Mimetes argenteus
Introduction
‘I once saw two men, veritable rough diamonds, who probably had never noticed a flower before, stop in their tracks before a vase full of these flowers. They looked half-bewildered as if they could not believe what they saw.’ This is quoted from Marie Vogts’ book titled Proteas: know them and grow them, and gives us a clue to the absolute splendour of this magnificent plant that could very well compete with the beautiful foliage of the much-adored silver tree.
Description
Description
Mimetes argenteus is a single-stemmed, sparsely branched, perennial shrub or small tree, reaching a height of 1.0–3.5 m and a spread of 0.5–2 m. The single main trunk can reach a width of about 80 mm in diameter, and branching occurs near the base of the trunk.
A distinctive feature of M. argenteus is its tendency to produce long, straight, unbranched shoots, sometimes as much as a metre or more in length, without developing any side branches. They are occasionally dichotomously branched.
Bark of the trunk is thin, smooth and grey. Stems are reddish rose near the tip and are clothed with hairs held at right angles.
Of all silver-leaved Proteaceae in southern Africa, Mimetes argenteus has the most brilliantly reflective, scintillating foliage (Rourke 1984). The leaves are elliptic to broadly elliptic (oval-shaped) and spread out at right-angles from the reddish stems; leaves nearest the tip are shaded with old rose, creating a dazzling sight. Leaves are 40–65 mm long and 18–36 mm wide, having 1 to rarely 3 glandular leaf tips. Leaves are densely silvery sericeous (silky, clothed with close-pressed, soft and straight pubescence) and the margins are sericeously ciliate (fringed with hairs), making the leaves luminous in the sunlight. These colourful, silvery leaves subtend (lay beneath) a headlet of 6–9 flowers. Leaves are brightly coloured with deep carmine to pale mauve during flowering, which occurs from autumn to winter (March to June).
The broadly cylindrical, terminal flowerhead can reach a length of 80–150 mm and a width of 100–120 mm. Floral bracts are relatively inconspicuous in comparison to the leaves, 7–15 mm long, 5–8 mm wide, tightly clasping perianths and becoming woody in the fruiting stage, with the outer surface slightly hairy.
Perianth segments are almost entirely free and symmetrical. Styles are yellow and 40–45 mm long, while the pollen presenter is 7–8 mm long, geniculate (knee-bent) at the style junction and cylindrical with a terminal spur.
The fruit or seed is an ovoid, whitish nut, 7–8 mm long, 5 mm wide, and is either smooth or covered with miniscule hairs. Seeds differ marginally in shape and size between species. Seeds are released 2–6 months after flowering and have fleshy, oily attachments known as elaisomes.
Conservation Status
Status
Mimetes argenteus is listed as Endangered (EN) on the IUCN Red List, since it is facing a high risk of extinction in the wild. Populations are currently decreasing because of habitat degradation, changes in native species dynamics, by invasive alien plant species, and mature individuals are disappearing due to ground water extraction. Too frequent mountain fires are also a threat, since plants are not given sufficient time to reach flowering and seed stage, thus regeneration is impaired.
The alien invasive Argentinian Ant (Linepithema humile) also poses a major threat, since M. argenteus relies solely on indigenous ants to disperse and bury seeds underground, whereas the Argentinian Ants simply eat off the seed elaisome in situ and leave seeds exposed on the soil surface, where they are predated on by birds and rodents or burnt by fires. In addition to cheating the plant, this ant also destroys indigenous ant colonies wherever it might settle.
Distribution and habitat
Distribution description
All species of Mimetes are endemic to the Cape Floristic Region in the Western Cape Province of South Africa, occurring nowhere else in the world, and M. argenteus is seldom seen except by mountain hikers. M. argenteus occurs mainly on the moist, southern slopes of the Hottentots Holland, Franschoek and Riviersonderend Mountains, forming a gentle arc in the southwestern Cape Mountains.
The silver pagoda is an exclusively montane species, growing at high altitudes near the coast where it is wreathed in cool, moist cloud mist carried in by the southeasterly winds, allowing it to receive additional summer moisture. The region in which this plant occurs receives over 2 000 mm rainfall annually.
M. argenteus favours cooler sites and is usually found in small populations or scattered groups of few individual plants which can be found growing along the middle slopes, at altitudes between 350–1 400 m in very well-drained situations on coarse, gravelly, heavily weathered Table Mountain Sandstone in association with ericoid and restiod fynbos. Occasionally, populations occur on deeper soils where black peaty deposits, highly acidic in character, have formed in seepage areas, which are well drained.
In drier situations, especially towards the eastern extremity of its distribution range, it tends to be much rarer and even more widely dispersed.
Derivation of name and historical aspects
History
The genus Mimetes is readily distinguished from all other Proteaceae, by the large cylindrical flowerheads. The genus consists of 13 species which are grouped together according to individual characteristics, namely the tube pagodas, the golden pagodas, the cowl pagodas and the silver pagodas. The silver pagodas are defined by their characteristic silver leaves, inconspicuous involucral bracts and horizontal leaves, which are brightly coloured during flowering. M. saxatilis forms part of this group, although it has grey leaves (Rebelo 1995).
