Gymnosperms are a group of seed-producing plants that include conifers, cycads, Ginkgo, and gnetophytes. Unlike angiosperms (flowering plants), gymnosperms do not have flowers and their seeds are not enclosed in an ovary. Let's look at each of the options provided to determine which one is not found in gymnosperms:

Option A: Sieve cells

Sieve cells are a type of cell found in the phloem tissue of vascular plants. Gymnosperms have sieve cells for their nutrient transport.

Option B: Albuminous cells

Albuminous cells, also known as Strasburger cells, are associated with sieve cells in gymnosperms. These cells play a role similar to companion cells in angiosperms by assisting in the function of sieve cells.

Option C: Tracheids

Tracheids are elongated cells in the xylem of vascular plants that serve in the transport of water and mineral salts. Gymnosperms rely on tracheids for their water conduction and structural support.

Option D: Vessels

Vessels are tube-like structures in the xylem that are responsible for the efficient transport of water. They are characteristic of angiosperms. Gymnosperms primarily use tracheids for water transport rather than vessels.

Based on the information above, the correct answer is:

Option D: Vessels