Hygroamblystegium is a member of the family amblystegiaceae. The name means Amblystegium of aquatic habitat, as such it is very similar to the genus Amblystegium, the primary differences being that it is larger and has a longer and wider costa or mid-rib (Crum 2004). Hygroamblystegium may contain one (Vanderpoorten 2004) to over 90 (MOBOT 2008) species.

Habitat: Hygroamblystegium is typically found on wet rocks in and beside brooks, some but not all species are limited to calcareous habitats (Crum. 2004).

Distribution: Hygroamblystegium can be found in Europe, North America, Canada, Chile, Mexico, Peru, Bolivia and Madeira.

Gametophyte appearance: Hygroamblystegium is a pleurocarpus moss, which is small to large, and coarse. It grows in dull, dark green, blackish or yellowish brown mats, and is found in moist to aquatic environments. The stems are prostrate or crowding and ascending, freely and irregularly branched and often have no leaves in older parts (Crum 2004). Occasional presence of paraphyllia is a defining feature of the genera (Vanderpoorten 2003). Leaves can be erect or slightly in-curved, rarely subsecund, oblong-obvate or oblong-lanceolate, gradually acuminate, usually bluntly acute, and slightly to none decurrent. The margins are plain, entire or nearly entire (Crum 2004). The costa is one of the most distinctive features and the primary differentiation between Hygroamblystegium and closely related genera (Vanderpoorten et al. 2001). It ends at or very near to the apex leaf and is broad (Crum 2004).

Sporophyte appearance: Hygroamblystegium is autoicous (Crum 2004). The sporophytes of all species in Hygroamblystegium are virtually identical (Vanderpoorten et al. 2001). The seta is red or red-yellow and smooth. The perichaetial leaves are erect and lance-acuminate. The capsules are curved-cylindric; with a well developed annulus, of two rows of cell; the operculum is acute to apiculate; the endostome with or without narrowly perforate segments and well-developed, nodose cilia in groups of 2 or 3 (Crum 2004).

Interesting notes: Hygroamblystegium is considered to be one of the most difficult to place mosses taxonomically speaking (Vanderpoorten 2003). It is very similar to other genera in the amblystegiaceae, and in various analyses some species included in Hygroamblystegium have been found to be more closely related to species of Amblystegiaceae (A. serpens) Cratoneuron, Vittia and Leptodictyum (Vanderpoorten 2004). One species of Hygroamblystegium (H. macroneuron) has even sometimes been placed in another family the Brachytheciaceae (Vanderpoorten 2004). This indicates the uncertainty within the genus. To add to those problems, it has been found that the morphological variation within the species H. tenax was greater than the variation within the genus Hygroamblystegium (Vanderpoorten 2001) and it has been suggested that they all be placed into one species of H. varium (Vanderpoorten 2004). All the Hygroamblystegium may be very closely related, and they may hybridize. But because all their sporophytes are identical and the have a very high morphological plasticity it is difficult or impossible to tell (Vanderpoorten 2001). One feature that does make Hygroamblystegium unique among other moss species with a fully sequenced genome is the presence within individuals of multiple copies of the adenosine kinase gene (Vanderpoorten 2003). There was no information available on the seasonality of Hygroamblystegium.

References:
Vanderpoorten, A. 2004. A simple taxonomic treatment for a complicated evolutionary story: The genus Hygroamblystegium (Hypnales, Amblystegiaceae). Monographs in Systematic Botany, 98: pp 320-327
Vanderpoorten, A. Shaw, J. A. and Cox C. J. 2004. Evolution of multiple paralogous adenosine kinase genes in the moss genus Hygroamblystegium: phylogenetic implications, Molecular Phylogenetics and Evolution 31: pp 505-516.
Vanderpoorten, A.. Shaw, J. A. and Goffiner B. 2001. Testing Controversial Alignments in Amblystegium and Related Genera (Amblystegiaceae: Bryopsida). Evidence from rDNA ITS Sequences, Systematic botany. 26 (3): pp 470-479.
Vanderpoorten A., Goffinet B., Hedena L., Cox C. J., and Shaw A. J. 2003. A taxonomic reassessment of the Vittiaceae (Hypnales, Bryopsida): evidence from phylogenetic analyses of combined chloroplast and nuclear sequence data, Plant systematics and evolution, 241;
Crum, H. 2004. Mosses of the Great Lakes Forest 4th ed. University Herbarium, University of Michigan, Ann Arbor, MI.
Missouri Botanical Gardens (MOBOT). 2006. Index of Mosses Database (W3MOST). Available at: www.mobot.org/MOBOT/tropicos/most/iom.shtml (Accessed May 20, 2008)

Written by Philip Green 2008