Articles: BULB CHAT June 2010 PDF Print E-mail
Thursday, 26 May 2011 23:47

Bulb Chat June 2010 No 75

As part of the ongoing theme of preserving our biodiversity and species distribution, including bulbous plants, the talk at the May meeting about the role and importance of wetlands is summarised in Bulb Chat this month. The Cape Floristic Region has a high number of endemic species, with particular water requirements, and a permanent decrease of the water table could lead to extinctions.

Wetlands: and their environment by Lynda Muller

Here in the Western Cape, we live in the sixth largest floral kingdom in the world with almost 9000 plant species, most found nowhere else, thus a major diversity hotspot.

However, rapid urban development, farming and recreational activities constitute a major threat to many species in the few surviving areas, but also increased demand on water resources. One of the most threatened components of fynbos is Renosterveld, rich in geophytes. Because of its fertility and suitability for agriculture, only 1% of what remains is protected.

The City of Cape Town and Cape Nature have created biodiversity corridors to link the isolated nodes and fragments of fynbos to facilitate preservation and distribution of the surviving species, and try to get developers to cooperate with this process. One of the ways in which developers can provide for natural systems, is by the provision of wetlands in their developments.


· Wetlands play an important role in our fynbos ecosystem providing habitat for many of our seasonal plant species and the ecosystem supporting them.

· Wetlands act as a sponge retaining water to re-charge our ground water supplies, attenuating floods and cleaning water by providing a nutrient and toxin sink

One of the most important functions of wetlands is that of flood attenuation. We have had graphic examples recently of wash-aways following a flood when wetlands are replaced with hard surfaces, such as Montagu Spa and Malgas.

Wetlands lead to sustainability of ecosystems, allowing the interaction of different plants and animals. Wetlands provide food and shelter to a wide variety of life, from simple forms such as diatoms to amphibians, reptiles and birds. Unicellular organisms and algae are the chief source of oxygen in the water, and thus play a vital part in nutrient supply.

The Department of Water Affairs defines wetlands as the interface between aquatic and terrestrial ecosystems, whether temporary or permanently inundated.

Identifying a wetland starts with identifying the plant species associated with wet areas: Geophytes are a dead giveaway, and also orchids, of which there are 110 spp in our area, many typically associated with wetlands in our area.

Other wetland plants include restios, sedges, grasses, geophytes as well as flowering plants. Aponogeton angustifolia, an aquatic plant, is common in the Western Cape in seasonal ponds, a sign of early rain.

Topography or lie of the land is another essential component of wetland Identification of salt pans, low-lying pan, dune slack, and seasonal wetlands such as flood plains which dry up in summer.

Soil: in permanent wetlands is grey, anaerobic and anoxic, but supports life and is a trap for poisons. The soil of temporary wetlands has a mottled appearance but none the less performs the same vital function of absorbing poisons and nutrient from enriched runoff.

Examples of local wetlands:

· Kuil's river has factories built right down into the flood plain, resulting in a major wash- away of 3 meters of sand after a very heavy rain. A sewerage pipe was thus exposed and dangling – a potential disaster, illustrating the necessity of wetlands in erosion control, and the prevention of loss of valuable soils.

· Century City, a major development, is built on a large wetland, and utilises canals and basements fitted with pumps to manage the water, routing it back into the constructed wetland ponds, where the water is purified in their soils and planted reeds. Algal blooms are caused during low oxygen conditions such as when carp stir up mud and cause a nutrient overload in the system. The wetlands are now fully functional, with many species of birds and amphibians making the area their home, an example of integration of wetlands.

· The Landfill site at Faure (nice name for the rubbish dump) is being capped and the large lined retention ponds built on the property will retain any drainage from the area. Typha, among other aquatic plants will be introduced to absorb all nutrients and noxious chemicals such as mercury.

· Greenpoint Common, upon which stands the new iconic Cape Town Stadium, was a wetland with waterways 80 years ago, but has now been filled.

Managing storm water attenuation can be a useful part of an urban development, creating ponds in winter which become playing fields in summer, as part of creative development.

Wetlands in urban areas in SA are often highly polluted with sewerage and industrial waste and toxins from road runoff etc. For example: ponds in Killarney receive highly polluted stormwater from the Dunoon area. Islands were introduced and planted and were flourishing within in a month with utilizing all the nutrients introduced by the polluted effluent into the ponds thus preventing the effluent from polluting the Diep river which is the end recipient of the stormwater.

Such floating islands are a new technique being pioneered in US.

In Nature peat bog fragments break off and float in a lake, allowing the plants which are growing on them to clean the water by uptake of chemicals in the polluted water. These pollutants such as phosphorous, and nitrogen are of course plant nutrients. The process of water-polishing by the increased surface area where this exchange can take place is ten times more effective than that of a flat surface of a lake bottom. This process is utilised by artificially constructed floating islands using recycled plastic woven into big potscourer -like mattresses which are then planted with appropriate vegetation for the area where they are to be used. Such islands can also provide platforms for natural hydroculture for vegetables, etc.

