Recovery Plan for Three Orchid Species in South Australia and Victoria: Caladenia richardsiorum (Little Dip Spider-orchid) Caladenia calcicola (Limestone Spider-orchid) Pterostylis tenuissima

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Part B: General Species Information

2.1 Nomenclature

This plan uses the current nomenclature in South Australia and Victoria for Caladenia richardsiorum (Little Dip Spider-orchid) and follows the authority of Jones (1991), Caladenia calcicola (Limestone Spider-orchid), following the authority of Carr (1986) and Pterostylis tenuissima (Swamp Greenhood), following the authority of Nicholls (1950).

In a taxonomic review in 2001, Jones et al. split the genus Caladenia and placed C. calcicola and C. richardsiorum in the newly described Arachnorchis genus. Similarly Jones and Clements (2002a) split Pterostylis and placed P. tenuissima in the newly described Diplodium genus. However both revisions are yet to be fully accepted by the Commonwealth Heads of Australian Herbaria, so the names Arachnorchis calcicola, A. richardsiorum and Diplodium tenuissima remain as synonyms.

2.2 Distinguishing Morphological Features

The morphological features that distinguish each of the species are summarised in Table 2. More detailed information is provided in Part C of this plan for each species.

Table 2. Morphological features, flowering and similar species.


Distinguishing Morphological Features

No. Flowers

Flowering Time

Similar Species

Caladenia richardsiorum
(Little Dip Spider-orchid)

  • Single lanceolate leaf 16-22 cm in length and densely hairy

  • Yellowish-green flower

  • Sepals have prominent blackish clubs 8-10 mm long

  • Labellum is greenish-cream with maroon calli and toothed margins



C. hastata

Caladenia calcicola
(Limestone Spider-orchid)

  • Single lanceolate leaf up to 15 cm long with dense hairs

  • Mostly red flower on a paler glossy background

  • Sepals are pale yellow in colour and end with prominent clubs varying in colour from yellow to red

  • Labellum obscurely lobed

One (rarely two)


C. reticulata

Pterostylis tenuissima
(Swamp Greenhood)

  • Non-reproductive stage form a ground-hugging rosette of three to eight dark green, glossy ovate leaves; the rosette is absent when in flowering form

  • Single, nodding flower, translucent white with green stripes and suffusions

  • Dorsal sepal extended into a long filiform, deflexed point as long as the galea itself

  • Lateral sepals erect, closely embracing the galea, sinus low, deeply notched, and protruding

  • Labellum to 10mm long green or brown


Oct-Mar but observed at other times throughout year

2.3 Ecology

2.3.1 Mycorrhizae

Many orchids require the infection of an appropriate mycorrhiza (soil root fungus) to germinate under natural conditions (Rasmussen 1995). This association continues into adulthood, with the mycorrhizal fungus supplying the orchid with carbon and nitrogen (Brundrett 2002, Cameron et al. 2006, Girlanda et al. 2006). The obligate nature of their mycorrhizal associations makes them vulnerable to extinction (Rasmussen 1995). Therefore, identification and subsequent mapping of suitable fungi is desirable in threatened orchid recovery.

Similarly many terrestrial Australian orchid species have highly specialised relationships with mycorrhizal fungi (Warcup 1971). Caladenia species are generally found growing in association with the mycorrhizal fungus Serendipita vermifera (formerly Sebacina vermifera) (Warcup 1971, 1981, 1988) or closely related fungi (Huynh 2003; Raleigh 2005, Bougoure et al. 2005; Bonnardeaux et al. 2007; Wright 2007).

