BIOSCI 108: Lecture 14 - Bryophytes & Pteridophytes

Lands Plants Derived From Green Algae

As we know, they share many characteristics:

• Both have chlorophyll a and b

• Same cell wall composition & synthesis

• Both have flagellayed sperm

• Similar genome sequences

Green algae also predates land plants.

Bryophytes

Nonvascular seedless plants. The lack of vascular tissue means they can’t readily circulate water and nutrients around their body and instead relies on absorbing them through their leaves from the air (foliar water uptake). This means they heavily rely on water and being close to it.

There are three main bryophytes: moss, liverworts, and hornworts

Bryophytes: Alternation of Generations

They follow an alternation of generations. Their dominant stage is their gametophyte phase, this is the moss that we think of. Its male (antheridium) and female (archegonium) will produce gametes through mitosis. These gametes, with the help of water, are fertilised and turns into a zygote.

The zygote, growing directly from archegonium, develops into a sporophyte which is essentially a seta (stem) and a capsule where spore production via meiosis occurs. Once these capsules open, spires are dispersed by wind and grows into a male or female gametophyte.

Bryophytes: Harsh Environment

Bryophytes have many adaptations that allow them to withstand and survive harsher environments.

• Waxy cuticles to prevent dessication (dying)

• Stomata to help with gas-air exchange

• Protective adaptations gor their reproductive structures, spores, and embryos

Moss

Considered the most diverse, specialised, and abundant (~12’000 species).

When in extreme conditions (too cold, too dry, etc) they tend to go dormant and remain dormant until conditions are ideal again. They also have slow growth, low light requirements, and can sexually reproduce, helping them thrive and survive easier.

Many mosses are used commercially. Sphagnum moss is commercially harvested in NZ for its amazing absorbent properties, ability to condition soil, and even act as packaging. They’re also great carbon storages.

Liverwort

It has two major groups, thalloid and leafy, and ~7,000 species.

They can undergo asexual reproduction. When water droplets splash onto gemmae cups on the surface of liverwarts, pieces of gemmae are splahsed out and can grow into a new gametopyte.

When undergoing sexual reproduction, they produce an umbrella-shaped sporophyte.

Hornwort

Only has ~300 species and are distinctive for their horn shaped sporophytes but very small gametophytes.

Pteridophytes

Vascular seedless plants. The adaptation of vascular tissue (xylem, phloem, and epidermis) allowed for further organisation of the plant’s bodies into roots, stems, and leaves (fronds). This allowed them to uptake water and nutrients from the environment and easily circulate & transport them around their bodies.

They grow in damp shady areas. There are two classes: lycopodiopsida and polypodiopsida. Their leaves are refered to as fronds and their “roots” are called rhizomes that grow laterally underground.

Xylem

Has a thin cell wall made up of lignin. It typically has one-way flow of sap that contains water, minerals, and nutrients. There is also no end cell wall between cells, making transport quick.

Phloem

Has a thin cell wall made up of cellulose. It has two-way flow of sap that contains mainly sugars, amino acids, and some water. There are end walls between cells that slows down transport.

Pteridophytes: Alternations of Generations

They follow an alternation of generations. Their dominant stage is their sporophyte phase, this is the ferns that we think of. In their sporophyte phase, they produce sporangia filled with spores, through meiosis, in clusters called sori on the underside of their fronds. Sori come in different shapes and sizes for different spore dispersal methods, mainly winds.

Once a spore lands on ideal soils and germinates, it develops into a gametophyte that has both male and female sex organs. Its male (antheridia) and female (archegonia) organz will produce gametes through mitosis. These gametes, with the help of water, are fertilised and turns into a zygote. Chemical deterrents also prevents self fertilisation.

Bryophytes vs. Gametophytes

Dominant Generation:

• Bryophytes: Gametophyte

• Pteridophytes: Sporophyte

Sexual Reproduction:

• Both: Dependent on water

Dispersal

• Both: With spores

Vascular Tissue:

• Bryophytes: No

• Pteridophytes: Yes

Independent Gametophyte:

• Bryophytes: Yes

• Pteridophytes: Yes (reduced)

Independent Sporophyte:

• Bryophytes: No (reduced)

• Pteridophytes: Yes