Greenhouse weeds in the botanical garden of Pas in Warsaw-Powsin.
Systematic studies carried out in the greenhouses of the Botanical Garden in Warsaw-Powsin, Poland, from 1992-95 revealed that the flora of weeds was very species rich. A total of 243 taxa of vascular plants and 17 species of bryophytes were recorded and lists of these species are presented. Native plants (89 species), greenhouse-escapes (87 species) and permanently established aliens (48 species) co-dominated in the garden. In addition, 10 species of garden-escapes, i.e. plants cultivated in the immediate neighbourhood of the greenhouses, were recorded indoors. Noteworthy were two species (Ruellia caroliniensis and Pilea microphylla) that had been brought accidentally to the glasshouses together with plant material - this group of plants is least numerous, but quite frequent in the study area. Observations made in the vicinity of the Powsin greenhouses showed that relationships between the studied flora and the plants growing outside were unilateral. In Powsin, no example of expansion of greenhouse plants to other parts of the Garden was recorded. By contrast, influxes of diaspores to the study area is observed frequently - the flora of greenhouse weeds is dominated by plants found also in the immediate neighbourhood (147 species). The most important factors affecting the composition of the weed flora of the glasshouses include the flora of the surrounding areas and the mode of greenhouse management (e.g. the range of species cultivated there). The diversity of the flora is not related to greenhouse size.