Table 1. Description of the ornamental plant species used in this study.

	Plant	Common English Name	Assessed Impact
Status of Origin: Non-Native
1	Buddleja davidii	Butterfly bush	Cause damage
2	Lonicera japonica	Japanese honeysuckle	Cause damage
3	Prunus laurocerasus	Cherry laurel	Cause damage
4	Robinia pseudoacacia	Black locust	Cause damage
5	Cornus sericea	Red-osier dogwood	Potential to cause damage
6	Lupinus polyphyllus	Russell lupin	Potential to cause damage
7	Viburnum rhytidophyllum	Leatherleaf viburnum	Potential to cause damage
8	Mahonia aquifolium	Oregon grape	Potential to cause damage
9	Paulownia tomentosa	Princess tree	Potential to cause damage
10	Sedum spurium	Creeping sedum	Potential to cause damage
11	Trachycarpus fortunei	Chinese windmill palm	Potential to cause damage
12	Lonicera henryi	Henry's honeysuckle	Potential to cause damage
13	Fallopia baldschuanica *	Russian vine	None
14	Syringa sp.	Lilac	None
15	Wisteria sp.	Wisteria	None
Status of Origin: Native
16	Ilex aquifolium	English holly	None
17	Prunus spinosa	Blackthorn	None
18	Euonymus europaeus	European spindle tree	None

Species are ordered according to their assessed impact. In the questionnaire, these plant species appeared in a random order.

Note: Status of origin for all species is taken from Flora indicativa [42].

Assessed impact is based on whether the species is listed on the Black-List, or on the Watch-List [43].

*At the time of our study, the use of F. baldschuanica in horticulture was allowed by Swiss authorities, although the species belongs to the Fallopia-complex, that was included in the list of prohibited plant species [46], but not in the Black- or the Watch-List.