June 2008


PLEASE NOTE: There will be no 3rd Sunday outing this month as all our usual leaders are away or not available.

28 June (4th Saturday):.  This month’s afternoon walk will be at  the home of Joy Peacock, who has kindly agreed to allow the Society to visit.  We will meet at 2.30 p.m.

I also have some sad news to report, namely that Bob Drummond passed away on Tuesday 3rd June.

Bob was probably the most knowledgeable person about the Zimbabwean flora. His memory was amazing and he was often able to identify plants from small unpromising scraps of plant material.

He also assisted the Tree Society in many ways over the years and we were proud to have him as an honorary member.


Please contact Jean Wiley or Gill Short for details of the next Matabeleland function.


Prof. Carl Linnaeus. Photo: Wikipedia

Prof. Carl Linnaeus. Photo: Wikipedia

Friday 23 May was a very important day for all of us who enjoy knowing what plant (or animal, for that matter) we are looking at. Why? Because 23 May 2008 was the 301st birthday of the great Prof. Carl Linnaeus, who invented the system of plant and animal names we use today.

In the days of way back when, simple single names were all that was needed: Olea would do very well, but only as long as there was no more than one kind of olive to get confused with. A few similar plants could be distinguished by using a single adjective; thus privileged readers in the library at Kew may be able to read in the mediaeval manuscript Hortus Sanitatis (c. 13th century) that Poplar is a tree with two kinds—the black and the white … and that’s where the problems start. A checklist of plants cultivated in southern Africa lists 11 species (and some hybrids and cultivars) of Populus, though only two are European. As more and more plants became known to western scientists, so names became steadily longer. By the time Commelin named a plant he received from the Van der Stels Aloe Africano coulescens foliis glaucis coulem omplectentibus lotioribus et undiquaque spinosis (the African tall-stemmed aloe with broader blue-grey leaves clasping the stem and spiny on both sides), the situation was getting out of hand.

Linnaeus’s genius-level contribution to plant-people’s happiness was to draw a distinction between a name (which is little more than a handle that gives access to information) and a description, which is an important part of that information. So while all the characters in Commelin’s unwieldy mouthful are undoubtedly true, the Linnaean-type name for the plant (actually given by his English contemporary Philip Miller) is much snappier and more memorable – Aloe ferox.

Carl Linnaeus was born on 23 May 1707, son of the pastor in the village of Stenbrohult in the Swedish province of Småland. He studied at both Lund and Uppsala, but needed to go overseas to complete his degree, as it was not possible to get a medical degree in Sweden at that time. And so he went to Holland, where his first stop was the University of Harderwijk, which accepted his thesis (which he had written in Sweden) and granted him a degree all in the space of a week. He made a point of meeting leading medical and biological scientists in the Netherlands, and through their good offices became physician to George Clifford, a wealthy director of the Dutch East India Company. Clifford funded several of Linnaeus’s early publications, most notably a sumptuous account of his garden at Hartecamp near Haarlem; the Hortus Cliffortionus appeared in 1737, and its associated dried specimens are among the treasures of the Natural History Museum in London. This work includes the first published account of many African plants, including Cliffortia, the Rice-bushes.

Linnaeus returned to Sweden in 1739, already with more than the beginnings of a reputation as one of the leading scientists of the day, not only in his own country. He practiced as a doctor in Stockholm for a relatively short while; his patients there included members of the Royal family. In 1741, he received a professorship at Uppsala and he remained there for the rest of his life. Here he was one of the founders of the Swedish Academy of Sciences and published his most important books: Species Plantarum, the foundation of modern plant names, in 1753; its companion Genera Plantarum the following year; and the 10th edition of Systema Noturae, the “baseline” of animal names, in 1758. All of these works ran to many editions during his life, and for about 50 years after he died, and were joined by a large number of books and almost 200 dissertations still consulted by biologists. It’s a small wonder then that Linnaeus was ennobled as Carl von Linné in 1757 and is still regarded as the national icon in Sweden. His legacy includes not only his specimens and writings, but a band of students who travelled to all parts of the world in search of plants (mostly) … and not all of whom survived to tell the tale. And other students went on to have students of their own, who had students… and so, although his blood-family has died out, his intellectual descendants now populate botanical institutions in the countries his ‘apostles’ (his word!) explored as his eyes and ears.