Pterostylis species generally are also found growing in association with mycorrhizal fungi (Warcup 1971; Clements 1988), often Ceratobasidium (Warcup 1981; Irwin et al. 2007), and Thanatephorus species (Bougoure et al. 2005).
2.3.2 Pollination

Pollination of Caladenia richardsiorum and C. calcicola is primarily achieved by male thynnid wasps (family Tiphiidae, sub-family Thynninae), as with other Caladenia, Section Calonema species. Orchids in this group are thought to mimic the sexual pheromone produced by a female thynnid wasp, emitting a kairomone or allomone from the glandular tip of their sepals to attract the male wasp (Stoutamire 1983). As the male wasp attempts to copulate with the labellum (pseudocopulation), it collects the sticky pollinia on its body and this is then transferred to the stigma of another flower (Stoutamire 1983). Caladenia pollinated by sexual deception have a highly specific, usually one to one, relationship with their wasp pollinator (Bower 1992). Sexually deceptive Caladenia are usually odourless, with dull yellow, green, maroon, or cream and maroon flowers, with maroon calli and a hinged labellum (Stoutamire & Bates 1990).

Pterostylis tenuissima belongs to a group of Pterostylis that are pollinated by small gnats and mosquitoes. It is thought that they are attracted to the flower by a scent undetectable by humans (Jones 2006). The Pterostylis flowers achieve pollination by utilizing a hinged labellum that is triggered when an insect crawls over its surface, propelling the insect forward onto the column. The column, labellum and galea ‘trap’ the insect, which is then forced to push past the anther to be able to exit the flower, where a previously acquired pollinia could be deposited (Backhouse & Jeanes 1995; Jones & Clements 2002b). The labellum then resets itself after approximately five to thirty minutes, awaiting the next pollinator visit.
2.3.3 Fire Regimes

Whilst studies have investigated the response of terrestrial orchids to fire in native grasslands (Lunt 1994; Coates et al. 2006), the role of fire ecology for many spider-orchids and greenhoods is not well understood. However, it is likely to be an important factor, particularly for spider-orchids, many of which have been observed to flower strongly post-fire, e.g. C. dilatata and C. hastata in south-west Victoria (A. Pritchard pers. obs.1997 & 2002 respectively). In Mediterranean climates, such as southern Australia, fire is important in maintaining many ecosystems in which orchids are known to occur (Roberts 2003). Fire reduces foliage cover, thereby increasing light availability; releases phyto-active materials such as ethylene; and provides a burst of nutrients (Roberts 2003). Brundrett (2007) comments that in south-west Western Australia altered fire regimes in semi-urban and rural areas, in combination with other threats, are known to be contributing to the decline of terrestrial orchids.

Timing and frequency of fires is particularly important as it stimulates different responses from different species of terrestrial orchids. Summer fires have been observed to produce the strongest post-fire flowering events for many species (Jones & Jones 2000). It is reasoned the best time for a burn to occur in Caladenia sub-populations is late summer to early autumn, after seed dispersal but prior to new shoot growth (Duncan & Coates 2007).

Caladenia richardsiorum, C. calcicola and P. tenuissima do not require fire to flower, and the latter is found in wet habitat rarely subjected to fire. Inappropriate fire regimes are likely to threaten all three species. Further research is needed into habitat burning requirements and how various regimes influence the recruitment of these three orchid species.

Currently little attention is given to the impact of fire on orchid pollinators when planning fire regimes for threatened orchids. The impact of fire on invertebrate assemblages is variable e.g. Friend (1994) highlights that post-fire invertebrate populations do not necessarily return to pre-fire levels and that invertebrate populations in mesic conditions are particularly sensitive to fire disturbance. However, more recent research (Wittkuhn et al. 2008) found no significant differences between fire regimes on assemblages within a vegetation community. It is thought that fire is generally not detrimental to thynnid wasp pollinators whilst they are dormant from December to July; however, little is known about thynnids and their relationship with fire (C. Bower pers. comm. 2007; G. Brown pers. comm. 2007). No information is known regarding the potential impact of fire regimes on the pollinators of Pterostylis species.

Orchids and their mycorrhizae have been found to have a strong relationship with soil texture, coarse organic matter and leaf litter (Brundrett et al. 2003). Brundrett (2007) highlights that this relationship requires further investigation as frequent fire, as experienced in Western Australia, has the potential to reduce the amount of coarse organic material and leaf litter that mycorrhizae and orchids rely on as a key resource.

