Polytrichastrum formosum

Polytrichastrum formosum generally inhabits shaded, poor soils and humus in damp coniferous forests and cool temperate rainforests. This species is most common in Europe and grows in grasslands, lowland heaths, acidic moorlands, rocky slopes, and old buildings. == Gametophyte ==

Like all moss, the haploid gametophyte is the dominant phase of the lifecycle of P. formosum. The moss gametophyte has photosynthetic leaves, a stem, and root-like rhizoids that anchor them to the substrate. Polytrichastrum formosum is a medium to large robust acrocarpous moss, growing in uncrowded, unbranching tufts. This process is made possible by a central conducting strand in the stem, made up of hydroids, which are cells specialized for water transport. The stem also contains leptoids and specialized parenchyma cells that are used for conducting sugars throughout the plant. Using a microscope, photosynthetic lamellae are visible in cross section, nearly covering the entire ventral surface of the leaf. Each lamella stands 3 to 7 cells high and the cells at the top are smooth and oblong. The lamellae are covered by a layer of hydrophobic wax that protects the air spaces between neighbouring lamella from being flooded with water, which would impede CO2 uptake necessary for photosynthesis. In this way, P. formosum is able withstand high irradiance better than other mosses. == Sporophyte ==

The diploid sporophyte generation of P. formosum matures in early summer and is short-lived. The seta is yellowish to reddish brown and is 3 to 6 cm tall. Like the stem of the gametophyte, the seta has a hydrome and leptome for conducting water and sugars from the gametophyte. The slender and short-rectangular capsule is ochre to brown and 4 to 7 mm long. The capsule is terete or 4-6 angled, which distinguishes Polytrichastrum species from Polytrichum species. In the early stages of growth the capsule is covered by a hairy calyptra that protects the capsule during development and influences it's shape. At maturity, the calyptra falls off to reveal a beaked operculum. Like most other moss in Polytrichaceae, under the operculum P. formosom has 64 nematodontous peristome teeth that surround an epiphragm. == Reproduction ==

Sexual reproduction Polytrichastrum formosum is sexually dioicous, meaning the male and female reproductive structures are on separate plants. == Classification ==

Varieties • Polytrichastrum formosum var. densifolium (Wilson ex Mitt.) Z. Iwats & Nog. (North American) • Polytrichastrum formosum var. formosum (Hedw.) G.L. Sm. Taxonomy disagreement When this species was first described by Johann Hedwig in 1801, it was classified as Polytrichum formosum. Polytrichastrum can be distinguished from Polytrichum by sporangial features including multiple-angled capsules (more than 4 sided), elongated peristome teeth surrounding the ridged epiphragm, and larger spores. However, more recent molecular data and phylogenetic analysis suggests that P. formosum should be reverted to its original genus: Polytrichum. Their study suggested that species in Polytrichastrum and Polytrichum are in fact distantly related, but because the Polytrichastrum genus is polyphyletic, authors suggested that some species, including P. formosum, return to the Polytrichum genus. Currently, these names remain synonyms. ==References==