TREE LIFE
FEBRUARY 2001
AS BEFORE PLEASE CONFIRM WITH ANY OF THE COMMITTEE MEMBERS THAT THE SCHEDULED OUTINGS AND WALKS WILL ACTUALLY TAKE PLACE. SEE THE BACK PAGE FOR PHONE NUMBERS.
MASHONALAND CALENDAR
Tuesday 6 February Botanic Garden Walk Meet in the car park of the Botanic Garden where we will meet Tom at 4.45 for 5pm. If there is a topic which you would like Tom to discuss please contact any of the committee members.
Sunday 18 February Once again James and Ann Sinclair are providing the venue for our outing in the Norton area. Although we have visited Serui Source on several occasions it appears there is no limit to new and delightful spots to explore.
Bring your chair and lunch and enjoy a refreshing day out of town.
Saturday 24 February. Mark’s Walk – back to Mr. Hatendi’s lovely property to study the progress made by Lyn Mullin in restoring the site to its original natural beauty. Take the Enterprise Road, 8.5 kms from the traffic lights at the Chisipite shops turn left into the Hatendi property signposted Charmwood. There will be a Tree Soc. Sign.
Tuesday 6 March. Botanic Garden Walk.
MATABELELAND CALENDAR
4 February Please phone any of the Bulawayo Committee members for details
MATABELELAND OUTING 5TH November 2001
Marine, estuarine or river deposits are known as alluvium. Soil that is washed down a slope and deposited at the bottom is called colluvium. Here endeth the lesson.
On Anne Visser’s Kloof Farm, on the Nyamandlovu Road, the colluvial soils are deep enough and sufficiently sandy to support forests of teak (Baikiaea plurijuga). Some eighty years ago this teak was felled and now coppice growth has replaced it.
The regeneration is so strong and the competition between trees so fierce that this forest now needs to be thinned, so that the long, spindly wood can fatten.
There are plenty of trees other than the teak. These include very many Combretum collinum. Although the foliage on these was extremely variable, the rough bark was always distinctive and diagnostic. Some of them still bore seeds.
There were also many Terminalia sericea. Their silvery leaves contrasted brilliantly with the vibrant green of the teak.
Schinziophyton rautanenii. Photo: Bart Wursten. Source: Flora of Zimbabwe
We wandered in these very pleasant environs. A Schinziophyton rautanenii, (previously Ricinodendron) provided a diversion. Anne showed us nuts that had fallen on the ground. These were very palatable when access to them was finally gained. The hard outer shell had to be cracked with a rock and eventually the kernel was also smashed to smithereens!
As the afternoon was already advancing we went to another place to have lunch. We had arrived very late because we were forced to waste much time finding Anne’s farm. Although I had been there twice, my memory proved very faulty. I was confused by the fact that we had visited other farms in the area.
The lunch rendezvous was beneath an enormous Ficus thonningii in a field where cattle and sheep were being herded while they grazed. A continuous conversation was being conducted between cattle and herders with whistled signals drifting distantly to the ears.
Birdsong sounded sporadically. In the teak forest we heard an oriole and here a fork-tailed drongo interspersed its trills and twitters with the creaky notes typical of its species. There was another most melodious bird-call which belonged possibly to a cisticola. I saw a little flock of Red-billed Hoopoes engaged in their endless employment of probing for prey beneath the bark of various trees.
After lunch Anne conducted a tour up and along a ridge of rock where considerably different genera of trees were to be found. Jenny and I remained beneath another gigantic Ficus, with her children.
We saw ten discrete Acacia species:- A. arenaria, A,. ataxacantha, A. erioloba, A. fleckii, A. galpinii, A. gerrardii, A. karroo, A. nigrescens, A. nilotica and A. rehmanniana.
However, this was not so surprising when one considers that Bickle’s farm which houses Jonathan’s experimental Acacia plots, is not so very far away as the eagle flies, down the Falls Road. This property contains eighteen species of Acacia.
