All angiosperms are tracheophytes, but not all tracheophytes are angiosperms. We group plant species together in a multitude of ways based on specific physiological (function) and/or anatomical (form) characteristics; tracheophytes and angiosperms are names given to two of those groupings.
It should be realized that this is purely a human thing, Mother Nature doesn’t give a toss about human naming conventions and quite frequently throws us a curve ball; a species that fails to fit neatly into one of our definitions. Our taxonomic system of classification has and continues to go through revisions, particular as our ability to determine the genetics of species has developed and expanded.
Tracheophytes are more commonly called vascular plants, or sometimes higher plants. They have specialized tissues called xylem that transport water and nutrients from their roots to their leaves and phloem that transport carbohydrates manufactured through photosynthesis in the leaves to the rest of the plant in the form of sap. All plants are either tracheophytes (vascular) or bryophytes (non-vascular), sometimes called lower plants.
All grasses, ferns, shrubs, cacti, bramble, bushes, scrub and trees are tracheophytes. Bryophytes are the mosses, liverworts and hornworts. The bryophytes are the earliest land plants; the current hypothesis is that they evolved from green algae since they share photosynthesis as their primary energy source, have genetic similarities and it is the green algae that inhabit the coastal areas closest to land. Over millions of years of living on the land, tracheophytes slowly evolved from the bryophytes that first colonized the land.
Angiosperms are more commonly called flowering plants and are comparatively recent on the evolutionary time-frame. They are seed producing plants that have their reproductive organs situated in flowers. Seed producing plants that do not produce flowers are called gymnosperms, such as conifers like pine trees.
Those angiosperms with brightly colored, obvious flowers predominantly require the assistance of insects, birds or small mammals to meet their pollination needs. This is a form of mutualism, the flowers supply nectar as a food source and their animal vectors transport pollen that attaches to them during their feeding from one flower to another, preferably on a different plant. The different flower colors and patterns are to distinguish them for the particular animal vector that provides pollination for a particular plant species or sub-species.
As stated earlier, all angiosperms are tracheophytes, they all have xylem to transport water and nutrients from their roots to their leaves and phloem to transport sap from their leaves to the rest of their structure. They differ from other tracheophytes, such as gymnosperms and polypodiophytes (ferns), in that they have flowers containing their reproductive organs where the others do not.
