ISimangaliso Flora: Isoglossa Woodii

16 Jul 2018

Recent visitors to the St Lucia Estuary, Maphelane and other coastal areas of the iSimangaliso Wetland Park may have noticed a proliferation of white flowers adorning the thick plant understorey.

Photos: Caroline Fox

This is Isoglossa woodii, commonly known as buckweed, which grows in relatively dense thickets up to 4m tall and dominates the forest floor, forming up to 95% of the cover in some areas. The plants provide shelter to many of the Park’s common coastal residents such as bushbuck, red duiker and Tonga red squirrels, all of which browse on the growth shoots. The nectar attracts honey bees, and the butterfly larvae of Protogoniomorpha parhassus and Celaenorrhinus mokeezi are known to feed on the leaves.

The Tonga red squirrel and shy bushbuck are two of the common residents that feed off and take shelter in the Isoglossa woodii thickets in iSimangaliso.


Photos: Caroline Fox

While for many years the uniform greenery of the plant is not eye-catching, on average every four to eight years (different periods have been recorded by various researchers, with some as long as ten years) there is a mass flowering which is what St Lucia has just experienced. According to Ezemvelo KZN Wildlife Research Technician, Caroline Fox, the St Lucia colonies last flowered in 2013. Bearing in mind the region has gone through several years of prolonged drought before the recent good summer rainfall, it is a pleasing sight to witness the liberal sprinkling of delicate white flowers decorating the foliage.

Once the flowering is over, the plants all seed and die off together within a short space of time, with the seeds germinating immediately.

Isoglossa woodii is on the Red list of South African plants under the category ‘least threatened’. A recent study undertaken in iSimangaliso by researcher Zivanai Tsvuura focused on the ‘Density Effects of a Dominant Understory Herb, Isoglossa woodii (Acanthaceae), on Tree Seedlings of a Subtropical Coastal Dune Forest’. He states that “The life cycle of I. woodii may hold the key to coastal dune forest dynamics. Since the herb likely suppresses the growth of tree seedlings, and the entry of new recruits into the population can only occur when I. woodii dies back, forest tree recruitment is predicted to be very closely tied to the life history strategy of I. woodii.”

As with so many features of our World Heritage Site, we may only be starting to understand the myriad roles of biodiversity in fauna and flora – a gentle reminder of our duty to protect our heritage as we continue to learn more about it.

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