Beautiful lilies are invading the Magoebaskloof valley

The indigenous vegetation of paradisiacal Magoebaskloof consists of grassland and forest that has, from the earliest years of human habitation, been adversely influenced by plants brought in from other areas. Most of these plants were well-behaved, but some species however, had wanderlust embedded in their genes and became the alien plant invaders of today.

Decades ago, Lilium formosanum was imported from Taiwan as an innocent ornamental plant. Also known as Formosa lily, St Joseph’s lily, Easter lily and Trompetlelie or Sintjosefslelie, the lily has a magnificent, pungent, white, trumpet-shaped flower, with subtle maroon stripes down the tube and a stem of soft linear leaves. Interestingly, lilies seldom become problematic in thecountries they’ve been imported into. They are quite particular about their pollinators and soil preference. Lilium formosanum, however, struck it lucky as its pollinator of choice is Agrius convolvulus, a hawk-moth look-alike that is a common and cosmopolitan creature in South Africa.

In Magoebaskloof these elegant invaders flower from February to mid-April and can be seen all along the winding roadsides. Each year the seeds spread further and further into the few remaining fragments of Woodbush Granite Grassland that are clinging to our mountain slopes. If left unchecked, the lilies could destroy the kaleidoscope of seasonal magic that arises from the rich variety of indigenous plants that decorate our mountain ecosystem: our purple fields of Agapanthus, clumps of perfect-white arum lilies, hollows of red Hesperantha, yellow and red dots of Kniphofias, pink Boophane flower wheels, blue and white Merwilla squills and brilliant Watsonias.

According to NEMBA legislation, L. formosanum is a category 1b alien invasive plant species. It is illegal to propagate, plant or trade in the lilies and it must be removed and destroyed wherever possible. Unfortunately, merely pulling out the plants leave treacherous bulbs behind that will sprout malevolently into new lilies. The most effective control method is to apply herbicide (5% Hatchet (active ingredient: Imazapyr) in water) to low-cut stems, immediately after cutting and while the plant is in its active growth stage. This way, poison will reach the bulb and prevent regrowth. Flower heads or buds and seed capsules should be cut off, concealed and incinerated since the seeds ripen even if the capsule is not on the plant.

Another beautiful white exotic lily, Lilium longiflorum, currently not listed as invasive, could be planted in L. formosanum’s place. However, since they are difficult to distinguish, L. formosanum was, until recently, considered merely a variety of L. longiflorum. It is safer to rather plant some colourful local bulbs or to choose from the myriad of indigenous South African plants instead. These are so valuable that their seeds are stored in cryogenic vaults for the future!