In article ,
wrote:
While the local library has a lot of books about microalgae and
surface bound macroalgae, planktonic macroalgae/plants are – if at
all – only mentioned in foot notes.

I'm looking for plant(including algae) species that are at least 0.4mm
large and tolerate the following habitat:

- free-floating, completely submerged
- 10-30 °C (usually: 16-23 °C)
- 5-8 pH (usually: 6.5-7.5 pH)

Salinity (in-)toleration isn't an issue.

Thanks for any hints/ideas.

Look into plants used in aquaria and ponds -- most common kinds do
well under a range of conditions. Some I can think of right off
are Naias, Elodea/Anacharis, Cabomba, Myriophyllum and Ceratophyllum
spp. In this context they are called 'bunch plants', because they
are sold as bunches of cuttings.

Note that if you are planning to keep these plants outdoors, make
sure they can't escape, since some can be appallingly invasive.