2.4 Distribution and Population Size

Caladenia richardsiorum is endemic to the coastal vegetation of South East Region, South Australia, with an approximate population of 11,075 individuals occurring across 46 sub-populations. Caladenia calcicola consists of only 277 recorded individuals across 8 sub-populations, which occur predominantly near Portland and Nelson, Victoria. In contrast, P. tenuissima has a relatively wide distribution, occurring in Silky Tea-tree (Leptospermum lanigerum) Scrub from near Robe in south-east South Australia, through to Wilson’s Promontory National Park in eastern Victoria. There are approximately 17,700 individual P. tenuissima distributed across 57 sub-populations.

A summary of the distribution and sub-populations for the three species is in Table 3.

Table 3. Sub-population and individual numbers for the three orchid species.



No. of sub-populations

No. of individuals







Caladenia richardsiorum

DEWNR, Robe District Council, Wattle Range District Council, private properties





10 651

11 075

Caladenia calcicola

Parks Victoria, private property







Pterostylis tenuissima

DEWNR, Parks Victoria, Corangamite Shire Council, Moyle Shire Council, private properties






17 703

*A Heritage Agreement is currently being processed for a property, which will provide protection for six of these sub-populations.

2.5 Sub-population and Habitat Critical to Survival

Due to small and isolated populations for the three orchid species, all known sub-populations are considered important for the survival of these species. Habitat critical to survival of these species has not yet been determined for sub-populations across the total range of the species, but is proposed as a recovery action in this plan.

2.6 Decline and Threats

The species in this recovery plan are impacted by a wide range of threats. The region where the species occur provides a wide range of opportunities for primary production including grazing, cropping, viticulture and forestry. As such, 87% of the original native vegetation in the south-east of South Australia has been cleared and is continuing to decline (Government of South Australia 2012), and the majority of wetlands have been drained for these purposes. Vegetation clearance may be the cause of the decline and fragmentation of sub-populations of the three threatened orchid species. Given its coastal setting, tourism and associated developments also play an important role in the regional economy. Coastal development and inappropriate subdivision continues to have a significant impact on coastal ecosystems in South Australia and Victoria (DEH 2004; Victorian Coastal Council 2002). As a result, much of the existing habitat of the three species occurs in small isolated fragments. General information about threats affecting the three species is provided below. More specific threats for individual species are included in Part C.
2.6.1 Vegetation Clearance

Clearance of native vegetation still remains a significant threat to biodiversity in the region. The Silky Tea-tree Scrub (Swamp-Scrub) habitat of Pterostylis tenuissima is mostly distributed across prime agricultural land and as a result continues to be threatened by clearance. For similar reasons most Caladenia richardsiorum habitats are subject to potential clearance, with only 24% of known sites reserved.
2.6.2 Fragmentation and Isolation of Native Vegetation

Australian terrestrial orchids typically depend on specific pollinators and mycorrhizae. Caladenia and Pterostylis species do not support their pollinators with food rewards and as a result these pollinators require other plant species for their food supply (Bates & Weber 1990).Little research has been undertaken regarding the specific ecological needs of orchid mycorrhizae; however it is believed that Caladenia and Pterostylis species are dependent on these fungi for nutrient exchange, particularly during germination (Bates & Weber 1990). It is also known that both Caladenia richardsiorum and C. calcicola each have a highly specific relationship with a male thynnid wasp pollinator (family Tiphiidae, sub-family Thynninae) (Bower 2007), which is required for successful reproduction.

Threatening processes may lead the required fungi and pollinator species to become locally extinct (Bower 2007), which in turn leads to the local extinction of the associated orchid species. It is believed that the orchid taxa discussed in this recovery plan require intact vegetation in order to maintain these complex relationships. The edge effects associated with fragmentation and isolation of vegetation are likely to lead to a decline in habitat condition, causing flow-on effects to mycorrhizae and pollinators.

2.6.3 Grazing

Some Caladenia richardsiorum and Pterostylis tenuissima sub-populations occur on private property and are subject to the impacts of grazing by stock. Orchids may be preferentially grazed due to their palatability. Associated damage to habitat from grazing such as soil compaction, altered nutrient levels and erosion can also significantly compromise the likelihood of survival of a sub-population. Disturbance caused by grazing can also result in increased weed invasion, particularly by introduced pasture species.

