Step 1: Understand the perianth.
The perianth is the non-reproductive part of a flower, which includes both the sepals and petals. It is responsible for protecting the reproductive organs and attracting pollinators.
Step 2: Review the options.
- Petals are part of the perianth, forming the colorful part of the flower.
- Tepals are the collective term for sepals and petals when they are indistinguishable.
- Thalamus is the floral receptacle, not part of the perianth.
- Stamen is the male reproductive organ of the flower, not part of the perianth.
Step 3: Conclude.
The petal is part of the perianth, making option (A) the correct answer.
Final Answer:
\[
\boxed{\text{Petal}}
\]