The Leaf | The Inflorescence | Pollination | Seeds | Growth

Pollination & breeding systems

The anthers consist of two lobes joined together by a connective at the apex of the stamen. Each anther lobe contains four locules and each locule contains 8, 12, or more frequently, 16 individual pollen grains (monads) massed together into a polyad. It is the polyad which is transferred to the stigma during pollination. During the development of the anther lobes the microspore mother cells are formed from the two primary sporogenous cells by meiosis. Two, three or more commonly four mother cells are produced in each lobe, each mother cell producing a polyad.

From the few studies which have been conducted^16,17 acacias have been found to be essentially outbreeding, that is, most fertilisation is by pollen from another plant. To help facilitate this outbreeding, the style is exserted through the top of the bud before the petals open, allowing the stigma to receive outside pollen before the anthers of the flower mature¹⁸, a condition known as protogynous. In the absence of other plants, self pollination readily occurs. It is believed that only one polyad can be accommodated on any one stigma, thus all the ovules (which become the seeds in a pod) within the ovary are fertilised by the pollen grains from one polyad. Following pollination, the growth of the pollen wall forms a pollen tube which grows down through the style, and it is through this pollen tube that the male gametes move to effect fertilisation of the ovules¹⁵.

The main pollination vectors are insects, and perhaps less often, birds²⁰.