The most basic distinction between plant species, all species that are part of the plant kingdom defined by the taxonomic system as Plantae, is that of either tracheophyte or bryophyte. Every terrestrial (land-based) plant species currently extant (existing) in today’s world is one or the other. Many of the descriptive names and groupings we apply to plants fail to completely encompass all plant species. Mother Nature doesn’t give a toss about our apparent need to classify Her organisms distinctly. Frequently there are species that fail to fit within taxonomic or other scientific descriptions, but the fundamental distinction between tracheophytes and bryophytes is clear -cut.
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.
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 grasses, ferns, shrubs, cacti, bramble, bushes, scrub and trees are tracheophytes.
Bryophytes do not have such transportation mechanisms, they do not have specialized cells and tissues to perform this function for them. As such, while some do have rhizomes, none have true roots. Every cell within a bryophyte plant’s structure must absorb its nutritional needs, including water itself, rather than have these needs met by transference from other parts, although these resources can diffuse through the plants structure.
As such, bryophytes typically prosper close to bodies of water or in land areas that frequently experience high humidity. During times when their local climate is dry, they survive by going dormant. So, many bryophyte species go dormant during warm, dry spells, while tracheophyte species that go dormant more often do so during local cold spells.
Because the bryophytes plant species do not contain specialized tissues to easily and fairly rapidly transport resources within themselves, they spread horizontally rather than vertically. This enables all parts of the plant to be near the resources they need.
While some tracheophyte species can be low growing, most are not. By having specialized transport tissues to supply their needs to all parts of the plant, they are able to grow to considerable heights, maximizing the amount of energy they receive from the sun. The canopy level trees are the epitome of this ability.
