Placentation in which ovule is born on central axis and septa are absent is found in :-Argemone and MustardDianthus and PrimroseRose and Tomato    Pea

The type of placentation described in the question refers to "axile placentation," where the ovules are attached to the central axis of the ovary, and there are no septa dividing the locules.

Here are the relevant options evaluated for their placentation type:

1. Argemone and Mustard: Both exhibit various types of placentation but typically show parietal placentation.
2. Dianthus and Primrose: Generally have axile placentation due to their structure.
3. Rose and Tomato: Both exhibit multiple ovules but can vary in placentation.
4. Pea: Known for having axile placentation.

Conclusion

Based on the descriptions provided, the correct answer is Dianthus and Primrose as they both typically exhibit axile placentation, where the ovule is attached to the central axis with septa being absent.