Banded Greenhoods Bundled Together

Here in South Australia we often have only one or two species of a complex or a genus but this is not necessarily the case in the rest of the country. One such instance is Urochilus sanguineus (syn Pterostylis sanguinea) or Maroon Banded Greenhood. It is possible that we may have a subspecies or possibly the Mallee form but nothing like the occurrence of  this species in Western Australia where it is but one of many in a complex of several – the Pterostylis vittata complex or Banded Greenhoods*.

Below, with permission, is Andrew Brown’s post on Facebook with notes and images about the complex as it is understood in Western Australia.

The Banded Greenhood complex in Western Australia

Members of this complex grow 150 to 450 mm high and have up to 20 green, brown or reddish-brown white banded flowers characterised by their, short, broad lateral sepals which are joined at the base and a small, insect-like labellum which flicks up when touched. In all species, flowering plants lack a basal rosette of leaves while non-flowering plants have a flattened, ground hugging, rosette of leaves.

Banded greenhoods are found over a wide geographic range between Binnu north of Geraldton and Eyre on the Great Australia Bight, growing in shrublands, woodlands, forests and shallow soil pockets on granite outcrops.

There are ten Western Australian species in this complex, seven of which are formally named. However, as two were named as species of Urochilus, a genus not recognised in Western Australia, only five of these names are currently recognised here. In Western Australia, all members of the complex are considered to be in the genus Pterostylis.

All are winter flowering.

Pterostylis concava

Pterostylis concava AB

Distinguished from other members of the complex by its prominently cupped lateral sepals and the upturned projection near the base of the labellum. Found between Bindoon and Mt Barker.

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Pterostylis crebriflora

Pterostylis crebriflora AB.jpg

Distinguished from the similar Pterostylis sanguinea by its often shorter stature and slightly larger flowers which are crowded in a dense spike near the top of the stem. Found on the Darling Scarp near Perth.

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Pterostylis sanguinea

Pterostylis sanguinea AB.jpg

A very common species that is also found in South Australia, Tasmania and Victoria. It was named from specimens collected in South Australia. The species is similar to Pterostylis crebriflora but is usually taller with smaller, more widely spaced flowers. Flower colour is variable and it is not uncommon to find brown and green flowered forms growing alongside one another. Found over a wide area between Mullewa and Eyre on the Great Australian Bight.

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Pterostylis sanguinea (Mallee form)

Pterostylis sanguinea mallee form AB.jpg

An unnamed member of the complex distinguished from Pterostylis sanguinea by its short stature and few flowered inflorescence. Found over a wide range from the Stirling Range to the north of Esperance.

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Pterostylis sp. Coastal

Pterostylis sp coastal AB.jpg

Some consider this to be a form of Pterostylis sp. small bands but it is usually taller with more widely spaced flowers. The sepals are also narrower and often slightly cupped. Found mostly in near coastal areas between Dongara and Bunbury. Similar looking plants have also been found further inland between Brookton and Mt Barker.

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Pterostylis sanguinea (green flowered form)

Pterostylis sanguinea green flowered form AB.jpg

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Pterostylis sargentii

Pterostylis sargentii AB

A common, widespread species, distinguished from other members of the complex by its smaller flowers and fleshy, tri-lobed, frog-like labellum. Found over a huge geographic range between Northampton and Mt Ney, north of Esperance.

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Pterostylis sp. Crowded

Pterostylis sp crowded AB

 

A widespread species named Urochilus atrosanguineus in June 2017. Distinguished from the similar Pterostylis sanguinea by its more robust habit and larger dark reddish-brown flowers. It is also similar to Pterostylis crebriflora but generally flowers earlier and has more widely spaced flowers in a longer spike. Found between Wongan Hills and Katanning with rare, scattered populations on the Swan Coastal Plain.

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Pterostylis sp. Eyre

Pterostylis sp Eyre AB

A distinctive member of the complex distinguished from others by its pale coloured flowers. Like Pterostylis sanguinea (mallee form) it has a short stature and few flowered inflorescence. Found along the coast between Toolinna Cove and Eyre on the on the Great Australian Bight.

