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ZYGNEMATACEAE
When the zygospores are fully mature, an equatorial suture
usually can be seen. In many collections the median wall is con-
tracted inwardly and the surface thrown into ridges. The ridges
are irregular in position and are not morphological features of the
wall. They disappear when the spores are treated with dilute
potassium hydroxide, while morphological features of the wall
become more distinct.
The species of Zygnemopsis may be distinguished readily from
those of Zygnema when in a fruiting condition by the cellulose
colloid accumulation in the cells, by the initial very narrow con-
jugating tubes, and by the round or quadrangular pillow-shaped
spores. They differ from the species of Zygogonium in the form
of the chromatophores, the absence of cytoplasmic residues in the
gametangia and sporiferous cells, in the form of the spores, and
in the stages of tube formation. From the species of Debarya they
may be distinguished by the Zygnema-like chromatophores; and
from Hallasia by the absence of aplanospores from which one,
two, or three sporelings develop.
Some of the species here classified in the genus Zygnemopsis
have been previously placed in the genera: Debarya, Mougeotia,
and Zygnema.
Key to the Species of ZYGNEMOPSIS
I. Reproducing by aplanospores 12
I. Reproducing by zygospores, sometimes aplanospores also 2
2. Diameter vegetative cells mostly less than Sjtt 3
2, Diameter vegetative cells mostly between 8 and 16 /a 4
2. Diameter vegetative cells mostly 16 /a or more 11
3. Median spore wall punctate, yellow,
diameter vegetative cells 4-6 /a i. Z. silvangen sis
3. Median spore wall smooth, goldenbrown,
diameter vegetative cells 6-7/^'. 2. Z.orientalis
3. Median spore wall scrobiculatc, yellow,
diameter vegetative cells 6-8 /i. 4. Z. floridana
4. Shorter axis of zygospores less than 32 /i 5
4. Shorter axis of zygospores 32/i. or more 8
5. Diameter vegetative cells mostly less than 12/1 6
5. Diameter vegetative cells mostly more than i2ij- 7
6. Median spore wall smooth, choco-
late brown 5. Z. minuta