Class: Charophyceae
Perhaps the most
differentiating aspect from the other 2 classes is that the
nuclear membrane disappears before metaphase. and the
spindle persists until after partitioning is
complete In some species furrowing
occurs and in others a phragmoplast
and cell plate is
formed Species produce a dormant
zygote that undergoes zygotic
meiosis so that
all multicellular stages are haploid; in higher speices
there is a clear case of oogamy = gametes differentiate into
large eggs and smaller sperm. Species are generally
freshwater Flagellated species are
inserted
laterally
and and attach
to a multilayered structure of microtubules so that the
cells are asymmetric.
Chara is quite intersting as
it is quite advanced with an egg protected by secondary
sexual cells.
The order which we'll further explore in lab is
Charales which includes Chara and Nitella.
from: http://vis-pc.plantbio.ohiou.edu/algaeimage/pages/Chara.html
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Zygnemataceae - there is argument here where this group belongs - your text places in the Ulvophyceae but other sources list it here....they are known as the conjugating algae as two filaments will meet and form conjugation tubes.See lab notes for more information... Spirogyra is another well known genera in this group. |
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Spirogyra
Desmids;can be quite beautiful; symmetrical 1-4+ celled floating phytoplankton.
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Coleochaetales |
The fifteen species of Coleochaetales have gained attention recently because they are implicated as the closest living relatives of the Plantae. Some species have parenchymatous growth, nurturing of the zygotes, and a fossil record of an appropriate age, all of which strengthen the implication
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Coleochaete is a small genus of filamentous or parenchymatous green algae. The ca. five species occur commonly in freshwater environments worldwide, where they usually are found as epiphytes on aquatic plants. Coleochaete, and the allied genus Chaetosphaeridium, are thought to be the closest living algal relatives of the stoneworts Individual vegetative cells of Coleochaete species are usually 5-20 µm in diameter and 1-4 times as long as broad, with a conspicuous cell wall. The cells contain a single plastid that occupies most of the cell periphery and contains at least one pyrenoid. (Chara), brittleworts (Nitella), and land plants. |
The cells are organized into branched filaments that, together, produce a plant body less than 2 mm in diameter. This plant body is prostrate on, or embedded in, the substrate, with no plastid-bearing "erect" filaments extending from the substrate plane. In some species, the filaments are laterally compressed, forming a circular thallus with no apparent gaps between cells. Cultured plants that do not become fixed to a substrate may form spherical balls of cells. |