R.A. Salisbury established the genus Mimetes, which is a word derived from the Greek word μιμητής, which translates into ‘imitator, copyist or a presenter of characters as an actor or dancer would’. This is likely referring to the leaves which in shape, size and arrangement, are remarkably like those of some species of other genera. The species name argenteus translates from Latin to ‘silvery, as to tint and lustre’ (Jackson 1979), and obviously refers to the gentle sheen and soft-glowing, silvery appearance of the leaves.
Mimetes argenteus was first described in 1809. However, there is an inconsistency between the collector’s name given in the original description of M. argenteus and the name inscribed on the ticket accompanying the type specimen in Salisbury’s herbarium. Salisbury’s published account of M. argenteus reads: ‘Mr. F. Masson discovered it by rivulets near the river Zonder End’, while a ticket in Salisbury’s hand, attached to the type specimen in the latter’s herbarium, now at Kew, reads: ‘by the mountain rivulets near the river Zonde Einde Niven 72’. It seems that Massons’s name was mistakenly substituted for Niven’s in the published description (Rourke 1984).
M. arboreus is the only other Mimetes species that could possibly be confused with M. argenteus. To compare, M. arboreus has lance-shaped leaves, thicker bark and a dense, rounded crown of repeatedly dichotomously branched stems and reaches an impressive height 2–6 m; it occurs mainly as solitary plants, sometimes as small groves, in the Kogelberg area.
Ecology
Ecology
Mimetes are almost entirely dependent on birds to effect cross pollination. Bees, flies and other small hymenoptera may occasionally be responsible for a chance act of cross pollination, but their effective role in this process is undoubtedly minimal.
Nectar is the chief attractant. Nectar droplets are secreted into the perianth tube from four nectaries at the base of each flower.
Malachite Sunbirds (Nectarinia famosa), Lesser Double-collared Sunbirds (Nectarinia chalybea) and Orange-breasted Sunbirds (Nectarinia violacea), are the principle sunbird species feeding on and cross pollinating species of Mimetes, with the latter species of Sunbird being most frequently in attendance (Rourke 1984).
All Mimetes (except M. cucullatus which has a resprouting subterranean lignotuber) regenerate by means of seed, do not resprout after fire and are dependent on myrmecochory (seed dispersal by ants). The elaisomes on the seed are irresistibly attractive to ants, which scatter from their nests within seconds upon detecting a ripe seed, and carry the seed off to their nest where they feast upon the highly nutrient and protein-rich appendage. This could be classified as a mutualistic relationship between the ant and plant since both benefit: the ant has a source of food and the burial of the seeds aids the plant to escape predation by seed-eating rodents and birds, and to ensure protection from fire and underground storage for maturation until the next regeneration.
It has been noted that very few seeds are ejected from ant’s nests once the elaisomes have been eaten. This could be due to the very hard and smooth seed cases remaining once the elaisome has been removed, making it difficult for the ants to grip and carry the seed away, this is a marvelous adaptation to ensure burial of the seed for future regeneration.
Another fascinating adaptation of Mimetes and a few other proteaceae genera is the tendency to release seed in the evening after 4pm—the exact time when ants are becoming most active. This is because ants ignore seed that has withered, dried or where the elaisome is less attractive. This precise timing further ensures seed dispersal (Slingsby & Bond 1981).
Growing Mimetes argenteus
Grow
Mimetes argenteus attracts sunbirds and sugarbirds to the garden and would be a beautiful addition to one’s plant collection. Plants are slow growing, but long lived in the right position (Duncan et al. 2013) and would therefore suit the care of a patient and careful gardener.
Anyone attempting to grow M. argenteus must keep in mind that it is a narrow endemic and may grow poorly outside of its natural environment. This more difficultly grown species of Mimetes would be well suited to cooler, misty, coastal or mountainous areas, where natural humidity can be provided (bear in mind that the leaves should not be sprayed with water or wet), and is best grown in a deep container or rock garden pocket.
M. argenteus should be placed in an area where the roots will not overheat on very hot days and receive a natural water supply not treated with chemicals. M. argenteus does not grow well in dry or waterlogged soil and should be planted in well-drained sandstone soil of an acid pH, without any compost, and placed in a full sun or lightly shaded position that is very well ventilated. Since the roots are highly sensitive to soil disturbance and prefer a cooler temperature, an acidic mulch of fine, composted pine-bark or pine-needles is recommended to keep the soil cool in summer (Duncan et al. 2013). Light pruning of the branches after flowering will enhance the shape of the plant and prevent it from becoming too lanky (Duncan & Brown 2006).
