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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.