2. All seed plants are heterosporous and produce pollen grains as well as seeds. However, there are examples of transitions between seedless vascular plants (lack seeds; generally homosporous) and seed plants. What seedless vascular plants are heterosporous?

Lycopodium which is an example of Club mosses are seedless vascular plants that are heterosporous.

Explanation:

The club mosses, or phylum Lycopodiophyta, are the earliest group of seedless vascular plants. They can either be homosporous or heterosporous

Some club mosses like Lycopodium clavatum, sporangia are arranged in clusters called strobili.

Lycopodium is heterosporous (while some club mosses are homosporus.

Heterosporus means that spores of two different sizes and sexes are produced by the sporophytes of land plants.