National recovery plan for the Tallong Midge Orchid (Genoplesium plumosum)

NSW National Parks and Wildlife Service, May 2002
ISBN 0 731 36457 0

3. Species Information

3.1 Description and Taxonomy

The Tallong Midge Orchid was first discovered on the Kurnell Peninsula in January 1928, and subsequently described by Rupp in November 1947. The species was not seen again until it was found at Tallong in 1988 by R. Tunstall. It was originally named Prasophyllum plumosum, but Jones and Clements changed this to Genoplesium plumosum in 1989.

Location of the villages of Tallong and Wingello
Figure 1. Location of the villages of Tallong and Wingello on the Southern Highlands of NSW.
With the exception of a single population to the SE of Wingello, all Tallong Midge Orchids have
been recorded within three kilometres of Tallong.

The Tallong Midge Orchid is from the group of terrestrial orchids known as Midge Orchids. The species produces a single flowering stem 10 - 20 cm tall which bears 1-8 small flowers clustered at the top of the stem. The following description is based on a description given in Jones (1998) and field observations in 2001.

Flowers about 8 mm across, green with purple stripes and a reddish purple tongue (labellum). Dorsal sepal narrow-ovate, 6-7 mm long, 2-3 mm wide, apex gradually tapering to a point, margins entire. Lateral sepals linear to lanceolate, 7.5-9 mm long, c. 1 mm across. Petals narrow-ovate 5.5-6.5 mm long, c. 1.5 mm wide, apex long-acuminate, margins entire. Labellum oblong, 5-5.5 mm long, c. 2mm wide, apex curved backwards, margins with small hairs c. 0.6 mm long; callus narrow-ovate to lanceolate, extending nearly to the labellum apex.

The almost leafless stems of the Tallong Midge Orchid are very thin, usually 10-15 cm long, and are superficially like the stem of a small sedge. Each stem produces a single leaf that is reduced to a stem-clasping bract-like structure located near the base of the flower cluster. The species is almost impossible to detect except when flowering. The front cover of this Recovery Plan includes an illustration of the flowering plant and enlargements of an individual flower.

3.2 Distribution

The Tallong Midge Orchid is currently only known from two areas, the village of Tallong and its immediate environs, and the other approximately 8.5 km south-east of the town of Wingello.

At Tallong, the Midge Orchid occurs extends no more than three kilometres north and east of the town centre. The largest percentage of the species occurs in a single large patch of about 80 ha of uncleared habitat. This patch consists of private land, Crown and SRA owned land. The remainder of the population is distributed within several small remnants of native vegetation, the largest of these being only about 0.5 ha in area and the others much smaller in size.

South-east of the town of Wingello, the Tallong Midge Orchid is also found at one site located in Morton National Park. This site was discovered in 2001 and is less than 0.2 hectares in area. Further survey is desirable to identify other possible new sites, particularly in the Wingello area. The distribution of the species near Tallong, however, is not likely to be much larger than that currently known, since there appears to be little additional suitable habitat which is yet to be searched.

The type locality for this species is the Kurnell Peninsula, but there have been no collections there since 1928. Since there is a considerable difference in the climate at Tallong compared to that at Kurnell, there is some doubt that the plants that grew at Kurnell were of the same species as that currently known from Tallong. Several orchid enthusiasts have searched extensively in the Kurnell area in recent years for this species, but without success. Only the re-discovery at, or near Kurnell of Genoplesium plants matching the original (Type) collection will enable this uncertainty to be resolved.

3.3 Land Tenure

At Tallong, several sites, including the largest population, are on private freehold land. The species also occurs on one Crown land block, on the Tallong Campus of Santa Sabina College, SRA land, two Crown road reserves, one block of land owned by MSC and on three privately owned housing blocks in Tallong village. Until recently, the species did not occur on any reserves or land managed specifically for conservation, however the site near Wingello now occurs within Morton National Park, as it was an area of State Forest that was transferred to NPWS as a result of the NSW Southern Regional Forest Agreement (RFA) in 2001.

