keys to the vascular plants of east texas - Botanical Research ...

leaf
blade
petiole
rhizome
root
scale
FERN WITH
LEAVES ALL
ALIKE
axillary bud
1° leaflet
(pinna)
indusium
2° leaflet
(pinnule)
sporangium
GENERAL CHARACTERISTICS OF THE FERNS [JEP]
lobe
vein
vein
sorus
indusium
sporangium
FOUR SORUS EXAMPLES
indusium
sporangium
sorus
POLYPODIOPHYTA 335
lion years ago). While ferns are an ancient group and some individual living species have extremely
long fossil histories (see further discussion under Osmunda), recent molecular evidence
suggests that the polypod ferns, which make up � 80% of living fern species, diversified in the
Cretaceous (145–65 mya) Period, possibly as a result of ecological opportunities associated with
the rise of the angiosperms—e.g., modern polypods thrive in the low light conditions of angiosperm
forests (Schneider et al. 2004b). The leaves of ferns are megaphylls (= with branched
veins) which apparently are derived from modified branch systems; spores are of one type
(plants homosporous—most living ferns) or two (plants heterosporous—Azollaceae,
Marsileaceae, and Salviniaceae). Modern species range from tree ferns (to 24 m tall) to freefloating
aquatics, but are mostly rhizomatous perennial herbs. The group is also referred to as
the Filicophyta or the Pterophyta (Bell & Woodcock 1983; Raven et al. 1986). The ferns have traditionally
been divided into a eusporangiate group and a leptosporangiate group. The
eusporangiate ferns, consisting of only two families, the Ophioglossaceae and the Marattiaceae,
have large thick-walled sporangia, each containing from several hundred to thousands of
spores and have the sporangia developing from several initial cells. These plants are apparently
only distantly related to all other ferns (see discussion under Ophioglossaceae). The
leptosporangiate group (the rest of the ferns) have small delicate sporangia, each usually containing
128 spores or fewer and have the sporangia developing from a single cell or a small
group of cells (Jones & Luchsinger 1986; Camus 1990; Wagner 1990; Doyle 1998). Recent phylogenetic
research (Pryer et al. 2001) suggests that both the Psilophyta and Equisetophyta are derived
from within the ferns. The word fern is “adapted from the Anglo-Saxon fearn and the German
farn with a lineage that goes back to the Sanskrit parna, which originally meant a wing or
feather” (Durant 1976). For a Key to Ferns and Similar Plants see page 309.
REFERENCES: Bush 1903; Reverchon 1903; Small 1938; Correll 1949, 1956, 1966a; Jermy et al. 1973;
Thieret 1980; Tryon & Tryon 1982; Bell & Woodcock 1983; Taylor 1984; Lellinger 1985; Raven et
al. 1986; Bold et al. 1987; Flora of North America Editorial Committee 1993; Wagner & Smith
1993; Peck & Taylor 1995; Pryer et al. 1995; Raubeson & Stein 1995; Smith 1995; Nauman et al.
2000; Nelson 2000; Hoshizaki & Moran 2001; Schneider et al. 2004b.
(indusium formed
by leaf margin)
fertile leaf
lobe
sterile leaf
spores
FERN WITH
FERTILE AND
STERILE LEAVES
root
rhizome