A type of fertilisation seen in plants where pollen tube plays an important role in carrying the male cells to the female egg.
First of all, to solve this question you should know what siphonogamy is. Siphonogamy is a type of plant reproduction or you can say it is a type of fertilisation in plants where there is formation of pollen tube in order to carry the male gametes to female gametes. Generally all the seed plants are found siphonogamous (where fertilisation occurs by pollen tube) but in lower plants there is no formation of pollen tube and therefore the male cells in the lower plants usually swim to the eggs. Due to this reason spermatophytes (seed plants) are sometimes called as siphonogamous and hence siphonogamy is characteristic of all the spermatophytes.
Thus, the correct answer is option A i.e., All spermatophytes.
Spermatophytes are the plants that produce seeds or you can say these are seed plants. It is divided into Gymnosperms and the Angiosperms. Gymnosperms are the plants with naked seeds or the plants whose seeds are not contained within an ovary or fruit. Angiosperms are the flowering plants or the seed-producing plants. In both of these siphonogamy is seen and it is characteristic of seed plants.
Note: Siphonogamy is seen in all the seed plants i.e., both in angiosperms and gymnosperms. In the seed plants, fertilisation takes place via pollen tube where the male gamete is carried by pollen tube and gets transferred to the female gametes and then the final fertilisation takes place.