TREE LIFE

April 2003

WHILE THE CURRENT FUEL CRISIS PERSISTS IT IS IMPORTANT TO CONFIRM WITH ANY OF THE COMMITTEE MEMBERS THAT THE SCHEDULED OUTINGS AND WALKS CAN ACTUALLY TAKE PLACE. SEE THE BACK PAGE FOR PHONE NUMBERS.

Annual subs are now due for 2003/04. Please pay your $1500 promptly if possible, as this would greatly help the financial situation of the Society.

 

MASHONALAND CALENDAR

Tuesday 1^st April: Botanic Garden Walk with Tom Müller. Meet in the car park at 4.45 for 5pm.  The subject will be Acacias.

Monday 21 April: Please note that as Sunday is Easter Sunday this month’s outing will be on Monday. Because of the very serious fuel situation it has been decided that an outing closer to Harare is essential. So we will instead spend the day at Cleveland Dam.

Saturday 26^th April: Mark’s Walk has been cancelled..

Saturday 3^rd May: Botanic Garden Walk.  NB Winter time again., so our walk will be switched to Saturday mornings.

 

MATABELELAND CALENDAR

Nothing has been arranged for April.

 

NOTICE OF ANNUAL GENERAL MEETING

Notice is hereby given that the 53rd Annual General Meeting of the Tree Society of Zimbabwe will be held on Sunday 18th May, 2003 at the home of Rob and Gillian Smith in Greystone Park.

Any proposals/resolutions and nominations for office bearers should be forwarded to:

P O Box 2128, Harare by Monday 12th May if possible, although proposals and nominations will be accepted from the floor.

AGENDA

1. Notice convening the meeting.
2. Apologies.
3. Minutes of the 52nd A.G.M.
4. Matters Arising.
5. Chairman’s Report.
6. Treasurer’s Report.
7. Election of Committee Members.
8. Any Other Business.

 

EWANRIGG: CHRISTMAS SOCIAL:  15 DECEMBER 2002 (part 2)

So much information about cultivated plants came out of the walk at the Christmas Social that the first write-up, which appeared in the January Tree Life really did not do full justice to the subject. So here is some additional information culled from the leadership of Tom and Lyn.

An attractive shrubby species of Carissa was seen; I thought it looked rather like C. bispinosa but Tom told us it was Carissa macrocarpa. In the wild, it occurs in coastal scrub and on sand dunes in South Africa and Mozambique and is also widely cultivated in the FZ region.

A number of cultivated Bauhinia variegata commonly planted in Harare; this is a tree with pink, reddish or purple flowers and hails from the Himalayas and China. A white-flowered variant is known as ‘Candida”. This species even escapes into the native flora, especially alongside ditches in Harare. Another cultivated species is Bauhinia purpurea. I must admit that I don’t know this species; the books tell me that it is separated from B. variegata in having 3 fertile stamens, whereas B. variegata has 5.

In addition to these two, there is also Bauhinia blakeana. This is said to be a hybrid between B. variegata and B. purpurea. It has more numerous larger flowers than B. variegata and the petals change to dark red as the flower matures.

We also had an opportunity to compare the two planted species of Thevetia, namely T. peruviana and T. thevetioides. These are from Mexico and C. America. The genus is in the Apocynaceae and has milky juice; unlike most of the Zimbabwean native species this genus has its leaves arranged alternately around the stem (perhaps spiral would be a better word to indicate that the leaves do not lie in a plane?). Tom remarked that T. peruviana is a real colonial garden plant; certainly it is very commonly planted in gardens in Harare. It is one of those species which seems to be always producing yellow flowers.

However, Thevetia thevetioides is the more spectacular plant with its larger yellow flowers and the greater contrast with its darker leaves. Tom noted that flower size is the best separator. I notice that FZ uses a character of the corolla lobes – “erect, remaining overlapping at anthesis” in peruviana as opposed to “spreading, separating at anthesis” in T. thevetioides.

