However, you could use some general collective nouns that fit well with the imagery of lotuses:
* A bed of lotuses
* A pond of lotuses
* A field of lotuses
* A cluster of lotuses
* A display of lotuses
You could also use more poetic options:
* A symphony of lotuses
* A tapestry of lotuses
Ultimately, the best collective noun depends on the context and the specific image you're trying to evoke.