Hidden in the host - Unexpected vegetative hibernation of the holoparasite Cuscuta epithymum (L.) L. and its implications for population persistence

Several reports have referred to the possible perennial character of holoparasitic Cuscuta species, but the frequency and ecological importance of perennation have not been studied yet. We determined that Cuscuta epithymum is capable of overwintering vegetatively, especially on its most common perennial host Calluna vulgaris. To examine the impact of successional stages on the capability of C. epithymum to perennate vegetatively, ten C. epithymum populations in Calluna-dominated sites in a successional gradient were studied. Although the number of overwintering haustoria varied between different populations, on average 85% of each C. epithymum population was the result of resprouting haustoria. Thus, the pseudoannual growth habit is an important, but overlooked life-strategy for long-term survival of this species. Furthermore, the stage of heath succession significantly determined the overwintering probabilities of C. epithymum and therefore strongly influenced its annual growth. Most sprouted haustoria were found in 1- or 2-year-old vegetation followed by a gradual decline at older successional stages. The parasite was more likely to overwinter on unlignified (and nutritious) than on lignified parts of C. vulgaris. The number of sprouted haustoria positively affects C. epithymum population size and thus flower abundance. Hence, vegetative perennation and subsequent increased flowering success are two aspects that may increase the chance for these populations to cope with environmental influences and survive in the long run.