MAJOR PLANT DIVISIONS

BYROPHYTES
Byrophytes are the first major plant divisions. There are three phyla of byrophytes: mosses, liverworts, and hornworts. Mosses are the most familiar byrophytes. All three byrophyte phyla, are the most conspicuous and dominant phase of life. Byrophyte gametophytes are about a few cells thick and are generated from meristems. Gene sequence data have proved that liverworts, hornworts, and mosses came about independently early in plant evolution. The gametophyte is the dominant generation in the life cycles of byrophytes.

PTERIDOPHYTES: SEEDLESS VASCULAR PLANTS
The two phyla of seedless vascular plants: phylum Lycophyta and phylum Pterophyta. They have separate origins from different families. "Pterophyta" is a formal name for on seedless plant phylum, the ferns. Pteridophytes provide clues to the evolution of roots and leaves. most pteridophytes have true roots with lignified vascular tissues. The tissue system in this root is similar to that of the stems of early vascular plants. Lycophytes, which are the modern vascular plants, have small leaves with a single branched vein. the leaves most likely evolved from tissue flaps on the surface of stems into which a strand of vascular tissue grew. These leaves are known as microphylls which basically means "small leaves". The leaves of other modern vascular plants are known as megaphylls, which means "large leaves". Pteriodphytes lack seeds, but they provide stepping stones to the evolution of life cycle adaptations which will eventually enhance the reproductive success of vascular plants on land.

GYMNOSPERMS
the most common gymnosperms are conifers. gymnosperms lack enclosed ovaries in which angiosperm ovules and seeds develop Instead, gymnosperm ovules and seeds develop on the scales of cones. The four phyla of gymnosperms are ginkgo, cycads, gnetophytes, and conifers. There are about 550 species of conifers, a few of those species dominate vast forested regions of the northern Hemisphere.

ANGIOSPERMS
Angiosperms are known as flowering plants and are vascular seed plants that produce the reproductive structures called flowers and fruits. All angiosperms are placed in a single phylum, the phylum Anthophyta. Up until the 1990s, angiosperms were divided into two main classes, the monocots and the dicots, which are different in several anatomical and morphological details. MOst monocots have leaves with veins running straight across, while dicots have netlike in their leaves similar to that of an oak leaf. The flower is an angiosperm structure specialized for reproduction. Fruits help disperse the seeds of angiosperms.

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