Life on Earth Kingdom Plantae Part III

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Life on Earth
Kingdom
Plantae
Part III
“Ferns”
Boston fern
Two Life Cycle Stages of Ferns
SPOROPHYTE
Pteridium
(bracken
fern)
GAMETOPHYTE
Phylum: Moniliophyta
• Subphylum: Pterophyta (typical ferns,
including water ferns, tree ferns, and
grape ferns)
• Subphylum: Psilophyta (wisk ferns or
psilophytes)
• Subphylum: Sphenophyta (horsetails and
scouring rushes)
Subphylum: Pteridophyta
(“typical ferns”)
• Plants with megaphyllous leaves (called
fronds) with branched veins
• Most species have no “stem” but a
perennial rhizome
• All species are homosporous except the
“water ferns”
• Some species produce dimorphic fronds
(vegetative and reproductive fronds)
Fern Terminology
Pinna
Rachis
Osmunda
(fertile and
sterile fronds)
Frond Development
• Fronds develop in a coiled
fashion known as circinate
vernation
• Young, coiled fronds are
called fiddleheads
• Some ferns are edible at this
stage
Fern Reproduction
• Fern plants ( diploid sporophytes)
produce spores by meiosis in sporangia
• These sporangia develop in small clusters
(called sori) on the underside of the
pinnae (or on separate pinnae)
• Some species produce a protective
indusium partially covering the sorus
Fern Sporangia
Pinna with Sori (no indusium)
sorus
Fern Sori with Indusia
Frond with Sori and Indusia
Fern Sporangia with Annulus
Sporangia forcibly eject the spores with
the action of the annulus and lip cells
Gametophyte Generation
• Spores develop by mitosis into haploid,
photosynthetic gametophytes
• The gametophyte thallus usually
produces male antheridia first, then
female archegonia
• Flagellated sperm fertilize egg cells and
the zygote develops into the next
sporophyte fern plant
Gametophyte Generation
Fern Antheridia
Young Sporophytes
Fern Life Cycle
Fern Diversity
• Some tropical species are “tree ferns”
and produce a erect stem (especially the
Order Marattiales)
• Many ferns are epiphytes
• Some ferns are aquatic (floating)
– These “water ferns” are heterosporous,
while all other ferns are homosporous
• Ferns are important economically as
ornamentals
Platycerium
Pleopeltis
polypoides
“resurrection fern”
Water Ferns (Azolla)
Azolla from a Distance
Marsilea
(another water fern)
Marsilea
Salvinia and Azolla
Tropical Tree Ferns (Marattiales)
Tree Fern
Tree Fern
Grape Ferns
Ophioglossum
and
Botrychium
Botrychium
Subphylum: Psilophyta (wisk ferns)
• Extant plants superficially similar to
rhyniophytes, but now known to be
“reduced” ferns
• No true roots or leaves; homosporous
• Erect “stem” and underground
“rhizome” have protostele structure
• Dichotomous branching common
Psilotum
• Psilotum (“wisk fern”)
– produces trilobed
sporangia on flaps of tissue
called enations
– previously viewed as a
separate division, the
Psilophyta
Psilotum
Tmesipteris (another Psilophyte
from SE Asia and New Zealand)
Subphylum: Sphenophyta
• Includes “horsetails” and
“scouring rushes”
• Only one extant genus:
Equisteum
• Characteristics:
– hollow, jointed stems
– microphyllous-like leaves
– homosporous
Equisetum
Sheathing Leaves and Plants with
Strobili
Equisetum
(strobilus)
Equisetum (cont.)
– spores with two wall layers
• outer wall is hygroscopic and
humidity changes cause unwrapping
of the 4 arms (elaters)
• this action helps to break up the
spore mass in spore dispersal
Equisetum spores and elaters
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