Trees of the year for 2023

Arbor Day originated in 1872 in the United States of America when a Mr J Sterling Morton persuaded the local agricultural board to set aside a day for planting trees in the then treeless plains of Nebraska. Since then the celebration of tree planting has spread throughout the world and in South Africa Arbor Day was first celebrated in 1983 and each year one tree was selected to be “the tree of the year”. This tradition has continued and from 1996 at least two or occasionally three different Trees of the Year are nominated annually by the Department of Forestry, Fisheries, and Environment. One tree being a relatively common one whilst the second and third being somewhat “rare” or “uncommon” species. This was done to promote some of the lesser known species.

The event was well received by society as a whole and in 1999 the event was extended into Arbor week which falls in the first week of September each year.

National Arbor Week creates an opportunity for all South Africans to plant and celebrate indigenous trees as a symbolic gesture of our commitment to a sustainable environment.

In this article we review two of the three “Trees of the Year for 2023”. Both are medium-sized trees suitable for sunny and dry positions.

Buddleja saligna Olive Sagewood – 2023 Common Tree of the Year

Olive Sagewood flowering in December in bushveld inland of East London.

Photo: Richard Boon

Buddleja saligna is an attractive single- or multi-stemmed shrub or small tree. It can reach about 8–10 m tall in ideal conditions but is usually smaller. The English common name is Olive Sagewood or False Olive, and in Afrikaans it is known as witolienhout. Sage comes from the resemblance of the leaves of Buddleja salviifolia to the leaves of sage in the genus Salvia, although buddlejas and sage are not related. Olive refers to the Olive Sagewood’s superficial likeness to the cultivated olive tree. In Zulu it is called igqeba-elimhlophe or the “white igqeba”. It shares the name iqeba with Tarchonanthus species or the Camphor Bushes. These trees have hard wood, which is used for various purposes like making sticks and fence poles.

The Olive Sagewood is found naturally in all South African provinces, eSwatini, Zimbabwe and Mozambique. It prefers bushveld, dry forest margins and wooded grassland. The species is common and has a wide distribution.

Close-up of Olive Sagewood flowers and leaves in October at Ashburton.

Photo: Richard Boon

According to various authorities, there are between 90 and 140 Buddleja species found in Tropical and Subtropical America, Africa and Asia. Some are ornamental and widely cultivated and are commonly known elsewhere in the world as butterfly bushes. There are seven indigenous species in South Africa, and all but one occurs naturally in KwaZulu-Natal. The genus was named by Linnaeus in 1753 in his Species Plantarum for Reverend Adam Buddle (1660–1715) who was an English vicar and botanist. The alternative spelling Buddleia is the correct Latinisation of Buddle, but Linnaeus spelt it Buddleja, pronounced ‘bud-lee-uh’. Buddleja is currently included in the large family Scophulariaceae but has formerly been placed in the smaller family Loganiacae, which includes Strychnos. It has also been classified in the even smaller family Buddlejaceae with Nuxia. Taxonomic changes can be frustrating to plant lovers but they usually make good sense as increased knowledge and improved techniques provide new classifications that are better representations of the evolutionary history and relationships of plants.

The Olive Sagewood has opposite leaves, which are much longer than wide. They are dark green to grey-green above and whitish below. Besides resembling olive tree leaves, they also look like those of willows, and saligna means willow-like. The veins are sunken on the upper surface, which makes them look quilted, and are raised below. The side veins join to form a continuous vein more or less parallel to the margin. Leaf margins can be smooth or irregularly toothed. The trunk is often fluted or twisted, and the pale brown bark flakes in longitudinal strips. Branchlets are square and may be winged. In most Buddleja species there are stipules or ridge-like scars between the leaf pairs, but in this species the scar is faint. Individual flowers are tiny and have four creamy white petals, which are joined to form a short tube. They are grouped in dense, round heads towards the ends of the branches. The Olive Sagewood flowers from early spring to mid-summer. A good flowering specimen is a showy plant, and the heavily scented flowers attract many insects. The seed capsules are small and non-descript.

Olive Sagewood trunk and bark at Vernon Crookes Nature Reserve.

Photo: Richard Boon

The heartwood is fine-grained, hard and durable. It has been used for fence poles, assegai shafts and to make small items of furniture. It makes a good fuel wood and produces hot fires. Roots are used as a purgative and leaves to treat coughs and colds.

Several Buddleja species are grown worldwide and locally as ornamental plants, e.g. Buddleja davidii Chinese Sagewood, which often has lilac flowers with orange throats, and B. madagascariensis Madagascar Sagewood with orange flowers. Buddleja flowers are attractive to bees, butterflies, beetles and other insects. Pollinators that visit the Olive Sagewood are likely to attract insectivorous birds and other insectivores. The dense crown will produce good shade and should provide good refuge for small birds to nest safely.