For me, the A. fleckii proved the most noteworthy. Not only were they exceptionally tall, but they also had very straight, well-developed trunks. The fact that they were in a small watercourse was possibly a contributory factor. Anne said it was remarkable how fast they grow. Although I had seen them before, I am sure they were larger.
We would like to thank Anne Visser and Judy Ross for their hospitality at Anne’s Kloof Farm, and for their excellent company. We are also grateful to Jonathan for his leadership and expertise.
-NORMA HUGHES
Fruit Note:- This year, in Bulawayo, the Rhus lancea are absolutely laden with fruit. While in a petrol queue I was interested to see a gang of workers devouring this fruit as they progressed in the queue. The street is lined with these trees. I am informed that these fruits make a good beer. N.H.
IN PRAISE – OR OTHERWISE OF THE JACARANDA.
There is controversy over who planted the first Jacaranda in our capital city. Sir William Milton must have had something to do with it. He was Administrator of S. Rhodesia from 1898 to 1914. His Secretary, Mr. A.H. Holland, a resident of Salisbury from 1897 to 1916, is credited with planting the first tree but a Mrs. J.M. Orpen is also recorded as having made the first planting.
However, it is generally agreed that the choice of the Jacaranda to line the avenues was made by Sir Ernest Montagu who was Chairman of the Tree Planting Committee under Sir William Milton. It all happened in Cape Avenue which subsequently was renamed Montagu Avenue, and which has again been renamed.
Today, so many years on, the magnificent growth, shadiness and annual flowering spectacle of these trees is widely known and appreciated.
Jacaranda mimosifolia, a native of Brazil, has long proved a successful garden tree in Mashonaland and particularly in the Harare area.
Each year, as a result of the July/August frosts, the leaves senesce, and leaf fall occurs in September. This is followed by profuse flowering in October when the trees are cloaked in their famed and very conspicuous mauve blue colour.
Flowering lasts for several weeks after which the new leaves emerge almost unnoticed. The hard springy wooden pods, now mature from the previous year’s flowering, fall to the ground in November at the commencement of the rainy season. The seed, copious, light and winged, is dispersed by wind.
This tree of great form and beauty has proved very hardy and well adapted to the climate of Mashonaland. Unfortunately, this success has given rise to a seamier side to the species which was brought home to me on a recent Society outing when an ardent and learned Member was seen uprooting self-sown Jacaranda seedlings from his garden in silent irritation. In fact it was this conduct that prompted this note for our journal.
You see, this tree has long been known as one of our worst invaders of indigenous woodland in the company of other noxious species like Lantana camara and Guava, Psidium guajava, both the latter, interestingly, also native to Tropical America. This encroachment is seen by Ecologists as greatly undesireable as they prefer the integrity of the woodland to be maintained. The seed, dispersed far and wide, soon germinates with the first rains sending down a deep taproot. The seedlings seem little affected by disease or pests and prove strong competitors to form thickets to the disadvantage of the indigenous woodland species.
To some there is another nasty characteristic associated with this tree. A hayfever-like malady occurs commonly amongst Harare residents at the time of jacaranda leaf fall in September and October. The symptoms include a runny nose, sneezing and itchy eyes and many sufferers suspect the cause of their distress to be the dry Jacaranda leaves. Of course there is no medical evidence yet to support this suspicion but the two are strongly correlated year in, year out.
The Jacaranda is very much a garden choice of the past when gardens were large and space was plentiful. Under favourable conditions it can grow easily to a height and canopy width exceeding 20 metres. Nowadays, other introductions and, happily for Members, indigenous species are commonly preferred. Nevertheless, following its hardiness, longevity and invasive ability, the Jacaranda is going to be around for a long time yet.
-JHWilson
BOTANIC GARDEN WALK:2 JANUARY 2001
This was the first walk of the new year. Unfortunately, Tom had car problems and needed to be rescued by Andy. We therefore started the walk rather late, but Tom made up for this by giving us an exceptionally long session.
