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Non-Vascular Plants
Non-Vascular Plants
The bryophytes are non-vascular plants (lacking xylem and phloem), bearing spores during reproduction, and exhibiting a haplo-diplontic lifecycle (alternation of generations) with a dominant gametophyte phase. It is a group of plants that share similarities in life cycle, ecology, and physiology, and are considered to be either monophyletic or paraphyletic grade of plants, depending on the research. The name bryophyte means "moss-plant", denoting the mosses as one of the groups under this term. This group combines three groups: the mosses, the liverworts, and the hornworts. The bryophytes appearing during the Ordovician Period (460 million years ago). Liverworts have a flat and green form (thalloid), with a superficial appearance to kelp-like algae, although this group later evolved a leafy habit. The hornworts are also thalloid, with persistent horn-like spore cases, on which their name is based. The most well-known and diverse are the mosses, with their small, spirally-arranged leaves.
Gametophyte (gamete-producing) phase
Gametophyte (gamete-producing) phase
Green, photosynthetic, multicellular and macroscopic
Usually a few centimeters in size; found on forest floors, bark, rocks, and leaves
The gametophyte is the dominant and persistent phase
It is independent, with a system for making food and absorbing nutrients
Many bryophytes are poikilohydric (poikílos means “variable,” and hydro refers to “moisture”), in which they can quickly take in and lose water and have little means to control it.
As an adaptation, the plants can survive drying out until their cells are entirely devoid of water.
When moisture returns, they quickly rehydrate, and their metabolism returns to normal (Proctor & Tuba, 2002).
Stems
Stems
Lack true vascular tissue, such as xylem or phloem
May have water-conducting cells called hydroids, which lack lignified thickenings on the cell wall
Some also have sugar-conducting cells called leptoids, which are similar to phloem
Leaves
Leaves
Some bryophytes are leafy (i.e., all mosses, some liverworts), and others are thalloid (i.e., some liverworts, all hornworts)
Roots
Roots
Most have rhizoids (root-like structures) for anchoring the plant to a substrate, and they have some capacity to absorb water and minerals
Reproduction
Reproduction
Bryophytes produce archegonia (with an egg) and antheridia (with sperm)
Sperm needs to swim on a film of water to reach and fertilize the egg.
Monoicious: male and female gametangia on the same individual
Dioicious: gametangia on separate individuals, creating male and female plants
Sporophyte (spore-producing) phase
Sporophyte (spore-producing) phase
Sporophyte is a stalk, called the seta, with a spore case at the end called the theca
This feature is found in the mosses and liverworts, but the hornworts lack a seta
Sporophyte is multicellular and macroscopic
The sporophyte stem does not branch, resulting in a single sporangium per sporophyte
Usually a few centimeters in size found growing of the top of the gametophyte
Sporophyte is epiphytic and dependent on gametophyte for nutrition;
Foot
Foot
A basal bulbous zone on the sporophyte that facilitates the transfer of these nutrients from gametophyte to sporophyte
Above: From Bechteler et al. 2023, Figure 2
Classification
Classification
└Bryophytes
├Hornworts
├Setaphytes
├Liverworts
└Mosses
Evidence indicates that bryophytes form a monophyletic group, and the mosses & liverworts form a subclade called the setaphytes (presence of a seta)
Above: the hornwort, Phaeoceros
Above: the moss, Dawsonia
Above: Liverwort, thalloid
Above: Liverwort, leafy
Additional Resources
Additional Resources
Mosses and liverworts found frozen with the Neolithic Iceman (Dickson et al. 2019)
Bryophytes as bio-indicators (Oishi and Huira 2017)
Bryophyte lifecycle video (YouTube 2013)
Bog People from National Geographic
Tiny arthropods may help mosses reproduce (Discover 2013)
400-year-old bryophytes resprout from under glacier (PNAS 2013)
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