A Key to the More Frequently Occurring Freshwater Algae - Freshwater Algae: Identification, Enumeration and Use as Bioindicators - page 143

rhizobenthos in freshwaters. Chara particularly
favours hard waters with a pH

6 (5) (a) Branches of filament rejoin to form a net
............................. Hydrodictyon 7.0 but the pH

range of the whole group is between 5.0 and
10.0. They are not present in polluted waters
especially where sewage is being discharged.
Some species of the Charales impart a garlic-
like odour to the water. Charophyta. Plate I.

>

Hydrodictyon (commonly known as the 'water
net') forms macroscopic nets that are free float-
ing (occasionally attached) and many centime-
tres in length. Populations may be large enough
to partially block small streams, especially in
more nutrient-rich waters. Cells are cylindri-
cal, joined at the ends to form a pentago-
nal mesh net. Individual adult cells can be
several millimetres in length and have a sin-
gle parietal, net-like chloroplast with several
pyrenoids. Widespread in ponds and slow mov-
ing ditch water. Can produce very large masses
in the summer which may be a nuisance block-
ing the watercourse. Chlorophyta. Fig. 4.1

3 (1) (a) Cells grouped together to form a filament,
strand or ribbon (see Glossary for definition of
these terms). Sometimes filaments can grow in
such profusion as to be visible, en masse, to the
naked eye or are visible as multiseriate rows
encrusting stones . ........................ 4

(b) Cells individual or in groups that may be
regular or irregular in shape but not forming a
filament, strand or ribbon. ................ 56

(b) Branches of filaments do not rejoin to form
anet.................................... 7

4 (3) (a) Cell pigments localized in chloroplasts ∗ .
Colour when fresh may be grass green, pale
green, golden to brown, olive green or (rarely)
bluish or reddish. ......................... 5

7 (6) (a) Each cell is enclosed in a flask-shaped lor-
ica which is narrow at one end and with a wide
opening at the other. One or two loricas may
arise from the mouth of the one beneath, form-
ing a forked or dendroid series. The algal cells
within each lorica are bi-flagellate with usually
twobrownishchloroplasts........ Dinobryon

(b) Cell pigments not localized in chloroplasts.
Colour when fresh is frequently blue-green but
maybeolivegreenorothercolour........ 43

5 (4) (a) Filaments branched (false or true), some-
times rarely. Filaments may branch only occa-
sionally (in some cases to generate reproductive
structures) so it is important to examine a rea-
sonable length to determine whether branching
occurs or not. . . . ......................... 6

Dinobryon can be solitary but more frequently
occurs in colonies. These are branched or den-
droid with each new lorica emerging from the
open neck of, and attached by means of a stalk
to, the old. Each lorica contains one biflag-
ellate cell attached to the base of the lorica
by a fine cytoplasmic thread. Flagella are of
unequal lengths (heterokont). There are typi-
cally two chloroplasts per cell with chrysolam-
inarin granules at the base. An eyespot is also
present. The lorica may be clear or coloured
brown, smooth or ornamented and vary in over-
all shape depending upon species. The lorica
maybeupto100+μm in length.

(b) Filaments or ribbons unbranched . . . . . . 24

∗ In some algae, particularly small coccoid species, the chloroplasts
may appear to fill the whole cell - giving the appearance of unlo-
calised pigment. In such cases, it is useful to check this apparent
non-localisation over a range of cells and also to look at fresh
material to see the true colour of the alga. It is also useful to look
for the range of features indicated in Table 1.2. The only group
of algae not having chloroplasts are the Cyanophyta and they, for
example, do not have flagella - so if the specimen is flagellate it
cannot be a cyanophyte and hence must have chloroplasts. Cross-
referencing to other features in the table can also help arrive at the
correct conclusion.

Dinobryon is widely recognised as a bacteria-
consumingmixotroph(atypeofnutritionwhere
both autotrophy and heterotrophy can be used).