Pests:
M. argenteus roots are susceptible to the water-borne root fungus Phytophthora cinnamomi. Leaves are susceptible to attack from leaf miner catepillars, which can cause considerable damage to the leaves. Stems are sometimes susceptible to stem-borer which has been noted on a few plants in the wild (Robbie Thomas pers comm.).
Propagation:
Propagation of M. argenteus is mainly by cuttings or grafting, the latter proving to be the more successful method.
Seed:
Seed germination has proven to be rather unsuccessful considering erratic germination rates and difficulty in sourcing sufficient seed quantities. However, it could be possible to increase germination rates by allowing a two- to three-year waiting period for the seed to mature (Robbie Thomas pers. comm.). Seeds do not respond to smoke treatment and should be sown during Autumn (March to April), after being scarified. Seeds can be scarified by soaking them in a 1% hydrogen peroxide solution for 24 hours. This will oxygenate the seeds by loosening the seed coat, which should then be rubbed off. Seed should be dusted or watered with a fungicide containing the active ingredient Metalaxyl to prevent fungal attack. Seeds can be sown in seed trays, in a well-drained acidic medium. For instance, 8 parts finely milled pine bark and 3 parts coarse sand can be mixed to form a medium (Duncan et al. 2013).
Once seeds are sown, the medium should not be allowed to dry at all. Keep it moist and at alternating temperatures between 10°C and 23°C (Robbie Thomas pers. comm.).
Germination can take up to two months, and seedlings can be planted into small bags once their first set of true leaves has developed. Thereafter, they should be allowed a grow-on period for about one year before planting out into the garden or permanent container. While transplanting, be careful not to damage the roots of the young plant, and do this at a cool time of day, making sure the roots do not dry out.
uttings:
Heel cuttings of M. argenteus can be taken from branch tips or side shoots, from young new growth that is slightly firm but also not too soft. Cuttings should ideally be 100–120 mm long, finger thickness, and kept cool after harvesting. Cuttings are best taken early morning while shoots are turgid and temperatures are low. Ensure that secateurs are sharp and cleaned with alcohol swabs before use.
Cuttings are to be treated with a rooting hormone suitable for semi-hardwood cuttings. These must be placed in multitrays or pots filled with a moist rooting medium made of 1 part finely milled bark and 1 part polystyrene balls (the medium should be sterile and treated with a fungicide before cuttings are placed into it). Place these in a well-aerated misting unit with bottom heating of 22–25°C.
Cuttings root well but slowly, taking between six weeks and four months. Check the cuttings regularly and remove any wilted or infected cuttings immediately. A general spraying programme may be necessary to control fungi.
Rooted cuttings must be potted into pots containing a moist medium of 1 part acidic river sand and 1 part composted pine needles or finely milled pine bark. These should be hardened off for three weeks under 50% shade cloth, before being placed in full sunlight.
Grafting:
For detailed, illustrated information on grafting Mimetes, please refer to the book Kirstenbosch Gardening Series ‘Grow Proteas’ 2013.
References
- Duncan, G., Brown, N. & Nurrish, L. 2013. Grow proteas. Kirstenbosch Gardening Series. South African National Biodiversity Institute, Cape Town.
- Daydon Jackson, B. 1979. A glossary of botanic terms. Duckworth, London.
- Eliovson, S. 1965. Proteas for pleasure: how to grow and identify them. Howard Timmins, Cape Town.
- Garrett Rice, E. & Compton, R.H. 1950. Wild flowers of the Cape of Good Hope. Cape Times Limited, Parow.
- Vogts, M.M. 1958. Proteas, know them and grow them . Afrikaanse Pers-boekhandel, Johannesburg.
- Rebelo, A.G. 2001. Proteas. A field guide to the proteas of southern Africa, edn 2. Fernwood Press, Vlaeberg, Cape Town.
- Paterson-Jones, J.C. 1978. ‘Mimetes’. Veld & Flora 64(3): 78–80
- Rourke, J.P. 1984. A revision of the genus Mimetes. Journal of South African Botany Volume 50.
- Slingsby, P. & Bond, W. 1981. ‘Ants-friends of the fynbos’. Veld & Flora 67(2): 39–45.
- Smith, C.A. 1966. Common names of South African plants. Memoirs of the Botanical Survey of South Africa No. 35. Government Printer, Pretoria.
Credits
Megan Blatchford
Kirstenbosch National Botanical Garden
May 2015
Acknowledgements
- Thanks to the library assistant at Harry Molteno Library for being so efficient and helpful in her duties.
- Thanks to Robbie Thomas who has shared a great deal of his knowledge on grafting of mimetes and is always willing to offer advice and help.
- Thanks to Alice Notten for always making herself available to help and being of great assistance in explaining botanical terminology.
Plant Attributes:
Plant Type: Shrub
SA Distribution: Western Cape
Soil type: Sandy
Flowering season: Autumn, Winter
PH: Acid
Flower colour: Pink
Aspect: Full Sun
Gardening skill: Challenging
Special Features:
Attracts birds
Horticultural zones
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