Anja Murray: Pretty invader is bad news for ecosystems

But this plant is far from wild, native or natural. Montbretia (Crocosmia X crocosmiflora) is a perennial plant that was developed in the 1880s in France for ornamental purposes. Its creators bred a hybrid of two flowering plants native to southern Africa, both belonging to the iris family, selected especially for beauty, vigour and ease of care. Montbretia fed an appetite for novelty and ease.

Its attractiveness has enticed many to celebrate its arrival in their gardens and to transplant a few clumps here and there to liven up their garden. I have friends and neighbours who have been delighted at how well the leafy green thickets initially took hold, only to be overrun within a few years. Montbretia soon takes over all available garden space, engulfing flower borders and lawns with its impenetrable thickets.

Feisty montbretia thrives in the mild and damp climate of the south and west of Ireland, it has also escaped its intended domain of ornamental gardens and has made itself at home along roadsides and hedgerows; in wet grasslands and rough pastures; in abandoned sites and waste ground too. It is now such a familiar sight that most admirers assume it to be a native plant. But make no mistake, this species is an alien invasive of the highest order, a man-made hybrid plant that smoothers diversity and leaves no room for others.

Montbretia grows from underground corms, swollen root tubers about the size of conkers, that store starchy energy from year to year. Each plant can produce up to 14 new corms each year, allowing to spread vigorously. Bits of these corms are often spread unintentionally as a result of ground disturbance, movement of soil, dumping of garden waste and by attaching to machinery.

In spring, long, narrow light green leaves grow fresh from the readily available energy stored in these corms.

I’ve spent days digging up these knobbly nodules from verges around the house and am barely managing to keep its spread at bay. I suspect a previous homeowner here planted a few to brighten up the stretch of road. They would have had no idea that within a few years, swathes of montbretia would take over and exclude the variety of native plants from their former habitat, and in turn, deprive whole layers of invertebrate life from the plant resources that they need to survive.

Native wild plants are the basis of diverse food chains. They have evolved together with their pollinators that occur in the region. Each native plant species provides specific resources for invertebrates such as hoverflies, bees, ladybirds, butterflies, moths, and shield-bugs, among others. Each species of native butterfly, for example, has evolved to lay its eggs on a select few plant varieties, known as the larval food plant. The caterpillars that hatch on to these larval food plants are specially adapted to eat that plant.

Where invasives such as montbretia have taken over, little room remains for the food plants that sustain the caterpillars. Songbirds in turn are deprived of the juicy, protein packed caterpillars that they need to feed their nestlings. Swallows, swifts and house martins are all exclusively insectivorous, and most songbirds depend on protein-rich insects during the breeding season too. they have had tens of thousands of years to evolve in co-dependant relationships. Only the most common and adaptable invertebrate species can make any use of newly introduced plants such as Montbretia.

Wild mammals too are dependant, either directly or indirectly, on native plants for their nutritional mainstay. Bats spend each night foraging on flying insects, which they need plenty of to get sufficient nutrition to produce the milk to feed their young. Badgers and hedgehogs feed on beetle larvae and other soil invertebrates.

Closely related to montbretia are hundreds of horticultural varieties of crocosmia. These are a also popular garden plant because of their colourful flowers and hardy growth habits, and not all are as invasive as montbretia. The risk, however, of future invasiveness would warrant that crocosmias should no longer supplied in garden centres or planted by homeowners.

Managing montbretia is one way to reclaim space for nature, an act of local ecosystem restoration. Inviting the many native species that might otherwise thrive in any given site helps provide the resources that wild food chains need to survive.

Eradicating montbretia, however, takes a good deal of effort over a number of years. Physically removing the corms at the start of summer, before flowering, is the most benign approach. Because montbretia can grow from fragments of corms, all material must be handled and disposed of carefully.

In the context of accelerating climate change and biodiversity loss, the presence of a few attractive invasive flowering plants may seem insignificant. But it is precisely because there are so many grave threats to the survival of healthy ecosystems that we must do all we can to protect what remains and restore habitats wherever possible.

Gardens, roadside verges, semi-natural wet grasslands and rough pastures all provide vital habitat to wild bees and butterflies, declining birds and diverse, wild food chains. Resilience is key to future proofing healthy ecosystems and it is up to us to intervene to restore the balance.