22
carolinea, 68
(2010)
P
entecost
(2003)
indicates that P. incrustatum,
known hitherto to only build up travertine depos-
its, during the beginning phase of settlement can
also display a chalk-boring behaviour (reaching
a depth of 100 µm). This ability brings it closer
to “Phormidium spec.”. In addition, possible small
trichome widths as mentioned in the literature
can overlap with those of “Phormidium spec.”
(
Table 1). However, the feature “width of the tri-
chomes” needs a critical consideration in relation
to P. incrustatum. In most of the common deter-
mination manuals as well as in the monographic
examination by
K
ann
(1973)
the trichom widths
of P. incrustatum are consistently indicated to be
4-5
µm. Diverging from these remarks, K
omárek
&
A
nagnostidis
(2005)
increase the span to
3-6,5
µm. The lower dimensions of 3 µm may be
a result of including the uncertain P. toficola and
P. umbilicatum, or the result of single recordings
in particular regions (such as Bihar, D
esikachary
1959,
p. 269). For the characterization of P. in-
crustatum, they are considered to be of low
value. This interpretation is confirmed by the re-
sults of P
entecost
(2003),
who, based on the
measuring of a great amount of P. incrustatum-
trichomes, detected the predominant range of
trichome width to be 5-6,5 µm with a statistical
mean of 5,7 µm. Simultaneously, it was estab-
lished that the cell lengths in general are 1/3 of
the cell widths. These taxonomical key-charac-
teristics are not compatible with the relationships
of “Phormidium spec.”, which has main trichome
widths between 2,9 and 3,7 µm only, combined
with isodiametric cells.
Leptolyngbya vandenberghenii (S
ymoens
)
A
nagnostidis
2001
In relation to the geometry of the cells, outline of
the trichome ends and the shape of apical cells,
there may be prominent similarities between
Leptolyngbya vandenberghenii and “Phormidium
spec.”. But the great difference between the tri-
chome widths of both should exclude the mutual
identification. The width of 2,3-3 µm mentioned
by S
ymoens
is confirmed by J
ohn
et al.
(2002)
with reference to rivers in England. They are sig-
nificantly lower than the span of 2,9-4,2 µm es-
tablished for “Phormidium spec.”.
3.2
Ecological characteristics
The distribution of “Phormidium spec.” within the
geologically widely diversified region of South-
West-Germany gave indications of its ecological
requirements. The local streams include waters
in pure granite- and gneiss-regions with corre-
sponding “soft” water, rivers in granite-chalk tran-
sition zones to rivers in pure shell limestone and
jurassic formations with corresponding extreme
“
hard” water (B
ackhaus
1973,
Geologisches
Landesamt B-W
1956).
Within this scale of water
hardness, the presence of “Phormidium spec.”
was restricted to river sections containing freight-
ed or occurring limestones and where the hard-
ness did not exceed more than about 10 °dH. A
low concentration of dissolved calcium with cor-
respondingly low values of ABC (acid binding ca-
pacity), electric conductivity and pH seemed to
play an important role. This leads to a particular
map of distribution of “Phormidium spec.” in the
Black Forest as shown in fig. 19. In streams with
water hardness > 15 °dH and mean pH-values >
7,5 ”
Phormidium spec.” was missing, even though
the same kinds of limestones were present. This
Fig.19. Places in the Black Forest where “Phormidium
spec.” was found.
