Rhodophyta-5

Florideophycidae

This is a much larger class in terms of Genera (800) & Species (5000).

They are mostly Marine with 3% inhabiting Freshwater.

Size Range = Microscopic to several meters in length.

Gelidium

Delessaria sp.

Pit Connections

PriSec-pit-conMod.jpg (93463 bytes)

Primary & Secondary Pit Connections

Primary Pit Connections are always present.

Secondary Pit Connections between adjacent cells occur with Larger Forms. This results in cytoplasmic continuity between the cells for a short time and then they are blocked by plugs. Some may reopen temporarily after fertilization. This has the effect of turning Filaments into Parenchyma-like tissue.

Similar pit connections form between host and parasite red algae.

Growth Forms

There are No Unicellular species.

They have Apical Cells.

Each Filament has its individual Apical Cell. This is fundamentally different from Apical Cells in land plants.

The Apical Cell in land plants produces all of the cells in that organ. This includes many longitudinal cell files that are joined at inception. This can result in flat thalli like thallose liverworts or fern gametophytes.

Adjacent cell files in the Rhodophyta can fuse. This produces a thallus that resembles the tissues we have seen in land plants but it is not the same because adjacent cells are derived from different Apical Cells & are not united at inception.

The type of cell fusion that occurs in the Rhodophyta is called "postgenital" (post genesis).

The Simplest growth form has Uniseriate, Branched Filaments.

The most Complex Forms are Multiseriate and have several central filaments that Branch. Branch filaments can be fused laterally.

This produces a "Pseudoparenchymatous" thallus that has two regions (Cortex & Medulla).

The outer "Cortex" contains Small Photosynthetic Cells while the central "Medulla" is composed of Loose Filamentous Cells

NewMomomerpicCortexMedLab.jpg (81443 bytes)

Cross Section through an Axis showing the more central Medullary Filaments and the smaller, peripheral Cortical Filaments.

In some cases there is an "Epidermal" Layer. However, this is not a true Epidermis.

The growth of each filament comes from a solitary Apical Cell.

Growth can be Uniaxial or Multiaxial

Link to Growth Forms

When one Filament comprises the main axis it is Uniaxial.

When there are numerous axial Filaments is it is called Multiaxial.

Each Filament is produced by an Apical Cell.

These comprise the central Medulla.

The Medullary Filaments branch subapically and produce the Cortical Filaments.