Freshwater Rhodophyta

Audouinella is a rather small plant, which forms a reddish or brownish turf on stones or on other algae.

The most common form is a pinkish hue when seen under the microscope, but there is also a variety which is a greenish-grey colour: in fact most of the freshwater rhodophytes are not red. It branches repeatedly, the branches often running almost parallel to the main branch. There is a reddish or grey parietal chloroplast which is plate-like, lying against the cell wall.

ILLUSTRATIONS:
click on an image to enlarge

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Batrachospermum species are filamentous red algae, which branch repeatedly in a characteristic fashion.

There is a multiseriate main axis of elongated, fasciated cells, which may branch several times. Along the main axis and branches, whorls of short filaments all of a similar length arise. The plant is large enough to be visible with the naked eye, but a microscope is necessary to examine the details.

The whole plant is enveloped in a slippery mucilage, which together with its beaded appearance has given rise to the name: "Batrachospermum" means "frog (or toad) -spawn alga".

The cells in the whorls are a different shape from those in the main axis: they are mostly elongated oval or drop-shaped, but in the tips of the branches some cells are almost hair-like.

The colour of the plant is not in fact red, but may be a range of colours from brown to green or olive-green. It grows attached to stable surfaces

The chloroplast is a parietal plate.

Batrachospermum reproduces sexually.

ILLUSTRATIONS:

click on an image to enlarge

 

1     2     3     4     5    




Lemanea   This is another Rhodophyte which is not red: it is usually greyish, and has rather a coarse, wiry feel.

Characteristically, it grows in moderate to fast currents; it branches rather sparsely, and the whole plant is quite streamlined in appearance. It can grow to 10 cm. or more (illustration 1: scale is mm graph paper). There are thickened nodes at intervals, which can be seen developing in a youngish plant in illustrations 2 and 4 below. The end of a branch is shown in image 5: it is uniseriate at the tip, but becomes multiseriate a few cells back.

The structure of a main branch is complex; there is a core of elongated cells (image 6), surrounded by large globular cells (image 7), with an epidermal layer of much smaller cells. The chloroplasts can be seen in these latter cells in image 8 below.

Again, this Rhodophyte reproduces sexually

ILLUSTRATIONS:

click on an image to enlarge

1   2  

3   4   5

6  7   8


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John Kinross