• Category
  • Length Range
    11.0-17.5 µm
  • Width Range
    5.0-6.0 µm
  • Striae in 10 µm
  • Synonyms
    Achnanthes lanceolata subsp. rostrata (Østrup) Lange-Bert.



Valves are linear-elliptical with rostrate, subrostrate or narrowly subcapitate apices. The raphe valve has a linear axial area and central area that varies in shape - from transversely rectangular to elliptical. The rapheless valve has a linear-lanceolate axial area, which in some populations, widens considerably in the valve center. The rapheless valve has a linear-lanceolate axial area and an asymmetrical central area containing a hood on the internal valve surface. The raphe is straight with expanded external proximal endings. Terminal raphe fissures are curved to the secondary side of the valve. The striae are multiseriate and radiate throughout both valves.


Original Description

L. 0,012 mm., B. 0,006 mm. Striæ 10 in 0,01 mm. The outline of both valve identical: elliptical with rostrate apices. Epitheca with an unilateral horseshoe-shaped mark, Hypotheca: central pores approximate, unilateral central area

  • Basionym
    Achnanthes rostrata
  • Author
    Østrup 1902
  • Length Range
    12 µm
  • Width
    6 µm
  • Striae in 10µm

Original Images

Orig Ill  Plrostr
Orig Descr  Plrostr

EMAP Assessment

EMAP Distribution

Planothidium Rostratum 40 Copy
Map 40

Response Plots

Planothidium Rostratum Copy

Cite This Page

Potapova, M. (2010). Planothidium rostratum. In Diatoms of North America. Retrieved November 21, 2019, from https://diatoms.org/species/planothidium_rostratum


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