Filamentous Algae

Occurrence and Distribution
Structure of Thallus
  Unicells and Unicell Colonial Algae
  Filamentous Algae
  Siphonous Algae
  Parenchymatous and Pseudoparenchymatous Algae

Filaments result from cell division in the plane perpendicular to the axis of the filament and have cell chains consisting of daughter cells connected to each other by their end wall. Filaments can be simple as in Oscillatoria (Cyanophyta) (Figure 1.7), Spirogyra (Chlorophyta) (Figure 1.8), or Ulothrix (Chlorophyta) (Figure 1.9), have false branching as in Tolypothrix (Cyanophyta) (Figure 1.10) or true branching as in Cladophora (Chlorophyta) (Figure 1.11). Filaments of Stigonema ocellatum (Cyanophyta) (Figure 1.12) consists of a single layer of cells and are called uniseriate, and those of Stigonema mamillosum (Cyanophyta) (Figure 1.13) made up of multiple layers are called multiseriate.

Simple filament of Oscillatoria sp.  Spirogyra sp. Ulothrix variabilis.
FIGURE 1.7 Simple filament of Oscillatoria sp.
FIGURE 1.8 Simple filament of Spirogyra sp.
FIGURE 1.9 Simple filament of Ulothrix variabilis.
False branched filament of Tolypothrix byssoidea.
FIGURE 1.10 False branched filament of Tolypothrix byssoidea.
FIGURE 1.11 True branched filament of Cladophora glomerata.
Uniseriate filament of Stigonema   Multiseriate filament of Stigonema
FIGURE 1.12 Uniseriate filament of Stigonema
  FIGURE 1.13 Multiseriate filament of Stigonema
Siphonous thallus of Vaucheria   Pseudoparenchymatous thallus
FIGURE 1.14 Siphonous thallus of Vaucheria
  FIGURE 1.15 Pseudoparenchymatous thallus
of Palmaria palmata.

Siphonous Algae
These algae are characterized by a siphonous or coenocytic construction, consisting of tubular filaments lacking transverse cell walls. These algae undergo repeated nuclear division without forming cell walls; hence they are unicellular, but multinucleate (or coenocytic). The sparsely branched tube of Vaucheria (Heterokontophyta) (Figure 1.14) is an example of coenocyte or apocyte, a single cell containing many nuclei.