Our walk began near the pond which has been cleaned out and re-landscaped so that it is now much more open and less overgrown than it was. At the edge were the leaves and the flower spikes of Gunnera perpensa. This is a rather local plant in Zimbabwe, occurring by streams in the eastern districts. When mature, the leaves are exceptionally large and other species of this genus are known as Giant-rhubarbs. Gunnera belongs to the family Haloragaceae, which contains many other slender aquatic plants – for example the exotic Parrots-feather, Myriophyllum aquaticum, which we see quite often around Harare.
Trichilia dregeana. Photo: Bart Wursten. Source: Flora of Zimbabwe
Two Natal Mahoganies were shown to us. Firstly, Trichilia emetica. This is a sometimes enormous tree which occurs mostly by rivers at low altitudes, where it is a most impressive objective with its relatively large dark green foliage. The forest species is Trichilia dregeana and is confined to the eastern Districts, where it may be found at Nyanga, Chirinda Forest and (rarely) in the Vumba.
Tom pointed out that T. dregeana typically has much glossier, darker green, leaves than emetica. The technical difference is that T emetica has a distinct stipe (i.e. a stalk below the fruit) whereas in T. dregeana, the stipe is absent.
A third, rare, species of Trichilia, namely Trichilia capitata also exists in Zimbabwe. It is a shrub which has been found in NE Zimbabwe and Tom has never seen it.
On next to the Annonaceae, the Custard-apple family and in particular, Annona senegalensis(the Wild custard-apple). The species of the family have alternate leaves arranged in a plane and therefore can at times resemble either Euphorbiaceae (e.g. Bridelia spp.) or Ebenaceae (e.g. Diospyros spp.). However, the leaves are aromatic when crushed and the family lacks stipules and these are usually sufficient characters to rule out the others.
Tom explained that A. senegalensis is a plant of either high rainfall areas at low altitudes or of medium altitude woodland, often occurring with mufuti.
Filicium decipiens. Photo: Bart Wursten. Source: Flora of Zimbabwe
In passing we examined Filicium decipiens (Fern-leaf). This is a tree with compound dark green, glossy leaves – but the most extraordinary feature is the striking winged rhachis. The genus is named after ferns (the Filicales) which it resembles. It is a rather local tree occurring by rivers in high rainfall areas at low altitudes (e.g. the Aberfoyle area).
One of the rarest trees in Zimbabwe is found at lower altitudes by the Mazowe River in the NE of Zimbabwe. This is Sterculia appendiculata (Tall sterculia). It has a maple-like leaf and greenish trunk and may attain a height of 50 m.
One of the most striking trees seen was Burttdavya nyasica, which is not in fact a Zimbabwean species but is found to our north in Malawi and E Africa. The genus is named after the botanist Joseph Burtt Davy. The one in the Botanic Gardens was covered in its spherical flower heads; it belongs to the Rubiaceae and is closely related to one of the other Rubiaceae with spherical heads, namely Breonadia salicina.
Finally, we looked at a very rare waterberry, Syzygium owariense, which is confined to the Rusitu forest and The Corner.
All in all, an interesting “mixed bag” and our thanks go to Tom for his knowledge and enthusiasm.
-MAHyde
OBSERVATIONS ON THE VEGETATION OF THE LOWER REACHES OF MT. GORONGOSA
By Tom Muller
Introduction
Two excursions were made to Mount Gorongosa in Mozambique. The first took place in October 1998 and the second in April 1999. There was continuous rain during the first trip which made it difficult to investigate the flora. It also necessitated an early break up of camp and return to base soon after the start of the second day, which shortened the time on the mountain. The fact that the first journey was spoiled by rain was the reason for the second trip.
Most of Gorongosa Mountain falls within National Parks and the mountain was approached towards the eastern end of the massif where the campsite allocated by National Parks, was situated. Unfortunately the campsite was a long distance from the over 1800 metres high main peak and the adjacent high plateau. In the time available, it was only possible to walk along the ridge, which formed the skyline above the camp, to a minor peak of about 1250m. Consequently it was not possible to reach the higher parts of the mountain, where it was assumed that the botany was at its most diverse and similar to the upper portions of the Eastern District mountains in Zimbabwe. However, this was no disadvantage, as many interesting and beautiful plants and some magnificent scenery were seen. It seemed that if one intends to venture higher, one would have to approach the mountain in the vicinity of the main peak.
