New Invasives: do you know something the rest of us don’t?

Plants that might previously have proved difficult to establish are now becoming not only more robust, but in some cases a nuisance and invasive

Reports from Austria that Rhus radicans has begun setting fruits on a regular basis has alerted the National Botanic Gardens, Glasnevin, to the advisability of removing the plant from their collections. The exceedingly unpleasant affects of its sap means that this species as an escapee from cultivation would be highly undesirable. With the launch of the all-Ireland Invasive Species Forum, it is timely to review our collections and ensure that potential invasives do not arise from them. A policy is therefore being drawn up to review new, and old, plants and to be vigilant to any change in their ability to establish themselves. At EuroGard IV it was no surprise that Heracleum mantegazzianum featured in at least three talks as a case for which horticulture is largely to blame.

At the recent meeting of the European Botanic Gardens Consortium in Paris, an initiative to collect information from individual gardens about emerging invasives in their collections was considered. Plants that might previously have proved difficult to establish are now becoming not only more robust, but in some cases a nuisance – in the University of Copenhagen Botanic Garden for example, Allium paradoxum has changed from a tender glasshouse plant to a highly invasive pest in the garden. Do you have a local or recent pest you haven’t read about elsewhere?

Please can you contact me with a list of those plants you suspect are making the change from ornamental to pest. It is greatly in our interest that gardens are not implicated when the next giant hogweed or Japanese knotweed gets a foothold. The intention is to develop a list that will help us share observations and identify future problems in a timely manner. I would be particularly interested to hear about instances of Euphorbia esula, or its hybrids, becoming rampant, since this species is now ranked as one of the world’s worst invaders by the Global Invasive Species database.

The National Botanic Gardens, Glasnevin, is planning to hold a conference on invasives towards the end of 2007. I would be pleased to hear from anyone who has noticed any species or cultivars that are becoming something of a nuisance in their collections, or that you may have already removed.

Matthew Jebb, National Botanic Gardens, Glasnevin
matthew.jebb@opw.ie