Abstract:
The architectural development of Acacia karroo conforms to Troll’s model. Growth of the branches
is modular and sympodial with heteroblastic leaves on all long shoots of the tree, including the
seedling. Axillary buds tend to proliferate especially on flowering shoots where they form fascicles
consisting of up to 10 inflorescences arranged in two parallel serial rows per leaf axil. Most axillary
buds are sylleptic and basal buds which give rise to short shoots, each producing two to five
cataphylls each season, but no flowers. Inflorescences are only produced on long shoots (modules)
of the current season. After flowering the terminal part of the module aborts, trees are usually
andromonoecious with capitate inflorescences containing 40 to 100 flowers each, with some male
and some hermaphrodite. Some trees produce only male flowers. Anthesis in the same inflorescence,
the same tree as well as amongst trees of the same community are synchronised and occur
at intermittent intervals, each lasting three or more days at a time. Flowers are protogynous and
pollen is produced in polyads, each consisting of 16 pollen grains. Ovaries contain 10 to 14 ovules
each. The concave stigma has space for only one polyad which can fertilise all ovules in the ovary
after a single pollination event. Fruit set is low with 0 to 10 fruits (pods) per inflorescence.
