Erica urna-viridis Bolus
Common names: green sticky heath (Eng.); groentaaiheide (Afr.)
Erica urna-viridis is a very unusual erica as it produces green sticky flowers. This is a very unusual colour in the Cape Flora.
The plants are fairly tall reaching a height of 1m and are easily recognized, as they grow taller than the surrounding vegetation. They characteristically produce long, thin, sturdy, bare woody stems, with small light green leaves, closely arranged around the stems near the ends of the branches.
The flowers are presented in groups of three or four, at or near the tips of the branches and are sticky and green. The main flowering period extends from midsummer into midwinter (December to July), although flowers may also be found at other times of the year.
Erica urna-viridis is classified as a rare plant in the Red Data book because it is restricted to a relatively small section of the Peninsula mountain chain.
Distribution and habitat
This erica is endemic to the central Cape Peninsula and is often found in large and scattered colonies on Steenberg plateau across to the high ridges above Kalk Bay.
Derivation of name and historical aspects
It derives its name from the Latin, urna, meaning 'an urn', and viridis, 'green', referring to the shape and colour of the flowers.
The sticky flowers are believed to serve as a protection against insects intent on robbing the flower of nectar by boring holes in the side of the corolla. The inflated flower narrows at the mouth and nectar is thought to be collected by hovering insects using their long proboscis. The process results in pollination through the transfer of pollen from flower to flower.
These assumptions need further investigation, as approximately 15% of the flowers were found on Steenberg with holes bored in the sides of the corolla. (pers. observation) Insects robbing the flower of nectar presumably cause the damage, as there is little evidence of damage to the ovary.
Malachite sunbirds were seen perching on the strong wiry stems and feeding from the flowers. This is contrary to the principles of pollination suggested by Rebelo, et al. They suggest that the urn shape of the E. urna-viridis flower would attract insect pollinators. It is probable that insects are also involved in pollination as a number were found crawling around inside the flowers.
Another interesting and unusual phenomenon was the presence of witch's broom on a number of plants. Witch's broom is commonly found on certain proteas, but not normally associated with ericas. The cause is not known, although it is believed that a mite insect is associated with this disease, which maifests itself in a bushy proliferation of malformed shoots and leaves. It was found on individual branches of some plants on Steenberg and appeared not to affect the rest of the plant.
This erica regenerates from seed after fire and does not have the ability to resprout.
Growing Erica urna-viridis
This species is relatively hardy and will tolerate a range of Mediterranean conditions provided the soil is well drained, acidic and the plant is growing in a sunny position. It must be staked if allowed to grow to its natural tall size.
Erica urna-viridis grows in sandy, acidic soils derived from quartsitic rock. It is most at home on stony soils chiefly on south and west facing slopes and ridges where the plants are exposed to cool summer winds. The ideal pH is between 5.5 and 6.7.
Its tall weedy growth habit is easily overcome by regularly pinching out the growth tips. This practice not only improves the shape of the plant, but also results in it living longer. The approximate life expectancy ranges from 7 to 12 years and sometimes longer. A suitable growing medium includes two parts acid, river sand, two parts composted pine bark or needles and one part loam.
There are no major pest or fungal problems to contend within the garden.
Weekly applications of organic seaweed derived fertilizers has proved a safe method of feeding. Better growth may be achieved by applying controlled release fertilizers. Trials using small amounts of the slow release granular fertilizer 3:1:5 have given very positive results. Care must however be taken not to feed too much, which will result in too rapid growth for the roots to support. Applications of seaweed based organic fertiliser have proved very useful in overcoming the effects of stress from excessive heat or root disturbance.
This plant is normally grown from cuttings as separating the seed from the sticky flowers is not easy. Cuttings are taken in autumn or spring and require bottom heat and overhead misting or fogging. Fresh, actively growing, shoot tips or heel cuttings root best. Cuttings are rooted in a medium consisting of equal parts decomposed milled pine bark and polystyrene pellets for drainage. Rooting is enhanced by the application of a rooting hormone suitable of semi-hardwood cuttings. Rooting may take from six to ten weeks. The roots are very delicate and rooted cuttings should therefore be planted out with great care.
If seed is collected it should be sown in autumn and subjected to the smoke treatment used to stimulate germination in many fynbos plants. The young seedlings should be protected from heavy rain, watering and direct sunshine. Seedlings will thrive under a covered area if provided with good light, air circulation and regular gentle watering. The seed should germinate within four to six weeks. The germination rate deteriorates as the seed gets older.
- Baker, H.A. and Oliver, E.G.H. 1967. Ericas in Southern Africa. Purnell, Cape Town and Johannesburg.
- Goldblatt, Peter and Manning, John. 2000. Cape Plants A conspectus of the Cape Flora of South Africa. Strelitzia 9. National Botanical Institute.
- Hilton-Taylor, Craig. 1996. Red Data List of Southern African Plants. Strelitzia 4 National Botanical Institute.
- Oliver, Inga & Ted. 2000. Field Guide to the Ericas of the Cape Peninsula. Published by the Protea Atlas Project, NBI, Cape Town.
- Rebelo, A.G., Siegfried, W.R. and Oliver, E.G.H. Pollination syndromes of Erica species in the south-western Cape. S. Afr.J. Bot., 1985, 51(4).
- Schumann, D (Dolf) & Kirsten, G (Gerard) 1992. Ericas of South Africa. Fernwood Press, Vlaeberg Cape Town.
Kirstenbosch National Botanical Garden
Plant Type: Shrub
SA Distribution: Western Cape
Soil type: Sandy
Flowering season: Late Summer, Autumn, Winter, Sporadic/All year
Flower colour: Green
Aspect: Full Sun
Gardening skill: Easy