GENERA starting with "P"

Symmetrical biraphid - Valves are rhomboid or bluntly lanceolate. The central area is variable in shape, from a large fascia-like central area to small and oval. The raphe is straight, with curved distal fissures. Frustules possess numerous girdle bands. Two chloroplasts with deep lobes are present in living cells. This genus includes primarily marine species, with few freshwater species. Some marine littoral species create mucilage tubes.

Symmetrical biraphid - Frustules of Pinnularia may be large, up to 300 µm in length. The striae are alveolate. Internally, the striae are positioned within chambers. The openings of the chambers are evident as longitudinal lines that cross the striae. The raphe system may be straight or complex. Externally, the proximal raphe ends are expanded and bent slightly to the same side. The distal raphe ends are deflected and may form a distinct,...

Symmetrical biraphid - The valve outline of Placoneis is linear to lanceolate, sometimes with rostrate or capitate ends. The areolae are loculate and internally occluded. Areolae form uniseriate striae. The axial area is narrow. The proximal raphe ends are straight and slightly expanded externally. The plastid is large, distinct, and divided into two X-shaped plates. Placoneis contains a number of species that grow in epipelic habitats of...

Symmetrical biraphid - The valve margins of Plagiotropis are lanceolate with narrow poles. The valve face is folded, with folds appearing as lines on either side of the raphe. The raphe itself is raised above the valve face and positioned within a keel. The axial area is narrow and the central area is variable in shape. Striae are parallel and composed of loculate areolae. In girdle view, cells appear constricted in the center. Plagiotropis...

Monoraphid - Frustules of Planothidium are heterovalvar, with slightly concave raphe valve and convex rapheless valve. Valves are elliptic to lanceolate, with rounded, rostrate or capitate apices. The striae are multiseriate. The raphe valve possess radiate striae and a prominent raphe. The terminal raphe fissures are deflected unilaterally. Many Planothidium species, but not all, possess an asymmetrical central area on the...

Monoraphid - Cells form single cells or short chains. Girdle bands are narrow and lack ornamentation. The genus Platessa was recently established (Lange-Bertalot, 2004) and contains the former Achnanthes conspicua Mayer and the A. holsatica Hustedt group. Members of this genus are widely reported, but low in abundance in collections.

Symmetrical biraphid - Frustules of Playaensis are small in size, less than 40 µm in length. Valves are spathulate in shape and the valve margins are ornamented with small, fin-like spines. Striae are uniseriate and punctate. The raphe is bordered on both sides by a longitudinal rib. Internally, this rib is visible as a broad structure. Externally, the surface of valves are ornamented with spherical nodules. Playaensis is known from northern...

Centric - Pleurosira has very large orbicular valves with 2-4 prominent ocelli, the number depending on salinity. The ocelli secret mucopolysaccaride pads that join cells together in large, zig-zag colonies. A single rimoportula is positioned near the center of the valve face. Colonies form filaments that are visible in streams. Pleurosira is widely distributed in naturally saline waters and polluted waters. In older literature...

Centric - The valve face of Pliocaenicus has a distinct transverse undulation. Areolae radiate from the valve center in single rows, rather than being organized into groups, or fascicles. A number of fultoportulae are positioned at the center of valve face. Marginal fultoportulae are present between the striae, near the valve/mantle interface. Species in Pliocaenicus lack areolae on the valve mantle, below the marginal strutted...

Monoraphid - Frustules are small, elliptic, lanceolate-elliptic, or linear-elliptic in shape. Frustules are bent in girdle view so that the raphe valve is convex and the rapheless is concave, an arrangement that differs from other achnanthoid genera. The length to width ratio ranges between 1.5 and 3.0. The valve apices are broadly rounded. The arrangement of areolae is similar on the raphe and rapheless valves. Striae are radiate...

Symmetrical biraphid - The genus Pseudofallacia was established in 2012 for small, solitary naviculoid species that had been included in Fallacia. Valves are symmetric with respect to the apical and transapical axes. The raphe is filiform and straight. A finely perforated conopeum is present, which extends along the raphe. Two pores are present at each terminal area of the valve. A single elongated areola makes up each stria. Externally, the...

Araphid - Frustules of Pseudostaurosira form chains with frustules linked valve face to valve face. Frustules rectangular in girdle view. Striae are uniseriate, composed of a few (usually not more than 4) elliptical areolae. Spines are present on the valve margin and may be branched. Pseudostaurosira includes the former Fragilaria brevistriata and is distinguished by the structure of the striae, rather than the shape of the...

Araphid - Pseudostaruosiropsis includes species that are small, with elliptic to rounded valves. The striae are uniseriate, composed of 2-6 round areolae externally occluded with discoid volae. Two apical porefields are present, composed of a few, isolated pores. Spines are present at the valve margin, aligned with a stria. The spines are flattened and bifurcate. Valves lack rimoportulae. To date, species have been described...

Araphid - Valves linear elliptical and may possess a central inflation. The striae are composed of a rectangular net of transapical and apical bars. Spines are present at the valve face/mantle junction on the costae, interrupting the striae, or both positions. The spines are variable in form. According to Williams and Round (1987) one apical porefield is present; according to Morales (2005) two apical porefields are present. The...

Centric - NOTE THE THE GENUS PUNCTICULATA, ALTHOUGH VALIDLY PUBLISHED, IS NOT LEGITIMATE (see below). The valve face is circular or oval. The central area is variable: with both areolae and fultoportulae, or areolae only, or fultoportulae only. Central area fultoportulae, when present, possess three satellite pores. One or more rimoportulae are present on the valve face, at end of a shortened stria, or shortened striae....