Unique fauna and flora of the Hermanus region
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Milkwoods

The White Milkwood (Sideroxylon inerme) is adapted to withstand harsh coastal winds and can grow into large, beautiful umbrella-shaped trees or can take on the form of shrublike bushes in the coastal forests. The greenish white Milkwood flowers have a distinctive smell which attracts insects. The ripe, edible, purplish-black, spherical fruit is sought after by birds and baboons. The name of the tree is derived from the milky latex present in the bark and fruit. Milkwoods are protected in terms of the Forest Act and a permit is required from Cape Nature Conservation for the pruning and removal of any of these indigenous trees.
Blue Cranes
The elegant Blue Crane , (South Africa's national bird), prevalent in the open farmlands of the Overberg region which they prefer for breeding and feeding, is now viewed as 'globally threatened'. Large flocks of blue cranes may be seen in winter, and breeding pairs in spring to summer. Due to the importance of this region as the last stronghold for blue cranes, the Overberg Crane Group was launched by Cape Nature Conservation and the local farming community in 1991.

SUNDEWS EAT INSECTS FOR SUPPER

Dainty and delicate, the pink and white flowers of the sundew are like small poppies carpeting burnt areas and delighting walkers along the damp rocky edges of mountain paths. One would never associate the carnivorous workings of the plant itself with such beauty.

The sticky glandular hairs co-vering the leaves with a reddish haze are called tentacles- They look like pins stuck into a pincushion and a mature leaf can have up to 200 of them. A glistening sticky sweet liquid is secreted from the head of the tentacle like a shiny dewdrop (hence "drosos" meaning dew) and small insects are duly attracted to the honey smell - and there they stick.

Enzymes are also secreted by the glands that help dissolve the entrapped insect down to its skeleton. The resultant fluid is absorbed into the plant's system.

Sundews grow in nutrient-poor soils, particularly deficient in nitrogen. Carnivory, combined with the ability to photosynthesize, seems to have been their answer to a problem, and a successful one. They vary in height round the world from 1 em to I.5m, from pitcher plants to those with leaves like steel traps. We have about 13 species in the South Western Cape.

Our famous Vliëebos Roridula gorgonias, rare and endangered, in the Fernkloof mountains, is not of this family and functions carnivorously in an entirely different way- See separate story

Sundew is the common name for the family Droseraceae. Below are some of the drosera which grow in the Fernkloof Nature Reserve:

Drosera hilaris photo by Christine Wakfer Drosera slacki photo by Christine Wakfer
Drosera cistiflora photo by Christine Wakfer Drosera aliciae photo by Christine Wakfer
Drosera trinervia photo by Christine Wakfer

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THE LARGEST CARNIVOROUS PLANT IN THE WORLD GROWS ON OUR DOORSTEP

says Bruce Anderson, UCT PhD graduate whose thesis on Roridulaceae in our area is the latest definitive study on this fascinating plant.

Most South Africans don't even realize that carnivorous plants grow in their own country, let alone that the largest carnivorous plant in the world grows on our doorstep.

In fact, South Africa has a great diversity of insect eating plants, mainly belonging to the genus Drosera (commonly called sundews). These plants capture their prey using sticky droplets on their leaves. The leaves of some species curl slowly around the prey enveloping them and exuding digestive enzymes. Another interesting carnivore is Utricularia whose traps are minute and occur underground…

The giant of the carnivorous plant world is called Roridula (or vlieëbos in Afrikaans). This plant can get up to two meters tall and like drosera, its leaves are bedecked in hairs with sticky droplets. The droplets are resinous and much more sticky than Drosera traps. In fact one species of Roridula (Roridula dentata) is even capable of capturing small birds.

BUG SCRUM!

Perhaps one of the most intriguing aspects of Roridula is that the plants have no digestive enzymes to digest their prey. This puzzled scientists for 90 years and initially they believed that Roridula was not a carnivore because it could not digest its prey. They postulated that the droplets were a defense mechanism to stop herbivorous insects from eating them.

