Tuesday, May 06, 2008

Argyroderma theartii Van Jaarsv.


Family : Mesembryanthemaceae Common names : baby-toes ( Eng. ); bababoudjies (Afr.) Argyroderma theartii is a beautiful, dwarf, cluster-forming, winter growing succulent plant, bearing striking, bright purple-pink flowers during the early winter months. It thrives in well drained soil and should only be watered during the autumn and winter and kept dry during the summer months. Description Dwarf, rounded cluster-forming succulent plant, bearing 3-10 grey-green heads up to 80 mm in diameter. Leaf pairs fused into a neat cylindric body (up to 35 x 20 mm) with its greatest diameter near the top. The leaf pairs are free and rounded towards the top. Flowers are produced singly, appearing from a fissure between the leaf pairs. It is rose-like, about an inch (25 mm) in diameter, bearing many oblong, narrow, brightly coloured purple-pink petals. The flower is succeeded by its capsule (fruit). Once dried out, the capsule is hygrochastic (term used to explain the opening mechanism of the expanding keels of the capsule lids by means of moisture), only releasing the seed during rain. The capsule ripens during spring and releases seed with each shower of rain. It is top-shaped and 9-12 mm in diameter. The seed are very small and protected within the capsule cavities. They are dispersed by falling raindrops which scatter seed in all directions (the method found in water pistols). This is an amazing adaptation (of most mesembs), where the plant makes use of the energy of the falling raindrops to scatter its seed. Status Although the plant is locally common among the sunny quartz gravel flats in its natural habitat, it is confined to a single farm on the northern Knersvlakte (Afrikaans name for region), thus it needs some form of protection. Fortunately it is easily grown from cuttings or seed. Distribution and Habitat Confined to quartz gravel hills and flats, growing scattered in full sun. It is associated with other dwarf succulent plants such as Argyroderma craterfiormis, A. fissum, Tylecodon reticulatus, T. occultans, Conophytum subfenestratum, Cephlalophyllum caespitosum, Crassula columnaris subsp. prolifera, C. deceptor, C. muscosa, Conophytum minutum. C. calculus, Oophytum nanum, Drosanthemum diversifolium, Adromischus marianiae and Antimima dualis . Rainfall is mainly during winter (May to September) and averages between 50-70 mm per annum. The summers are dry and very hot (up to 40ยบ C on hot days). Winters are cooler but warm during the day and if frost occurs, it is very light and for short periods. Derivation of name and historical aspectsArgyroderma theartii was discovered in 1990 by Major Jan Theart (9 th South African Infantry Battalion), a keen gardener and succulent enthusiast. Argyroderma theartii is one of 12 known Argyroderma species all confined to quartz gravel flats of the northwestern part of the Western Cape . This region is known as the knersvlakte (literally meaning grinding flats, and pertaining to the grinding of the quartz gravel when walked upon). The genus name Argyroderma is Greek, derived from, argyros , silver, and derma, skin, pertaining to its silvery grey-green leaves. The genus was established by Dr N.E. Brown, a botanist from the Royal Botanical Gardens, Kew in 1922. Argyroderma species are popular among succulent enthusiasts due to their appealing, small, sculptural, plant bodies. They grow well camouflaged among the white quartz pebbles. Other popular species include A. delaetii, A. pearsonii, A. patens, A. framesii and A. fissum . The genus Argyroderma is part of the mesemb family (Mesembryanthemaceae) and almost all of its members are confined to southern Africa and its centres of diversity in the winter rainfall region of South Africa and Nambia. EcologyArgyroderma theartii is conspicuous when in flower and pollinated by bees and small beetles. Seeds are dispersed during the first autumn rains. The small seeds germinate among the gravel and look like stones when small, thus very difficult to detect. Its silvery grey-green skin is tough and reflects the sun effectively during the warm dry summers. Uses and cultural aspects Argyroderma theartii is grown by succulent enthusiasts mainly as a potplant. The soil needs to be well-drained sand with quartzitic gravel added. A loam-based garden soil mixed with sand and gravel is ideal. Seed should be sown during the autumn. Germination is within three weeks and the small plants can be transplanted after a year. Sow seed in shallow trays in a sandy mixture. Cover with a thin layer of sand (2 mm) and water by capillary action (place bottom of seed tray in a shallow bucket of water for a while, until sufficient water has been absorbed). Keep in a sunny corner. Water sufficiently during the first winter but keep dry during the summer. The young seedlings can be planted out after a year. Cuttings can be made from leaf pairs during autumn. Cut from as close to the base as possible. Allow to dry out for a week. Plant in sand and water well. Keep in a sunny corner. Rooting should take place within a month. Outside of its habitat it is best grown in a glasshouse. Argyroderma theartii is best grown as a potplant. It also thrives in miniature gardens grown with companion plants such as Crassula and other dwarf mesembs such as Conophytum . It can be grown in rockeries only if the rainfall and climate allows it. Gardens within the karoo region or similar situations are ideal. Soil should consist of gravel and sand with ample loam or clay. This plant needs a sunny site. Only water during autumn and winter and withhold water during summer months. Containers should be well drained. Place a gravel layer at base of container. Water sparingly during the cool months and a liquid organic fertilizer can occasionally be added. Plants can remain in the same container for a number of years. The plant skin should become wrinkly during this time but it is perfectly normal. Pests include the caterpillar of the tiger moth. It is easily controlled by hand or spraying with a contact poison. Author: Ernst van Jaarsveld Kirstenbosch National Botanical Gardens

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