Document ID: chunk:federal_register_of_legislation:F2007B00384:body:0:p10
Version: federal_register_of_legislation:F2007B00384
Segment Type: other
Provision Reference: 
Character Range: 24462–27284

at elevations below the occurrences of Asplenium listeri (which are >100 metres elevation).

It is interesting to note that the first collection of the species by Lister took place at the peak of the dry season and probably on the northern side of the island (DuPuy 1993b).  The specimen that Lister collected may have been in an ideal microhabitat, perhaps associated with a seep, or it may have been collected after unseasonal rain.  In 2001 specimens kept at a nursery on Christmas Island would apparently die off when deprived of water for a short period and quickly recover when watered again.  This suggests that the vegetative parts would more normally die off during the dry season, and re‑sprout during the next wet (Sewell pers. comm.).  It was observed that the specimens did not appear to benefit from regular abundant irrigation, as befits the habitat preferences of the species (Claussen pers. comm.).

The habit of growth in rock crevices is likely to afford the rhizome a degree of protection from drying out in the dry season, a protective effect heightened by accumulation of organic debris as mulch in the crevices (Hart pers. comm.).  In other situations, this habit may also protect the rhizome from occasional fire, which is not currently seen as an issue on Christmas Island (Claussen pers. comm; Reddell pers. comm.)

The species appears to be slow-growing and not vigorous (Reddell pers. comm.).  Its restricted distribution and its apparent absence from potential habitat suggest that the species is by no means aggressive in colonising or propagating.

Despite the high degree of specialisation implied by the habit of growing in exposed rock crevices, Asplenium listeri was recorded in one location growing in the same crevice as the closely related but larger Asplenium polyodon G. Forst. (Sickle Spleenwort, Mare's Tail Fern).  This is an unusual occurrence for the latter, which is more normally (and frequently) found in epiphytic situations utilising the root ball of Asplenium nidus L. (Bird's Nest Fern) (DuPuy 1993b).

One can only speculate on the implications of the two cohabiting in a rock crevice.  The rarity of the situation might suggest A. polyodon is not a significant competitor for A. listeri.  Alternatively, the already more widespread A. polyodon might be capable of broadening its habitat choices at the expense of A. listeri.

It has been speculated that A. listeri is actually a variant of A. polyodon that has become a rock crevice specialist (Reddell pers. comm.).  If this is so, the occurrence of two distinct forms in the one crevice is of considerable interest.  Greater certainty would require professional taxonomic review.

C.2 Identification of threats

Potential threatening processes for Asplenium listeri include:
    * removal or modification of actual