Lantana
Lantana is an perennial, woody plant that has been spread mainly due to its use in garden landscaping. Lantana camara is commonly referred to just as lantana but there are other species in this genus, and L. camara now has many variants due to horticultural breeding efforts over at least the last 200 years.
The Misplaced
Appearance and Reproduction
- L. camara presents as a medium-sized, perennial (10 year life span), aromatic shrub, approximately 2-5 m tall
- Quadrangle shaped stems, sometimes having prickles. The posture may be semi-erect or occasionally clambering into other shrubs or low trees, clinging to points of contact by means of its prickly branches. Frequently, multiple stems arise from ground level. Stems become rounder with age.
- The leaves are generally a mid-green colour, oval shaped, about 2-12 cm in length, and 2-6 cm across, with a rough surface and a toothed edge.
- The root system is very strong with a main taproot and a mat of many shallow side roots.
- The flower stems appear as flat-topped clumps, each arising from a single point at the end of a stem emerging from a leaf attachment point. The flowers are multicoloured (white, yellow, orange, red, pink, purple) and have 4 fused petals. Flower colour may change with age.
Sexual Reproduction
Lantana flowers in most places all year round if adequate moisture and light are available.
Pollen transfer is carried out by insects e.g. butterflies, bees, thrips; the flowers do not self-pollinate.
Once the ovaries of the flower are fertilised, seeds are formed, 1 - 2 per fruit. The fruits are round and fleshy, about 5mm across and start out green eventually turning black. They are commonly distributed by the fruits being eaten by birds and and other animals.
Mature plants can produce up to 12,000 seeds annually. Seed longevity in the soil is not well documented, but seeds are thought to remain viable for several years under natural conditions.
Asexual reproduction
In addition to being spread by seed, L. camara is able to produce shallow lateral roots, following mechanical damage. Hence, it is also able to spread and establish dense thickets by vegetative (disrupted roots sending out shoots) means.
Ecology
Lantana camara occurs along roadsides, in degraded lands, on river banks, along fence lines and in pastures and parklands, in plantations, forest edges and gaps and invading native vegetation in woodlands and savannas.
L. camara can grow between the latitudes 45°N and 45°S.
Habitat Condition | Preferred Range |
---|---|
Light | Full sun, partial shade |
Altitude | Upper limit 1500 m |
Rainfall | 200 - 4000 mm/year |
Termperature | Cannot tolerate frequent frosts |
Soil texture | Inhibited by waterlogged conditions, heavy clays, salt-affected soil |
Soil pH | Wide tolerance; 4.5 to 8.5 |
Due to its tolerance for a wide range of conditions, this plant has the ability to adapt to climate change.
The Displaced
Lantana's main impact on native vegetation is through vigorous competition and replacement.
Lantana produces allelopathic chemicals in its roots and shoots that inhibit other plants from growing nearby.
As can be seen from the table above, L. camara can tolerate a wide rage of environmental conditions, and it lacks the predators it evolved with in its home territories in Central and South America, so the plant's growth is not inhibited by these factors. Also L. camara has a marked ability to compensate for herbivore attacks as shown by the plants surviving experimental deliberate leaf removal for two years.
The capacity of the species to spread vegetatively, and to inhibit both the growth of other vegetation and seed germination, in conjunction with heavy and regular fruiting, is the main reason why L. camara forms long-lasting permanent thickets which replace the biota native to the region. Because the thickets may become nearly impenetrable, some larger organisms are blocked by their inability to negotiate paths through the thickets.
In areas where natural fires occur, they may stimulate thicker regrowth of lantana.
According to Weeds Australia at https://weeds.org.au/profiles/lantana-common-kamara/
Lantana dominance appears to adversely affect the species richness of soil fauna assemblages, such as ants, and decreases the diversity of soil fungi. It can also affect flora diversity by reducing seedling germination and by increasing the chance and severity of fire in plant communities such as dry rainforest. Lantana has been identified as a potential threat to many threatened and endangered plants and animals and a number of endangered ecological communities.
