Diplodium robustum

Diplodium robustum or Diplodium sp Adelaide Hills?

The following article has been adapted from the 2019 July Winning Photograph

The July competition resulted in a draw. This article will concentrate upon only one of the winner’s – Lisa Incoll’s photograph of a Diplodium sp. found in the Southern Lofty Ranges.

Sometimes images are sent through unnamed or with only the genus named as in the case of Lisa’s picture. Unfortunately, it is not always possible to determine the identity from only one photograph beyond the genus level. In this case it can be seen that it is a Pterostylis but since the introduction of a segregate genera it is possible to narrow it down further to Diplodium sp.

Since there are two main Diplodium found in the Adelaide Hills (D. robustum and D. sp Adelaide Hills), I thought it would be a good opportunity to compare these two species.

The phrase name D. sp Adelaide Hills is used to distinguish it from D. alatum (syn. Pterostylis alata) which is considered to be endemic to Tasmania. The mainland species P. striata was previously known as P. alata. The eFlora-SA, the Adelaide Herbarium online key and census of the SA Flora has D. sp Adelaide Hills listed as P. alata (syn D. alatum).

D. sp Adelaide Hills and D. robustum share many similar feeatures. In the dichotomous fey found on the eFlora-SA, the separation between the two is primarily based upon size. D. sp Adleaide Hills is generally a taller-stemmed plant with a smaller flower and smaller, more slender cauline leaves. D. robustum is mainly a larger flower on a shorter stem. However there is an overlap between D. robustum and small specimens of D. sp Adleaide Hills which can make determination of species difficult.

Based upon the descriptions and the key from eFlora-SA, Orchids of South Australia (1990) and South Australian Native Orchids (2011), the following table shows the similaritites and differences between the two species. For completeness, shared features (highlighted in bold) are also included.

	*Diplodium robustum* (syn. Pterostylis robusta)	Diplodium sp Adelaide Hills (syn. D. alatum, P. alata)
Plant Height	5-20cm tall (usually less than 10cm tall); robust stem	8-25 cm tall; slender stem
Sterile plants	Yes	Yes
Leaves	6 – 7 ovate or elliptic-ovate (ie range from oval to egg-shaped) leaves in rosettes on long petioles	3 – 8 ovate leaves in small rosettes on long petioles
Leaf edges	Smooth
Flowering Plants	No rosettes or basal leaves	No rosettes or basal leaves
Cauline Leaves	Alternating leaves clasping the base & increasing in size from the base upwards. Acuminate (long drawn out point)	Alternating leaves clasping the base & increasing in size from the base upwards. Acuminate
	Broad (up to 8mm wide) lanceolate serrulate (tiny teeth) cauline leaves more than 3cm long	Slender lanceolate, cauline leaves less than 3cm long
FLOWER
	Blooms can last up to 8 weeks in sheltered places	Delicate flowers can soon collapse with strong drying winds
Inflorescence	Singular flower	Singular flower
Colour	Bright green & white with deeper green, longitudinal stripes	Pale-green or white with darker striations
Galea	Erect; bulbous near the base	Erect; bulbous near the base
	Length 25 – 45 mm; diameter more than 20 mm; gradually curved forward at the apex	Length 20 – 25 mm long; Diameter less than 18 mm; gradually incurved
Dorsal Sepal	Ends in a long fine point to 5 mm long	Apex blunt; ends in a short fine point
Petals	Blunt	Blunt or acute
Lateral Sepals	Erect; conjoined basally; distally, the tips produced into long filiform erect points, embracing the galea & greatly exceeding it	Erect; conjoined basally; distally, the tips produced into long filiform erect points, embracing the galea & greatly exceeding it
Sinus (region where lateral sepals separate)	Flat, with a wide, shallow central v-notch; protruding in a shallow curve whenviewed from the side	Narrow sinus, with a notch in the middle; not bulging
Labellum	Movable claw; nearly straight	Movable claw; nearly straight
	Dark green	Greenish
Erect potition	Recaches height of the column	Slightly exceeding the height of the column
Column	Column erect	Column erect
Habitat	Forms small to extensive colonies	Forms small to extensive colonies
	in rocky places; forest or scrublands	in rocky or shady locations; forest or forest heathlands
Regions	Mt Lofty Ranges	Mt Lofty Ranges
	Flinders Ranges; Eyre Peninsula; Yorke Pensinsula; Upper South East	Kangaroo Island; South East; possibly Eyre Peninsula
Rainfall area	Greater than 250 mm	Greater than 600 mm
Flowering Time	May – September	May – July

Of course, as these two hybridise, that will complicate things, Hybrids will have characteristics of both parents but, with hybrid vigour; and vigour is one of the separating features between the two!

References
http://flora.sa.gov.au/cgi-bin/speciesfacts_display.cgi?genus=Pterostylis&species=robusta Accessed 6 September 2019

http://flora.sa.gov.au/cgi-bin/speciesfacts_display.cgi?genus=Pterostylis&species=alata Accessed 6 September 2019

Bates RJ, 2011 South Australia’s Native Orchids, electronic

Bates RJ Weber JZ, 1990, Orchids of South Australia,

Monthly Terrestrial Orchid Culture – June

It’s June and the the orchids tubers are on the move. And yes there are some tasks for this month but as can be seen by Les Nesbitt’s notes in the June 2019 NOSSA Journal (Volume 43 N0 5) there is not a lot to do.

