What part of an orange blossom flower is diploid and which part of the seed is triploid?

The parent citrus (sporophyte) grows an orange flower as a reproductive structure.

The sporophytes' megasporangium produces and retains the functional female haploid megaspore.

The megaspore matures & develops into the megagametophyte or ovule still encased in integument (seed coat) from the maternal sporophyte.

Once the ova are fertilized, the ovule holds both the new embryo and the triploid nutritive tissue. The seed has double or central cell fertilization producing triploid endosperm next to the diploid embryo.

Angiosperm seeds
1- Maternal sporophyte diploid tissues are in the ovary, megasporangium, and the seed coat
2 – Spore grows into the haploid megagametophyte & produces the ova
3 – Fertilized ova:
a – Embryo or diploid progeny
b – Endosperm 1 male + 2 female nuclei fuse - triploid