Premise of the Study Herbarium specimens are increasingly used in phenological studies. However, natural history collections can have biases that influence the analysis of phenological events. Arctic environments, where remoteness and cold climate govern collection logistics, may give rise to unique or pronounced biases. Methods We assessed the presence of biases in time, space, phenological events, collectors, taxonomy, and plant traits across Nunavut using herbarium specimens accessioned at the National Herbarium of Canada ( CAN ). Results We found periods of high and low collection that corresponded to societal and institutional events; greater collection density close to common points of air and sea access; and preferences to collect plants at the flowering phase and in peak flower, and to collect particular taxa, flower colours, growth forms, and plant heights. One‐quarter of collectors contributed 90% of the collection. Discussion Collections influenced by temporal and spatial biases have the potential to misrepresent phenology across space and time, whereas those shaped by the interests of collectors or the tendency to favour particular phenological stages, taxa, and plant traits could give rise to imbalanced phenological comparisons. Underlying collection patterns may vary among regions and institutions. To guide phenological analyses, we recommend routine assessment of any herbarium data set prior to its use.
Phi thickenings are lignified wall thickenings in the radial and tangential walls of the root cortex of some plant species and are so named because they resemble the Greek letter φ in cross section. Although their occurrence has long been known in gymnosperms, a systematic survey of their presence has never been undertaken. Such a survey may be useful to future studies of the functions of these structures. Roots of 22 species of gymnosperms representing all of the major groups were hand sectioned, stained with phloroglucinol (a lignin stain), and examined for the presence of phi thickenings using light microscopy. Detailed observations on Thuja occidentalis (Cupressaceae) were made to provide a baseline for comparison in this study. Phi thickenings were absent in the species examined in the Cycadaceae, Gnetaceae, Pinaceae, and Podocarpaceae and were present in the Ginkgoaceae, Araucariaceae, Taxaceae, and Cupressaceae (s.l.). These results, when combined with previous literature reports, indicate that the occurrence of phi thickenings is consistent within a family. Their occurrence is also correlated with current hypotheses of phylogenetic relationships within the gymnosperms, which may indicate their usefulness as a systematic character.Résumé : Les épaississement phi sont des épaississement pariétaux lignifiés dans les parois radiales et tangentielles du cortex racinaire chez certaines plantes; on les nomme ainsi parce qu'ils ressemblent à la lettre grecque φ en section transversale. Bien qu'on connaisse leur existence chez les gymnospermes depuis longtemps, aucune revue systématique n'a été conduite jusqu'ici. Une telle revue pourrait être utile pour des études à venir sur les fonctions de ces structures. Les auteurs ont prélevé les racines de 22 espèces de gymnospermes représentant tous les groupes importants; le maté-riel recueilli a été sectionné à main levée et coloré au phloroglucinol (colorant la lignine) avant de chercher la présence d'épaississements phi en microscopie photonique. Les auteurs ont effectué des observations détaillées sur le Thuja occidentalis (Cupressaceae), afin d'établir une base de comparaison pour cette étude. Les épaississements phi sont absents chez les espèces de Cycadaceae, Gnetaceae, Pinaceae et Podocarpaceae examinées, et sont présents chez les espèces de Ginkgoaceae, d'Araucariaceae, de Taxaceae et de Cupressacées (s.l.). Ces résultats, lorsque reliés avec la littérature existante, indiquent que la présence d'épaississements phi est constant à l'intérieur de la famille. Leur présence est également corrélée avec les hypothèses courantes de relations phylogénétiques chez les gymnospermes, ce qui suggère leur utilité comme caractère systématique.
Dynamic climate changes and expansion of new biomes characterize the late Pleistocene-early Holocene of eastern Beringia. Analysis of plant macrofossils from an early Holocene (ca. 9 300 14 C yrs BP) beaver dam in central Alaska provides insight into the local environment and vegetation. The plant macrofossil assemblage comprises remains of trees and shrubs, graminoids, and forbs, including Betula sp., Carex sp., Rubus sp., Eleocharis sp., Scirpus sp., Potamogeton sp., Najas flexilis and Typha latifolia, indicative of standing water of a beaver pond. Bryophytes from the beaver dam include Warnstorfia spp. and Drepanocladus aduncus, suggesting shallow, stagnant, or slow-moving water. The presence of Najas flexilis, Typha latifolia, and modern beaver (Castor canadensis) suggest that central Alaska had a warmer climate during the early Holocene.
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