The B chromosomes of Claytoniacaroliniana (Portulacaceae) and maple forest dieback

Abstract

Claytoniacaroliniana (Michx.) is a perennial early-flowering species regularly occurring in northeastern American maple forests and frequently possessing accessory (B) chromosomes. A cytological study of Claytonia populations growing in eight maple stands diversely affected by dieback has shown important variations in their B chromosome levels. The severity of dieback was negatively correlated with the presence of the B chromosomes, the observed data being adequately adjusted (R = 0.957 and 0.947) to the values estimated from the explicative variables. Different hypotheses are considered to explain the phenomenon: coincidence with a preexisting situation related to marginal habitats; ecological changes in dieback-damaged zones; or the present influence of stresses affecting both B chromosomes of Claytonia and maple trees by divergent or anologous processes.