National recovery plan for the East Lynne Midge Orchid (Genoplesium vernale)
NSW National Parks and Wildlife Service, May 2002
ISBN 0 731 36253 5
Species Information
Description and Taxonomy
The East Lynne Midge Orchid is from a group of orchids known as the Midge Orchids. The species is a ground dwelling herb which produces an underground tuber.
Jones (2001) described the East Lynne Midge Orchid as follows:
Leaf 10-18 cm long, 0.15-0.3 cm wide, terete, dark green, reddish at the base; with a small sheathing bract, ending 5-20 mm below the first flower. Inflorescence 15-25 cm tall, bearing 10-25 flowers in a densely crowded spike 2-4 cm long. Flowers 3.5-4.5 mm diam., dark purplish black, semi-nodding; lateral sepals obliquely erect. Dorsal sepal hooded, broadly ovate, 3-3.5 mm long, 2-2.3 mm wide, concave; margins with minute glandular hairs; apex pointed. Lateral sepals narrow 4-4.5 mm long, 1.2-1.3 mm wide, obliquely erect, nearly parallel; apex narrowly pointed, sometimes with a vestigial gland. Petals c. 3 mm long, c. 1.2 mm wide; margins with minute glandular hairs; apex pointed. Labellum attached by its base directly to the apex of the column foot; lamina narrowly oblong, 2.5-2.8 mm long, 1.2-1.5 mm wide, gently curved throughout, suddenly contracted to a pointed apex, margins slightly irregular. Callus oblong, sometimes constricted above the middle, fleshy, occupying most of the ventral surface of the lamina, dark purple to brownish black, base yellow, extending nearly to the labellum apex. Column c. 2 mm long, c. 1.8 mm wide. Wings lobed about halfway to the base, the lobes not divergent; posterior lobe linear, whitish, obtuse; anterior lobe ovate-lanceolate, dark red, acute, the margins irregularly toothed. Capsules narrowly obovoid, 4-5 mm long, c. 0.3 mm wide, erect (See illustration on front cover).
 |
| Figure 1. The distribution of the East Lynne Midge Orchid |
Distribution
The East Lynne Midge Orchid is currently known from only a narrow belt (approx. 12 km wide) of predominantly dry sclerophyll forest from approximately 17 km south of Batemans Bay to 24 km north of Ulladulla.
For three years following its discovery in 1995, the East Lynne Midge Orchid was only known from the Type locality at East Lynne, a small town located approximately 17 km north of Batemans Bay. However, surveys by members of the Recovery Team in the 1998 and 2000 flowering seasons recorded the orchid from 28 additional sites (see Figure 1). The survey conducted in 2000 found a total of 436 individuals within all known sites. This number, however, is thought to be an underestimate of the total population size, as all suitable habitat within the distribution of the species has not been surveyed and some known populations have not been thoroughly counted. The species appears to occur at low densities at all known sites, but indications are that it extends over large areas of forest within its known range.
A new record for the East Lynne Midge Orchid has recently been reported (June 2001) for a site in Booderee National Park, near Jervis Bay in Commonwealth Territory. This specimen was collected in November 1996. This area was re-surveyed in 2001, but the species was not located. It is proposed to include this site in subsequent survey seasons.
Land Tenure
The Type locality of the East Lynne Midge Orchid occurs across two portions of land. One is owned by SCC, the other is within National Park. Until recently, the species did not occur on any reserves or land managed specifically for conservation, however some SF sites supporting the species have now been transferred to NPWS as a result of the recent NSW Southern Regional Forest Agreement (RFA).
| Tenure | No. Sites | No. Plants | % of total population |
|---|---|---|---|
| SCC | 1 | 14 | 4 % |
| National Park | 12 | 212 | 48 % |
| State Forest | 13 | 183 | 42 % |
| State Forest road easement | 3 | 27 | 6 % |
| Total | 29 | 436 |
Twelve of the known sites now occur within NPWS Reserves (see Table 1), representing 48% of the total number of East Lynne Midge Orchids counted in the November-December 2000 survey. Most of the other known sites occur in State Forest. There are known small areas of suitable habitat on private land, however these have not yet been surveyed.
Habitat
The East Lynne Midge Orchid grows in 'poorer' Dry Sclerophyll woodland / forest on the south coast of NSW between Mogo and Ulladulla. It is confined to areas with good drainage and shallow, low fertility soils. Most sites have a 'sandy-clay' soil, usually with associated quartzite gravel. Individuals are usually found where the groundcover is sparse and there is little competition for light.
