Q.Which group of plants was, evolutionarily, the first to possess true vascular tissue (xylem and phloem) along with true root, stem and leaves?

Pteridophyta ('feather-plants') were, evolutionarily, the first plants to combine true vascular tissue (xylem of tracheids, phloem of sieve cells, but no cambium and hence no secondary growth) with a genuinely differentiated root, stem and leaves -- making them the first true vascular land plants, even though they still reproduce by spores rather than seeds.

The sporophyte is diploid, autotrophic and fully independent -- the plant we recognise as 'the fern' -- bearing true adventitious roots (the short-lived primary root is soon replaced) and leaves that are either small with a single unbranched vein (microphylls, e.g. Selaginella) or large and often pinnately compound with branched veins (macrophylls/fronds, e.g. Nephrolepis, Dryopteris). Fertile fronds bear sori -- clusters of spore-producing sporangia -- typically on their undersurface. …