A South African Plant "Plant of the Year" for 2010: Insights from Chelsea Flower Show

This article may be a 'first' for "Bulbchat". Yes, it is about a genus that is Indigenous to South Africa and yes, many members of our Association have it, but it is a Gesneriad, not a bulb. Furthermore it is about a hybrid and the art of hybridization, words that are used in hushed tones at IBSA meetings, if at all! However this is a rather special hybrid since it was recently named as The Chelsea Flower Show 'Plant of the Year for 2010'.

It is 'Harlequin Blue', a Streptocarpus hybrid developed by Rex Dibley and his colleagues at their family-run nursery in N.Wales and launched at the Chelsea Flower Show which my wife and I were fortunate enough to attend. We were there at 07h20, near the front of the queue, and when the gates opened at 08h00 we were among the first to be admitted. So, when we came to the Dibleys stand I was able to have a long chat to Rex Dibley before other people arrived.

Rex bred streps as a hobby, while a teacher, and converted his hobby into a business after taking early retirement. He was joined by other members of the family and today Dibleys is almost a household name in gardening circles.

We discussed breeding in general and how they had learned by trial and error over the years which genes were dominant and which were recessive. Blue is dominant over the other colours. There are also genes which determine the prominence of the lines and markings and their positioning on the petals. Dibleys have developed strep hybrids with smaller leaves and many flowers which bloom over an extended flowering period. Having achieved a desired result from cross-pollination, an F1 seedling is multiplied from leaf cuttings. If the F1's are crossed they are unlikely to breed true from seed. He told me that they aim to get two generations a year when cross-breeding, very much faster than breeding clivias, which is my interest.

Another topical reason for my writing this article is that Cameron and Rhoda McMaster brought a specimen of S. kentaniensis in flower to the May IBSA meeting. This drought-tolerant species is endemic to forests in the Kentani area of the Transkei, between Butterworth and the coast near Kei Mouth. I was not at the meeting but hear that it attracted much attention on the plant table, not least because it flowers well in winter short-day conditions, unlike many other species. Mature plants produce small flowers in great numbers over an extended flowering period.

Have a good look at the attached picture of 'Harlequin Blue' (on the right-hand side). The judges at Chelsea consider it a very special plant, and as a hybridizer I appreciate the art and work that have gone into it. Given some of its traits I would not be surprised if S. kentaniensis figures in its background –see picture from the McMasters (on the left).

Streptocarpus kentaniensis Streptocarpus hybrid 'Harlequin Blue'

In fact, Dibleys have used S. kentaniensis in their breeding programme for some years in order to incorporate its favourable characteristics into some of their showy hybrids, a well-known example being the multiflorous 'Crystal Ice'.

'Harlequin Blue' shows what can be done with some of the wonderful plant material that exists right here in our own South African back yard.

John van der Linde

Notes on Plants exhibited at the Plant Table in May

There were some very interesting exhibits displayed on the Plant Table at the last meeting.

The members who grew them are to be congratulated, Hennie Delport on winning the cups for the Syringodea longituba and G recurvus and G priorii, and Cameron McMaster for the beautiful Pelargonium caffrum and Streptocarpus kentaniensis, the latter growing on the moss in the spray along waterfalls, a very topical plant (see John van der Linde's article from Chelsea).

Pelargonium caffrum (Geraniaceae)

by Rhoda McMaster

P. caffrum falls in the Section Polyactum of the Pelargonium genus. It is classed as a geophyte because of its large, woody underground tuber. Its distinguishing features are the spreading (25 mm diameter) fimbriate petals (divided into many long, fine segments) which cause the flowers to look feathery, and the leaves (about 10 cm diameter) which are also deeply dissected into long segments, and these segments are again divided into 'fingers'. The whole plant has a most attractive appearance – fluffy leaves and flowers – and is always a 'talking point'. The first few leaves on juvenile plants are entire, and subsequent leaves become more and more divided.

The particular form that was shown at the May meeting had striking dark maroon flowers, but they can also be yellowish green to purple. The long unbranched peduncle held the 14 flowers well above the leaves. It is grown together with the bulb collection, in similar soil and under very light shade cloth, but watered all year.

P. caffrum occurs naturally in grassland along the southern coast and the adjoining inland areas, from Knysna to Grahamstown, and up to elevations of 1650 m. In nature it tends to flower from October to March, and be deciduous (and is sometimes burnt in the grass fires, or at high elevations there could be frost), but in cultivation it can remain evergreen and flowers sporadically at any time of the year.

References: Pelargoniums of South Africa, Vol 2, Van der Walt & Vorster, 1981; and Cape Plants, Goldblatt & Manning, 2000.


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