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Probabilities of Survival and Reproduction Relative to Rosette Size in the Common Burdock (Arctium minus: Compositae)

1983; University of Notre Dame; Volume: 109; Issue: 1 Linguagem: Inglês

10.2307/2425529

1938-4238

Ronald S. Gross, Patricia A. Werner,

Plant Parasitism and Resistance

Individual plants of Arctium minus (Hill) Bernh. (common burdock), a biennial, were marked and followed for 3 years in an old-field population in southwestern Michigan. In addition, growth and survival of A. minus individuals derived from seed sown in cleared plots and natural vegetation were monitored for 2 years. Seedling emergence and survival were reduced by the presence of litter and vegetation. The relationship between rosette size and the probability of an individual flowering, remaining vegetative or dying was calculated from autumn to autumn and spring to spring. Arctium minus rosettes must reach a critical size before flowering; above this size the probability of flowering increased and the probability of dying decreased with increasing rosette size. Arctium minus plants generally take 4 or more years to flower under field conditions with moderate to high densities of grasses and herbaceous dicots. INTRODUCTION Plants with true biennial life cycles grow vegetatively for 1 year, and then produce flowers, set seed, and die in the 2nd year following germination. Although some plant species adhere to a strict biennial life cycle (e.g., Melilotus alba; Klemow and Raynal, 1981), many species classified as biennials vary in time of vegetative growth prior to flowering (e.g., Werner, 1975, 1977; Baskin and Baskin, 1979a,b; van der Meijden and Waals-Kooi, 1979; Holt, 1972, and Gross, 1981). For several species of purported biennials, the probabilities of an individual plant flowering, remaining vegetative or dying are more accurately predicted by its size than by its age (Werner, 1975; van der Meijden and Waals-Kooi, 1979; Baskin and Baskin, 1979b; Gross, 1981; Evans, 1982). We report on a 3-year study which relates the probability of Arctium minus (common burdock) rosettes flowering, remaining vegetative or dying to their size and age. METHODS Arctium minus (Hill) Bernh. (common burdock), a native of Eurasia, is a common weed found in abandoned fields, pastures and along roadsides and streambanks throughout much of North America, especially northern United States and Canada. Burdock is generally classified as a biennial herb (cf., Gleason and Cronquist, 1963; Fernald, 1950). Individual plants are monocarpic, growing vegetatively as broadleaved rosettes, then dying after producing a tall (0.5-2 m) flowering stalk. Burdock rosettes are easily identified by their long-petioled leaves which may become very large (laminas may reach 40 cm or more in length). Gross et al. (1980) review the biology of A. minus. Monitoring natural populations. To determine the probability of flowering, remaining vegetative or dying for rosettes of different sizes, previously established rosettes were individually marked with numbered flags in a field abandoned from agriculture Present address: Department of Biology, Oberlin College, Oberlin, Ohio 44074.