Silva Center for Phycological Documentation: Index Nominum Algarum

The INA is a card file and online reporting system maintained at the Silva Center for Phycological Documentation of the University Herbarium, University of California, Berkeley. It contains nearly 200,000 names of algae (in the broad sense). The BPU is a card file containing bibliographic references pertaining to algal taxonomy.
A working list of algal type specimens at UC is available here

Results from INA database

Nitzschia gracilis f. acicularoidesM. Coste & M. Ricard Cryptogamie: Algologie 1: 191, pl. 1: fig. 2 1980
Nitzschia gracilis f. brevisManguin image
Nitzschia gracilisHantzsch in Rabenhorst Alg. Sachs. Dec. 95/96: no. 946 1860
Nitzschia gracilis var. capitataWislouch & Poretsky in Poretsky Trudy Leningradskago Obschchestva Estestvoispytatelei 53(3): 147, fig. 9 1924
Nitzschia gracilis var. minorSkabitschevskii image
Nitzschia gracilis var. turfaceaSteinecke image