Practice question

Lycophytes, representing oldest living vascular lineage diverged from euphyllophytes about 400 million years ago, bear microphylls defined by single unbranched median vein associated with leaf trace not leaving leaf gap in protostele or actinostele. They include club mosses Lycopodium, spike mosses Selaginella and quillworts Isoetes with ligules. Megaphyllous leaves with reticulate venation characterize ferns and seed plants. Microphyll nature, protostele, exarch xylem maturation, and axillary or adaxial sporangia distinguish Lycophyta from other groups ecologically and morphologically. This structural framework illustrates phylogenetic relationships and adaptive significance highlighted in competitive examinations focusing on comparative plant morphology and systematics.