Two trees with 2-pinnate leaves, both legumes, were encountered. The first was Enterolobium contortisiliquum. This is a S American (Brazil, Argentina) legume with, as the name suggests, twisted pods. It makes a medium-sized tree.

Another legume seen was Delonix elata. This is an east African species and, Tom noted that, unlike the usual Flamboyant, Delonix regia, it has white flowers which quickly fade to become a creamy yellow. Otherwise it has the same 2-pinnate leaves as the flamboyant; however it lacks the pinnate stipules of the latter.

A very different plant is the Swamp cypress, Taxodium distichum. It is of course a conifer, native to wet places in SE USA, from Florida through Texas and Delaware. I believe that it will grow successfully in very wet places but also manages quite well in ordinary soil. The tree is deciduous and produces a strong brown autumnal coloration.

Another commonly-planted tree which one often sees in gardens is Hamelia patens. It has orange tubular flowers and darkish leaves; it is a Rubiaceae and has the typical features of that family, namely opposite leaves and interpetiolar stipules. It is native to central and S. America and the W. Indies.

Finally, a very pretty tree is Vitex agnus-castus. Known as the Chaste tree, it is native to southern Europe. It has the usual palmate leaves of a Vitex.

Once again, I would like to thank Tom and Lyn for so interesting a morning.

-Mark Hyde

 

CHAIRMAN’S REPORT TO THE AGM ON MAY 18^TH 2003

I have pleasure in presenting the Chairman’s report for the period since the last AGM in May 2002.

General

At the national level, both political and economic factors deteriorated during the year. From the narrower view point of running the Tree Society, the main issues were:

• the very high and continually rising levels of inflation (currently 220% per annum officially) affecting our costs;
• the continuing highly negative real interest rates destroying our savings;
• the dire fuel shortage affecting our outings;
• the destruction of commercial agriculture which has removed many suitable places for us to visit; and
• the decline in membership, partly caused by continual emigration.

However, despite all of these factors the Society has managed to survive and indeed to some extent the adversity has engendered a will to see that it does not fold. Furthermore, as in the previous year, there have been many positive events and activities.

Outings

During the year, a full complement of main 3^rd Sunday outings was held; these were at Mhowani Hills, Mufuti Farm, Sanganayi Creek, Pax Park, Irvine’s game park, Mtoroshanga, Ewanrigg, Christon Bank, Henry Hallam Dam, Domboshawa and Ruzawi School. We are very grateful to the various landowners (or their representatives) for giving us permission to visit and to the leaders of our walks for their time and knowledge.

Once again, Tom Muller each month gave us his time to lead us in the Harare Botanic gardens. Subjects covered included the various subfamilies of the Leguminosae, Rubiaceae and a walk devoted to riverine trees. We are very privileged to have someone of his calibre. Tom also attended our Christmas Social at Ewanrigg and our outing to Eastern Highlands Tea Estates.

A nearly complete set of 4^th Saturday walks was led by me at which we as usual attempted to the best of my ability to widen the scope of the Society by looking at herbaceous plants and exotic trees.

Matabeleland branch

This has been quiet during the year with members joining in with the Matobo Conservation Society outings. A New Year social took place.

Membership

We report with sadness the death of three members during the year. Shirley Dodds frequently attended the Society’s outings despite ill-health in recent years. She was also very knowledgeable on biological subjects and will be very much missed by us all. Also during the year, there was the shocking murder of Tom Raub, a retired American surgeon, whose body was found outside Bulawayo in suspicious circumstances. He had been a keen and very active member of the Matabeleland branch.

More recently we have heard the sad news of the sudden death of Elizabeth Ogilvie from Mutare. She and her husband Pat attended most of our outings in the Eastern Districts. Elizabeth was energetic and enthusiastic and was particularly knowledgeable about indigenous orchids. She will be greatly missed and we send our condolences to Pat.

