Platessa stewartii

(Patrick) Potapova 2004      Category: Monoraphid
BASIONYM: Achnanthes stewartii Patrick 1945
SYNONYM(S): Planothidium stewartii (Patrick) Lange-Bertalot in Krammer and Lange-Bertalot 

Platessa lutheri

 

Pleurosira laevis
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LM scalebar = 10 µm = 80 pixels.

Observations

Contributor: Marina Potapova - December 2010
Length Range: 11–16 µm
Width Range: 5.7–7.0 µm
Striae in 10 µm: 14–18

Description

Valves are elliptic. Both valves have a linear axial area. The central area on the raphe valve is transapically rectangular, often reaching the valve margin. The central area on the rapheless valve is small and often asymmetric. The striae are radiate and biseriate. The raphe is straight, filiform and lacks terminal fissures. Distal external raphe ends are slightly expanded and straight. Proximal external raphe ends are expanded and sharply turned to one side. Areolae are round. There is a row of areolae on the valve mantle, with one areola at the end of each stria.

Original Description

Basionym: Achnanthes stewartii
Author: Patrick 1945
Length Range: 16 µm
Width Range: 7.5 µm
Striae in 10 µm: 14

Original Description

Valvae ellipticae, 16 μ longae, 7.5 μ latae, area axiali angusta, costis tenuibus 14 in 10 μ, serie duplici punctorum parvorum interpositu

Original Images

Cite This Page:
Potapova, M. (2010). Platessa stewartii. In Diatoms of the United States. Retrieved May 25, 2013, from http://westerndiatoms.colorado.edu/taxa/species/planothidium_stewartii

Species: Platessa stewartii

Contributor: Marina Potapova

Reviewer: Sarah Spaulding

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Image Credit: Marina Potapova

  1. Valves elliptic
  2. Axial area narrow
  3. Central area on raphe valve transversely rectangular
  4. Central area on rapheless valve small, often asymmetric
  5. Stria density 14-18 in 10 µm

Valves are elliptic. Both valves have a linear axial area. The central area on the raphe valve is transapically rectangular, often reaching valve margins. The central area on the rapheless valve is small and often asymmetric. Striae are radiate and biseriate. The stria density on both valves is 14-18 in 10 µm.

Compare

Platessa stewartii differs from P. hustedtii by the narrow axial area on rapheless valve and more narrow central area on raphe valve. The raphe valves of P. stewartii can be confused with those of other Platessa species and some Planothidium species with elliptical valves. Observations of rapheless valves are helpful in distinguishing these taxa. For example, the rapheless valve of Planothidium joursacense can be distinguished by the presence of a hood.

Platessa hustedtii

Planothidium joursacense

Citations

Krammer, K. and Lange-Bertalot, H. (2004). Bacillariophyceae 4. Teil: Achnanthaceae, Kritische Erganzungen zu Navicula (Lineolatae), Gomphonema Gesamtliteraturverzeichnis Teil 1-4 [second revised edition]. In: H. Ettl et al., Suesswasserflora von Mitteleuropa. Spektrum Akademischer Verlad Heidelberg, 468 pp.

Patrick, R.M. (1945). A taxonomic and ecological study of some diatoms from the Pocono Plateau and adjacent regions. Farlowia 2(2):143-221.

Potapova, M. (2012). New species and combinations in monoraphid diatoms (Family Achnanthidiaceae) from North America. Diatom Research 27(1): 29-42. doi:10.1080/0269249X.2011.644636

Links & ID's

Index Nominum Algarum (INA)

California Academy of Sciences (CAS)

Platessa stewartii CAS

North American Diatom Ecological Database (NADED)

NADED ID: 155035

Autecology Discussion

Platessa stewartii was shown to have preference for a low calcium content, while its conductivity optimum (based on a dataset of 2674 river samples from the USA) was 134 μm/cm (Potapova & Charles 2003).

Habits

Size Range

101-1000 µm3 (ie Amphora veneta)

Motility

slightly motile (e.g. Cocconeis)

Attachment

prostrate (e.g. mucilage pad)

Habitat

benthic

Colony

solitary

EMAP Assessment

Sampling for the Environmental Protection Agency (EPA) western Environmental Monitoring and Assessment Program (EMAP) study was completed during the years 2000-2004 (see citations at bottom of this page). Streams and rivers in 12 western states (Arizona, California, Colorado, Idaho, Montana, Nevada, North Dakota, Oregon, South Dakota, Utah, Washington and Wyoming). Over 1200 sites on streams and rivers in 12 western states (Arizona, California, Colorado, Idaho, Montana, Nevada, North Dakota, Oregon, South Dakota, Utah, Washington and Wyoming) were selected for sampling based on a stratified randomized design. This type of design insures that ecological resources are sampled in proportion to their actual geographical presence. Stratified randomized design also allows for estimates of stream length with a known confidence in several “condition classes” (good or least-disturbed, intermediately-disturbed, and poor or most-disturbed) for biotic condition, chemistry and habitat.

EMAP Distribution

Platessa stewartii

Distribution

The distribution map represents the relative abundance of this Platessa stewartii in the western EMAP study. Relative abundance is a measure of the proportion of cells of this species based on a "fixed count" of 300 total diatom cells counted and identified. Each of the western EMAP sample sites is shown, either with a black dot for sites where Platessa stewartii was not recorded, or with a red circle indicating the relative abundance of Platessa stewartii.

Note that the size of the proportional symbols varies between species to help show both abundant and rare species.

Scale for the map to the left

EMAP Response Plots

Platessa stewartii

Responses

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

EMAP citations

Results are published in:

Johnson, T., Hermann, K., Spaulding, S., Beyea, B., Theel, C., Sada, R., Bollman, W., Bowman, J., Larsen, A., Vining, K., Ostermiller, J., Petersen, D. Hargett, E. and Zumberge, J. (2009). An ecological assessment of USEPA Region 8 streams and rivers. U.S. Environmental Protection Agency Region 8 Report, 178 p.

Stoddard, J. L., Peck, D. V., Olsen, A. R., Larsen, D. P., Van Sickle, J., Hawkins, C. P., Hughes, R. M., Whittier, T. R., Lomnicky, G. A., Herlihy, A. T., Kaufman, P. R., Peterson, S. A., Ringold, P. L., Paulsen, S. G., and Blair, R. (2005). Environmental Monitoring and Assessment Program (EMAP) western streams and rivers statistical summary. U.S. Environmental Protection Agency Report 620/R-05/006, 1,762 p.

Stoddard, J. L., Peck, D. V., Paulsen, S. G., Van Sickle, J., Hawkins, C. P., Herlihy, A. T., Hughes, R. M., Kaufman, P. R., Larsen, D. P., Lomnicky, G. A., Olsen, A. R., Peterson, S. A., Ringold, P. L., and Whittier, T. R. (2005). An ecological assessment of western streams and rivers. U.S. Environmental Protection Agency Report 620/R-05/005, 49 p.