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Pterostylis sp. small bands

Pterostylis sp small bands AB

A northern species named Urochilus orbiculatus in June 2017. It is regarded by some researchers to be a form of Pterostylis sp. coastal but is usually shorter with a more densely crowded spike of flowers. Its sepals are also broader, more rounded and flattened rather than slightly cupped. Found north of Perth between Cataby and Binnu.

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Pterostylis vittata

Pterostylis vittata AB.jpg

A widespread species distinguished from other members of the complex by its less fleshy, paler coloured, predominantly green flowers and narrower, elongated, slightly cupped sepals. The flowers also have a more translucent appearance. The typical form is found between Bindoon and Balladonia. There is a northern form with a shorter spike of often fawn coloured flowers found between Cataby and Binnu.

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It should be noted that in South Australia and Victoria U. sanguineus was originally called P. vittata but that species is now recognised as being endemic to Western Australia.

*As an aside, the common name Banded Greenhoods is used in South Australia for the subgenus Bunochilus (previously Pterostylis longifolia which is now considered endemic to New South Wales).

 

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Greenhood Pollination Strategy

Since orchids, and Australian orchids in particular, first came to the attention of the western world in the 1800s researchers have been fascinated by the so many different aspects of the orchid’s morphology and life cycle. One area of interest has been that of how orchids are pollinated. The mechanism of pollination has not always been clear as the orchids seem to use different and complex methods.  From time to time various papers have been published of observations by researchers.

One such paper was published in the Annals of Botany 113: 629 – 641, 2014 titled ‘Caught in the act: pollination of sexually deceptive trap-flowers by fungus gnats in Pterostylis (Orchidaceae)’ by R D Phillips, D Scaccabarozzi, B A Retter, C Hayes, G Brown, K W Dixon and R Peakall.

The ‘question and answer’ style of the paper helps with ease of reading and is worthwhile perusing, even for the lay person. The accompanying VIDEO is also of interest.

The essence of the paper was to establish whether sexual deception was used to facilitate pollination.  The species researched was Pterostylis sanguinea (syn. Urochilus sanguineus) and the researchers confirmed that this did happen.  Their research showed that the attraction for the insect came only from the labellum which exuded an alluring chemical.  P. sanguinea has a mobile hinged labellum which is a feature of other sexually deceptive orchids such Paracaleana, Caleana, Arachnorchis.

Urochilus sanguineus RWL

Pterostylis sanguinea syn. Urochilus sanguineus with the untriggered labellum

Urochilus sanguineus RWL(1)

Pterostylis sanginea syn. Urochilus sangineus with a side view of the labellum

 

The Role of Orchids

October is Orchid Month with the greatest number of species flowering throughout South Australia; so it is worth considering the role of orchids in the Australian bushland.  Hence this week’s blog is an article written by Belinda Newman, Western Australia.

Orchids: The Canary in the Coal Mine was published in the Friends of Kings Park magazine For Plants and People, Issue 70 p 22-24, 2010.  The article is both a good introduction to, and summary of, her 2009 thesis Orchids as Indicators of Ecosystem Health in Urban Bushland Fragments

Orchids: The Canary in the Coal Mine

Belinda Newman – Research Scientist BGPA

What could orchids and canaries possibly have in common?

Before occupational health and safety and ventilation systems were commonplace in the mining industry, a caged canary would be bought down to the coal seam by the miners.  Canaries are particularly sensitive to methane and carbon dioxide which made them excellent indicators for the build-up of dangerous gases.  A singing canary meant everything was fine, a dead canary spelt trouble and an immediate evacuation.

