Plant Classification
AP Biology
Unit 5
Plant Diversity
• All plants are
thought to have
evolved from
ancestral green
algae
• Within the plant
kingdom, there are
many different
types
Algae– NOT a plant!
• Algae is a multicellular
protist
• Green algae has many
characteristics in
common with plants,
but also some
distinguishing
characteristics
Land versus Water Plants
• What are the advantages of
being a water plant?
– More access to water
– More support (from the
surrounding water)
– Water helps disperse gametes
Image taken without permission from http://www.blupete.com/Nature/PictureFlowers/WaterLilyPink2.jpg
Land Plants
• What are the advantages of
being a land plant?
– High concentrations of CO2 in
air (compared to water)
– More access to sunlight
– Initially: less competition for
resources, fewer predators
Nonvascular vs. Vascular
• Land plants can be
classified as vascular
or nonvascular
• Nonvascular
(Nontracheophyte) =
no xylem or phloem
• Vascular
(Tracheophyte) = has
a xylem and phloem
Nonvascular Plants
•
•
•
•
No internal transport system
Smaller in size
Grow in large, dense mats
Have rhizoids = structures that
help anchor the plant into the
ground
• Ex. Mosses, Liverworts,
Hornworts
Question…
• Why can’t nonvascular plants be very tall?
• Without xylem and phloem, they are unable
to transport water and nutrients efficiently
throughout the plant  can’t grow as tall
since they can’t get the water up very high.
Vascular Plants
• Vascular tissue used to
transport water, minerals,
sugar, hormones
• Have the potential to grow
taller
• Can be further divided into
seed and nonseed plants
• Ex. Ferns, conifers,
flowering plants
Vascular Plants- Nonseed plants
• Pterophytes (Ferns)
– Have a xylem and phloem
– Do not have seeds to protect plant embryo
Vascular Plants- Seed plants
• Gymnosperms (Conifers)
– Seed is not protected by fruit
– Has cones
• Angiosperms (Flowering
Plants)
– Seed is further protected by a
fruit
– Has flowers
Alternation of Generations
• All land plants can exist in
two different multicellular
forms
– Sporophyte (2n)
– Gametophyte (n)
• In a life cycle, plant
generations alternate between
sporophyte and gametophyte
• Each form gives rise to the
other form
Sporophyte vs. Gametophyte
• Sporophyte (2n)
– Diploid, multicellular form
of a plant
– Forms haploid spores
through meiosis
• Gametophyte (n)
– Haploid, multicellular form
of a plant
– Forms gametes through
mitosis
Alternation of Generation
How is this different from other
organisms?
• In other organisms the haploids are
unicellular (Sperm and egg)
• In plants both forms (sporophyte and
gametophyte) can be multicellular