Plants having vascular tissues but lacking seeds are Pteridophyta.

Explanation:
Pteridophytes are a group of plants that possess vascular tissues for the transportation of water, minerals, and nutrients. However, they do not produce seeds for reproduction. Instead, they reproduce by spores.

Characteristics of Pteridophytes:
1. Vascular Tissues: Pteridophytes have specialized vascular tissues called xylem and phloem. Xylem transports water and minerals from the roots to other parts of the plant, while phloem transports sugars and organic compounds from the leaves to other plant parts.

2. Spore Reproduction: Pteridophytes reproduce by producing spores instead of seeds. Spores are tiny, single-celled structures that are capable of growing into new plants under suitable conditions. These spores are produced in structures called sporangia, which are typically found on the underside of the leaves.

3. Dominant Sporophyte Generation: Pteridophytes have a dominant sporophyte generation. The sporophyte is the diploid phase of the plant's life cycle that produces spores through meiosis. The spores give rise to a gametophyte generation, which is the haploid phase of the life cycle.

4. Lack of Flowers and Fruits: Pteridophytes do not produce flowers or fruits. Unlike angiosperms (flowering plants), they have inconspicuous reproductive structures. The gametophytes produce male and female gametes, which fuse to form a zygote. The zygote develops into a new sporophyte.

5. Examples of Pteridophytes: Some common examples of pteridophytes include ferns, horsetails, and clubmosses. Ferns are the most diverse group of pteridophytes, with over 12,000 known species.

In conclusion, pteridophytes are plants that possess vascular tissues but lack seeds. They reproduce by spores and have a dominant sporophyte generation. Examples of pteridophytes include ferns, horsetails, and clubmosses.