The Society has also lost a number of members by emigration. In particular, one of our trustees, John Cottrill, and his wife Lilian. Sadly, they were unable to remain at their farm and are now living in the UK. We will never forget the interesting visits we made there.

We were also very sorry to lose John and Wendy Wilson. John was a staunch committee member, wrote a number of articles for Tree Life and he and his wife Wendy had been on many of our interesting longer trips.

Another Committee member we lost during the year was Joan McAfee. She had been a member for many years and regularly attended our functions; she is now in Australia.

Doug and Klara Ball contributed in many ways to the Society; particularly in providing advice, articles and information and frequently attending our events. They are now lecturing in Kuwait.

We wish all these people success in their new lives, wherever they are in the world.

Tree Mapping

Maureen has continued to make progress with this project. Work is at present underway on creating

various templates with the assistance of Fr. Brendan Conway.

Tree Life

Tree Life has made its regular monthly appearance throughout the year. I would like to thank Maureen for her indefatigable work in seeing that it appears every month, namely arranging contributors, editing articles, creating the original and arranging delivery to the printers. Once again I would like to thank Vida for her monthly collation of the copies.

During the year, rising costs forced us to think again about our printers and a more favourable price was obtained from a new firm. In order to further to save money, font size has been reduced while keeping the newsletter readable. Our aim is to continue producing Tree Life monthly but this will only be possible as long as our finances permit.

I would like to thank all those who contributed articles and write-ups, particularly: Lyn Mullin, John Wilson, Meg Coates Palgrave, John Laurence and Peter Taylor.

Finance

The year under review was exceptionally difficult financially. Sadly, our Treasurer, Rose Greig has decided to call it a day after 10 years. We will miss her support and advice but I do quite understand that after all this time she needs a change. Thank you, Rose for all your assistance over the years.

Other projects

Two afternoons of labelling trees took place at the Mukuvisi Woodland during the period.

A meeting was held with Environment Africa on January 2003 at which the Society agreed to assist EA. Initially, we shall be compiling a checklist of trees (and indeed other plants) for the part of Cleveland Dam which has been leased by EA.

Publications

During the year, a major event was the publication of the new edition of Meg Coates Palgrave’s Trees of Southern Africa. This work has been considerably extended and enlarged with many new species included and a large number of taxonomic changes incorporated. We would like to warmly congratulate Meg on this major achievement.

In addition, Lyn Mullin is compiling a list of vernacular names of Zimbabwean plants – this includes Shona,

Ndebele and English names. This work is at an advanced stage and it is hoped to publish it during the year. It is also expected that Lyn’s book on notable trees will appear shortly.

The Mweb web site has been maintained on a regular basis by Odette Lind; it now has two years worth of newsletters on it, effectively a searchable database of our recent activities. We are very grateful to Odette for her hard work and to Mweb for providing the hosting at no cost. We now get regular requests from all over the world for information

Finally,

2003 is going to be a challenging year, particularly from the financial aspects. However, I have been very encouraged by the response to the request for donations so far; these will be very helpful in seeing us through the year.

The Committee is now down to 4 members which is a bit on the light side; we really need more people and in particular we need a treasurer.

I would like to thank my Committee members for their very considerable support during the past year.

Mark Hyde  Chairman

 

THE PROPELLER TREE OF EWANRIGG

Generations come and generations go, while the earth endures forever. ECCLESIASTES 1:4

This is an enduring tree, the propeller tree, an almost unchanged survivor in tropical America, Africa, Asia, and Australia after more than 130 million years of continental drifting after the breakup of ancient Gondwanaland. There are three species of Gyrocarpus, but only one, G. americanus , subdivided into 8 subspecies, seems to have anything written about it in the literature. Our propeller tree is Gyrocarpus americanus subsp africanus, and currently available information on this, and the other subspecies, appeared in TREE LIFE No 230 (April 1999). Whatever the basis for separating G. americanus into 8 subspecies, it seems clear that the distinctions between them are not very great in spite of all the millions of years of climatic changes they must have endured.

