Biodiversity

Tuesday, March 13, 2007

RESTIONACEAE - THE ONLY GRAMINOIDS THE DINOSUARS MIGHT HAVE SEEN!

Restionaceae are one of the three commonly referred to elements of the Cape Floral Kingdom. They are all perrenial, evergreen and have a grass-like form and all have reduced leaves (only sheaths) and the stems are the site for photosynthesis. Sexes are on separate plants (dioecious), and their flowers are usually small and wind pollinated. The seed of restios are small seeds, nut(winged or non-winged)and a significant number possess an elaiosome for dispersal by ants. The Family Restionaceae is represented most dominantly in South Africa (350 species, subspecies and varieties) and Australia (ca. 150 species). New Zealand has four species and South America has one species. There is only one representative north of the equator and is wide spread in South East Asia. Restios are becoming increasingly popular world-wide in the horticultural industry since they are tough, virtually maintenance free and have slightly unsual decorative value (visit Willowbridge Shopping Malls/Tyger Valley Waterfront) to see en-mass landscaping).

Restionaceae Origins

The Cape Floristic Region is the real heartland of the Restio family, where they dominant much of the landscape. Their origins appear to date back to the Cretaceous (60 million years ago)- so they were around well before grasses and sedges made their appearance. Possibly there were the only grass-like angiosperms that lived when the last dinosaurs were around – but they would not have attempted to eat them. There are few plants, if any as inedible as restios (that’s why horticulturalists like them), and really only specialized insects can make a living on restio salad. The Restio Leafhopper (Cepalelus) is one highly adapted insect that is present in large numbers on the Restios in the Dog-Leg section of the UWC Campus where the University Admin propose to build the new Life Sciences Centre (see my posting). It is generally accepted that restio have an ancient Gondwana origin and is based on some fossil pollen records. This would explain their presence from South America to New Zealand when the land masses had not broken up and the group had already radiated into each of the future regions of the southern hemisphere. An alternative hypothesis for their distribution across all southern land masses is that the family crossed the Pacific Ocean only relatively recently (30 million years ago) leading to the establishment of the sole South American representative which is closely related to a species from New Zealand.

Restionaceae in Africa

In Africa there are some 350 taxa, but they are overwhelmingly concentrated in the Western Cape (341 taxa) with Eastern Cape and Northern Cape having 47 and 35 taxa each. The Northern Province and Kwazulu Natal have 10 and 6 taxa respectively. There is one taxa each in Lesotho, Mapumalanga and Zimbabwe and two taxa in Malawi and Madagascar.

Restionaceae: Habitat preference

The majority of Restios occur on Table Mountain Sandstone (302 taxa), with a further 42 taxa found on the acid coastal sands. A further 23 and 21 taxa are found on the more nutrient –rich granites and shales respectively. Limestones and alkaline sands have only 15 and 8 representatives. Consequently restios generally most speciose on nutrient poor and acidic conditions such as occurs in our Mountain Fynbos vegetation.

Restionaceae: Fire adaptations

Since fire is an important form of disturbance in Fynbos communities, restio are fire adapted with virtually equal representation (122 and 123 taxa) in coppice regeneration and by seed (where the parent plants are killed). There is only one species that appears not to be fire-adapted Thamnochortus spicigerus which the parent plants are killed by fire and there is poor regeneration from seed. There appears to be little information on germination cues but some eight taxa postively responded to the influence of fire smoke.

Restionaceae: Seed dispersal

Some Restionaceae have relatively simple seeds contained in capsules which splits to release them. The seed size is typically 1-2 mm. In other species a single seed is formed to produce a nut with a variaety of dispersal methods ranging from winged seeds to possessing an elaiosome for dispersal by ants. Even the colour of the elaiosome is white, green or olivaceous. In some species the nut can become quite large (>11 mm) as can the elaiosome (10 mm).

Restionaceae: Growth forms

In growth form most restios are tufted, but sprawling and grass –like forms also exists Less than a third (100 taxa) of Restios appear to have a rhizome and some 77 have a stolon. About 211 restios are without rhizomes or stolons. Restios generally range in size from about 100 mm to the largest forms that are almost 3 m in height.

Restionaceae: Economic value

In terms of economic value, their most important use would be for the thatching industry where nine species are commonly used (Cannomois, Thamnochortus and Willdenowia). Thamnochortus insignis is especially abundant and used in the Bredasdorp area. At least 39 taxa are used in the horticulture industry from the UK to California with Cannomois, Elegia, Ischyrolepis, Restio and Thamnochortus being the most popular. Virtually no restio have economic value for grazing. Although there are no records of restios becoming invasive outside of their home country (I checked using Google Search and various Invasive Alien Species checklists), Thamnochortus insignis populations have established all around Hermanus and where it was introduced as thatch material for roof construction.

Restionaceae Conservation

Since Mountain Fynbos is relatively well conserved most members (256 taxa) are not threatened. Only one species of restio is know to have become extinct Willdenowia affinis) with only eight taxa endangered, 21 vulnerable and 53 considered to be rare.

Links


http://www.dicksonia.com/index.php?id=430

Additional Notes

I have illustrated what can be extracted within 15 minutes of use of Peter Linders’s The African Restionaceae Delta Database vs 2. July 2002. It took about 60 minutes to write this posting. In class you were provided with more than this time. You can either post your own description of the Restionaceae or post comments on this article indicating gaps and other useful information. The intention was to make you think about what features are useful in developing a taxonomic key – it was NOT meant as another exercise. Please remember the external’s evaluation of your work is based mostly on how you have contributed to our Course Blog.

3 Comments:

  • Hi Richard

    I just thought I would point out the word "stolen" (stolon) in the Growth forms paragraph.

    Cheers

    David

    By Blogger davidvaughan, at March 13, 2007 7:45 PM  

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