Thelymitra Benthamiana (Blotched Sun-Orchid)
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Listing Statement for Thelymitra benthamiana (blotched sun-orchid) Thelymitra benthamiana blotched sun-orchid T A S M A N I A N T H R E A T E N E D S P E C I E S L I S T I N G S T A T E M E N T Image by Hans and Annie Wapstra Scientific name: Thelymitra benthamiana Rchb.f., Beitr. Syst. Pflanzenk. 55 (1871) Common name: blotched sun-orchid (Wapstra et al. 2005) Group: vascular plant, monocotyledon, family Orchidaceae Status: Threatened Species Protection Act 1995 : endangered Environment Protection and Biodiversity Conservation Act 1999 : Not listed Distribution: Endemic status: Not endemic to Tasmania Tasmanian NRM Region: North Figure 1. The distribution of Thelymitra benthamiana Plate 1. Thelymitra benthamiana inflorescence within Tasmania (image by Hans and Annie Wapstra) 1 Threatened Species Section - Department of Primary Industries, Parks, Water and Environment Listing Statement for Thelymitra benthamiana (blotched sun-orchid) IDENTIFICATION AND ECOLOGY green, leathery and obliquely upright. It has the Species of Thelymitra are commonly called sun- most distinctive leaf of any Thelymitra species in orchids because the flowers of most species Tasmania. The flower stems are 20 to 40 cm open only in warm to hot weather, particularly tall and are green with several small bracts. The on bright, sunny days. Thelymitra species are inflorescence comprises 2 to 10 flowers, which terrestrial orchids that die back after flowering are 30 to 40 mm across, greenish yellow with to fleshy subterranean tubers. They are all numerous reddish brown to dark brown spring or summer flowering. Most species have blotches and suffusions and externally dull a single narrow basal leaf although that of greenish brown. The flowers open freely in Thelymitra benthamiana is unique among warm weather and are long lasting. The sepals Tasmanian species in being ovate and leathery and petals are 15 to 20 mm long and 6 to 10 making the species identifiable to species level mm wide, the labellum being the narrowest of even in the vegetative state. Unlike most the flower segments. The column is yellow, orchids, the labellum (lip) of the Thelymitra spotted or blotched, very broadly winged, with flower is generally similar in shape and size to the wings spreading like a mantle and also the petals. Features of the column in the centre yellow, spotted and deeply fringed. The post- of the flower are important in the identification anther lobe is narrow, thick and bulbous. of most species. In all species the column has two arm-like projections that flank the anther [description from Jones 2006] (pollen holding structure). Confusing species Flowers of Thelymitra , which often open widely Thelymitra benthamiana is unlikely to be confused in warm weather, are thought to mimic native with any other Tasmanian species because of its irises and lilies, thus attracting a similar suite of large, bright green, leathery leaf and highly pollinating insects, such as small native bees, distinctive blotched yellow-brown flowers (it is that attempt to collect pollen and often bring one of only three yellow-flowered species and about pollination (Jones et al. 1999). Thelymitra easily distinguished from the other species due benthamiana has long-lasting flowers that open to its blotchy brown flowers). freely and can be both insect-pollinated and self-pollinating (Jones 2006). The flowering of many sun-orchids is enhanced by disturbance, DISTRIBUTION AND HABITAT and as a result some species may be prominent Thelymitra benthamiana occurs in southern in disturbed sites such as slashed areas, or along Victoria, South Australia, Western Australia and track verges and road embankments. Thelymitra in northeastern Tasmania. Within Tasmania it is mucida is one such species, responding only known from three locations on Flinders positively to summer fires and the species can Island (Table 1, Figure 1), separated by about 4 be found in disturbed areas. km and occupying less than 2 hectares. The flowering period of Thelymitra benthamiana On the mainland, Thelymitra benthamiana is on mainland Australia is September to widespread and common, growing in open December (Jones 2006). In Tasmania, flowering forest, heathy forest and heathland in well- commences in late October so late October to drained sandy soil and clay loam (Jones 2006). late December is the likely flowering period in In Western Australia, the species is often found this State and the recommended timing for in association with winter-wet soil and on surveys (Wapstra et al. 2008). Note that margins of granite outcrops (Jones 2006). On identification prior to this period is possible Flinders Island, Thelymitra benthamiana occurs on from leaves due to their distinctiveness. slopes