Desert ferns: Adaptations and
possible origin from epiphytic
ancestors
Cheilanthes gracillima
What are the desert ferns?
• Desert ferns, often referred to as
Cheilanthoids, are all in the family Pteridium
which includes 4 groups:
• Adiantoids
• Cheilanthoids
• Hemiontidoids
• Pteroids
Cheilanthoids consist of 6 genera
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Argyrochosma - false cloak ferns
Aspidotis - lace ferns
Astrolepis - star-scaled cloak ferns
Cheilanthes - lip ferns
Notholaena - cloak ferns
Pellaea - cliff brakes
All are known to inhabit xeric enviroments
Source: Wikipedia
Cheilanthoids have developed many
adaptations to allow them to survive in
very dry environments
• Microphylly, or reduced frond and pinnea size
Argyrochosma dealbata Reference: R. H. Hevly
Adaptations continued…
• Partially sunken and fewer stomata, reduces
water loss through transpiration
• Reduced cell size, reduce likelihood of
plasmolysis and resulting plasmadesmata
rupture
• Increased palisade tissue, spreads illumination
to a larger volume of cells decreasing stress on
chloroplasts and improves translocation of
water, nutrients and photosynthates
Reference: R. H. Hevly
Adaptations continued…
• Heavily cutinized epidermis, particularly in
glabrous (free of hair/scale) species
• Lamina of nonglabrous species partially or
completely obscured by hair, scale and gland
in various combinations
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Cheilanthes parryi (hair)
Reference: R. H. Hevly
Adaptations continued…
• Impregnation of epidermal and cortex cell walls
with suberin and lignin particularly in stipe and
rhizome.
• Sclerification of cell walls extending to the stele
as well as epidermal appendages of rhizome and
stipe.
• Cortex cells filled with gum or tannin-like
substances
• All of these deposits are designed to control
water loss from the main plant body
Reference: R. H. Hevly
Some Cheilanthes have even been found to
utilize mycorrhizal VAM relationships that
ostensibly help them to better deal with
water stress and nutrient uptake
(M. Palmieri, L.T.Swatzell)
And the most common adaptation to
the xeric environment…
• Poikilohydry- curling of leaves under drought
stress. It has been shown that desert ferns
curl differently depending on their
morphology. Ferns with coverings on the
lower epidermis curl to protect the upper
epidermis from exposure, while ferns without
lower epidermal coverings curl such that the
lower epidermis and stomata are protected
Reference: R. H. Hevly
Notholaena standeyi Maxon
Pellaea mucronata
The gametophytes of Cheilanthoids
are also adapted to xeric enviroments
• The prothallus is able to recover from
desiccation severe enough to destroy all but a
few cells
• The mode of reproduction is apomictic
• Remember Cheilanthes yavapensis?
(A.L. Grusz et al.)
The southwest is a biodiversity hot
spot for Cheilanthoids
So how do Cheilanthoids fit into the
phylogeny of ferns? (What about the
epiphyte part of this talk?)
• As previously state Cheilanthoids are in the
family Pteridaceae.
• They are polypods, not eupolypods
• Pteridaceae have a false indusium, never a
true indusium, vertical interrupted annulus
with mixed development of sporangium
• Pteridaceae is the only polypod (excluding
eupolypods) not in the double indusium group
the divergance point (50) was estimated to
be 124.92 MYA (K.M. Pryer et al.)
Divergence of Pteridaceae
• The initial divergence point (50 ) was
estimated to be 124.92 MYA while the
divergence of Pteridaceae proper (52) was
92.03MYA this put the divergence point in the
mid to late Cretaceous period
Diversification of epiphytes
• According to research done by Eric
Schuettpelz the bulk of epiphytic radiation
occurred after the K/T boundary about 65
MYA
• However epiphytism is a trait that has arose
independently as well as subsequently lost,
several times in ferns
• So what does this mean?
• Maybe nothing, One of the earliest families of
ferns to diverge, estimated in Pryer et al. at
272.89 MYA, during the Permian, was
hymenophyllum, the filmy ferns. This family
today has an very high percentage of epiphytes.
The fact is that desert ferns and
epiphytic ferns share many
characteristics
• Most of these are characteristics that help the
plants prevent water loss.
• Most epiphytic ferns have also lost their
indusium like Cheilanthoids.
Works cited
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Comparative Desiccation Tolerance of Three Desert Pteridophytes: Response to Long-term Desiccation
James B. Harten, William G. Eickmeier
American Midland Naturalist, Vol. 118, No. 2 (Oct., 1987), pp. 337-347
Published by: The University of Notre Dame
Stable URL: http://www.jstor.org/stable/2425790
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Adaptations of Cheilanthoid Ferns to Desert Environments
Richard H. Hevly
Journal of the Arizona Academy of Science, Vol. 2, No. 4 (Dec., 1963), pp. 164-175
Published by: Arizona-Nevada Academy of Science
Stable URL: http://www.jstor.org/stable/40026172
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Mycorrhizal Fungi Associated with the Fern Cheilanthes lanosa
M. Palmieri, L. J. Swatzell
Northeastern Naturalist, Vol. 11, No. 1 (2004), pp. 57-66
Published by: Humboldt Field Research Institute
Stable URL: http://www.jstor.org/stable/3858543
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A Fossil Fern Indicator of Epiphytism in a Tertiary Flora
Imogen Poole, Christopher N. Page
New Phytologist, Vol. 148, No. 1 (Oct., 2000), pp. 117-125
Published by: Blackwell Publishing on behalf of the New Phytologist Trust
Stable URL: http://www.jstor.org/stable/2588907
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Phylogeny and Evolution of Ferns (Monilophytes) with a Focus on the Early Leptosporangiate Divergences
Kathleen M. Pryer, Eric Schuettpelz, Paul G. Wolf, Harald Schneider, Alan R. Smith, Raymond Cranfill
American Journal of Botany, Vol. 91, No. 10 (Oct., 2004), pp. 1582-1598
Published by: Botanical Society of America
Stable URL: http://www.jstor.org/stable/4123853
Schuettpelz, Eric. "THE EVOLUTION AND DIVERSIFICATION OF EPIPHYTIC FERNS." Diss. Duke University, 2007. Dukespace. Web.
<http://dukespace.lib.duke.edu/dspace/bitstream/10161/181/1/D_Schuettpelz_Eric_a_052007.pdf>.