The reproductive organs of the Charales show a high degree of specialization.
The female organ, called an oogonium is a large oval structure with an envelope of spirally arranged, bright green filaments of cells.
It is termed an oogonium.
The male organ or is also large, bright yellow or red in colour, spherical in shape, and is usually termed an antheridium, though some workers regard it as a multiple structure rather than a single organ.
The sex organs are developed in pairs from the adaxial nodal cell at the upper nodes of the primary lateral branches, the oogonium being formed above the antheridium.
They are sufficiently large to be easily seen with the naked eye, especially the bright orange or red antheridium.
Many species are dioecious.
In others the monoecious condition is complicated by the development of the antheridium before the formation of the oogonium, thus preventing fertilization by antherozoids of the same alga.
In this case the two types of sex organs usually arise from different points on the lateral branches.

All cells of the Charales are haploid except for the fertilized zygote, the large single cell in the interior of the oogonium, which becomes enclosed in a thickened hard wall to form an oospore that awaits favorable conditions for germination.
 Upon germination the diploid oospore undergoes meiosis, producing four haploid nuclei.
 A septum divides a small apical cell with one haploid nucleus from a large basal cell containing the other three nuclei, which will slowly degenerate.
 The oospore apical cell divides to produce the protonemal initial, from which the primary protonema arises, and the rhizoidal initial, from which the primary rhizoid descends.
 From these the alga continues its development.
The reproductive organs of the Charales show a high degree of specialization. The female organ, called an oogonium is a large oval structure with an envelope of spirally arranged, bright green filaments of cells. It is termed an oogonium. The male organ or is also large, bright yellow or red in colour, spherical in shape, and is usually termed an antheridium, though some workers regard it as a multiple structure rather than a single organ. The sex organs are developed in pairs from the adaxial nodal cell at the upper nodes of the primary lateral branches, the oogonium being formed above the antheridium. They are sufficiently large to be easily seen with the naked eye, especially the bright orange or red antheridium. Many species are dioecious. In others the monoecious condition is complicated by the development of the antheridium before the formation of the oogonium, thus preventing fertilization by antherozoids of the same alga. In this case the two types of sex organs usually arise from different points on the lateral branches.
All cells of the Charales are haploid except for the fertilized zygote, the large single cell in the interior of the oogonium, which becomes enclosed in a thickened hard wall to form an oospore that awaits favorable conditions for germination.  Upon germination the diploid oospore undergoes meiosis, producing four haploid nuclei.  A septum divides a small apical cell with one haploid nucleus from a large basal cell containing the other three nuclei, which will slowly degenerate.  The oospore apical cell divides to produce the protonemal initial, from which the primary protonema arises, and the rhizoidal initial, from which the primary rhizoid descends.  From these the alga continues its development.
Charophyta