Pachypodium namaquanum
Introduction
Pachypodium namaquanum must rate as the most sought-after and popular of all large succulents from the arid Northern Cape and southern Namibia, otherwise known as the Gariep Region (Orange River region). These iconic survivors of the Richtersveld have stood the test of time and have a peculiar beauty about them, and a mysterious, almost magical side that has fascinated generations upon generations.
Description
Description
Pachypodium namaquanum, the halfmens (half plant, half human), is a succulent plant that can attain a tree-like appearance when fully grown. The stem height may range between 1.5 and 2.5 m, although 4 and 5 m specimens have been observed. The stems are mostly unbranched and cylindrical but may become branched from near the base and occasionally have a few shorter branches near the apex (tip). Plants are characteristically thickset at their bases, tapering toward the apex, which gives them an unmistakable bottle-like appearance when mature. The stems are covered with warty tubercles (knob-like projections), from which spines protrude in a slightly downward direction. The spines are more abundant along the top half of the plant and decrease towards the base where tubercles are more prominent.
The leaves, which are borne in rosettes (cluster of densely spirally arranged leaves arising from a central point), are simple, obovate to oblong, green-grey, and densely velvety on both surfaces. Leaf apexes are tapering or rounded, and the bases narrowly tapering. The leaf margins are entire and very wavy which is another distinctive characteristic of this succulent. Leaves are always formed in crowded rosettes near the stem apex.
The flowers, which appear from July to September, are tubular, up to 50 mm long and 10 mm across at the mouth. They are red on the inside and yellow-green outside.
The fruits are horn-like, with twin pencil-thin tapering capsules of up to 50 mm long that are joined at the base. Short, soft and grey hairs densely cover the fruit. Fruits are pale brown and split to release the wind-dispersed seeds which are about 4 mm long and are attached to a tuft of whitish hairs that act as parachutes. Seeds normally ripen from September to December. Plants are extremely slow growing, around 0.5-1.5 cm per year, and can attain an age of one hundred years or more.
Conservation Status
Status
Pachypodium namaquanum is listed as a Lower Risk (LR) and Near Threatened (NT) species according to the Southern African Plant Red Data List (Golding 2002). This means that after the species had been evaluated, it failed to meet the criteria for Critically Endangered (CE), Endangered (E), or Vulnerable (V). This succulent does not qualify for Conservation Dependent (species which are the focus of continuing conservation programmes), but maybe is closer to qualifying for Vulnerable, i.e. plants that are at risk of becoming endangered.
However, notwithstanding its local status, this particular plant is listed on CITES as an Appendix 1 and 2 species, which means that its trade is prohibited and the import or export of such plants is subject to the obtainment of certain certificates and permits. For further information on the Convention on International Trade of Endangered Species of Wild Fauna and Flora (CITES), log on to www.cites.org.
Threats to P. namaquanum and associated flora include mining for diamonds and other minerals, overgrazing by sheep and goats in mountainous areas, alien plant invaders (e.g. Prosopis spp.), and illegal removal of succulents by collectors and traders (Van Wyk & Smith 2001).
Distribution and habitat
Distribution description
Pachypodium namaquanum is found in dry rocky deserts at altitudes from 300-900 m above sea level in the Gariep Centre (a centre of floristic endemism), which has the greatest variety of succulents on earth. The climate is harsh and the weather can be quite unpredictable. Rainfall varies from as little as 50 to 150 mm, and occurs mainly in winter. Extreme aridity is experienced in rain shadows of some mountains where as little as 0-15 mm falls annually. Additional precipitation is supplied by thick layers of fog that occasionally move inland from the coast. The maximum temperature in summer may reach 48 °C with a mean of approximately 25 °C.
The plant is associated with the Succulent and Namaqualand Karoo vegetation types which, according to recent floristic status assessments, is one of South Africa's most important regions. Regionally, it is classified as a botanical hotspot in terms of its botanical diversity and the degree of endemism found in the region.
Plants seem to favour rocky and stony hill slopes that are exposed to extreme summer conditions particularly heat and wind. Populations are relatively common in the northwestern mountains of South Africa and the southern mountains of Namibia. Well-known populations are found in the Richterveld National Park which consists of a vast series of rugged mountains and the hot dry Gariep River (Orange River) Valley that divides the lunar-like landscapes of South Africa and Namibia. The areas around Umdaus north of Steinkopf and Rosh Pinah in Namibia are among the places of distribution.
