Question

The first true leaves appear in the seedless vascular plants.

Explain what key steps might have lead to the evolution of leaves and describe what advantage it provided to this group compared to Bryophytes.please use the mechanism of evolution.

Answer 1

True leaves first evolved in seedless vascular plants or tracheophytes, prior to the appearance of seed plants.

Leaves and branches come out as whorls from the evenly-spaced joints. The needle-shaped leaves do not contribute greatly to photosynthesis, the majority of which takes place in the green stem.

Seedless vascular plants have a waxy cuticle, stomata, and well-developed vascular tissue. Their vasculature allows them to grow to larger sizes than the nonvascular plants, but they still largely occupy moist habitats. While this lineage is more well adapted to drier habitats than are the nonvascular plants, they still require moisture for reproduction. Although the developing diploid embryo is dependent on the haploid gametophyte for survival (like mosses), the diploid sporophyte is more conspicuous and is the prominent generation of seedless vascular plants. Phylogenetically, seedless vascular plants are basal to the seed plants.

Eg. ferns,horsetails ,club mosses.

Bryophytes do not have true roots, leaves, or lignified cell walls.Vascular tissues were absent in bryophytes. Because they lack substantial vasculature, plants in this lineage are generally small in size, lack significant structural support, grow close to the ground in moist areas, and lack significant water-conducting cells. Plants first evolved in environments that were transitional between the land and the sea, and although modern nonvascular plants are dependent on water to complete their life cycles, they are able to withstand long periods of desiccation.Eg.Mosses,hornwort and liverworts.