But in l996, a student Allan Ellis and his supervisor Jeremy Midgley took an interest in this plant which captured such an abundance of insects. They noticed that there were small bugs (Pameridea-Miridae) which lived on Roridula in a great abundance. The bugs hold their bodies away from the traps and, with specially adapted feet, they can run at great speed over what would be a death trap for any other insect.

These bugs roam the plants in search of food - insect food. When an insect is found, struggling helplessly against the stickiness, the bugs approach cautiously. A jousting match ensues. The bugs probe with their probosci looking for a weak spot in the exoskeleton of the prey. Each time the prey moves, the bug retreats, only to probe again and again. With each probe, a tiny amount of venom is injected and soon the insect prey succumbs and dies.

Within half an hour black bugs would have flown from close by and a massive seething scrum would have developed, vying for a place at the carcass, using their hind legs to lash out at rivals that get too close. The fat, red bug larvae creep unseen between the leggy forest, also keen for some of the bounty. Soon the prey is reduced to a dry husk and the bloated bugs slowly disperse.

NITROGEN FEAST FOR RARE PLANTS….

But before they disperse, they defecate on the leaves of Roridula. The nitrogen rich faeces are fertilizer for Roridula which can absorb the nitrogen straight through their leaves. So Roridula does not need digestive enzymes - it has an army of living organisms to do the job of digestion!

The plant family to which Roridula belongs is called Roridulaceae and it is a special family because it is only found in the Cape Floristic Region. There are also only two species in this family, one (R gorgonias) of which occurs in the mountains around Betty's Bay, Hermanus and Caledon, and the other (R dentata) which occurs in the Ceres mountains, the Kouebokkeveld and the Cedarberg. Both plants occur in isolated populations numbering from a few plants to 2 000 plants. R gorgonias is a red data book species as it is so uncommon. It is generally found in very moist habitats such as bogs, marshes and on the banks of rivers.

AND RARE BUGS ….ITS MUTUAL

The bugs which live on Roridula are also very special because they occur nowhere else in the world. Without Roridula plants they would die. The bugs need to eat insects caught by Roridula in order to mature and reproduce but when there are no insects around to eat, they suck sap from the Roridula plants themselves. The relationship between bug and plant can be described as mutualism which is when two different species are dependent on each other. But the mutualism between plant and bug is even more intimate than only the provision of tasty morsels for each other.

INCESTUOUS POLLINATION?

Juvenile bugs are also the primary pollinators of Roridula. At any time, they can be found crawling around the reproductive parts of the flowers and these bugs are responsible for a large proportion of the seeds set. However, the juvenile bugs have no wings and so more of the pollination by them is between flowers on the same plant. The genetic equivalent is even worse than mating with a twin sister!

Very occasionally, bees can also be seen pollinating Roridula. This may be both important and necessary as it serves to enhance geneflow because bees often fly long distances and can move pollen between distant plants.

The interaction between plant and bug is the basis for a rich ecosystem with plenty of food. One animal group has managed to exploit this system better than any other - spiders.

Roridula gorgonias - flower - Photo by Christine Wakfer Roridula gorgonias - flower - Photo by Christine Wakfer
Pameridea-Miridae with captured moth on Roridula gorgonias - Photo by Bruce Anderson Pameridea-Miridae on Roridula gorgonias - Photo by Bruce Anderson
Pameridea-Miridae - Juvenile bugs are also the primary pollinators of Roridula gorgonias - photo by Bruce Anderson Roridula gorgonias - flower bud - Photo by Bruce Anderson
Pameridea-Miridae with captured moth on Roridula gorgonias - Photo by Bruce Anderson Roridula gorgonias - Photo by Christine Wakfer Roridula gorgonias - flower bud - Photo by Bruce Anderson

          

          

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This website was last updated on
2014 / 4 / 22