Lower Vascular Plants
Lower vascular plants include divisions Lycophyta, Sphenophyta, and Pterophyta. Division Lycophyta includes club mosses and ground pines. Sporophytes of these have stems covered with small, scaly leaves. Sporangia appear on the upper surface of the leaves and are structures that produce spores. Lycopods have small leaves that each contains one vein that brings water to the leaf from the roots and carries away extra food. Division Sphenophyta is made up of horsetails or scouring rushes. Similar to the lycopods, horsetails have an underground rhizome that produces tiny roots and stems. A small ring of leaves grows around the stem at each joint. Another similarity to Lycopods is their environment, carboniferous forests. Division Pterophyta is ferns. Ferns have large, multiple-veined leaves. Leaves of ferns are called fronds and generally arise from a rhizome. Ferns can range many heights depending on their environment. Tropical ferns can grow very high while ferns in temperate areas can be rather small.
Sporangium is generally found on the underside of fern leaves. Cells in the sporangia undergo meiosis and form haploid spores that are released into the air.
Gymnosperm, meaning naked seed includes some of the tallest and oldest plants in the world. It differs from lycopods, horsetails and ferns because they're fully adapted to life on land and live in dry places. An evolutionary achievement is their strong, woody tissue, made up of xylem. Another evolutionary advance is that gymnosperm reproduction doesn't require liquid water; instead they have wind-borne pollen and seeds. A good example of this is the reproduction of a pine tree. Pine trees form two different kinds of spores; microspores and megaspores. A microspore is the small pollen cones and the megaspores are the larger seed cones. The megaspores have the female gametophytes and the microspores have the...