Download Charales (Stoneworts) Hepaticophyta (Liverworts)

Charales (Stoneworts)
There are several hundred species in this group. They are
collectively known as stoneworts, because they commonly accumulate crusts of calcium carbonate 1CaCO32 over their surfaces.
All are multicellular. Some species can be a meter or more in
length.
The stoneworts are freshwater algae. Certain species are specialized for growing in relatively deep waters, though most live in
shallow water near lake beaches or pond edges.
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Chapter 29 Green Plants
Globularis species (tall)
and C. fibrosa (short)
Reproduction Primarily sexual reproduction occurs, with production of prominent, multicellular gametangia similar to those
observed in early land plants. Eggs are retained on the parent
plant, which supplies eggs with nutrients prior to fertilization.
Life cycle Alternation of generations does not occur. Multicellular individuals are haploid; the only diploid stage in the life cycle is
the zygote.
Human and ecological impacts Some species form extensive
beds in lake bottoms or ponds and provide food for ducks and
geese as well as food and shelter for fish (Figure 29.29).
Nonvascular Plants (“Bryophytes”)
The most basal lineages of land plants are collectively known as
nonvascular plants, or bryophytes. The three lineages with living
representatives (liverworts, hornworts, and mosses) do not form a
monophyletic group, but instead represent an evolutionary grade.
All of the species present today have a low, sprawling growth
habit. In fact, it is unusual to find bryophytes that are more than 5
5 cm
FIGURE 29.29 Stoneworts Can Form Beds in Lake Bottoms
to 10 centimeters (2 to 4 inches) tall. Individuals are anchored to
soil, rocks, or tree bark by specialized structures called rhizoids. No
bryophyptes have true vascular tissue where cells have reinforced
walls. In the lineages present today, simple water-conducting cells
and tissues are found only in some mosses. All of the bryophytes
have flagellated sperm that swim to eggs through raindrops or
small puddles on the plant surface. Spores are dispersed by wind.
Hepaticophyta (Liverworts)
Liverworts got their name because some species native to Europe
have liver-shaped leaves. According to the medieval Doctrine of Signatures, God indicated how certain plants should be used by giving
them a distinctive appearance. Thus, liverwort teas were hypothesized to be beneficial for liver ailments. (They are not.) About 6500
species are known. They are commonly found growing on damp forest floors or riverbanks, often in dense mats (Figure 29.30), or on the
trunks or branches of tropical trees.
Adaptations to land Liverworts are covered with cuticle. Some
species have pores that allow gas exchange; in species that lack
pores, the cuticle is very thin.
Human and ecological impacts When liverworts grow on bare
rock or tree bark, their dead and decaying body parts contribute to
the initial stages of soil formation.
Scapania undulata
Reproduction Asexual reproduction occurs when fragments of a
plant are broken off and begin growing independently. Some species
also produce small structures called gemmae asexually, during the
gametophyte phase. Mature gemmae are knocked off the parent
plant by rain and grow into independent gametophytes. During
sexual reproduction, sperm and eggs are produced in gametangia.
Life cycle The gametophyte is the largest and longest-lived phase in
the life cycle. Sporophytes are small, grow directly from the gametophyte, and depend on the gametophyte for nutrition. Spores are shed
from the sporophyte and are carried away by wind or rain.
1 cm
FIGURE 29.30 Liverworts Thrive in Moist Habitats