The genus Pachypodium belongs to the Apocynaceae (oleander) family, a well established family in gardens all over the world. There are 23 different species of Pachypodium in the world and 18 of them occur in Madagascar. Pachypodium namaquanum is one of five southern African species. The other members are P. bispinosum (bobejaankos) and P. succulentum (ystervark kambro) from the Karoo, P. saundersiae (kudu lily) from the Lowveld, and P. lealii (bottle tree) from the Kaokoveld in Namibia.
Most members of the Apocynaceae family are found in the tropics where they are usually evergreen trees, shrubs or climbers. In southern Africa, particularly in the warmer drier areas, they are mostly stem succulents or caudiciforms (succulents with swollen stem bases). Popular examples of these plants are Adenium obesum, A. multiflorum (impala lily of the Kruger National Park), A. boehmianum (pylgif) and Fockea edulis (kambro), etc. Another well-known South African plant in this family that is also commonly used in indigenous gardens locally is Carissa macrocarpa (num-num) and C. bispinosa from the Karoo, which bear edible red fruits.
Derivation of name and historical aspects
History
The generic name Pachypodium is derived from the Greek word pachys meaning thick and podion which means foot. The specific name namaquanum refers to Namaqualand, a semi-arid region in the northwestern part of South Africa which is renowned for its spring displays of wild flowers.
Ecology
Ecology
Pachypodium namaquanum belongs to the Apocynaceae family, a group of plants with milky or watery sap and generally simple, opposite leaves. It is pollinated by ants and bees which are able to enter the tubular flowers with ease.
Sugarbirds have been observed pollinating cultivated plants in the Karoo Desert National Botanical garden in Worcester, South Africa. Whether the same is true in wild populations is uncertain. After fertilisation, the fruits take two to three months to ripen after which the seeds are dispersed. The seeds are about 4 mm long and are attached to silky hairs which act as parachutes. In the presence of winds, particularly updrafts, the seeds can be blown over vast distances. The parachute seed strategy is also employed by other members of the family, and is an effective way of ensuring healthy, reproductive populations.
It is known that desert plants normally limit exposure to solar radiation but P. namaquanum is simply doing the opposite. In response to the lower position of the sun on the horizon during winter and the associated cooler conditions, these plants have adopted a clever method to increase the photosynthetic effect of the sun. This is particularly important as most growth takes place during winter. The stem with its leafy flower heads always inclines towards the north at an angle varying between 20 °C and 30 °C. This tendency, which is shared by some low-growing succulent euphorbias and the Chilean cactus (Copiapo cinerea ), is sometimes explained by the so-called 'magnetic plant' theory. However, it is unlikely that these plants are attracted to the poles by magnetism. A more probable theory is that plants such as P. namaquanum are strongly phototrophic (grow in response to stimuli by sunlight) and grow in places where the sun is in the north for the greater part of the year. They lean northwards to allow maximum exposure to their growing shoots as well as to use the sunlight in the winter to make their flowers more visible to pollinators, thus increasing the plant's chances for seed set. It is a bizarre spectacle indeed when one observes these plants 'looking' towards the north.
As with most plants in the arid Richtersveld and surrounds, survival is of extreme importance. The swollen stem bases act as moisture reservoirs to help the plant cope with extreme drought periods. It does not have succulent leaves to store water, and in fact the leaves shrivel up and fall off in the hot summer months. The tufts of velvety leaves appear again during the brief winter growing period, and act as solar panels that manufacture the energy needed for growth and reproduction.
Uses
Use
Whether succulent or shrubby, most members of the Apocynaceae family have milky white sap, and many are known to possess poisonous alkaloids in their tissue. It is therefore not surprising that the sap of some members such as Pachypodium lealii (bottle tree) and Adenium boehmianum (pylgif) is still used for arrow poison. There are numerous examples of fatalities caused by the extremely potent glycosides and alkaloids found in these plants and, although the family Apocynaceae contains attractive garden subjects, it is best to treat all members of this family as poisonous, or to at least caution their use in horticulture. There are some exceptions such as Carissa macrocarpa which bear highly nutritious edible fruits which are eaten fresh or made into a jam.
It is known that P. namaquanum also contains poisonous alkaloids as its sap is also used for arrow poisons. The sap can also cause blindness when in contact with the eyes. It is said that when the spines that arise from the stem are stroked, the plant produces a series of clicking sounds that supposedly mimics the clicks of the Nama language (a population of people found in northwest Namaqualand).
