• Category
  • Length Range
    8.5-12.5 µm
  • Width Range
    4.9-5.5 µm
  • Striae in 10 µm
  • Synonyms
    Achnanthes lanceolata var. rostrata Hustedt



Valves are linear-elliptic, with subrostrate apices. The raphe valve has a narrow linear axial area and a very small transversely elliptic or rectangular central area. The raphe is straight with expanded external proximal ends. The rapheless valve has a narrow linear-lanceolate axial area. The asymmetric central area on the rapheless valve contains a cavum on the internal valve surface. The striae are slightly radiate throughout both valves.

Observations of P. rostratoholarcticum from California show size ranges of 3.7-4.6 µm wide, 6.3-11.7 µm long, and 13-18 striae in 10 µm (Stancheva, submitted 2020). This taxon is also reported from Europe, where dimensions differ somewhat: 3.8-6.4 µm wide, 6.4-13.5 µm long, 13 to 17 striae in 10 µm (Wetzel et al. 2019).


According to Bak and Lange-Bertalot (2014), P. rostratoholarcticum is found in Europe "mainly in eutrophic alkaline rivers and lakes with medium to high conductivity, likewise in estuaries, lagoons, and backwater of the North Sea and the Baltic Sea". As this species was likely included with other species in the P. rostratum species complex, its distribution in North America is uncertain.

Original Description

  • Basionym
    Achnanthes lanceolata var. rostrata
  • Author
    Hustedt 1911

Original Images

Alanc Vrostr Hust Or Ill1
Alanc Vrostr Hust Or D2

Cite This Page

Potapova, M. (2020). Planothidium rostratoholarcticum. In Diatoms of North America. Retrieved May 30, 2024, from https://diatoms.org/species/planothidium-rostratoholarcticum


The 15 response plots show an environmental variable (x axis) against the relative abundance (y axis) of Planothidium rostratoholarcticum 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.