Several indigenous Buddleja species are grown in South Africa and at least one would make a good addition to a local garden. Buddleja saligna is fast-growing, evergreen and drought- and cold-hardy, which makes it suitable for low-maintenance gardens. It forms a good screening plant or clipped hedge. Pruning after flowering will improve shape and stimulate better flowering in the following growing season. The root system is not aggressive. Plants can be easily grown from seed or cuttings. As the seed is fine it can be mixed with sand for even sowing. Seed trays should be watered from below to prevent disturbing the seeds. Germination is uneven but should be complete within a month. Seedlings can be carefully transplanted into larger containers.

Bolusanthus speciosus Tree-wisteria – 2023 Rare Tree of the Year

Frequent visitors to the bushveld of northeastern South Africa will know the Tree-wisteria or Bolusanthus speciosus. In KwaZulu-Natal, Tree-wisterias are found in Zululand and do not occur naturally in Durban. The species is not particularly rare in its preferred habitat. Tree-wisterias tend to occur on heavy, alkaline soils and are found as far north as Zambia and Angola. Flourishing specimens in their wooded grassland habitat, or when thriving in cultivation, can be very floriferous, producing masses of bluish mauve pea-like flowers with a white ‘blaze’ in the centre. The name speciosus, which means beautiful, is apt, but blooms are short-lived and you need to be fortunate to find trees in full bloom in the wild.

Cultivated Tree-wisteria specimen at Pretoria National Botanical Garden.

Photo: David Becking

Bolusanthus is a monotypic genus, which means there is only one species in the genus and it has no close relatives. The genus name honours Harry Bolus (1834–1911) who founded the Bolus Herbarium at the University of Cape Town. The English common name Tree-wisteria, sometimes spelt wistaria, is given for its resemblance to true Wisterias, which are woody climbers or lianas from Asia and North America. Both Tree-wisterias and true Wisterias belong to the legume family Fabaceae. The Afrikaans common name is vanwykshout. Unfortunately the origin of the name is unknown. Zulu speakers call it umhhohlo or umwohlo. Professor Adrian Koopman tells me that but umwohlo has a number of apparently unrelated meanings, one of which is “old wizened person or animal”. Tree-wisterias have rough, fissured bark, and in nature the canopy is often sparse. Such specimens may look elderly and gnarled.

Tree-wisteria flowering in the Kruger National Park.

Photo: David Johnson

Tree-wisterias are small, often multi-stemmed trees with narrow crowns. They are deciduous but only lose their leaves briefly in late winter. In Durban they will retain most of their foliage through our mild winters. The compound leaves are held in pendent clusters and the leaflets are asymmetric and greyish green with long, narrow tips. Flowers are produced in early spring on bare trees or with the new leaves. Pollinated flowers produce flat pods which split reluctantly.

The likeness to true Wisterias is striking—flowering branch in late August at Phongolo Nature Reserve.

Photo: Hugh Chittenden

Close-up of pea-like flowers.

Photo: Richard Boon

Bark and roots are used to treat abdominal disorders. The wood is termite resistant and is used for fence poles, tools and small items of furniture and for firewood. Trees are occasionally damaged by elephants, pods and leaves are browsed by game and monkeys, and flowers attract carpenter bees.

Tree-wisterias are attractive, hardy feature trees for even small gardens as the roots are not invasive. They grow best in sunny positions where summers are hot and rainfall is low. Do not expect good flowering where summers are cool and wet. Growth rate is moderate and first flowering may be at about five years old. They can be grown from seed soaked overnight, starting in hot water. Seeds should be sown in a seedling mix (usually equal parts sand, loam and compost) no deeper than the seed diameter. Young plants may dislike being transplanted, although some sources say otherwise.

Acknowledgements

Thank you to Adrian Koopman and Braam van Wyk for advice on Zulu and Afrikaans names and David Becking, Hugh Chittenden and David Johnson for permission to use their photographs.

References

About the author

Richard Boon is well-known not only for his outstanding book Trees of Eastern South Africa – A Complete Guide but also for his environmental work at WESSA in the 90’s and later as part of the Environmental Planning and Climate Protection Department at eThekwini where he headed up the Biodiversity Planning Branch until end 2018. Richard is a practical botanist with over 25 years of field experience. He also enjoys photographing plants and other natural subjects. This article was written for The Leopard’s Echo from his new home in Melbourne, Australia. He currently works for the Victorian state government on native vegetation offset management. The role includes travelling statewide to visit new places and meet landowners. Work involves lots of learning and is much more field-based which has been a nice change. In his spare time, he learns the local ecology, flora and fauna.