Two main groups of plants

Two main groups of plants

Vascular plants (from Latin vasculum: duct), also known as tracheophytes (from the equivalent Greek term trachea) and also higher plants, form a large group of plants that are defined as those land plants that have lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified tissue (the phloem) to conduct products of photosynthesis. Vascular plants include the clubmosses, horsetails, ferns, gymnosperms (including conifers) and angiosperms (flowering plants). Scientific names for the group include Tracheophyta and Tracheobionta.

Vascular plants are distinguished by two primary characteristics:

1. Vascular plants have vascular tissues which distribute resources through the plant. This feature allows vascular plants to evolve to a larger size than non-vascular plants, which lack these specialized conducting tissues and are therefore restricted to relatively small sizes.
2. In vascular plants, the principal generation phase is the sporophyte, which is usually diploid with two sets of chromosomes per cell. Only the germ cells and gametophytes are haploid. By contrast, the principal generation phase in non-vascular plants is the gametophyte, which is haploid with one set of chromosomes per cell. In these plants, only the spore stalk and capsule are diploid.


Non-vascular plants are plants without a vascular system (xylem and phloem). Although non-vascular plants lack these particular tissues, many possess simpler tissues that are specialized for internal transport of water.

Non-vascular plants do not have a wide variety of specialized tissue types. Leafy liverworts have structures that look like leaves, but are not true leaves because they are single sheets of cells with no cuticle, stomata or internal air spaces and have no xylem or phloem. Consequently they are unable to control water loss from their tissues and are said to be poikilohydric.

All land plants have a life cycle with an alternation of generations between a diploid sporophyte and a haploid gametophyte, but in all non-vascular land plants the gametophyte generation is dominant. In these plants, the sporophytes grow from and are dependent on gametophytes for taking in water and mineral nutrients and for provision of photosynthate, the products of photosynthesis.

Non-vascular plants include two distantly related groups:
·   Bryophytes - Bryophyta (mosses), Marchantiophyta (liverworts), and Anthocerotophyta (hornworts). In these groups, the primary plants are the haploid gametophytes, with the only diploid portion being the attached sporophyte, consisting of a stalk and sporangium. Because these plants lack lignified water-conducting tissues, they can't become as tall as most vascular plants.
·   Algae - especially the green algae. Recent studies have demonstrated that the algae actually consist of several unrelated groups. It turns out that common features of living in water and photosynthesis were misleading as indicators of close relationship. Only those groups of algae included in the Archaeplastida are still considered relatives of land plants.