The most common tetrad within the Annonaceae is the tetragonal tetrad, although among angiosperms as a whole, the tetrahedral tetrad is the most common (Walker 1971b). The tetrahedral tetrads were frequently reported in Pseudoxandra, Mitrephora, Pseuduvaria, and Goniothalamus.

Tetrad is a group of four spores formed by meiotic division in the sporangia of plants. In angiosperms, the most common type of tetrad is the tetrahedral tetrad. Let's discuss this in detail.

Tetrahedral Tetrads:

- The tetrahedral tetrads are named so because the four spores in the tetrad are arranged in a tetrahedral shape.
- In angiosperms, the tetrahedral tetrads are formed by meiotic division of the microspore mother cell (MMC) during the microsporogenesis process.
- The four spores of the tetrad are of equal size and shape, and each spore has a distinct outer wall called the exine.
- The tetrahedral tetrads are seen in the pollen grains of angiosperms and are considered as the most common type of tetrad in this group of plants.
- The spores in the tetrad can either be separated from each other or remain attached to each other in the pollen grain.

Other types of Tetrads:

- Isobilateral Tetrads: These are found in some ferns and liverworts. The four spores in the tetrad are arranged in a plane and are of equal size and shape.
- T-Shaped Tetrads: These are observed in some mosses. The spores in the tetrad are arranged in a T-shaped pattern, with three spores forming the stem of the T and the fourth spore attached to the top of the stem.
- Linear Tetrads: These are found in some algae and fungi. The spores in the tetrad are arranged in a linear fashion, with each spore attached to the previous one.

In conclusion, the most common type of tetrad in angiosperms is the tetrahedral tetrad, which is formed during microsporogenesis in the MMC. The tetrahedral tetrads are arranged in a tetrahedral shape and are seen in the pollen grains of angiosperms.