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Pterygoneurum Juratzka, 1882.

Key to Pterygoneurum

Mosses included in this section are costate acrocarps with hyaline awns. Inserted on the adaxial face of the costa are 2-4 rather high photosynthetic lamellae, and these will be obvious as lamellae even under the dissection microscope. Pterygoneurum can be confused only with the two other Pottiaceae with photosynthetic processes on the adaxial face of the leaf. The lamellae on the leaves of Pterygoneurum are not crowded, and are therefore easily seen as separate entities. In contrast Aloina and Crossidium (with the exception of C. aberrans) have such crowded photosynthetic filaments that dissection microscopes may not easily allow visual resolution of the individual filaments.

Species included in this key are all in Pottiaceae:
Pterygoneurum californicum H. Crum
Pterygoneurum lamellatum (Lindberg) Juratzka
Pterygoneurum ovatum (Hedwig) Dixon
Pterygoneurum subsessile (Bridel) Juratzka

This is the most widespread in California of the three Pottiaceous genera with adaxial photosynthetic processes. Whereas Crossidium and Aloina are largely plants of calcareous sites, our four species of Pterygoneurum seem indifferent to the presence of calcium ions. Pterygoneurum is not only a plant of soil but our two common species are regular occupants of the tops of decomposing grass tussocks in desert habitats. Of the four species in the genus in California, only P. ovatum and P. subsessile are of regular occurrence; the other two species are very local and rare.

A. Leaves on at least some specimens elongate, somewhat spatulate, 3-4:1; peristome present, fugacious and clinging to operculum; urn oblong to cylindric, 4-6:1; cells papillose on back, at least in the distal end of the leaves .....Pterygoneurum lamellatum
A. Leaves ovate, often broadly so, never spatulate; peristome absent; urn mostly ovoid to hemispheric; cells smooth or somewhat papillose dorsally near leaf apex .....B

B. Sporophyte emergent or exserted with seta longer than the urn .....Pterygoneurum ovatum
B. Sporophyte immersed on a seta shorter than the urn .....C

C. Spores densely papillose; calyptra mitrate; median laminal cells mostly with corner thickenings .....Pterygoneurum subsessile
C. Spores smooth; calyptra cucullate; median laminal cells evenly thick-walled .....Pterygoneurum californicum

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