistency and ambiguity in the data set is modeled using the rough set concept of boundary region adjoining lower and upper approximation of risk classes. Finally, we present an extension of rough set to evidence a theoretic interpretation of risk measures of invasive species in a spatial context. In this approach, the multispecies interactions in an invasion risk are approximated with imprecise probability measures through a combination of spatial neighborhood information of risk estimation in terms of belief and plausibility.

Etivirotimental stress can disrupt developmental processes on biological, physiological, and chemical levels and thereby affect the symmetry of a trait. For this reason, fluctuating asymmetry is often proposed as a measure of stress encountered by an individual. One problem is that asymmetry may bave multiple causes, including developmental noise and genetic background, and genetic differences may interact with any physiological stress imposed by the environment. The main objective of tbis research was to determine whether developmental noise and genetic stress can be separated from environmental effects on leaf asymmetry. Tbe experiments were conducted on two wetland plants, Lytbrum salicaria (purple loosestrife) and Pentborum sedoides (ditch stonecrop). Replicates of different genotypes were measured wben young and after tbey matured, with the latter group grown under two nutrient treatments. Tbe largest and healthiest leaf of each plant was measured for lengtb, widtb, and differences in widtb between the left and right sides (measuring from the central vein at the widest point). Nutrient enrichment increased leaf asymmetry, wbile age reduced asymmetry in L. salicaria. However, leaf asymmetry cbanged only as a consequence of development in P. sedoides and decreased. Genotype didnot affect asymmetry in either species.

No abstract

No abstract

Lythrum salicaria (purple loosestrife) is an exotic weed that arrived in North America from Europe during the early 1800s. It is a herbaceous perennial with a trimorphic breeding system. Seventy-four populations of L. salicaria were surveyed from Windsor, Ontario, to the Gaspé Peninsula in Quebec. Fifty of the populations were significantly anisoplethic (i.e., unequal frequencies of the three flower morphs), including 10 populations that were nontrimorphic. Populations with fewer than 100 plants tended to have one or even two morphs missing. Although larger populations rarely lacked a morph, they did show significantly skewed morph frequencies. Indices of clonal size, such as number of ramets per genet and genet diameter, differed significantly among sites, and clonal growth also showed significant interaction between morph and site. One-way analyses of variance indicated that morphs differed in terms of either number of ramets per genet or genet diameter in 16% of populations. Morphometric analyses of flowers from 49 populations showed significant variability in floral traits among genets, flower morphs, and sites. Results indicated frequent reduction in herkogamy (spatial separation between anther and stigma), with variant flowers having very little or no stigma–anther separation. Mean stigma–anther separation was lowest in the mid-morph individuals, followed by the short and long morphs. Correspondingly, the frequency of variant flowers was greatest in mid-morph individuals and least in long-morph individuals. Isoplethic and anisoplethic populations did not differ, for any morph, in the frequency of occurrence of these variant flowers. Key words: Lythrum salicaria, purple loosestrife, isoplethy, morph frequency, heterostyly, variant flowers, stigma–anther separation.