Pterostylis tenuissima colonises very moist soils under dense Silky Tea-tree (Leptospermum lanigerum), sometimes only millimetres above the water table. These waterlogged soils tend to be very soft and easily damaged. As such, grazing can damage the orchids’ sensitive microhabitat by pugging these soils, crushing and/or submerging plants.

Grazing by native herbivores (kangaroo and emu) has also been observed in many of the sub-populations. These herbivores can remove or trample orchid biomass that may prevent flowering and photosynthesis, ultimately exhausting the energy reserves of orchid tubers (Croft et al. 1999).

2.6.4 Weed Invasion

A large number of orchid sub-populations identified in this recovery plan are subject to weed invasion. Weed invasion is the most serious threat to Caladenia richardsiorum. Weeds of particular concern to all orchid species include Bridal Creeper (common form and Western Cape form) (Asparagus asparagoides), Myrtle-leaf Milkwort (Polygala myrtifolia), Bluebell Creeper (Billardiera heterophylla), Italian Buckthorn (Rhamnus alaternus), Blue Periwinkle (Vinca major), Dolichos pea (Dipogon lignosus, formerly Dolichos lignosus), Freesia (Freesia sp.) and Arum Lily (Zantedeschia aethiopica).

Bridal Creeper and the recently recognised “Western Cape” form pose the greatest threat of any weed in south-east South Australia (Croft et al. 1999). It has a climbing habit and stores its energy in numerous underground tubers. Bridal Creeper smothers trees, shrubs and ground covers and is capable of preventing light from reaching herbs and geophytes such as orchids. Bridal Creeper reproduces both sexually and vegetatively, making its management extremely difficult. The introduction of pathogenic rust as a biological control has had some success. The rust can limit flowering, seed set and plant biomass by reducing the plant’s photosynthetic surface (DWLBC 2006). The “Western Cape” form has been found to be resistant to all biological controls, except possibly at seedling stage, which suggests that the Western Cape form has the potential to displace Bridal Creeper affected by biological controls (DWLBC 2006). Bridal Creeper has invaded large tracts of coastal vegetation at Robe and in Little Dip and Beachport Conservation Parks and Coorong National Park, threatening sub-populations in these areas. It may also have eliminated another sub-population of C. richardsiorum in this region (D. Jones pers. comm. 2001). The level of infestation is so great at some sites that it is beyond the capacity of current government resources to control.

Coast Wattle (Acacia longifolia subsp. sophorae), an Australian species of debated natural distribution, has spread extensively across the coastal regions of south-west Victoria and south-east South Australia and threatens all three orchid species discussed in this plan. Its growth is dense and its presence appears to be detrimental to the survival of ground flora. Research has found a significant decline in understorey diversity of native species following invasion by Coast Wattle (McMahon et al. 1996). The wattle has also been known to compromise the survival of other threatened orchids in the region (Carr 1993).

The South African Orchid (Disa bracteata) is a potential minor threat to C. calcicola sub-populations, given their close proximity to pine plantations where D. bracteata has formed heavy infestations. Due to its relatively low profile, little is known of the ecological impact on threatened orchid populations from this species. Currently it is not considered feasible to allocate finite resources to the control of this widespread and difficult-to-control weed, when the benefits would probably be minimal.

2.6.5 Site Disturbance

Visitor impacts from naturalists and field officers also threaten many of the sub-populations and are identified as a potential threat for all three species. The best intentions of many enthusiasts and staff can sometimes be to the detriment of these species. Excessive visitation can damage plants, cause soil compaction, and introduce and spread weeds and potential pathogens.

Potential damage to sub-populations from off-road vehicles, especially four-wheel drives and motorbikes, and pedestrian traffic on public and private land is considered a threat to the two Caladenia species.

      1. Illegal Collection

Although there has been no evidence of illegal collection of these orchid species by plant enthusiasts, it is considered that there is a potential for illegal collection as these are attractive species, especially C. richardsiorum, which also has many easily accessible sub-populations.
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