Habitat
S. papillosum typically forms dense carpets and is commonly found growing in lawns of poor fens and rarely occurs in bogs.
Gametophyte
Overall structure:
S. papillosum is a dioicous species that is moderately-sized and considered to be a fairly robust plant. The capitulum is typically compact and not really enlarged when compared to other Sphagnum species. The color of the gametophytes allow for easy recognition at times, being a greenish brown to a golden brown.
Stem:
The stems are usually brown in color. Furthermore, a closer look at the cortical layer of the stem will reveal that the hyaline cells have spiral fibrils as well as can have 1-2 pores per cell.
Stem leaves:
The leaves of the stem can range in shape from short-ligulate to oblong-ligulate, while the rounded apex of these leaves can be slightly fringed. Moreover, the hyaline cells are not ornamented but most will be divided.
Branch fascicle:
The fascicle is generally comprised of two divergent branches and two-three pendent branches. The branches of this species are typically short and blunt, which is another characteristic that allows for easy recognition in the field.
Cross-section of branch:
Branch leaf:
The branch leaves of S. papillosum are usually spreading and are broadly ovate in shape.
The chlorophyllose cells, which have a trapezoidal to truncate-elliptic shape, can either be exposed to both surface equally or may be more broadly exposed on the concave (top) surface.
A closer look at a cross section will show that the hyaline cell walls near the chlorophyllose cells are covered in papillae.
Papillae can be seen by making a wet mount of a leaf.
Branch stem:
The hyaline cells on the branch stem are fibrillose often with a single large pore at the upper end of the cell.
Sporophyte
Overall structure:
The sporophyte of S. papillosum tends to mature in mid to late summer. A closer look at the sporangium will reveal that the capsule of this species has numerous pseudostomata.
Spores:
It is very common to see rough papillae on the spores of this species.