The propeller tree is not common in Zimbabwe, or anywhere else in Africa. In this country it is usually found scattered on rocky hillsides in the Zambezi Valley or the southeastern lowveld, but there are occasional almost pure stands, such as the one near Tamboharta Pan in Gonarezhou National Park, a little to the north of the Save-Runde confluence. The species has no special uses, but its rarity and its ancient origins make it interesting. It generally grows to a height of about 10 metres, with a diameter of about 40 cm. The bark is smooth and grey, bleached to silvery-white on the side that catches the sun. Its fruit is a hard, oval-shaped nut that terminates in two long, thin wings, which spin helicopter-wise as the fruit falls to the ground. It is this spinning fruit that has given rise to both the Latin and the English names. The Tonga and Hlengwe names are mundari and muganavalo, respectively, but the species seems not to be known to the Shona and Ndebele people.

The propeller tree can be grown easily from seed, and there is a very fine specimen at Ewanrigg Botanical Garden, about 40 km north of Harare along the road to Shamva. Its age is unknown, but it would have been planted by the late Harold Basil Christian, who acquired Ewanrigg in 1914 and donated it to the Government shortly before his death in 1951. The propeller tree possibly dates back to the 1920s or early 1930s, and although it is right out of its climatic element it has grown to a larger size than it normally reaches under natural conditions. In December 1987 it was 16 metres tall, with a diameter of 75.7 cm and a crown spread of 16 metres. There was no sign that it had ever produced any fruit, which is not surprising at that altitude – 1 280 metres. Temperatures at Ewanrigg would usually be too low for the tree to produce its yellowish-green flowers, which have the foul smell of cat’s urine.

-Lyn Mullin

 

In Retrospect Lyn Mullin

INSECT-PLANT RELATIONSHIPS

TREE LIFE No.153 (November 1992) contained a very interesting article by Rob Paré on the close relationships between insects and plants. This is worth reproducing in full:

Virtually every species of butterfly or moth, worldwide, depends on the leaves of one plant or another as food for its developing larvae. A few species utilize either flowers, fruits, or seeds, some bore into the stems, some exist on various algae, and some are even carnivorous – but that is a subject all on its own.

There is virtually no plant anywhere that doesn’t bear evidence of having had part of it eaten by some insect or other. There are many recorded relationships between plants and insects, but those we know nothing about must run into millions. I have been studying the life histories of the Zimbabwean butterflies for several years, so my observations are restricted to that field.

Some of our butterfly species are dependent on a single plant or tree species for their larval food, while others are liable to utilize two or more species. It is very significant that where additional plant species are used, they are usually quite closely related – same genus or same family. Certain butterfly species are able to utilize a very wide range of plants. The Painted Lady (Vanessa cardui) is a good example of this ability, and as a result it is found almost anywhere in the world where there are butterflies. At the other extreme, some butterfly species occupy very restricted ranges, sometimes as little as one or two hectares, although to be fair, climatic and geographic factors are often part of the cause. The presence of a particular butterfly species in an area is usually an indication that its foodplant also occurs there. The converse doesn’t necessarily apply, as climatic factors sometimes restrict [a butterfly’s] range in spite of wide-ranging foodplants. A good example of this is the beautiful Flame-bordered Charaxes, Charaxes protoclea azota, which uses both Brachystegia spiciformis(musasa) and Afzelia quanzensis (pod mahogany), and yet is restricted to a fairly narrow strip along the moister (?) Eastern Highlands. Another Charaxes species, C. guderiana, turns up fairly often along the Zambezi River around Chirundu, at least 30 kilometres from the nearest Brachystegia and Julbernardia on the Escarpment, which are its known foodplants. Occasional individuals could certainly fly that distance, but the regularity of its occurrence, and the fresh condition of specimens taken at the river, indicate that it is using an, as yet, unknown tree there. I’m assuming it will be a tree, as the Charaxes, almost without exception, use trees or their saplings. Knowing that, it will most likely be a tree fairly close to the known ones. Tamarindus indica (tamarind) is my guess, or possibly Cordyla africana (wild mango). I have both of these growing at home, so it will be a fairly simple matter to trap a live female, and sleeve-net her on a spray of fresh foliage, where she will lay her eggs if the leaves give her the correct signals. If not, we scratch our heads and try again – Dalbergia or maybe Xanthocercis?

