Karura Forest #33: Lantana Land
The cache, a small screw-capped plastic tube, is hidden at waist/chest height under twigs/leaf litter in the fork of a multi-stemmed small tree just off the northernmost Tara Path in the forest.
To reach the cache location, after parking at KFEET head north via Junctions 12, 11, 27, 26, 30 and 37 to access the Tara Path which crosses the Ruaka River just east of Huruma Village (see here for map with trail names and Junction numbers). Follow this up and across east to the cache location (passing numerous caches along the way!). See GC4PD3V Karura Forest #1 for background information on the forest, including features, access, maps and useful links.
Lantana camara, also known as wild sage, is probably the most common and widespread plant in the forest. It also has the dubious distinction of being the most studied weed on the planet! It is a species of flowering plant in a 150+ species genus within the verbena family, Verbenaceae, native to Central and South America but which has spread and become naturalised in around 60 tropical and sub-tropical countries worldwide. It is found frequently in East and South Africa where it occurs below 2000m often invading previously disturbed areas such as logged forests and areas cleared for agriculture
It is rarely found in natural or semi-natural areas of forest as it is can't compete with taller trees due to its lack of tolerance for shade, growing instead at the forest edge. It can survive in a wide range of climatic conditions, including drought, different soil types, heat, humidity and salt. It is also relatively fire tolerant and can quickly establish itself in recently burnt areas of forest.
It is a small perennial shrub which grows to around 2m in height and forms dense thickets in a variety of environments. Due to extensive selective breeding throughout the 17th and 18th Century for use as an ornamental plant there are now many different forms of L. camara present throughout the world.
It has small tubular shaped flowers which each have four petals and are arranged in clusters (umbels) at the end of stems. The flowers come in many different colours including red,
yellow, white, pink and orange which differ depending on location, age and maturity. After pollination occurs the colour of the flowers change (typically from yellow to red/pink/orange). This is thought to be a signal to pollinators that the pre-change colour contains a reward as well as being sexually viable, thus increasing pollination efficiency. Its berry-like fruit turns a deep purple colour when mature.
It will often out-compete other more desirable species, leading to a reduction in biodiversity and can also cause problems if it invades agricultural areas as a result of its toxicity to livestock as well as its ability to form dense thickets which if left unchecked can greatly reduce the productivity of farm land.
There are many reasons why it has been so successful as an invasive species. The main factors are:
- Wide dispersal range made possible by birds and other animals which eat the berries
- Less liable to be eaten by animals due to toxicity
- Tolerates a wide range of environmental conditions
- Increase in logging and habitat modification benefits L. camara as it prefers disturbed habitats
- Produces toxic chemicals which inhibit competing plant species
- Extremely high seed production (12,000 seeds from each plant per year)
Control Measures
Effective management of invasive L. camara requires reduced degradation of habitats. Maintaining functioning (healthy) ecosystems is the key to preventing invasive species from establishing themselves and outcompeting native fauna and flora.
Insects and other bio-control agents have been tried - it was the first weed ever subjected to biological control - but without success despite 36 control agents being used across 33 regions. This failure is probably due to its many hybrid forms and the large genetic diversity making it difficult for control agents to effectively target all plants.
Mechanical control involves physically removing the plants which although effective is labour-intensive and expensive, and therefore only appropriate for small areas. Another method uses fire treatment followed by revegetation with native species.
Chemical control with herbicides is very effective but also expensive (prohibiting use in many poorer countries where Lantana is well established).
Uses
Stalks are flexible and have been used in the construction of furniture, such as chairs and tables, but the main uses are medicinal and ornamental.
Studies have shown that the leaves have antimicrobial, fungicidal and insecticidal properties and the plant has been used in traditional herbal medicines for treating a wide variety of ailments, including cancer, skin itches, leprosy, rabies, chicken pox, measles, asthma and ulcers.
It has been grown specifically as an ornamental plant since Dutch explorers first brought it back to Europe from the New World. Its ability to last for a relatively long time without water and the fact that it does not have many pests or diseases which affect it have contributed to it becoming a common ornamental plant. It also attracts butterflies and birds and is often used in butterfly gardens.
See here and here for more information on this attractive but destructive floral invader! See here for a Food & Agriculture Organisation Invasive Pest Fact Sheet.