A Simple Key to the Main Genera of Diatoms

ORDER CENTRALES
2a. Valves mostly in girdle view; Melosira
2b. Valves mostly in valve view; striae evident Cyclotella

ORDER PENNALES
3a. Valves without raphes 4
3b. Valves with raphes [sub-order Raphidinae] 5
4a. Hypovalve only with a raphe [Family Achnanthaceae] 12
4b. Both valves without raphes [sub-order Araphidinae] 10
5a. Raphes vestigial at valves ends (pseudoraphes) [Family Eunotiaceae] Eunotia
5b. Raphes entire 6
6a. Epivalve without a raphe [Family Achnanthaceae] 12
6b. Both valves with a raphe 7
7a. Raphes in canal, 8
7b. Raphes not in canal, generally dividing valve in two longitudinal halves [Family Naviculaceae] 13
8a. Valves linear, narrow; without costae (heavy ribs) [Family Bacillariaceae] 21
8b. Valves costae 9
9a. Valves with very coarse costae [Family Surirellaceae] Surirella
9b. Valves with costae consisting of punctae. [Family Epithemiaceae] 23

SUB-ORDER ARAPHIDINAE

Family Fragilariaceae
10a. valves heteropolar Meridion
10b. Valves isopolar 11
11a. valves with swollen ends and central area Tabellaria
11b. otherwise Fragilaria, Synedra,

SUB-ORDER RAPHIDINAE

Family Achnanthaceae
12a. Valves bent girdle view Achnanthes
12b. Valves not bent in girdle view; disc shaped. Cocconeis

Family Naviculaceae
13a. valves heteropolar 14
13b. valves isopolar 15
14a. 1 valve with poorly developed raphe; valves bent in girdle view. Rhoicosphenia
14b. Both valves with complete raphes Gomphonema
15a. Valves dorsoventral Amphora, Cymbella
15b. Valves bilaterally symmetrical 16
16a. valves and raphe bent into an s-shape Gyrosigma, Pleurosigma
16b. otherwise 17
17a. punctae not visible Pinnularia
17b. otherwise 18
18a. raphe with strong inneraxial ribs Frustulia
18b. otherwise 19
19a. Striae clearly punctate; stigma present in broad central area. Luticola
19b. otherwise 20
20a. Valve with a stauron (central area extending to valve margin) Stauroneis
20b. Otherwise (generally) Navicula

Family Bacillariaceae
21a. Raphe canals of cells diagonally opposite 22
21b. Raphe canals superimposed; central node, ends drawn Hantzschia
22a. Valve wide, with a hyaline fold Tryblionella
22b. valves usually narrow (<< 6 (m); no fold. Nitzschia

Family Epithemiaceae
23a. Valves linear Denticula
23b. Valves dorso-ventral 24
24a. Raphe canal meeting midway at an acute angle Epithemia
24b. Raphe otherwise, generally following dorsal margin Rhopalodia

Other salt lake genera include:
Anomoeoneis, Berkeleya (syn. Amphipleura), Diploneis, Entomoneis (syn. Amphiprora), Grammatophora, Mastogloia, Opephora.