Question

Why do gymnosperms lack vessels?

Answer 1

The gymnosperms which are also known as Acrogymnospermae, are a group of seed-producing plants that includes conifers, cycads, and also gnetophytes. The term gymnosperm comes from the Greek word gymnos which means naked and sperma meaning seed, which literally means 'naked seeds'. The name is based on the unenclosed condition of their seeds, called as ovules in their unfertilized state.

Complete answer:
Gymnosperms are fruitless seed plants that are made up of a heterogeneous group of plants which are characterized by the production of naked seeds. Hence, Gnetophytes are the most distinctive of the gymnosperms because of their similarities with angiosperms, which are the flowering plants.
Estimates from fossil records indicate that gymnosperms must have evolved approximately three hundred million years ago from non-seed producing ancestors of the extinct division of Progymnosperm Ophyta, which were fern-like in appearance.
They do not have the folded, marginally sealed carpels that characterize the flowering plants. The pollen-receptive structures are basically the ovules rather than the stigmatic portion of the carpels.
Except for gnetophytes which have vessels, most gymnosperms lack vessel elements in their xylem, unlike flowering plants which have both vessels and tracheids. This is because gymnosperms do not produce flowers.

Note:
Gymnosperms differ from seedless plants like the mosses and ferns in not requiring water for sperm to swim in order to reach the egg. This means that the movement of pollen which are the male gamete to ovule, the female gamete in seed plants relies on airborne transport, not water transport. Consequently, most gymnosperms produce huge amounts of pollen.