User:HannahML23/Polytrichum formosum

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Polytrichastrum formosum, commonly known as the bank haircap moss is a species of moss belonging to the family Polytrichaceae.

It has cosmopolitan distribution, found mostly in temperate latitudes in the Northern Hemisphere and especially dominant in Europe and North America. However, it has also been identified in India, China, Nepal, Japan, Algeria, Australia, New Zealand, Russia, Turkey, Syria, and the Atlantic islands (ie Iceland).

This species was previously called Polytrichum formosum but has been reclassified as Polytrichastrum formosum due to sporangial features. Recent molecular studies suggest that it should be moved back to its original genus (Polytrichum), however bryologists have not yet reached a consensus.

Habitat
P. formosum generally inhabits shaded, poor soils and humus in damp coniferous forests and cool temperate rainforests. In Europe the moss is more common and grow 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, 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. Its colour ranges from green to dark olive green to greenish black. The stems of mature plants are generally 3 to 8 cm tall, however they can be as short as 2 cm or as tall as 20 cm. P. formosum, like all members of Polytrichaceae, is an endohydric moss, meaning water conduction occurs internally. This process is made possible by a central conducting strand in the stems, 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. The hydrome (made of hydroids) and leptome (made of leptoids) are considered analogous in function to xylem and phloem in vascular plants. For structural support, which helps this moss remain erect and grow tall, there are also thick-walled stereids circling the hydrome. The leaves of Polytrichastrum formosum are lanceolate to linear/linear-lanceolate, and are usually 6 to 8 mm in length, but can be up to 12 mm long. They are erect to spreading when the moss is dry but become broadly recurved when moist. The leaves have a toothed margin and a prominent costa, where guide cells help conduct water throughout the leaf, and thick-walled stereid cells on the dorsal side provide protection. Using a microscope, photosynthetic lamellae are visible in cross section, nearly covering the entire ventral surface of the leaf. A feature unique to Polytrichaceae, lamellae are often compared to the mesophyll of vascular plants due to their role in photosynthesis. Each lamella stands 3 to 7 cells high and the cells at the top are smooth and oblong. Lamellae function in increasing desiccation tolerance and photosynthetic efficiency by providing more surface area for light absorption and gas exchange The lamellae are covered by a layer of hydrophobic wax that protects the air spaces between lamellae (mesophyll-like tissues) from being flooded with water, which would impede CO 2 uptake necessary for photosynthesis. In this way, P. formosum is able withstand high irradiance better than other mosses (Bippus et al 2018).

Sporophyte
The haploid sporophyte generation of P. formosum matures in early summer and is short-lived. The solitary sporophyte grows out of the female gametophyte, relying on it for energy and nutrients (Glime 5-9). It is anchored to the gametophyte by a foot, and has a stalk (seta) elevating a capsule (sporangia) in which spores will develop. 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 (Glime 4-13). At maturity, the calyptra falls off to reveal a beaked operculum. Under the operculum P. formosom, like most other Polytrichid mosses, has 64 nematodontous peristome teeth that surround an epiphragm.

Sexual Reproduction
P. formosum is sexually dioicous, meaning the male and female reproductive structures are on separate gametophyte plants. Polytrichastrum formosum, like all members of the Polytrichaceae family is an acrocarpous moss with reproductive structures borne at the terminus of the main stem. (Bippus et al 2018, Glime?). The perichaetial leaves surrounding the archegonia (female reproductive structure) resembles the other stem leaves besides being longer. The antheridia (male reproductive structure) are at the apex of the male gametophyte in a cup-like structure formed by perigonial leaves. Sperm is produced in the antheridia via mitosis, and when mature, are released from the splash cup by raindrops splashing onto the cup. Sperm can be dispersed up to one meter away, and if they successfully reach a female archegonia, the egg will be fertilized and grow into the diploid sporophytes.

Asexual Reproduction
Asexual reproduction is not extensive in P. formosum, however occurs on a local scale by the vegetative proliferation of genets.

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 "father of bryology" Johann Hedwig in 1801, it was classified as Polytrichum formosum. Then upon further analysis it was determined by G.L. Smith that the moss is better described by the Polytrichastrum genus. Polytrichastrum can be distinguished from Polytrichum by sporangial features including multiple-angled capsules (more than 4 sided), and elongated peristome teeth surrounding the epiphragm, and larger spores. According to several sources Polytrichastrum formosum remains the most accurate taxonomic classification, however more recent molecular data and phylogenetic analysis suggests that P. formosum should be reverted to its original genus: Polytrichum. In their study they found that species in Polytrichastrum and Polytrichum are in fact distantly related, but because the Polytrichastrum genus is polyphyletic, authors suggested some species, including P. formosum, return to the Polytrichum genus. Currently, these names remain synonyms.