Reproductive biological studies of Asclepias syriaca L. stands in Pest County, Hungary.

Abstract

In the beginning Asclepias syriaca was used as ornamental plant in Hungary. After escaping from cultivation it has become wide spread during last decades of the 20th century. Nowadays, it covers large areas especially on sandy soils, and its further appearance is expected on dry, treeless and degraded areas of the country.
For our research two uncultivated fields and one abandoned vineyard were selected. For sampling a 2 m by 4 m quadrat was used at each stand. The stands were characterized by the following variables: density, percentage of the reproductive specimens, average number of inflorescences, average number of fruits, fruits per all inflorescences on a stem, pods per fruited inflorescences on a stem, average number of seeds per fruit.
In the same quadrats the seed content of the soil was studied at two depths (from 0 to 5 cm and front 5 to 10 cm).
The results showed that the extent of area, density of stand, percentage of the reproductive specimens, average number of fruits were higher on the uncultivated fields than on the abandoned vineyard. In the upper soil-layer 2750-18563 seeds per m2 were detected in the fallow lands, whereas in the lower soil-layer seeds were found only in one of the fallow lands. Common milkweed seeds were practically missing from the soil of the abandoned vineyard. The seed production of the fallow land population can reach 70-100 millions per hectar, which are very strong propagulum load on the surrounding areas. Therefore, the uncultivated areas occupied by Asclepias syriaca must be treated much more carefully.