Nuevos xenófitos de La Palma (Islas Canarias, España), con énfasis en las especies naturalizadas y (potencialmente) invasoras

Varios años de trabajos de campo en La Palma (Islas Canarias occidentales) han posibilitado el descubrimiento de nuevas plantas vasculares no nativas. Amaranthus blitoides, A. deflexus, Aptenia cordifolia, Argemone ochroleuca, Begonia schmidtiana, Capsella rubella, Cardamine hamiltonii, Centratherum punctatum, Cerastium fontanum subsp. vulgare, Chasmanthe floribunda (ampliamente confundida con C. aethiopica y Crocosmia xcrocosmiiflora en Macaronesia), Chenopodium probstii, Commelina latifolia var. latifolia, Dichondra micrantha, Dysphania anthelmintica, Epilobium ciliatum, Erigeron sumatrensis, Erodium neuradifolium, Eucalyptus globulus, Euphorbia hypericifolia, E. maculata, Gamochaeta antillana, Geranium pyrenaicum, Hedychium coronarium, Hypochaeris radicata, Kalanchoe daigremontiana, K. delagoensis, K. xhoughtonii, Kickxia commutata subsp. graeca, K. spuria subsp. integrifolia, Lactuca viminea subsp. ramosissima, Landoltia punctata, Malvastrum coromandelianum subsp. capitatospicatum, Oenothera jamesii, Orobanche nana, Oxalis latifolia, Papaver hybridum, P. setigerum, Pilea microphylla, Podranea ricasoliana, Polygonum arenastrum, Portulaca granulatostellulata, P. nicaraguensis, P. nitida, P. papillatostellulata, Rumex crispus subsp. crispus, R. pulcher subsp. pulcher, R. xpratensis, Sechium edule, Sida spinosa var. angustifolia, Silene nocturna, Solanum abutiloides, S. alatum, S. decipiens, Sonchus tenerrimus, Spergularia marina, Stellaria pallida, Tragopogon porrifolius subsp. australis, Tribulus terrestris y Trifolium repens subsp. repens son xenófitos naturalizados o (potencialmente) invasores, que se citan por primera vez para las Islas Canarias o para la isla de La Palma. 37 táxones adicionales, probablemente casuales, se dan a conocer por primera vez de las Islas Canarias, y 56 táxones de la isla de La Palma.

Dose Response of Weed Seeds, Plant-Parasitic Nematodes, and Pathogens to Twelve Rates of Metam Sodium in a California Soil

Metam sodium (sodium N-methyl dithiocarbamate, metam-Na) is widely used in agricultural and floricultural production for controlling soilborne plant pathogens, parasitic nematodes, and weeds. It undergoes rapid decomposition to the biocide methyl isothiocyanate (MITC) in moist soils. In this study, the efficacy of 12 concentrations of metam-Na (10 to 2,650 μmol kg–1 soil) to control seeds or tubers of five major weed species, three soilborne pathogens, and one parasitic nematode was evaluated in a sandy loam soil under controlled conditions. Soils were exposed to the fumigant in microcosms for 24 h at 10 and 20°C. Generation and dissipation curves of MITC in soil under controlled conditions showed that MITC concentrations in soils were highest 2 h after metam-Na application and decreased steadily over the 24-h incubation period. After 24 h, remaining MITC concentrations in soil microcosms at 10 and 20°C were 53 and 38% of the original amount applied, respectively, indicating a 20% reduction in MITC dissipation at the lower soil temperature. Logistic dose-response models were used to estimate the effective concentration necessary to reduce soil pest viability by 50 (LC50) or 90 (LC90) percent under both temperatures. Seed of Portulaca oleracea, with LC90 values of ≤1,242 μmol kg–1 soil, was the most sensitive to soil fumigation with metam-Na, followed by Polygonum arenastrum with LC90 values of ≤1,922 μmol kg–1 soil. At 10°C fumigation temperature, metam-Na at the highest dose tested in this study, 2,650 μmol kg–1 soil, was not sufficient to achieve adequate control of Stellaria media and Malva parviflora seed and Cyperus esculentus tubers. Weed control efficacy (average reduction in LC90 values) of metam-Na was between 25 and 60% higher if soils were fumigated at 20°C compared with 10°C, with the exception of M. parviflora. Phytophthora cactorum and Pythium ultimum were more sensitive to soil fumigation with metam-Na (LC90 ≤ 165 μmol kg–1 soil) than Verticillium dahliae (LC90 ≤ 737 μmol kg–1 soil). The nematode Tylenchulus semipenetrans was highly sensitive to soil fumigation with metam-Na (LC90 ≤ 98 μmol kg–1 soil), and the efficacy of control increased by 30% if soil was fumigated at 20°C compared with 10°C. In this sandy loam soil, metam-Na at a concentration of 850 μmol kg–1 reduced the viability of Portulaca oleracea and Polygonum arenastrum seeds, C. esculentus tubers, and all soilborne pathogens and parasitic nematodes tested by 90% at 20°C after 24 h exposure. These results indicate that metam-Na can provide effective pest and disease control at maximum label rate for the commercial formulation, but there was a reduction in efficacy at low temperature.

Cytotaxonomic studies on Polygonum section Polygonum in eastern Canada and the adjacent United States

A total of 183 chromosome counts on plants representing nine species of Polygonum section Polygonum in eastern Canada and the United States is presented. Documented counts are published here for the first time for P. franktonii (2n = 60) and P. neglectum (2n = 40 and 60). In addition, previously unreported counts for P. achoreum (2n = 60), P. aviculare (2n = 40), and P. fowled (2n = 60) are presented. A review of previously published counts and an examination of voucher specimens have revealed a number of errors, negating many reported counts, including all of those for P. erectum and most of those for P. buxiforme. Polygonum arenastrum and P. raii are entirely tetraploid (2n = 40) and P. franktonii and P. ramosissimum entirely hexaploid (2n = 60), whereas the remaining species have both tetraploid and hexaploid elements. In contrast to previous reports, no diploid or octoploid plants have been detected.

The taxonomy and distribution in eastern Canada of Polygonum arenastrum (4x = 40) and P. monspeliense (6x = 60), introduced members of the P. aviculare complex

The introduced nonmaritime knotweeds have generally been regarded in North America as comprising a single species called P. aviculare L. In recent years cytological and morphological studies have suggested that at least two chromosome races are present and that certain morphological features are correlated with chromosome number. There have been, however, discrepancies in the reports of the distribution and relative abundance of the two races. Studies of the morphology and cytology of introduced knotweeds in eastern Canada confirm the existence of two groups that are recognizable at species rank, and establish that the most common knotweeds in open habitats, e. g., along roadsides and sidewalks, are tetraploid plants distinguishable from their hexaploid relatives by the relatively uniform size of their leaves, the short and narrow free portion of the perianth segments, and by one side of the fruit being very much narrower than the other two. These plants are referable to P. arenastrum Boreau. This species is compared with the heterophyllous hexaploid, usually called P. aviculare sensu stricto, or, if that is considered a nomen ambiguum, P. monspeliense Pers. A table of distinguishing features, illustrations of the two species, and maps of their distribution in eastern Canada are provided.