Ulvophyceae

Ulvophycean algae are diverse in morphology. The thalli are typically colonial (some are unicellular). A few taxa have flagella in their vegetative stage, such as Oltmannsiellopsis. Common forms include filaments (both unbranched and branched), tubular and blade-like thalli (such as in Ulva), and siphonous thalli. Siphonous thalli are composed of a single giant cell (siphon) with thousands of nuclei and chloroplasts. ==Ecology==

The Ulvophyceae are most diverse in marine habitats. A substantial number of species also live in brackish or freshwater habitats; in temperate regions they are typically most abundant during the spring and summer months. They may be found in still (e.g. lakes and ponds) or flowing waters (e.g. rivers and streams); they are typically attached to a substrate such as rocks, sediments, other aquatic algae, or occasionally animals like turtles or mollusc shells. Similarly, some species live in terrestrial habitats growing on soil, rocks, trees, plants, and other artificial substrates. The family Trentepohliaceae is unusual in that it contains a few parasitic genera. For example, Cephaleuros is an endophyte within the leaves of vascular plants. Cephaleuros can cause significant economic damage to crop plants. ==Evolution==

The origin and early diversification of the Ulvophyceae likely took place in the late Neoproterozoic, though may have taken place earlier, in the Mesoproterozoic. Although most contemporary ulvophytes are marine macroalgae (seaweeds), ancestral ulvophytes may have been freshwater, unicellular green algae. Molecular phylogenetic evidence suggests that macroscopic growth was achieved independently in the various major lineages of Ulvophyceae (Ulvales-Ulotrichales, Trentepohliales, Cladophorales, Bryopsidales and Dasycladales). Because Ulvophyceae lacks a consistent set of ultrastructural characteristics, its monophyly has been questioned. Molecular phylogenetic studies have found Ulvophyceae to be monophyletic, albeit without strong support. The internal relationships between the different clades is also unclear. Current hypothesis on relationships among the main clades of Ulvophyceae are shown below: }} }} }} }} }} }} }} }} }} }} == See also ==