3.4 Habitat

The known locations of this species are characterised by having very shallow soils overlying flat to gently sloping sheets of sandstone. The vegetation is low scrub/heath dominated by Violet Kunzea (Kunzea parvifolia), Common Fringe-myrtle (Calytrix tetragona) and Eggs and Bacon (Dillwynia sp.), with scattered shrubs of Hairpin Banksia (Banksia spinulosa), Black She-oak (Allocasuarina littoralis), Bitter Cryptandra (Cryptandra amara), Slender Wattle (Acacia elongata), Narrow-leaf Geebung (Persoonia linearis), Coral Heath (Epacris microphylla) and a Beard Heath (Leucopogon sp.) Other herbaceous species also present include Kangaroo Grass (Themeda australis), Wallaby Grasses (Austrodanthonia spp.), Purple Wire Grass (Aristida racemosa), a Spear Grass (Stipa sp.), a Crab Grass (Digitaria breviglumis), Rock Fern (Cheilanthes sieberiana), Spiny-headed Mat-rush (Lomandra longifolia), a Purple Flag (Patersonia sp.), Rock Isotome (Isotoma axillaris), Matted St John's Wort (Hypericum japonicum), Grass Triggerplant (Stylidium graminifolium), Lepyrodia scariosa, two Lepidosperma spp. and Isolepis sp. Five other autumn flowering Midge Orchids, Genoplesium sagittiferum, G. apostasioides, G. aff. ciliatum, G. oliganthum and G. fimbriatum, with which the Tallong Midge Orchid could be confused, also grow at the same sites, as do several other orchid species, including Purple Donkey Orchid (Diuris punctata), A Midge Orchid (Genoplesium aff. morrisii), Eriochilus aff. cucullata, Lyperanthus suaveolens, Microtis parviflora, Orthocerus aff. strictum, Pterostylis parviflora, P. truncata and a Sun Orchid (Thelymitra aff. pauciflora.). At all sites the habitat is surrounded by Brittle Gum (Eucalyptus mannifera) and Scribbly Gum (E. rossii) low woodland, with Argyle Apple (E. cinerea) present at some sites.

3.5 Ecology

Life Cycle

Very little is known about the biology of the Tallong Midge Orchid. Midge orchids in general die back after flowering and fruiting and exist only as a dormant tuber for much of the year. During either spring or autumn (depending on the species), they will produce a single erect stem. The flower spike emerges through the leaf near the apex of the stem (Jones 1988). Midge orchids will not necessarily flower every year and all the factors that affect flowering are not currently known.

In the case of the Tallong Midge Orchid, initial observations suggested the species flowers 4-6 weeks following good autumn rains. However, flowering behaviour is now known to vary. In autumn 2000, even though there had been plentiful autumn rains, no flowering specimens of the Tallong Midge Orchid were found despite several searches at sites where the species was observed flowering the previous year. In contrast, despite only average rainfall in late summer / early autumn 2001, numerous plants of the Tallong Midge Orchid were observed to flower at most previously known sites. The proportion of the population that will flower in any individual year is not known and varies from year to year. Successful flowering and reproduction are likely to be dependent on favourable weather conditions, however other factors may also influence flowering.

While the pollination biology of the Tallong Midge Orchid is not known, most Midge Orchids are pollinated by vinegar flies, although some are self-pollinating (Jones 1988).

Population Size and Structure

At present virtually nothing is known about the age structure of plants in the population, the longevity of individuals, nor the time required for seedlings to reach a reproductive stage. Current recruitment rates have not been determined, and it is not known whether recruitment occurs at a steady rate or occurs in pulses influenced by seasonal conditions.

During March 2001 the eight previously known sites were re-surveyed and accurate population counts obtained. The results are presented in Table 1. Until the results of several years of detailed monitoring are available it will not be possible to know what the true total population at each site might be. This cannot be determined until the proportion of plants flowering in each year over several years is known.

Table 1 - Number of individual Tallong Midge Orchids observed in 2001 and tenure for each site.
Site/ Tenure No. of individuals
Santa Sabina College 1
Crown Reserve 88
State Rail Authority 36
Tallong Park 81
Private Residential blocks 25
Roadside (East side of Tallong) None found
Mulwaree Shire Council 20
Crown road reserves (adjacent to Railway) 21
Morton NP 12
Total 293

Disturbance Regimes

Most of the areas where this species occurs have significant patches of exposed sandstone rock and support stunted woodland with an open-heath understorey with much bare ground also present. Such sites would not be prone to frequent fire, however they may burn occasionally.

There is no specific information on the response of the Tallong Midge Orchid to fire. Fire may assist the species by opening up the ground cover and reducing competition for light, but on the other hand fire could also kill some of the orchid tubers and destroy the mossy ground cover which might be important to the survival of the species.

Fire may have a greater impact on the Tallong Midge Orchid if the habitat is burnt whilst the species is flowering or in fruit. Such a fire event would destroy the reproductive effort for that year and perhaps weaken the tubers by reducing the photosynthetic period for the growing season, possibly also resulting in reduced flowering the following season.

During autumn 1999 it was observed that a large proportion of the fruiting stems had been eaten, presumably by native herbivores, but possibly also by rabbits. NPWS monitoring data collected in 2002 confirmed a high level of predation, with 26% of all plants (both flowering and in leaf) were found to be browsed. If this browsing occurs every year then it is likely to result in a substantial reduction in the amount of seed being produced compared to that otherwise expected. At this stage the impact of such browsing is unknown. However, should the monitoring program reveal that browsing is a common occurrence then an investigation of recruitment and mortality rates under browsed and unbrowsed conditions will be considered.

3.6 Ability of Species to Recover

NPWS monitoring data collected so far shows that many flowering plants develop mature fruit (37% of all plants marked on the plots in 2002 produced mature fruits despite the high levels of browsing) and there is no evidence to suggest that recruitment does not occur in the field. Given that there are no immediate threats to most of the populations and providing that other potential threats can be controlled with the cooperation of the landowners, there appears to be no reason that the Tallong Midge Orchid cannot be maintained in the wild in the long term.