Transcript Vascular Seedless Plants

Vascular Seedless Plants
Whisk Ferns, Club Mosses and
Horsetails
Whisk Ferns
• Whisk ferns are widespread, rootless and greenstemmed.
– Instead of leaves, they possess enations along the
angular stem axis.
• They contain a 3-lobed spore-producing structure
called a synangium.
Whisk Ferns cont.
• Whisk ferns are regularly branched, with
scale like outgrowths that resemble small
leaves.
– They are anchored by a rhizome, or root-like
stem, which absorbs nutrients by means of
filaments called rhizoids.
• Whisk ferns are some of only a few
surviving members of an ancient group of
vascular plants.
Life Cycle of Whisk Ferns
• There are two phases in the life cycle of a
whisk fern.
• The large asexual plants (sporophytes)
produce spores that develop into small,
sexual plants (gametophytes).
– Eggs and sperm are produced in special
structures on their surfaces.
• They then reproduce sexually to create the
next plant.
Where can they be found?
• Whisk ferns thrive in
the warm weather of
the tropics and
subtropics, so there
are no species of
them in our area.
Club Mosses
• Club mosses are flowerless and seedless plants that
were dominant during the coal age (360-286 million
years ago) and many were shrubs or large trees.
– Many of those species have since died out.
• About 10-15 genera and 400 species are still around.
Structure
• Club mosses are
structurally similar to
the earliest vascular
plants.
• They contain small,
scale-like leaves,
spores borne in
sporangia at the base
of the leaves, and
branching stems.
Life Cycle of Club Mosses
• The spores germinate to produce bisexual gametophytes
that are green and photosynthetic.
– The maturation of a gametophyte may require 6 to 15 years.
• Biflagellated sperm are produced in an antheridium
(male reproductive organ) and an egg is produced in a
flask-shaped archegonium.
– Water is required for the sperm to swim to another gametophyte
and down the neck of an archegonium to reach the egg at the
bottom.
• The young sporophyte produced after fertilization may
remain attached for many years, and in some species
the gametophyte may continue to grow and produce a
succession of young sporophytes.
Species in Minnesota
• There are about 12 species in Minnesota. They
are mainly the smaller species.
– They are all terrestrial, and grow in the pine woods.
They are also known as ground pines.
More about club mosses
• Many club mosses produce masses of
sulfur-colored spores that are highly
inflammable and were once used as a
constituent of flash powder in early
photography and in fireworks.
• They were also formerly used by
pharmacists to coat pills.
Horsetails
• Horsetails are very nearly allied to ferns.
• Their stems spring from a creeping
rhizome, which produces roots.
– Both barren and fertile stems are produced.
They are erect, jointed, brittle and grooved.
• They are hollow everywhere except at the
joints, and have air-cells in their walls
under the grooves.
Horsetails cont.
• They contain no leaves, the joints terminate in
toothed sheathes, with the teeth corresponding
with the ridges and representing leaves.
• The branches arise from the sheath bases and
are solid.
– Usually, the fruiting stem is unbranched and withers in
spring.
• They contain microscopic spores, attached to
elastic threads, which are coiled around the
spore when moist and uncoiled when dry.
Life Cycle of Horsetails
• Sporangia are clustered in cones (strobili) at the
tips of vegetative shoots.
– They hang in groups of 5 to 10 from umbrella-like
sporangiophores that compose the strobili.
• Each spore is wrapped in four thickened bands
called elaters. As the elaters dry, they twist and
turn giving buoyancy to the spores.
• The spores germinate and produce
gametophytes, which anchor with rhizoids to a
moist surface rich in nutrients.
Horsetails life cycle cont.
• Multiflagellate sperm swim in water to the
archegonium, and the egg at the base is
fertilized.
• The zygote forms an embryo in the
archegonium and the young sporophyte is
nourished by the gametophyte to which it
is attached until the organs are sufficiently
developed to sustain the sporophyte
independently.
Species
• There are about 30 species of horsetail in
the world.
• A few of them are common right here in
Minnesota, such as the scouring rush
horsetail, which is commonly found in
ditches alongside roads.
• Another is the forest horsetail, which is
commonly found in northern Minnesota.
Pictures of Horsetails