Boston ivy: a growing threat?

Boston ivy (Parthenocissus tricuspidata) is a long-lived woody vine that can fasten on to walls and buildings by the sticky disc-like tips of the branched tendrils. As with many common plant names, “Boston ivy” is misleading – it is neither from Boston, nor an ivy. It is actually native to eastern Asia (Korea, Japan, northern and eastern China) and is in the grape family, Vitaceae. It is so commonly cultivated in the USA, especially on their university buildings, that it is the “ivy” of their Ivy League. Around Auckland it is commonly cultivated in the older suburbs, usually covering walls or fences, sometimes covering buildings. Boston ivy’s leaves are usually 3-pointed or trifoliate, which separates it from its two relatives which are also in New Zealand: Virginia creeper (P. quinquefolia) and false Virginia creeper (P. inserta, syn. P. vitacea) that both have 5-leaflets.

Further investigating revealed even more instances of self-established seedlings sprouting up across Auckland, and the problem is likely more widespread than what’s been documented so far.

To find out how commonly Boston ivy is establishing itself by seed, Ewen, and Museum Botany volunteer Shelley Heiss-Dunlop recently jointly published an article (Cameron & Heiss-Dunlop 2022) outlining these seven different localities and encouraged members of the Auckland Botanical Society to examine their surrounds for more juvenile plants.

Already three new localities have been reported. These naturalisations of seedlings are pressed, dried, mounted on card and form a permanent record as specimens in the Museum’s extensive herbarium collection. You can explore some of these records through Collections Online.

Boston ivy is insect pollinated (by flies, wasps, bees) and each fleshy fruit contains 2-3 seeds. The blue-black ripe fruit (8 x 5mm) is eaten by frugivorous birds, e.g., starlings or tui, which widely disperse the seed.

This could be the start of a large naturalisation, or it might be the result of a short-term unusual weather event. Time will tell – however, it certainly warrants monitoring at this stage. There are now more wild exotic vascular plant species in New Zealand than native species. Large vine species that naturalise, like Boston ivy, pose a distinct threat to native plants – they can smother them, and also by climbing up on trees they may pull them down with the extra weight.

References

Cameron, E.K. 2021: Boston ivy (Parthenocissus tricuspidata) – the first wild seedling in New Zealand? New Zealand Botanical Society Newsletter 146: 10–​12.

Cameron, E.K.; Heiss-Dunlop, S. 2022: Boston ivy (Parthenocissus tricuspidata) – reacting to climate change in New Zealand? Auckland Botanical Society Journal 77: 124–130.