This brings us to the really interesting bit. Leaves of almost any plant, anywhere in the world, contain all the nutrients that any caterpillar needs for growth. The implications of that fact are potentially catastrophic for this planet – all plant life would have been guzzled out of existence long ago if it were not for the control mechanisms built into insects. Let’s examine briefly how a female butterfly locates the foodplant in order to lay her eggs. Firstly, the air temperature must be at a reasonable level – at least 25 degrees C. The female first detects the presence of the required plant with her antennae, picking up the minute traces of volatile `essential oils’, as they are known, given off by the plant into the surrounding air. Once she has located it, she flies through and around the foliage, alighting every so often to check the suitability of the leaf via special sensory organs in her feet, known as chemoreceptors, which must give the correct signals if she is to continue.

The age of the leaf is important here, as most species can only use fairly young to mature material.

Dust on the leaf surface will usually make the female reject the plant and move on, as will various repellant substances, like ethylene, which the plant emits when it is already being fed upon by caterpillars. Once the chemoreceptors in the feet, and others at the tip of the abdomen, have been satisfied, egg laying begins. Somehow the butterfly has gauged the size of the foodplant, and will lay only a few eggs on it before moving on to seek out others. This dispersion seems to be beneficial to both parties, as the plant is not overgrazed’, and the predators and parasites have a hard time finding the larvae. The abundance of any particular foodplant seems to have very little bearing on the population level of the butterfly species that feeds on it. Julbernardia globiflora is a good example. It is arguably the commonest and most widespread of all Zimbabwe’s trees, and is known to be the foodplant of at least 11 different butterfly species, none of which is particularly common. In all my wanderings in the bush, I have seldom come across larvae of more than one species on an individual J. globiflora. It seems to be a case of first-come-first-served! Once the eggs hatch the larvae usually eat their egg shells as their first meal before starting to eat the foliage, which must now pass a further series of chemoreceptors in and around the mouthparts. Firstly, small 3-segment antennae on either side of the jaws must satisfy the larva that the food is the correct one. Then, tiny sensory palps must also be satisfied. Interestingly, the surgical removal of these palps has resulted in the larva happily eating almost any type of leaf material offered. As if that were not enough, a final set of chemoreceptors is [located] at the beginning of the digestive tract, and these cause a violent reaction if offended, causing the larva to vomit up all it has eaten.

In the wild the larval chemoreceptors are largely a formality, but when one comes to introduced plants of similar genera to local ones, although the female may be fooled by them, the larvae seldom are.

I have done some interesting experimentation where, although a female cannot be induced to lay on a plant closely related to her usual foodplant, her offspring, transferred as eggs, have no choice but to eat the new plant, and it often passes their test, even having failed their mother’s!

While searching patiently a few years ago for larvae of the, then, unknown Charaxes chittyi (recently named after the late JCO Chitty, of Harare), I noticed something very interesting. I had seen females of that species showing more than passing interest in Brachystegia boehmii(mupfuti), and decided that that must be its foodplant. In an area where at least 50% of the trees were B. boehmii, it was a long, drawn-out search, eventually rewarded by the discovery of a few larvae that did finally turn out to be C. chittyi. During the search I had noticed that the very occasional tree had smooth (glabrous) leaves instead of the usual hairy ones, and it eventually dawned that larvae had been found only on these glabrous ones. Thereafter, the search became easy, as I only needed to feel the leaves to know whether to search or pass on to the next tree. I tried to feed hairy leaves to some of the larvae, and they reacted so violently that I might as well have fed them with DDT! It was lethal to them. Can this just be the hairs, or is there a significant chemical difference in the leaves? I have been able to force females to lay their eggs on the hairy leaves, but the larvae were unable to eat them. I have noticed a similar situation with a different butterfly species on Dichrostachys cinerea (Chinese lantern, or sickle bush), where the subspecies nyassana, with its hairless leaves, supports larvae, while ssp africana cannot; and yet another on Ficus sur (Cape fig), where only the occasional glabrous specimen will support larvae of the Map butterfly (Cyrestis pantheus), whose life history has only recently been discovered.