Overview
From the base, which was at a height of about 300m above sea level, to the 1250m ridge, the vegetation varies between woodland and rainforest and intermediates of the two. The type of vegetation, which occurs on a specific site, is dependent on the amount of moisture available during the dry season, which in turn is determined by the topography and aspect. The wetter areas which support a mesic vegetation are essentially found in depressions and gullies, and the woodland occurs mainly on ridges. Up to about 600m the flatter portions of the slope were covered with agricultural fields, and from about 800m upwards, probably due to human influence, scrub and grassland replaced much of the woodland. The abundance of coppice growth from several tree species in the grassland, indicated that there must have been more woodland in the past.
Plantlife.
The path to the base of the mountain led through arable fields and on the second trip was lined by an over 2m tall Hyparrhenia species, and dense carpets of the blue flowering weed, Ageratum conyzoides (Floss Flower or Todd’s Folly). On the first trip, often close to villages two types of rather similar, shrubby Morning Glories, were observed both with conspicuous flowers. One was the pan-tropical (originally South American) poisonous ornamental – Ipomoea carnea subsp. fistulosa. The other, with smaller flowers and a more compact growth form, was the indigenous Astripomoea malvacea var. malvacea. On reaching the base of the mountain the path led through groves of naturalised mango trees.
After climbing up to approximately 480m, a small lowland rainforest, consisting mainly of evenly aged, relatively young trees, were encountered. The dominant tree species was Albizia glaberrima, a tree found along lowveld rivers and also in the Rusitu Forest in Zimbabwe. Other occasional tree species were Albizia adianthifolia, Blighia unijugata, Celtis camphophylla, Croton sylvaticus (Mount Selinda Linden), Ekebergia capensis, Millettia stuhlmannii (Panga Panga) and Pteleopsis myrtifolia. The most common shrub was Rothmannia manganjae, a shrub or small tree also found at the edge of Chirinda Forest. Other shrubs were Dracaena usambarensis, Justicia nyassana, Psilotrichum scleranthum, Tabernaemontana ventricosa and Tricalysia pallens. On the ground Oplismenus compositus was a common grass. Also noted were Tacca leotopetaloides and Zamioculcas zamiifolia, both usual herbaceous species found in the Rusituy/Harone Forest. Trailing in the shrub layer, a peculiar herb was seen, reminiscent of a flame lily, which turned out to be Flagellaria guineense, a tropical species not recorded from Zimbabwe.
On the October trip the white flowering Byrsocarpus orientalis and Erythroxylum emarginatum were conspicuous shrubs on the lower slopes.
At an altitude of approximately 600m, where the first camp was made on the second trip, a forest patch which had the physiognomy of rainforest with a close canopy, an understorey of smaller trees and shrub layer, was looked at. However, it consisted of an unusual mixture of woody species, some of which are normally found in dry woodland; others from riparian fringes and a third group typical of rainforest or rainforest edges. The main tree was Pteleopsis myrtifolia, reaching a height of over 30m. This species is found in Zimbabwe in dry forest (Jesse Bush), on lowveld kopjes and in the Harone/Rusitu Forest. Other occasional large trees were Albizia adianthifolia, Croton sylvaticus, Lannea schweinfurthii, Millettia stuhlmannii, Pericopsis angolensis (muwanga), Schrebera alata, Trichilia emetica (Natal mahogany) and Vitex doniana. Among the smaller trees recorded were Antidesma venosum, Brachylaena rotundata, Cussonia arborea (Cabbage Tree), Heteromorpha trifoliata, Markhamia obtusifolia, Steganotaenia araliacea (Popgun Tree), Tabernaemontana elegans (Toad Tree), Trema orientalis, Voacanga africana (only recorded once in Zimbabwe) and Vangueria esculenta. Acalypha ornata and the climbing fern Lygodium kerstenii made up the bulk of the shrub layer, with the tall shade grass – Setaria megaphylla also prominent. The trifoliate Dioscorea dumetorum and the arid Gonatopus boivinii were, because of their large leaves, noticeable herbaceous species, and the creeper Podranea brycei (Zimbabwe Creeper) was seen in the shrub layer as well as climbing up the trees.