The Consequences
The plant is native to the Mexico, Central America, the Caribbean (i.e. the Bahamas, Cuba, Hispaniola, Jamaica and Puerto Rico) and tropical South America (i.e. Venezuela and Colombia)
It has now been recorded as introduced in 193 countries or islands. In many of these locations, it has been recorded as disrupting ecosystems by replacing the native vegetation, which then causes herbivore species to disappear due to lack of suitable food.
Lantana Global Distribution
The two maps below record an accelerated spread of lantana over the last 30 years. Each map represents cumulative lantana occurences over the stated time period.
Case study - Queensland, Australia
In Australia, Lantana camara is a Weed of National Significance. Lantana covers 5 million hectares throughout most coastal and hinterland areas of tropical and sub-tropical Australia, from north Queensland to southern New South Wales and including the Northern Territory and Western Australia. Research indicates more than 1300 native species are negatively affected by lantana invasion, including many endangered and threatened species. Queensland is particularly badly effected, as shown by the slideshow below.
Case study, India
Lantana was initially brought to India in 1807 as an ornamental plant at the National Botanical Garden), and as an ornamental hedge plant in Calcutta in the early nineteenth century. It has spread rapidly, forming impenetrable thickets.
A recent study found Lantana camara has invaded more than 40 percent of India’s tiger habitat. The Shivalik hills, Central India, and Southern Western Ghats mountain range are the worst hit.
The species now threatens about 300,000 sq.km of Indian forests.
The map on the left comes from A Battle Lost? Report on Two Centuries of Invasion and Management of Lantana camara L. in Australia, India and South Africa
Controlling the invaders
Prevention
As it is considered very attractive plant, it is still sold widely as an ornamental, although this practice is forbidden by law in many countries. This, of course, means that there is a steady supply of garden plants from which birds and other animals will spread the seeds after eating the fruit. This makes prevention difficult.
Physical control
Hand pulling can work on small infestations, isolated plants and in steep areas that machinery cannot access. Bulldozing or slashing can remove large bushes, and allow access through dense thickets. Both these methods need persistent followups, and can be extremely expensive.
Fire is sometimes used as a control method, but lantana can regenerate after being burnt and the fires may have a deleterious effect on surrounding vegetation.
Chemical control
Many different herbicides have been tried. According to CABI notes:
A number of factors affect the effectiveness of the chemical treatment and they include: plant size, time of application, mode of application, and the use of surfactant. Use of herbicide in uncut stands may not be effective in preventing eventual regrowth. Combination of mechanical and chemical control may be needed.
Biocontrol
Biocontrol agents have decreased the volume of individual plants making other control methods considerably easier. None of the over 40 agents trialled have resulted in total control but some have been partially successful, according to GISD. Because there are so many varieties of lantana bred over the last 200 years, there is a high level of genetic diversity in lantana and this tends to make biocontrol difficult as control organisms may only work with restricted subsets of the species.
Here is a list of trialled organisms from a biocontrol program report from Queensland, Australia, plus a sample factsheet on the first organism on the list.
Other factors influencing control measures
Lantana may be regarded by some sectors of society as useful
- as a raw material for weaving items such as baskets and for making paper.
- as a source of a range of chemical compounds including several for pharmacology usage e.g. The identified constituents of the extracted oil have established pharmacologic and insecticidal activities, and these compounds are also used in the drink, food, and cosmetic industries. This extract is highly valuable for the medical treatment of various ailments. - Chromatographic and spectroscopic determination of solvent-extracted Lantana camara leaf oil
It is claimed to be effective in treating chicken pox, wasp stings and itching skin, measles, influenza, cough, mumps, hemoptysis, pulmonary tuberculosis, hermatitis, eczema, pruritus, rheumatism, sprains, wounds, contusions. - as an erosion control barrier when grown as a hedge
- leafy twigs of Lantana are kept in the bottom of grain containers to avoid termites, mice and other insects.
It should be noted that ongoing exploitation of Lantana camara as a resource will most likely result in major disruption of local ecosystems. The longer term implications of these lantana conserving practices must be weighed against this damage as it likely to be unsustainable.
Ironically, leaf extract of Lantana is highly toxic to water hyacinth (Eichhornia crassipes), another invasive weed.