It is not every day that one sees such a really huge specimen of Euphorbia tirucalli, the rubber-hedge euphorbia, even if the size is only suggested by looking at some lower branches (SA Tree List No. 355). Plant descriptions often give a typical size that a plant might reach, its average height. Coates Palgrave (2002) state the height for this species to be 3 m to 5 m, the unusually tall one reaching 10 m.

Plants do not stop growing abruptly like people when they reach a given age. They will grow more slowly as they get older. The specific conditions like soil type, quality and depth, rainfall, temperatures in the different seasons, the species genetic characteristics and many more factors determine how big each one will become.

If a normal distribution of heights reached by all the plants of one species could be made, wherever they grow, it would have to be stratified according to age, habitat and the other relevant factors impacting on the measurements for anybody to make sense of the data. Still the overall measure of the universe of plants of a species might hold some interest; for instance to compare with another species.

Botanical gardens have special advantages for growing bigger perennial plants and trees. Continued care and protection over long periods by botanists and horticulturists ensure this. Visits to any of the ten National Botanical Gardens of South Africa bring enjoyment and learning of a special kind. That is why nearly 1,5 million visits to these gardens occur per annum (www.sanbi.org).

The big lower stems of this E. tirucalli or kraalmelkbos, with just a few of the characteristic thin green upper stems in sight at the top to help identification, can be observed at Kirstenbosch.