Diatoms  and  other  algae  were  collected  and  identified  from  subaerial habitats (wetwalls) in Great Smoky Mountains National Park as part of a larger bio- diversity survey of the Park. Algal collections were made across a range of moisture gradients and bedrock mineralogies with pH ranging from 3.8 to 7.7. None of the communities collected were entirely submerged in water, but were often associated with moist bryophytes, cyanobacterial mats, and dripping groundwater seeps. Some of the collections were from cliff faces wetted only periodically. 

To date, 41 diatom genera  and  over  223  species  have  been  identified  from  these  habitats.  Several  of these genera are widely distributed across aquatic habitats; however, several of the genera  are  “subaerial  specialists”  and  possess  morphological  features  such  as  reduced size, reduced external openings in the cell wall, or additional external siliceous membranes that allow them to survive in relatively dry habitats. Widely distributed species  with  high  fidelity  to  subaerial  habitats  occur  in  the  genera  Achnanthes, Cymbopleura,  Decussata,  Diadesmis,  Luticola,  Melosira,  Microcostatus,  Nupela, Psammothidium, and Orthoseira. Many of the species constitute new Park records,

national records, or are new to science.