Perhaps the most fascinating story that links these plants to the people of Namaqualand is the legend of the halfmens. It is believed that these trees are half human, half plant, which is easy to understand because, when seen in the distance against the skyline, they could easily be mistaken for humans especially when in family groups. Nama folklore provides a delightful explanation for the tilting of the halfmens. A tribe which once occupied a more forgiving part of southern Namibia was driven southwards after a long and bloody conflict. Eventually its members found themselves fleeing to the Richtersveld, a forsaken mountain desert with a fiercely broken landscape that must have been created by the gods in a moment of rage. Overcome by grief and longing for their homeland, a few among the tribe paused to gaze northward for the last time. The gods took pity on these wretched souls and turned them into half humans or halfmens in order to comfort them with a distant view of their lost homeland for eternity (Cowling & Pierce 1999).
Unlike some other plants from the Richtersveld and northern Namaqualand, Pachypodium namaquanum does not do at all well away from its natural environment. Although seeds germinate readily, it is not easy to cultivate plants in gardens. They are also not common in cultivation as the plants are protected by conservation law.
Growing Pachypodium namaquanum
Grow
Pachypodium namaquanum grows easily from seed as long as the seeds are fresh and without signs of parasitism. The silky-haired parachutes are removed prior to sowing. Seeds can be sown in the summer using a mixture of river sand and sifted compost or bark at a ratio of 1:1. After germination, care should be taken not to overwater as this encourages rot and fungal infestations. Keep plants well ventilated and in good light, and dry plants out in the dormant season which is summer (October to March).
Pachypodium namaquanum can also be grown from cuttings, although success is not guaranteed. Cuttings also take an extremely long time to show active growth. They should be taken in the period just before the growing season starts. The apex (tip of the shoot or leaf) of the stem which contains actively dividing cells is used and the wound is treated with a fungicide or flowers of sulphur and then left to dry for at least two weeks. Cuttings are inserted vertically into a well-drained, sandy medium. The same medium used for germinating seeds can be used for cuttings. Cuttings are kept in a hot, well-lit and ventilated area, and watered sparingly in the winter months; once a week should be more than enough.
Plants in cultivation at the Karoo Desert National Botanic Garden and the Kirstenbosch succulent collection seem to benefit greatly from organically derived fertilisers. Plants in the succulent collection at Kirstenbosch are provided with additional heat by means of heat cables that are buried in the soil. It is inevitable that these plants would require this essential heating in the northern hemisphere countries and be sheltered from the colder wet weather.
References
- Coates Palgrave, M. 2002. Keith Coates Palgrave Trees of southern Africa , edn 3. Struik, Cape Town.
- Court, D. 1981. Succulent flora of southern Africa. Balkema, Cape Town.
- Cowling, R. & Pierce, S. 1999. Namaqualand , a succulent desert. Fernwood Press, Cape Town.
- Germhuizen, G. & Meyer, N.L. (eds). 2003. Plants of southern Africa : an annotated checklist. Strelitzia 14. National Botanical Institute, Pretoria.
- Golding, J. 2002. Southern African plant Red Data List. SABONET, Pretoria.
- Jackson , W.P.U. 1990. Origins and meanings of South African plant genera. University of Cape Town Ecolab.
- Leistner, O.A. 2005. Seed plants of southern tropical Africa : families and genera. SABONET, Pretoria.
- Nichols, G. 2005. Growing rare plants. Southern African Botanical Diversity Network Report No. 36. SABONET, Pretoria.
- National Botanic Gardens of South Africa , 1980. Wild Flowers of South Africa , Cape Town , Struik
- Smith , C.A. 1966. Common names of South African plants. Memoirs of the Botanical Survey of South Africa No. 35.
- Stearn, W.T. 2003. Stearn's dictionary of plant names for the gardener. Cassel , UK.
- Van Jaarsveld, E., Van Wyk, B-E. & Smith, G. 2000. Succulents of South Africa. Tafelberg, Cape Town.
- Van Wyk, A. & Smith, G. 2001. Regions of floristic endemism. Umdaus Press, Hatfield, Pretoria.
- Van Wyk, A.E. (Braam) & Van Wyk, P. 2000. Trees of southern Africa. Briza Publications, Pretoria.
- Van Wyk, B-E. & Gericke, N. 2000. People's plants. A guide to useful plants of southern Africa. Briza Publications, Pretoria.
- Williamson, G. 2000. Richtersveld, the enchanted wilderness. Umdaus Press, Hatfield, Pretoria.
Credits
Werner Voigt and Olivia Pekeur
Kirstenbosch NBG
June 2007
Plant Attributes:
Plant Type: Succulent
SA Distribution: Northern Cape
Soil type: Clay, Metal-rich
Flowering season: Winter
PH: Acid, Alkaline
Flower colour: Red, Yellow
Aspect: Full Sun
Gardening skill: Challenging
Special Features:
Attracts birds
Drought resistant
Feature plant
Good potplant
Poisonous
Horticultural zones
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