• Category
  • Length Range
    8.8-11.2 µm
  • Width Range
    2.7-3.0 (broadest point), 1.9-2.4 (center) µm
  • Striae in 10 µm



Valves are distinctly undulate, with a deep constriction in the central valve and sub-apically inflation. Apices are weakly rostrate to cuneate, with rounded ends. The axial area is linear to slightly lanceolate. The central area is nearly circular and slightly enlarged due to the shorter central striae. Areolae are transapically elongated. Under SEM, the proximal raphe ends terminate in laterally expanded, T-shaped depressions. The distal raphe ends terminate in T-shaped or anchor-shaped depressions. Internally, small pseudosepta are present at both apices.


This species is widespread on volcanic wet walls of the Hawaii'n Islands. The largest populations are on Oahu, where H. undulata is occasionally found in small streams.

Original Description

Valves distinctly undulate with a relatively deep constriction in the middle of the valve leading to sub-apical inflations and terminating in weakly rostrate to cuneately rounded valve apices. Valve dimensions (n=25): length 6.5‒15.2 µm, width 2‒2.3 µm at the constricted center. Axial area linear to slightly lanceolate, gradually tapering toward the apices. Central area almost circular, slightly enlarged due to the shorter central striae. Striae 29‒31 in 10 µm, each composed of one transapically-elongated areola. Near the central area areolae shorter, almost circular. Mantle areolae continuing around the valve apices without any interruption near the apex. Proximal raphe endings terminating in a laterally expanded T-shaped depressions. Distal raphe endings terminating in T- to anchor-shaped depressions, often curved toward the valve center. Internally, small pseudosepta present at both apices.

  • Author
    Lowe et al. 2014
  • Length Range
    6.5-15.2 µm
  • Width
    2-2.3 (center) µm
  • Striae in 10µm

Original Images

Orig  Lm

Cite This Page

Lowe, R. (2015). Humidophila undulata. In Diatoms of North America. Retrieved April 16, 2024, from https://diatoms.org/species/humidophila_undulata


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