Based on a piece by Dr Hugh Glen, a scientist at the KwaZulu-Natal Herbarium, and published in The Gardener June 2008.


In this fourth in the series on invasive aliens, Lesley Henderson discusses Eucalypts and Myrtles (Myrtaceae).

Sixteen of the 198 species (8%) listed as declared plants in South Africa [see below] belong to the Myrtaceae. This group of plants is unusual in that almost half of the listed species are regarded as both a threat to natural resources and as valuable commercial and utility trees.

The Myrtaceae is predominantly a woody family of the subtropics and tropics, particularly Asia, America, and Australia. Leaves are usually opposite, simple, and glandular-dotted. The Eucalyptus species, however, are unusual in having adult leaves that are apparently alternate. Flowers have many showy stamens and the ovary is usually inferior. The fruit is usually a berry or capsule and is tipped with the remains of the calyx.

The genus Eucalyptus has the highest number of invasive species in the myrtle family in all of southern Africa. The eucalypts are best known for their commercial use as timber trees and windbreaks. They are also cultivated for shade, firewood, ornamental purposes, and honey production. The public are often surprised to hear that some species are invasive and a threat to natural resources. In southern Africa. The listed species are Eucalyptus camaldulensis (Red River Gum), E. cladocalyx (Sugar Gum), E. diversicolor (Karri), E. grandis (Saligna Gum), E. lehmannii (Spider Gum), E. paniculata (Grey Ironbark), and E. sideroxylon (Black Ironbark).

They originate from Australia and are invading watercourses, forest margins, forest gaps, and fynbos zones. With the exception of spider gum, all are recognised as being valuable commercial or utility trees but may be cultivated only in demarcated areas under controlled conditions. Spider Gum has been listed as a category 1 plant (prohibited) in the Western Cape, as it is a serious threat to coastal fynbos, and its use as a sand-binder and windbreak could be performed by other, non-invasive species. The common name probably alludes to the spider-like inflorescence with its strange elongated, curved bud caps covering the stamens.

Eucalypts are well known for their ability to use large volumes of water, which increases with growing availability of water, for example, along watercourses. All the declared eucalypts invade watercourses, and they should be removed from these habitats. Red River Gum, in particular, can form extensive stands along watercourses and is one of the primary target species for removal. Red River Gum is the most widespread eucalypt in Australia, growing along and near watercourses, and potentially has a very wide distribution in southern Africa. Sugar Gum and Karri have been cultivated mainly in the Western Cape of South Africa, and it is here that they are invasive. Saligna Gum is better suited to the more tropical regions of KwaZulu-Natal and the northern provinces [similar to much of Zimbabwe] and is invasive in these regions. Grey Ironbark is suited to the warm and humid summer rainfall zone, but few data are available on its naturalised distribution. Black Ironbark is adapted to dryer and colder areas.

Leptospermum laevigatum (Australian Myrtle) has a similar distribution to Spider Gum, invading sandy coastal areas in South Africa. It is a large, densely branching shrub or small tree up to 8 m high and is used as a windbreak and hedge. It is an aggressive invader, forming dense stands that exclude indigenous scrub and forest species. In places, this invader is replacing another invasive species, Acacia saligna (Port Jackson), which has been brought under bio- control by a gall-forming rust fungus. A bio-control programme against Australian Myrtle is progressing well in South Africa and should help to curb its further spread.

Metrosideros excelsa (New Zealand Bottlebrush or Christmas Tree) is a popular ornamental tree and hedge plant in coastal areas of the Western Cape in South Africa. In its native New Zealand, it is known as “Pohutukawa” meaning “spray-sprinkled”, as it rarely grows far from the sea or an inland lake. It is so well adapted to sea conditions that oysters may even be found on branches that dip into the sea! In South Africa this species is invading hygrophilous fynbos (fynbos on moist peaty soils) in some areas. Large plants are difficult to eradicate because they coppice when cut and the wood is very tough; roots can penetrate rocky crevices and cracks. It produces large quantities of fine, wind-blown seed. Moist conditions are necessary for seed germination and establishment.