and hill tops associated with areas of heathy eucalypt woodland, open Description heathy/scrubby vegetation, bare ground and exposed rock that is sedimentary in origin and Thelymitra benthamiana has a leaf that is ovate, 5 unique to this part of Flinders Island. to 15 cm long and 2 to 3.5 cm wide, bright 2 Threatened Species Section - Department of Primary Industries, Parks, Water and Environment Listing Statement for Thelymitra benthamiana (blotched sun-orchid) Table 1. Population summary for Thelymitra benthamiana within Tasmania Subpopulation Tenure NRM 1:25000 Year last Area Number Region * Mapsheet seen occupied of mature (ha) plants 1 Centre Hill, Flinders Island Private North Memana 2005 0.5-1 c. 130 property 2 Melrose Road, Flinders Island Private North Memana 2001 0.1? < 20 property 3 north of Mulligans Hill, Private North Memana 2005 0.005 c. 10-20 Flinders Island property *NRM region = Natural Resource Management region POPULATION ESTIMATE THREATS, LIMITING FACTORS AND MANAGEMENT ISSUES Thelymitra benthamiana is represented by three subpopulations, totalling fewer than 200 Stochastic risk: Low numbers and the highly individuals. The first subpopulation discovered localised distribution of Thelymitra benthamiana on Centre Hill in 1999 supported about 130 on unreserved private land makes the species individuals (spread over 130 by 60 m). The susceptible to chance events. This is second subpopulation discovered in 2000 about exacerbated by the relationship with 3 km to the west of Centre Hill supported mychorrizal fungi which may make the species fewer than 20 plants (precise extent not susceptible to additional factors The precise documented but indicated as being a small area extent of each of the subpopulations is also not only). These two subpopulations are separated formally documented so disturbance from by unsuitable habitat (i.e. pasture). The third nearby activities has the potential to impact the subpopulation occurs about 1 km further west sites supporting the species. on a ridge north of Mulligans Hill and was also Land clearing: Any clearing activities discovered in 2000. It seems unlikely that conducted near Thelymitra benthamiana are likely significant range extensions will be made to deleteriously affect the species through because the habitat (especially the geology) with changes to vegetation and soil structure, and which Thelymitra benthamiana is associated is associated impacts of altered grazing/browsing relatively restricted and much of Flinders Island regimes. Any clearing of vegetation on similar has been well surveyed for orchids by local geology on Flinders Island may result in the specialists and the species is distinctive. Even if further loss of potential habitat for the species. new subpopulations are discovered, the Inappropriate grazing and disturbance conservation status of the species would likely regime: The known subpopulations are subject remain unchanged. to grazing and stock trampling and there are signs of erosion caused by stock trampling, RESERVATION STATUS which could lead to changes in population Thelymitra benthamiana occurs on unreserved structure. A change from sheep to cattle grazing private property. is likely to increase impacts to the habitat e.g. from the introduction of weeds. Changes to CONSERVATION ASSESSMENT fertilising practices are also a threat (e.g. even a one-off fertiliser application is likely to Thelymitra benthamiana was listed in 2005 as eliminate the species). Part of the area endangered on schedules of the Tasmanian supporting Thelymitra benthamiana on Centre Hill Threatened Species Protection Act 1995 , meeting has been disturbed by heavy machinery, and the criterion B because there are fewer than 250 site north of Mulligans Hill occurs on disturbed mature individuals and its range is severely heathland that has been scraped by machinery. restricted (it occupies less than 2 hectares, and Inappropriate fire regime: The flowering of it occurs in only 3 nearby subpopulations). Thelymitra benthamiana is likely to be enhanced 3 Threatened Species Section - Department of Primary Industries, Parks, Water and Environment Listing Statement for Thelymitra benthamiana (blotched sun-orchid) by summer fires. For safety reasons, fire • implement a fire management regime management at the known sites and in potential suitable for dry heathy scrub and woodland habitat for Thelymitra benthamiana is usually should the vegetation become too dense for directed towards preventing the type of fires the species, especially in the absence of considered ideal to stimulate flowering. A more stock grazing; frequent lower intensity fuel reduction fire • regime is unlikely to benefit the species and in monitor known sites and nearby similar habitat during the flowering season to the long term may reduce