Archidium moss  (Archidium elatum)

Classified as Endangered (EN) on the IUCN Red List (1).

Archidium elatum is a tufted moss that grows in dense carpets, ranging in colour from dark brown-green to yellow-brown (2) (3). The individual plants comprise simple or weakly branched stems, with spreading leaves up to 1.5 mm in length (2) (4). The lower stems creep prostrately along the ground and produce erect branches that in turn develop rhizoids (4), a root-like structure that anchors the moss to the ground and can absorb water and minerals (5).

Archidium elatum is endemic to New Zealand, where it is known from no more than five localities on the North Island and offshore islands (2) (4).

Grows mainly on coastal rocks, typically in damp or waterlogged depressions (1) (3) (4).

As one of the least documented mosses in New Zealand (4), little is known about the specific biology of Archidium elatum. However, like all bryophytes (mosses, liverworts and hornworts) it has a two-stage life cycle, comprising a gametophyte generation (the familiar green photosynthetic part of the moss) and a sporophyte generation (a stalk and capsule, dependent on the gametophyte for support and nutrients). Reproduction takes place during the gametophyte generation, with fertilization leading to the development of the sporophyte. When the capsule of the sporophyte is ripe, it releases thousands of tiny spores, some of which grow into new plants (6).

Archidium elatum is among the most threatened mosses in New Zealand (3). It is not known whether historically it was more common, but its range and habitat is likely to have been reduced by disturbance to coastal habitats (4). The invasive spread of the exotic kikuyu grass has already led to the extirpation of Archidium elatum from one site (2) (4). There is however the possibility that this species has been over looked over large parts of its range, and may actually be more common than realised (2) (3).

Two sites in the Bay of Islands on the North Island are considered critical to the survival of Archidium elatium. The Moturoa Island site is privately owned but managed as a nature reserve, while the Crater Rim Rock site is a scenic reserve, with limited access, managed by the New Zealand Department of Conservation. At both sites, weed control is thought to be the most important protective measure (4).

To find out more about the conservation of plants in New Zealand see:

• The New Zealand Plant Conservation Network:
  http://www.nzpcn.org.nz

• Endemic: A species or taxonomic group that is only found in one particular country or geographic area.
• Gametophyte: A life cycle stage in plants, which has one set of chromosomes (threads of DNA protein) in the cell nucleus (a condition known as ‘haploid'), which arises from a spore (which is also haploid). Sex cells (gametes) are produced during the gametophyte stage. This is the dominant life-cycle stage in liverworts and mosses.
• Rhizoids: Thread-like structures that help to anchor the plant to the substrate, and absorb minerals and water. In liverworts they consist of a single cell, in mosses they are multi-cellular.
• Spores: Microscopic particles involved in both dispersal and reproduction. They comprise a single or group of unspecialised cells and do not contain an embryo, as do seeds.
• Sporophyte: The stage of a plant life cycle that produces spores (microscopic particles used in dispersal and reproduction). This stage is diploid (in the cell nucleus there are two sets of chromosomes - threads of DNA protein) and is dominant in ‘higher' plants such as flowering plants.

1. IUCN Red List (May, 2009)
   http://www.iucnredlist.org/
2. The New Zealand Plant Conservation Network (May, 2009)
   http://www.nzpcn.org.nz/liverwort/detail.asp?CryptogamID=71
3. Taylor, R. and Smith, I. (1997) The state of New Zealand’s environment 1997. The Ministry for the Environment and GP Publications, Wellington, New Zealand.
4. IUCN SSC Bryophyte Specialist Group (May, 2009)
   http://www.artdata.slu.se/guest/SSCBryo/SSCBryo.html
5. Allaby, M. (1998) Oxford Dictionary of Plant Sciences. Oxford University Press, Oxford.
6. Royal botanic Garden Edinburgh (May, 2009)
   http://www.rbge.org.uk/science/cryptogamic-plants-and-fungi/bryology