Journal Number 111
February 2009

ORIGINAL PAPERS

Population Ecology of Thelymitra matthewsii
By E Anne Fraser  ( the abstract of her MSc Thesis )

The terrestrial orchid Thelymitra matthewsii (Cheeseman), uncommon in New Zealand,
was studied to increase knowledge of the species' life cycle, morphology and ecology.
Results will enhance future conservation management for the species. New information
related to the morphology of T. matthewsii was obtained.

The species was found to emerge in one of four discrete life stages of distinctive morphology
and height range that remained constant for the season, not developing into a more advanced
life stage. The leaf of the three pre-adult life stages designated a hook, a spiral, and a non-
flowering stage, did not inflate at the base, but rose smoothly from the tuber.

Apparent morphological differences in the column between descriptions of the Australian
taxon and the small New Zealand sample examined suggested further study was needed.

Comprehensive monthly monitoring was carried out at five study sites in three locations in
the Te Paki area of the Far North, from 2002 to 2004. No patterns emerged in plant life stage
succession, flowering, and presence or absence at labels reinforcing the concept that variability
was a common component of the population census.

Seasonal and partial absence was a major component of the populations. An average of
32.8% of plants, over five study sites, were present throughout three seasons, while 66.9%
were recorded as absent (not visible) at monitoring.

New plants appearing in 2003 and 2004 showed a high percentage of subsequent absence
(mean 85.7%).

To determine population stability, recruitment and absence were compared.

Plant absence exceeded recruitment by 7% (mean plant absence 30.5%; mean recruitment 23.4%).

Plants continued to appear during the monitoring period, and labeled plants increased two-fold
over commencement numbers.

Adults recorded as 28% of labelled plants over three seasons, were outnumbered by pre-
flowering stages. Only 5% of population numbers exhibited succession from a smaller to a
flowering plant. Life stage modelling indicated a life stage was more likely to be followed by
the same stage than an expected successive stage.

Thelymitra matthewsii was found to be present in four substrates in the Far North.

The survey of vegetation found the indigenous species Kunzea ericoides and the exotic Hakea
gibbosa dominant for both height, and cover. Litter and bare ground dominated ground cover.

Differences in vegetation and ground cover, of sites supporting T. matthewsii and comparison
sites that did not, were minor and suggested that another factor, for example a suitable fungal
partner, influenced the species' presence or absence.

The results of the study indicated the present threat classification of Thelymitra matthewsii is
inadequate in the light of the species relatively circumscribed, widely separated habitats, the
small number of reproducing individuals and vulnerability to habitat modification.

Reference
Fraser, E.A. 2008. Population ecology of Thelymitra matthewsii, Cheeseman, Orchidaceae, in northern New Zealand. Master of Science Thesis, University of Waikato.