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Diatoms of the United States is now known as Diatoms of North America.
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GENERA starting with "h"


Halamphora 9

  1. Raphe eccentric, positioned along ventral margin
  2. Dorsal margin of valve deeper than ventral margin
  3. Raphe ledge present on dorsal side of raphe
  4. Dorsal fascia usually absent

Asymmetrical biraphid - Valves are moderate, to strongly, asymmetric to the apical axis. Valves are symmetric to the transapical axis. The valve mantle is deep on the dorsal margin and shallow on the ventral margin. Most species of Halamphora lack a distinct marginal ridge; instead, the interface of the face and margin is gradual. A ‘raphe ledge’ is present on the dorsal side of the raphe. In most Halamphora species, a dorsal fascia, or hyaline...

Hannaea 2

  1. Valves arched
  2. Poles capitate to rostrate
  3. Valve with central ventral swelling
  4. Faint (ghost) striae near central swelling

Araphid - Valves are linear and arched. One or two rimoportulae occur on each valve, located near the valve ends. The ventral (concave) side of the valve has a central swelling. Faint, or ghost striae, are often present near the center of the valve. Hannaea is characteristic of oligotrophic streams and large lakes, where it grows attached in tufted colonies to benthic surfaces.


  1. Valves asymmetric to apical axis
  2. Raphe eccentric
  3. Frustule with both raphes on same side
  4. Striae uniseriate

Nitzschioid - Valves are asymmetric to the apical axis. Like Nitzschia, the raphe is contained within a canal and eccentrically positioned on the valve margin. In Hantzschia, the raphe is always located on the concave, or ventral, margin of the valve. Striae are uniseriate. The genus Hantzschia differs from Nitzschia in symmetry. Within a Hantzschia frustule, the raphes of the two valves are on the margin of the same side. In...


  1. Valves lanceolate with acute apices
  2. Central costae thickened, forming a stauros-like structure
  3. Raphe sternum with asymmetric thickened area in the central valve
  4. Striae crossed by longitudinal strips

Symmetrical biraphid - Valves are lanceolate with acute apices and a central raphe system. Two or three thickened transapical costae on either side of the valve center form a stauros-like structure. The raphe sternum is thickened on one side of the axial area and is fused to the central ribs, giving valves a cruciform appearance. Striae are uniseriate, containing rectangular or square poroids, and overlain externally by fine longitudinal...

Hippodonta 6

  1. Striae distinct, broad
  2. Striae uniseriate or biseriate
  3. Valve termini with thickened silica

Symmetrical biraphid - Species in Hippodonta possess thick, heavily silicified valves. Valves are generally lanceolate in valve outline with variously shaped poles. The striae are distinct, broad and may be uni-seriate or biseriate. The valve termini are thickened bands of silica.The raphe is straight and the proximal raphe ends are dilated. Two chloroplasts are present in living cells. Hippodonta includes the former Navicula capitata...

Humidophila 4

  1. Striae composed of single elongate areola
  2. External raphe ends curved or T-shaped

Symmetrical biraphid - Valves are small, usually less than 20 ┬Ám. Valves are linear, linear-elliptical to elliptical. The apices are broadly rounded. The central nodule is small and rounded. Other features of Humidophila are visible under SEM. The valve face is flat, and may have a narrow rim, or ridge, differentiating the valve face from the mantle. Striae on the valve face are composed of one usually transapically elongated, elliptical to...

Hydrosera 1

  1. Valve margin appearing doubly triangular
  2. Porefields three, with ocelli present, positioned on the ends of one of the "triangles"
  3. Rimoportula distinct

Centric - Hydrosera is a large multipolar, centric diatom. Frustules are heavily silicified. Valve margins appear to be in the shape of two superimposed triangles. A distinct rimoportula is present. Porefields, containing ocelli, are positioned at the three poles of one of the apparent triangles. Frustules form large zig-zag colonies, joined by mucilage secreted from the porefields. Hydrosera grows in streams of southern coastal...

Hygropetra 1

  1. Striae broad
  2. Striae alveolate
  3. Robust transapical costae

Symmetrical biraphid - The species in Hygropetra are small in size, with broad, V-shaped striae. The striae are alveolate, or composed of very small pores, in rows of 3-4. A small septum is present. Internally, robust transapical costae are positioned between the striae. The raphe is filiform, with a relatively large gap between proximal raphe ends. Hygropetra is a genus of small taxa previously considered within Pinnularia. The group is...