• Category
  • Length Range
    18.3-20 µm
  • Width Range
    5.8-6.6 µm
  • Striae in 10 µm
    18-21 in the center, 22-24 at the valve ends
  • Synonyms
    Navicula declivis Hust.
    Navicula inflata var. declivis (Hust.) Cleve-Euler



Valves are elliptic-lanceolate, with capitate apices. The raphe is filiform and the axial area is narrow. A small, round central area contains a single stigma, or in rare specimens, two stigmata. In practice, however, the stigma can be difficult to resolve using LM due to its close proximity to the middle striae. The striae are radiate throughout the valve, with widely spaced, nearly parallel striae in the center valve. The apices contain annulae, which may be difficult to resolve in LM. This taxon exhibit a narrow size range; there is little variation in cell size.

This taxon was described as Navicula declivis Hust. from Poggenpohls peat bog, near Dötlingen in Oldenburg in northwest Germany (Hustedt 1934). In the original description, Hustedt states that this new taxon is probably the same as one that Donkin shows (in Brit. Diat. Plate 3, Fig. 9), and refers to as Navicula inflata. However, N. inflata as described by Kütz. was not a valid publication.

Later, this taxon was considered a variety of Navicula inflata (N. inflata var. declivis (Hust.) Cleve-Euler 1953). In 1996, it was transferred into Geissleria as G. declivis (Hust.) Lange-Bert.


Specimens for this page were collected in a stream downstream of Currant Creek Reservoir, Utah. Only empty valves were observed in the raw sample so it is unclear whether these Utah populations were inhabiting the stream or reservoir (personal observation). In North America, this taxon has also been reported from the Great Lakes (Stoermer et al. 1999, Reavie 2020).

Records from Europe document this taxon in the benthos of freshwater streams and littoral zones of lakes. A study in south-eastern Poland reported populations in multiple locations along the Czarna Staszowska River (Rakowska and Szczepocka 2015). A study of oligotrophic lakes in Finland, Germany and Austria, found it in only one lake in Finland (Julma Ölkky) that was characterized as low in electrolytes and high in humic acids (Lange-Bertalot and Metzeltin 1996). A study in Polish lakes found that it seemed to prefer waters with moderate organic content, neutral pH, low to medium electrolyte content and oligosaprobous (Noga et al. 2013).

Original Description

126. Navicula declivis nov. sp. Schalen elliptisch-lanzettlich mit kopfig abgeschnürten Enden, 19-22 µ lang, 6-7 breit. Raphe gerade, fadenförmig. Axialarea sehr eng, um den Zentralknoten zu einer kleinen, rundlichen Zentralarea erweitert, an einer Seite am Rande des Zentralknotens mit einem isolierten Stigma. Transapikalstreifen im mittleren Teil leicht radial, an den Enden senkrecht zur Raphe, in der Mitte wit gestellt, etwa 16 in 10 µ, gegen die Enden viel enger werdend, zwischen Mitte und Enden etwa 26 in 10 µ. - Nicht selten in Laubmoosen im Wasserniveau am Nordende des Moores. Fig. 12.

Sehr wahrscheinlich is diese Art identisch mit der von Donkin als Navicula inflata abgebildeten Form (Brit. Diat. T. 3, F. 9). Er bezieht sich jedoch auf Kützing, dessen Art aber undefinierbar ist, ebenso wie die von W. Smith und Rabenhorst als Nav. (oder Pinnularia) inflata Kütz. gegebenen Figuren. Aus diesem Grunde ist der von P.T. Cleve eingeführte Name Nav. inflata Donkin (!) als unzulässig aufzugeben. Die von ihm abgebildete Form kann keinesfalls auf Donkins Abbildung bezogen werden, sondern bedarf weiterer Prüfung und etwiger Neubennung. Die Bezeichnung Nav. inflata (auct. nonnull.!) ist zu streichen.

  • Basionym
    Navicula declivis
  • Author
    Hust. 1934
  • Length Range
    19-22 µm
  • Width
    6-7 µm
  • Striae in 10µm

Original Images

Navicula declivis orig illus
Navicula declivis orig desc

Citations & Links


  • Index Nominum Algarum
  • DiatomBase
  • The Academy of Natural Sciences, Drexel University

Cite This Page

Davis, C. (2022). Geissleria declivis. In Diatoms of North America. Retrieved September 23, 2023, from https://diatoms.org/species/geissleria-declivis


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Geissleria declivis from all the stream reaches where it was present. Note that the relative abundance scale is the same on each plot. Explanation of each environmental variable and units are as follows:

ELEVATION = stream reach elevation (meters)
STRAHLER = distribution plot of the Strahler Stream Order
SLOPE = stream reach gradient (degrees)
W1_HALL = an index that is a measure of streamside (riparian) human activity that ranges from 0 - 10, with a value of 0 indicating of minimal disturbance to a value of 10 indicating severe disturbance.
PHSTVL = pH measured in a sealed syringe sample (pH units)
log_COND = log concentration of specific conductivity (µS/cm)
log_PTL = log concentration of total phosphorus (µg/L)
log_NO3 = log concentration of nitrate (µeq/L)
log_DOC = log concentration of dissolved organic carbon (mg/L)
log_SIO2 = log concentration of silicon (mg/L)
log_NA = log concentration of sodium (µeq/L)
log_HCO3 = log concentration of the bicarbonate ion (µeq/L)
EMBED = percent of the stream substrate that is embedded by sand and fine sediment
log_TURBIDITY = log of turbidity, a measure of cloudiness of water, in nephelometric turbidity units (NTU).
DISTOT = an index of total human disturbance in the watershed that ranges from 1 - 100, with a value of 0 indicating of minimal disturbance to a value of 100 indicating severe disturbance.