Spoon-leaved moss (Bryoandersonia illecebra) COSEWIC assessment and status report: chapter 6

Biology

The biology of Bryoandersonia illecebra is not well-researched. The information presented below is characteristic of other moss species that share features with B. illecebra.

General

The moss life cycle has four main stages, each of which is characterized by different ecological requirements:

  1. Dispersal - Mosses such as Bryoandersonia illecebra are dispersed as spores, which sift into the air through specialized teeth surrounding an opening, or “peristome”, at the end of the capsule. Upon contact with a favourable substrate in a suitable microhabitat, spores germinate to produce protonemata.
  2. Establishment - At the protonemal stage, mosses may be very sensitive to desiccation, and require high moisture. Leafy plants called gametophores grow from the protonemata. These plants generally possess features that allow them to withstand the challenges characteristic of their preferred habitat.
  3. Growth - Moss gametophytes proliferate vegetatively as colonies. Pleurocarpous mosses such as Bryoandersonia illecebra are generally much branched, allowing them to spread efficiently over their substrates. Moisture is required for photosynthetic activity and growth, but the species readily survives periods of drought.
  4. Reproduction - Gametophytes produce sessile eggs and flagellate sperm, and free water is required for the two to unite. A fertilized egg, still enclosed within the gametophyte, grows into a sporophyte consisting of a spore-filled capsule at the end of a stalk, or ‘seta’.

Reproduction

Bryoandersonia illecebra is dioicous, meaning that the sperm-producing antheridia and egg-producing archegonia occur on different plants (as opposed to ‘monoicous’ species, in which both structures occur on each fertile plant). Sexual reproduction therefore requires that male and female plants occur in close proximity (within a few centimetres (Mishler 1988, Schofield 1985)). Sporophytes have been shown to be less frequent in dioicous species than in monoicous species (Gemmell 1950, Longton 1992, Longton & Schuster 1983, Mishler 1988). Longton (1992) also found that rarity of dioicous species is closely linked to failure to produce sporophytes, although his analysis excluded ‘pseudo-rare’ species that were rare only because they occurred at their range limits in his study area (as exemplified by B. illecebra in Canada). Sporophytes are not present and were not previously noted in Canadian collections of B. illecebra.

Bryophyte rarity and absence of sporophytes in Britain may be related to ‘sub-optimal’ growing conditions at the edge of species’ distributional ranges (Longton 1992). At least two mechanisms may play a role. Firstly, the increasing rarity of appropriate growth conditions at a species’ range limits makes the coincident establishment of male and female plants, and, in turn, the production of sporophytes, increasingly unlikely. Gemmell (1950) and Longton (1976) suggested that the failure of dioicous species to produce sporophytes may be related to spatial separation of male and female plants. Distance between male and female representatives of vascular species is a concern for other Carolinian plants: Ambrose and Kevan (1990) report that a lack of suitable (near or numerous) mates may limit some rare dioecious vascular plant species in southern Ontario.

Secondly, Longton and Schuster (1983) discuss the possibility that uneven sex ratios inhibit sporophyte production in some mosses. Bopp (1983) summarizes several environmental factors (e.g. light intensity, day length, and temperature) affecting antheridial and archegonial production. Climatic factors may differ enough at the edge of Bryoandersonia illecebra’s northern range compared with more central locales to affect the production of one or both types of gametangia.

All Canadian collections of Bryoandersonia illecebra for which sex has been determined are female, with abundant perichaetia (female inflorescences). Because the most effective way to search for perigonia (male inflorescences) and perichaetia involves stripping leaves from the stems, no collections could be examined thoroughly in this respect. The possibility exists, however, that all remnant southern Ontario populations of B. illecebra are female.

Movements/dispersal

Bryoandersonia illecebra is probably largely spore-dispersed, as it has no known asexual propagules. It may be categorized as a ‘perennial stayer’, according to During (1979) meaning it displays characteristics (such as a large, pleurocarpous gametophyte) that are adapted to stable habitats. Mosses of stable habitats, as opposed to those adapted to highly temporary substrates and habitats, may devote more resources to vegetative growth than to the production of sporophytes (Longton 1992). In areas such as southern Ontario, however, perennial stayers may not be able to disperse and colonize new sites at the same rate as these are altered by human activity.

An important means of short-distance movement may be vegetative growth. Soil substrates may be relatively continuous, and on soil banks (preferred by Bryoandersonia illecebra), new patches may open frequently.

Behaviour/adaptability

Bryoandersonia illecebra can apparently tolerate a range of substrates (Crum & Anderson 1981) and habitats. However, as noted above, its dispersability may prevent it from taking advantage of many available habitats.

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