As an interesting aside, in April 1992 I took a walk in the Fuller Forest, just south of Victoria Falls, and found that the Brachystegia boehmii there are, almost without exception, all glabrous-leaved. I don’t think Charaxes chittyi has discovered this situation yet! Unfortunately, it was the wrong time of year to collect seed; those that I have carefully collected at Bindura off glabrous trees, and germinated, have produced hairy seedlings, much to my frustration!

One final interesting observation, by no means exhaustively researched, but nonetheless significant, is the fact that of the 85 families of the National Tree List (Drummond 1981), only 31 contain species that are known to be foodplants of butterfly species. Many life histories are yet to be discovered, so there is an incredible amount of hands-on, eyes-on work to be done. Worldwide literature is full of clues for us – for example, the Map butterfly, just mentioned, has related species in South America and the Far East, but no relatives in Africa. Those relatives whose life histories are known are dependent on various Moraceae, which give the clue to where to start looking here. Examining saplings of Trilepisium madagascariensis in Chirinda Forest led to the discovery of very strange larvae, which turned out to be those of Cyrestis pantheus – a great thrill. Since this species occasionally turns up hundreds of kilometres away from its `home’ habitats in the eastern districts forests, we assumed it would also be using a Ficus species, and F. sur proved to be the one – although only the glabrous individuals. The possibility that other Ficus species are also used is very real, and only time and search will reveal it – and such discoveries are their own reward.

[Comment 2000: According to Richard Cooper (1973), Butterflies of Rhodesia (Longman’s Bundu Series), Charaxes protoclea azota is known only from the Burma Valley and Mount Selinda areas in Zimbabwe, but is common in parts of Mozambique. Mean annual rainfall in the Zimbabwe part of its range would be around 1400-1500 mm, and this could not really be described as the “moister” Eastern Highlands.

Rob Paré’s discovery that the larvae of Charaxes chittyi will not touch Brachystegia boehmii that have hairy leaves is extremely interesting, and it makes one wonder whether it is the hairs, per se, that make the leaves unpalatable, or some chemical within the hairs, or in hairy leaves generally. “The Book” (Coates Palgrave) says that the upper surface of mature leaves of B. boehmii are without hairs, but that all other parts are finely hairy; Rob Paré’s observations indicate that this description needs revision. Similar observations were made on glabrous and hairy leaves of other tree species with other butterflies, which brings up the question of chemical analyses of hairy and glabrous leaves within a tree species. Chemotaxonomy has been used as a tool in the classifications of Pinus and Eucalyptus, and it would be interesting to see whether it could be applied in some of our own genera. Insect feeding preferences associated with apparently minor morphological differences within a plant species suggest that there may be scope for research into this phenomenon.

Rob Paré’s frustration at finding only hairy seedlings germinating from seed collected from glabrous B. boehmii is understandable, but this is quite common in other species. However, the hairy, juvenile leaves of seedlings give way, in due course, to glabrous leaves in the older plant. It would be interesting to know if this is happening in his mupfuti.

As a follow-up to his article on Plant-Insect Relationships, Rob Paré hosted a Tree Society outing to his farm near Bindura on 15 November 1992.]

In Retrospect is to be continued

This issue of Tree Life has kindly been sponsored by the actuarial firm Pentact (Pvt). Ltd.

 

MARK HYDE  CHAIRMAN