Although orchids can’t sing, they do possess a number of traits that make them sensitive ecological indicators.  The relationships that orchids have with their surroundings form part of a complex ecological web.  Orchids have specific relationships with mycorrhizal fungi, which they require both for germination of their dust-like seed and ongoing growth of plants in adulthood.  These fungi in turn rely on the appropriate soil moisture content and carbon sources.  Above ground, the majority of terrestrial orchids in the south west of Western Australia rely on pollinators for successful seed set.  For some orchids this plant-pollinator relationship has become so highly evolved that removal of the pollinator would spell the end of the orchid.  The pollinators also have specific requirements for habitat, appropriate food sources and nesting sites.  These above and below ground links to the ecosystem make orchids particularly sensitive to disturbances and changes in their surroundings.

The potential for orchids to be used as indicators of ecosystem health formed the basis of a study between Kings Park and Botanic Gardens and Murdoch University.  The coal seam was eleven urban reserves of varying condition on the Swan Coastal Plain.  The canaries were seven orchids common to Perth’s urban bushlands; the Carousel spider (Caladenia arenicola), Cowslip orchid (Caladenia flava), Pink Fairy orchid (Caladenia laitfolia), Pansy orchid (Diuris magnifica), Dark Banded Greenhood (Pteryostylis sanguinea), Purple Enamel Orchid (Elythranthera brunonis) and the Mignonette orchid (Microtis media).  Before it was possible to see which orchids made the best canaries, it was important to determine the health of each of the bushland sites.  A number of environmental variables were chosen that best reflected the health of the ecosystems.  Extensive surveys and analysis of species composition, plant functional groups against these environmental variables revealed a range of site conditions from close to pristine to highly degraded.  This provided the backdrop against which to determine the effectiveness of orchids as indicators through the measured responses of the orchid species.

Firstly orchid presence and abundance was measured across sites to determine if particular orchid species showed a preference for particular site conditions.  Diuris magnifica and Microtis media showed strong correlations and were most abundant in poor condition sites and Pteryostylis sanguinea showed strong correlations to sites in good condition.  While the abundance and presence of orchids appeared to correlate with site condition, we wanted to know what other aspects of the orchid we could measure as a means of judging the health of an ecosystem.

Successful seed set in plants reflects a healthy ecosystem and the reproductive success of the seven orchid species was investigated to determine the effects of declining site condition on seed set.  Pollination trials were set up to measure natural and artificial pollination events across all sites.  Widespread depression in pollination across all species and sites was found to be occurring, rendering seed set a poor measure of ecosystem health.

Investigations into the below-ground links orchids have with the ecosystem were undertaken by determining the presence and abundance of orchid mycorrhizal for the seven orchid study species across all sites.  Mycorrhizal distribution was found to be patchy within urban reserves and also revealed unoccupied niches capable of supporting orchid germination.  A greater abundance of Microtis media mycorrhizal at sites of poor condition supported earlier correlations of plant abundance at sites of poor condition.  The higher abundance of mycorrhizal symbionts for Caladenia arenicola at sites of very good condition also suggests its potential as an indicator species.

The study also looked at seedling growth in urban reserves.  This was the first time that biomass allocation in orchids has been investigated in light of ecosystem health.  In poor condition sites, Diuris magnifica and Caladenia arenicola increased growth effort to the above ground leaf. In sites of very good condition, these two species increased growth to the tuber to take advantage of being able to store starch as a result of both fungal and photosynthetic activity taking place.  Most importantly this shows a measurable change over a short period time.  Although it is effort intensive, planting orchid seedlings of a standardised size into the field may provide a useful and rapid measure of ecosystem health, much like caged canaries were used in the past.

This research into using orchids as an indicator species is the first of its kind and suggests that orchids can be used as an indicator of ecosystem health.  Future research will need to focus on the thresholds of the species identified as potential indicators in this study.  What aspect of the orchid’s ecology will give clear and repeatable data linked to ecosystem health?  Following the canary analogy, how long can orchids hold their breath? Future studies would need to focus on testing these thresholds.  The results of this study suggest that orchid presence and abundance, orchid growth and orchid symbionts can be used as indicators of ecosystem health, although work needs to be undertaken to refine the understanding of their response to specific disturbances.  This study provides a baseline for investigating the utility of orchids as indicators of ecosystem health in highly fragmented systems.  Perhaps orchids and canaries have more in common than first thought.