At an altitude of about 750m, there was an extensive grove of extraordinarily large specimens of Brachystegia microphylla, a species also found on the Chimanimani Mountains. All the way up from 500 to 900m exceptionally large specimens of Burkea africana (Wild Seringa), Millettia stuhlmannii and Pterocarpus angolensis (Mukwa) were observed. Other woodland trees and shrubs frequently seen during the ascent were Annona senegalensis (Wild Custard Apple), Bauhinia galpinii, Combretum adenogonium, Dalbergia boehmii, Diplorrhynchus condylocarpon (Rubber Tree), Harrisonia abyssinica (a small tree with pinnate leaves and a winged rachis not found in Zimbabwe and belonging to the Family Simaroubaceae), Holarrhena pubescens, Hymenocardia acida, Oncoba spinosa, Pericopsis angolensis and Psorospermum febrifugum (False Holly). It was a surprise not to see Brachystegia speciformis (msasa). In more mesic areas, species such as Cussonia spicata (Cabbage Tree), Englerophytum (Bequaertiodendron) magalismontanum (Stemfruit), Erythrina lysistemon (Lucky Bean Tree), Erythroxylum emarginatum, Harungana madagascariensis, Syzygium cordatum (Water Berry) and the climber Landolphia kirkii were characteristic.
Close to the ridge, which formed the skyline for some time during climb, at a height of nearly 1000m, the path followed along the edge of a sizable evergreen rainforest which occupied a wide gulley. A brief investigation of this forest was carried out during the first visit, in heavy rain. The trees had the dimensions of the ones in Chirinda Forest (up to 50m). The main species of the canopy trees were Blighia unijugata, Chrysophyllum gorungosanum, Crabia brevicaudata, Croton sylvaticus, Khaya anthotheca (Red Mahogany), Maranthes polyandra, Newtonia buchananii with conspicuous sharp buttresses and Trichilia dregeana(Forest Natal Mahogany).
The National Parks camping site was in a small patch of marginal forest and the tree we actually camped under was a sizable specimen of Vitex doniana.
The main vegetation type above 1000m was Loudetia simplex-dominated grassland, with Hyparrhenia rufa prominent in places. Flowering herbaceous plants seen in the grassland during the first visit were Erioseme psoraleoides. Helichrysum nudifolium, Margaretta rosea and Pachycarpus bisacculatus. Flowering bulbous plants were Ledebouria vefoluta, Millera loculata and the beautiful Gladiolus juncifolius, our collection of which was a new record for Mozambique. The plant has also been collected on Nyangani and the Chimanimani Mountains. The most common shrub in the grassland was Aeschynomene nodulosa, which was in flower at the time.
During the second trip a small party walked for several kilometres, westwards along the main ridge to a fairly prominent peak. The very scenic walk took us mainly through grassland but also through a fairly large and well preserved rainforest, similar to the one encountered on the way up, at an altitude of 1000m. Unfortunately time did not allow us to identify the species, which in rainforest is a rather slow exercise. Noticeable flowering herbaceous plants seen in the grassland were Chamaecrista stricta, Crotalaria natalitia var. natalitia, Dissotis senegambiensis, Haumaniastrum venosum, Helichrysum setosum with bright yellow showy flowers, Indigofera lyallii subsp. lyallii, Leonotis mollissima and Triumfetta pilosa var. tomentosa. On the forest fringes, the shrubby Tephrosia grandibracteata and Clematis brachiata were also in flower.
An interesting growth form was observed in the grass species Coleochloa setifera, It formed up to 1m tall slender tussocks which, burn annually giving the plant the appearance of grass tufts on black stilts. On a small promontory, Diplolophium swynnertonii, the well-known Blister Bush was encountered, which was previously assumed to be confined to the Chimanimani Mountains.
