• Category
  • Length Range
    13-35 µm
  • Width Range
    3.3-4.8 µm
  • Striae in 10 µm



Valves are asymmetric to the apical and transapical axes, with one apex wider than the other. The ventral margin is straight to weakly concave, and the dorsal margin is convex. The apices are rounded, tapered and slightly delimited by a change in the slope of the dorsal margin. These characteristics of the apices, combined with the inset position of the helictoglossa on the ventral margin of each apex, give the apices a 'nose-like' appearance. Helictoglossae are set in at different distances from each apex (asymmetry to the transapical axis). One apical rimoportula is present at the wider apex, at the center of that apex. The distal raphe ends curve onto the valve surface. The striae are slightly radiate. Areolae approximately 50 in 10 µm.

Specimens of E. papilioforma are variable in the width of the valve apices and the relative position of the helicotoglossae. Some of this variation is a result of the plane of focus in the microscope; optical dissection is critical to observe valve morphology. Some specimens of E. papilioforma have one more attenuated apex and the helictoglossa is more removed, relative to the opposite end. The shape of the apex with the inset helictoglossa is more characteristic of E. incisa. These valves, however, are dissimilar to the overall E. incisa morphology, which lacks a strong heteropolar variation in apex width and position of the helictoglossae. Specimens of E. papilioforma are similar in morphology to the more asymmetric valves of E. rhomboidea. Eunotia papilioforma, however, is consistently wider than E. rhomboidea (as shown by Camburn et al. 1978; Krammer & Lange-Bertalot 1991). Figures 1-12 (Wuthrich 1975) were classified as E. rhomboidea but are likely more than one taxon. These illustrations show some of the variability discussed here, including variation in the width of the valve apices, position of the helicotoglossae and valve width.

In some specimens of E. rhomboidea, one apex is rounded and the other end is more shaped like the “snout of a shark”. Some specimens possess a small pseudoseptum. The pseudoseptum prevents observation of the base of the rimoportula (in SEM). The rimoportula of E. papilioforma also consistently occurS on the wider end of the valve.


Eunotia papilioforma is widespread on bryophyte substrates in streams throughout the Great Smoky Mountains National Park.

Gsm 6 27 05 3  F 0227  Algal Twig  Type Locality
Credit: Paula C. Furey
Type locality. Samples collected from bryophytes in Steeltrap Creek, Forney Creek watershed, Swain County, North Carolina, Great Smoky Mountains National Park.

Original Description

Frustules asymmetric to the apical and transapical axes, with one end wider than the other. Valves straight to weakly concave on the ventral margin, convex on dorsal margin, 13 – 35 μm long, 3.3 – 4.8 μm wide. Apices rounded, tapered, slightly delimited by a change in the slope of the dorsal margin, appearing nose-like. Helictoglossae set in from ends, often positioned at different distances from each end, giving appearance of an indentation in the light microscope. Rimoportula at the wider valve end, at the center of the apex. Raphe with distal ends curved onto the valve surface. Striae slightly radiate, 13 – 16 in 10 μm. Puncta 50 in 10 μm.

  • Author
    Furey, Johansen and Lowe 2011
  • Length Range
    13-35 µm
  • Width
    3.3- 4.8 µm
  • Striae in 10µm
    13-16 , areolae 50

Original Images

Eunotia papilioforma orig illus
Eunotia Papilioforma Textscan

Cite This Page

Furey, P. (2011). Eunotia papilioforma. In Diatoms of North America. Retrieved April 16, 2024, from https://diatoms.org/species/eunotia_papilioforma


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