Key to the species of Microdictyon
| 1 | Plants frequently covered with epiphytes, especially crustose coralline algae; nets coarse and conspicuous; individual cells frequently between 0.5 - 0.7 mm | M. setchellianum |
| 1 | Plants rarely carrying epiphytes, nets delicate, individual cells rarely more than 0.15 mm diam | M. japonicum |