Non-Vascular Plants

Evolution of Land Plants

• Land plants evolved from green algae

• The green algae called charophyceans are the closest relatives of land plants

• Comparisons of both nuclear and chloroplast genes– Point to charophyceans

as the closest living relatives of land plants

Chara, a pond organism

(a)10 mm

Coleochaete orbicularis, a disk-shaped charophycean (LM)

(b) 40 µm

Origin and Diversification of Plants

• Fossil evidence indicates that plants were on land at least 475 million years ago

• Whatever the age of the first land plants those ancestral species gave rise to a vast diversity of modern plants

Plant Evolution

Bryophytes(nonvascular plants) Seedless vascular plants Seed plants

Vascular plants

Land plants

Origin of seed plants(about 360 mya)

Origin of vascular plants (about 420 mya)

Origin of land plants(about 475 mya)

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Bryophytes

• Life cycles of mosses and other bryophytes are dominated by the gametophyte stage

• Bryophytes are represented today by three phyla of small herbaceous (nonwoody) plants– Liverworts, phylum Hepatophyta– Hornworts, phylum Anthocerophyta– Mosses, phylum Bryophyta

Bryophytes

• Nonvascular (pass water cell-to-cell)

• Seedless (reproduce by spores)• Low growing• Phylum Bryophyta (also includes

liverworts & hornworts)• Grow on moist brick walls, in

sidewalks, as thick mats on forest floors, and on the shaded side of trees

Bryophytes

• Can survive periodic dry spells, reviving when water becomes available

• Require water for fertilization so sperm can swim to egg

• Rhizoids (root like structures) anchor mosses

• Have waxy covering called cuticle on aerial parts to prevent desiccation

• Dominant form of a moss is a clump of leafy green gametophytes  (photosynthetic)

•  Moss alternates between a haploid (1n) gametophyte and diploid (2n) sporophyte

• Gametophyte generation produces gametes (eggs & Sperm)

• Sporophyte generation forms at the top of the gametophytes and produces spores 

• Stalk-like sporophytes lack chlorophyll

• Capsule at the top of the sporophyte forms haploid (1n) spores

 a Diploid (2n) sporophyte stage (contains two sets of chromosomes, one from male and one from female) and a

Haploid (1n) gametophyte stage (contains one set of chromosomes)

This type of life cycle is called Alternation of Generations

• Sexual reproduction in Moss:

• Moss produce 2 kinds of jacketed gametes --- eggs & sperm• Egg producing organ is called the archegonium• Eggs are larger and nonmotile• Sperm producing organ is called the antheridium• Sperm are smaller, flagellated cells• Antheridia & archegonia are both part of the gametophyte

plant• Fertilization can occur only during or soon after RAIN  when

the gametophyte is covered with Water• Sperm swim to the egg by following a trail of

chemicals released by the egg in the water• Fertilization produces a zygote that becomes a sporophyte• Mature sporophytes produce homosporous spores (all the

same type)• Mature capsules open & release spores spread by wind• Spores landing on moist places germinate

into protonema that become new gametophytes

Only the zygote is 2n

Liverworts

• Have no true roots or shoots

• Non- vascular• Require water to

reproduce• Have no or very

little leaf structure• Cannot live in

sporophyte form

Hornworts

• Free-floating aquatic plant, or land plant

• No vascular tissue• No true leaves or

roots• Can live in both

gametophyte and sporophyte forms

Mosses

• Land plant

• Most have no vascular tissue

• Majority of life spent in gametophyte stage

• Need water to breed

• No leaves or roots

• Sporophytes are capsules on stalks