Psidium guajava (Guava) is a shrub or small tree of tropical American origin. It is grown commercially in warm, frost-free areas for its edible fruit. It is also one of the most aggressive invasive species in these regions, rivalling even Lantana camara. Its fruit is eaten by birds and mammals, which spread the seed far and wide.  P. guineense (Brazilian Guava) is an ornamental species whose fruits are bitter and resinous, but still attractive to birds and other animals, which assist in dispersing its seed. Psidium x durbanensis is a hybrid between P. guajava and P. guineense and is found on the KwaZulu-Natal coast. It is apparently sterile and spreads by suckering.  P. cattleianum (= P. littorale var. longipes; Strawberry or Cherry Guava), native to Brazil, is grown for both its ornamental value and its edible fruit. This species is invasive in coastal areas and probably also in lowveld areas.

Eugenia uniflora (Pitanga or Surinam Cherry) is another Brazilian tree that has been cultivated for hedging, for use in producing ornaments, and for its edible fruit. It is an aggressive invader of riverbanks, coastal bush, forest edges, and forest understories and has been declared a category 1 plant (prohibited) in the parts of South Africa that support its growth. Pitanga can be easily distinguished from other Eugenia and Syzygium species by its very distinctive eight-ribbed fruits, which are yellow, turning deep crimson when ripe.

Syzygium cumini (Jambolan) and S. jambos (Rose Apple) are evergreen trees of Asian origin that have been cultivated as ornamentals and for their edible fruit. They invade coastal bush and savanna in frost-free areas. Jambolan can easily be confused with the indigenous S. guineense (Water Pear); however, Jambolan can be distinguished by its longer leaves (up to 150 mm) with many closely spaced lateral veins, abruptly tapering leaf apex, oval to pear-shaped fruits, and much-branched sub-terminal inflorescence, usually arising from old leaf scars. Jambolan fruits are purplish-black when ripe; those of Rose Apple are creamy yellow, tinged with pink.

Unlisted Species
Three additional myrtaceous species have been proposed as declared plants in South Africa, but more information is required before they can be listed. They are Callistemon rigidus (Stiff-leaved Bottle-brush), a popular ornamental shrub, which has been seen to invade forest edges, Leptospermum scoparium (Manuka Myrtle or New Zealand Tea Tree), and Syzygium paniculatum (= Eugenia myrtifolia; Australian Brush-cherry).  Australian Brush-cherry is a popular ornamental tree and hedge plant with edible fruits. Birds favour it, and it is likely to become invasive beyond the urban environment.

Other myrtaceous species that have been recorded as naturalised in the Western Cape region of South Africa, but have not yet been proposed as declared plants, are Melaleuca hypericifolia (Red-flowering Tea Tree), M. wilsonii (Violet or Wilson’s Honeymyrtle), and Callistemon citrinus (Lemon Bottle-brush).

Declared Plants in the Myrtaceae in South Africa
[The controls concerning categories 1, 2 and 3 are briefly summarised here. Readers interested in further details may contact me for references to the full South African regulations. Ed.]

Category 1: Prohibited; must be controlled, or eradicated where possible.
Eucalyptus lehmannii (only in certain areas)
Eugenia uniflora (only in certain areas)
Leptospermum laevigatum

Category 2: Allowed only in demarcated areas under controlled conditions; prohibited within 30 m of the 1:50-year flood line of watercourses or wetlands.
Eucalyptus camaldulensis
Eucalyptus cladocalyx
Eucalyptus diversicolor
Eucalyptus grandis
Eucalyptus lehmannii (only in certain areas)
Eucalyptus paniculata
Eucalyptus sideroxylon
Psidium guajava

Category 3: No further planting or trade of propagative material is allowed; existing plants may remain but must be prevented from spreading; prohibited within 30 m of the 1:50-year floodline of watercourses or wetlands.
Eugenia uniflora (only in certain areas)
Metrosideros excelsa
Psidium cattleianum
Psidium X durbanensis
Psidium guineense
Syzygium cumini
Syzygium jambos

Proposed category 3 plants: More information is required before these can be listed.
Callistemon rigidus
Leptospermum scoparium
Syzygium paniculatum (=Eugenia myrtifolia)

-Lesley Henderson  Source: SABONET News 7.2: 106



Paperbark Albizia, Albizia tanganyicensis. Photo: Bart Wursten. Source: Flora of ZimbabweErythrina lysistemon (sacred coral tree). Photo Wikipedia