Altogether two most enjoyable and interesting outings in congenial company, which left one with the hope that another opportunity will arise to return in order to investigate the rainforests properly and botanize the mountain vegetation in its upper reaches.
From Newsletter, Vol.3 No. 1.
Reproduced with thanks to the Eastern Districts Natural History Society and to Tom Muller.
In Retrospect By Lyn Mullin
COMMIPHORA GUNPOWDER
Another ROOTNOTE from Kim Damstra in TREE LIFE No.47 (January 1984):
An interesting historical note on the use of Commiphora wood comes from Dr Phelps of the University of Zimbabwe. Apparently in the northeast of the country, where the Mazowe River flows into Mozambique in Mkota Communal Lands, a number of villages failed to join the 1896 uprising, and so were allowed to keep their old muzzle-loaders. Dr Phelps reports watching them make their own gunpowder. At the base of Umbga Hill a nitrogenous salt percolates upwards with the ground water, and crystallizes out on the surface when the water evaporates. The salts are scraped off the sand. This mixture may be further purified by dissolving the salt in water and filtering through a grass mat to remove the sand. The water is then allowed to evaporate in the sun. The salt is [then recovered and] ground with charcoal made from a specific Commiphora wood. The resultant mixture forms a gunpowder that is apparently fairly successful. A similar method, using dassie urine as the nitrogenous source, is also used.
THE RUBBER HEDGE AND SLEEPING SICKNESS
TREE LIFE No.49 (March 1984) included a ROOTNOTE from Kim Damstra on a possible source of sleeping sickness:
The early part of this century was wrought with scientific arguments on the possible source of sleeping sickness in man and cattle. It was discovered that the latex of a member of the family Euphorbiaceae, Euphorbia tirucalli, the rubber hedge, had microscopic flagellate animals swimming inside it. These appeared identical to the beast responsible for trypanosomiasis, or sleeping sickness. It was postulated that these were transmitted to man by the tsetse fly, Glossina pallidipes, after it had fed on members of the Euphorbiaceae. This vegetable-diet idea was rejected in the 1930s when extensive experiments failed to encourage the tsetse fly to suck plant latex, and if forcefully fed they died before they could have bitten anyone. The vegetable diet of tsetse fly was not really such a ridiculous idea as the proboscis appears suitable for sucking up nectar, and some male mosquitos suck both blood and nectar. The little trypanosomatid beast, now called Phytomonas, is now known to occur in the latex of a number of Euphorbiaceae, and is transmitted by a plant-sucking bug, Pachybrachius bilobata scutellatus. The latex is rich in dumbbell-shaped starch grains on which they feed. It would be interesting to see how many of our local Euphorbiaceae are inhabited by similar parasites.
(To be continued)
THE RARE MORNING-GLORY TREE
The 500 or so species of morning-glory, Ipomoea (Convolvulaceae), are mostly twining vines prized for their large, showy flowers. One species, I. batatas, is the well-known sweet potato, which is widely cultivated in the tropics for its edible tubers. And among all of these species there are actually a number that are trees.
As far as we know, only two of the tree species have been introduced into Zimbabwe. Both are from Mexico, and one of them, I. arborescens, is represented by only one known specimen, which grows in the grounds of the Harare Forest Nursery, off Orange Grove Drive in Highlands. Its age is unknown but it has probably reached its maximum size, and in June 1987 it was 11 metres tall, with a diameter at ground level of 96.1 cm and a crown spread of 14 metres. The tree has three main stems arising from about 60 cm above ground level; the largest of these was 52 cm in diameter at breast height.
The more common morning-glory tree in Zimbabwe is I. intrapilosa, but it is often erroneously referred to as “arborescens”.
-Lyn Mullin
The recent huge increases in postal rates and printing costs have unfortunately forced an increase in subs. The new annual rate will be $200 per annum with effect from 1 April 2001. We are looking into the possibility of sending Tree Life by e-mail to anyone who would prefer this method.
Your comments would be welcome when remitting your subs.
ANDY MACNAUGHTON CHAIRMAN