Sites are usually dominated by Yertchuck (Eucalyptus consideniana), Sydney Peppermint (E. piperita), White Stringybark (E. globoidea) and Silvertop Ash (E. sieberi) with one site dominated by Blackbutt (E. pilularis). Other associated species include Red Bloodwood (Corymbia gummifera) which is present in the majority of sites, and Blue-leaved Stringybark (E. agglomerata) and Large-fruited Red Mahogony (E. scias), with a reliable indicator species being the Sedge/Grass (Cyathochaeta diandra). Two atypical sites southwest of Mogo are dominated by White Stringybark (E. globoidea) and have Spotted Gum (Corymbia maculata) present as well as Red Bloodwood and Ironbark (E. fibrosa).
Other understorey species occurring at many of these sites include an Egg and Bacon Pea (Pultenaea villosa), Golden Glory Pea (Gompholobium latifolium), Gorse Bitter Pea (Daviesia ulicifolia), a Tetratheca (Tetratheca bauerifolia), Prickly Shaggy Pea (Oxylobium ilicifolium), Pale Wedge Pea (Gompholobium huegelii) Hairpin Banksia (Banksia spinulos) Saw Banksia (B. serrata), Sunshine Wattle (Acacia terminalis), Black She-oak (Allocasuarina littoralis), Narrow Leafed Geebung (Persoonia linearis), a Conestick (Petrophile pedunculata), Bushy Needlewood (Hakea sericea), Broad-leafed Geebung (P. laevis), Tea Trees (Leptospermum polygalifolium & L. trinervium), Dotted Sun Orchid (Thelymitra ixioides), Large Duck Orchid (Caleana major), Small Duck Orchid (C. minor), Sundew (Drosera sp.), Tetraria capillaris, Lepidosperma laterale, Poranthera microphylla, Conospermum tenuifolium and Pomax umbellata.
Ecology
Life Cycle
Very little is known about the biology of the East Lynne Midge Orchid. Midge orchids in general die back to a dormant tuber over the winter. During spring they will produce a single erect leaf. The leaf and flower spike develop simultaneously with the flower emerging through the leaf near the apex (D. Jones, CSIRO, pers. comm.). Midge orchids will not necessarily flower every year, often skipping years. The proportion of the population that flowers in any year is not known and appears to vary from year to year. Flowering may be dependent on the previous seasonal conditions.
The East Lynne Midge Orchid flowers from mid November to late December. Observations at known sites in 1998, 2000 and 2001 indicate that, as with other midge orchids, only a proportion of the population of the East Lynne Midge Orchid will flower in any one year. At one site orchids were observed and marked in 1998. A survey of this same site in 2000 found no orchids present in the previously marked locations, but found new clusters of orchids within 15 metres of the original location.
While the pollination biology of the species is not known, most midge orchids are pollinated by vinegar flies, although some are self-pollinating (Jones 1988).
Population Structure
At present virtually nothing is known about the age structure of plants in the population nor the longevity of individuals. 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. It is known that seedlings of Midge Orchids take between 3-5 years to flower, this timing being dependent on tuber size, which is influenced by the conditions in the previous season (D. Jones, pers. comm.).
Disturbance Regimes
The sites where this species grows are not prone to frequent fire, however they may burn occasionally.
Fire is more likely to have a short-term impact on the East Lynne Midge Orchid if the habitat is burnt whilst the species is in flower or fruit. Such a fire event would destroy a season's reproductive effort and perhaps weaken the tubers by reducing the photosynthetic period for the growing season, possibly resulting in reduced flowering the following season.
There is no information on the long-term response of the species to fire. It is possible that fire may assist the species in the long-term by opening up the ground cover and reducing competition for light. The impact of fire can be only determined through long term monitoring of populations pre- and post-fire events, and the response may be affected by the season in which a fire occurs.
The East Lynne Midge Orchid has been found growing on various previously disturbed sites, including old forestry snig tracks and old log dumps, firebreaks and also mounds left following gravel extraction. It is not known whether the plants growing in these situations have arisen from existing tubers that survived these soil disturbances or have re-colonized the areas from seed dispersed from elsewhere.
Ability of Species to Recover
There are no immediate threats to most known populations of the East Lynne Midge Orchid. It seems that most potential threats within State Forests can be controlled with the cooperation of SFNSW. Monitoring to date suggests the species is reproducing adequately and has an ability to re-colonize previously disturbed sites. There appears to be no biological reason why the East Lynne Midge Orchid cannot be maintained in the wild in the long term.