The Botany of Iceland - 01.12.1945, Side 37

THE VEGETATION OF CENTRAL ICELAND
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2. THE AQUATIC VEGETATION
The vegetation which grows in open water in which hardly any
or no moss covers the bottom I have called the aquatic vegetation.
According to the size and nature of the waters we may distinguish be-
tween the vegetation in small lakelets, in large lakes, and in running
water.
In the highland regions investigated by me there are several lakes
of considerable size. All those investigated by me are devoid of
phanerogamous vegetation, though they are surrounded by land covered
with vegetation. However, as several of them harbour some animal
life, they must contain some plankton. I suppose that the absence of
the phanerogams is due to the generally very sandy bottom, and every
year fresh supplies of blown sand are carried by the wind into the
lakes. This loose sandy bottom must be very unfavourable to the vege-
tation. All the rivers with fairly abundant flows, the glacier rivers and
others, are likewise devoid of phanerogamous vegetation. Thus the
aquatic vegetation of the highland is associated exclusively with the
small pools and rivulets. The following species were observed: Batra-
chium paucistamineum, Potamogeton filiformis, both species found in
several places though none of them can be said to be common, Callitriche
autumnalis, Hippuris vulgaris, each of them in only a single place near
Landmannahellir. In running water I have only found Batrachium
paucistamineum in a rivulet in Hvannalindir. In the hot rivulet in Lau-
gar on Landmannaafrjettur I found Callitriche stagnpiis and Potamoge-
ton pusillus. Thus it may be established that above an altitude of 500 m
the aquatic vegetation is very poor. The only species that are fairly
common are Batrachium and Potamogeton filiformis; however, these
two species are as a rule of scattered occurrence and do not form
actual growths, and they are rarely found in the same locality. The
highest locality for these two species is a small lake near Hvannalindir
at 670 m above sea-level. The occurrence of the other species is quite
sporadic.
3. PLANT COMMUNITIES ON MOIST SOIL
(MÝRI SERIES)
To this series I refer all the plant communities which grow in such
moist soil that the water reaches the surface of the soil or the soil is
flooded by it at any rate for part of the year. Often there is no sharp
limit between the mýri series vegetation and the aquatic vegetation,
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