Diplodium robustum (syn Pterostylis robusta) – one of the cauline greenhoods

June is cold, often with frosty mornings and sunny days. Terrestrials can take -20C but any colder results in permanent damage. If you live in the country, you may need a solid roof for frost protection. Frosts are rare these days in Adelaide. I have black rubbish bins full of water under the benching in my glasshouse to moderate the temperature. The bins absorb heat in the daytime and radiate it out at night. If it is not frosty it will be cold wet and cloudy. Growth will be slow and there are few flowers out. There is not a lot to do in the terrestrial house.

Pterostylis robusta and Acianthus pusillus flower this month. If there are no flowers this year, they probably aborted due to high temperatures or excessive dryness over summer/autumn. Try putting the pots under the bench in a cooler position next summer.

The last of the terrestrial orchid leaves should appear this month although there are always a few stragglers. Tubers that formed in the bottom of a pot have a long way to grow to reach the surface. Sometimes they come out the drainage holes. If no plants appear, do not throw the pot away. Sometimes orchids take a year off and send up a leaf the following year. They are capable of forming a new tuber from the old without making a leaf. Gather together the “empty” pots in a corner. They can be left for another year or you can knock them out next month to try to establish what can be improved. Most weeds have germinated by now so weeding gets easier.

It is hard to drag yourself away from the heater this month but at least once a week go out on a wet night with a torch and examine your orchids for slugs, snails, earwigs, cockroaches, grubs and beetles. They always feed on your best orchid buds.

The SAROC Fair is in June. Clean up your flowering pots for the NOSSA stand. Other orchid clubs hold winter shows in June & July. Go along and see if there are any interesting terrestrials on the trading table.

When do I stop watering my Greenhoods?

This was the question posed to Les Nesbitt at the September monthly meeting. Later there was some further discussion, of which see below:

When do I stop watering my Greenhoods?

The short answer is when the leaves go yellow and start to die off, usually in October- November. Allow the pot to dry out completely to dry up the roots and old tubers so that they do not go mouldy and rot the new tubers.

Australian terrestrial orchids form tubers underground. The mature plant dies back at the end of the growing season and enters a period of dormancy which for South Australian terrestrials is over summer.

A general principle of watering is to match the watering to the rainfall pattern. Whilst there is minimal rain over summer, when dormant tubers are in pots it is important to not let them stay dry for months and become desiccated. A light sprinkling every week or two is sufficient.

Unicode — Pterostylis ‘Nodding Grace’ This is an hybrid between P. nutans and P. curta. Obviously it is not time to stop watering.

When do I start watering again?

For the cauline group (Diplodiums) from South-eastern Australia start watering at the end of January as the tubers are starting to shoot by then. For other greenhoods start light watering in late February and gradually increase the water until shoots appear usually in March-April. Do not let the pots dry out once leaves are visible.

Diplodium robustum - one of the cauline greenhoods — Diplodium robustum – one of the cauline greenhoods. Note difference the between the leaves of the non-flowering rosettes and the flowering plants.

Other cultivated Australian terrestrial orchids require a similar watering regime although leaves of some appear later in May or June.

2015 June Winning Photograph

Of the five entries this month, four featured winter orchids. Lorraine Badger entered a Diplodium robustum, whilst Claire Chesson, Robert and Rosalie Lawrence all entered Urochilus sangineus. Though not the winning photographs it was interesting to see the differences between the U. sangineus with one being no taller than the small Acianthus pusillus next to it and another being taller than the rapier sedge.

But the winning photograph was the spring flowering Arachnorchis argocalla (White Beauty Spider Orchid) by Pauline Meyers. This is amongst our most threatened orchids and is dealt with in depth in the Recovery Plan For Twelve Threatened Orchids in the Lofty Block Region of South Australia 2010. This fungi dependent endemic orchid is rated Endangered both at State and National level.

Found in the Southern and Northern Lofty regions, it range has been severely reduced by possibly 80%. Since 1918 no plant has been found south of Adelaide.

Flowering from September to October, it is often found in grassy woodlands often growing on gentle southerly-facing hill slopes. The soil is a clay loam with a high humus content.

This beautiful orchid has one to two non-perfumed white flowers with thickened but not clubbed drooping lateral sepals and petals. The strongly recurved broad labellum is usually white, sometimes crimson, fringed with short teeth.

This is one of our larger spider orchids reaching a height of 60cms. The size of the plant flower and leaf help to distinguish it from other similar appearing orchids such as A. brumalis and albino flowers of A. behrii.

Like many of the spider orchids it takes 2 – 5 years to reach maturity and then has a potential reproductive life of 10 years. With an average pollination rate of less than 10%, the potential to increase the population is low and any threat to survival of the individual plants needs to taken seriously.

Some threats are obvious such as weed invasion including the garden escapees such as Topped lavender (Lavandula stoechas spp. stoechas) and action is being taken to curb the spread of weeds through targeted weeding programs.

Another threat is habitat loss. This has been the result of land clearing but sites are being protected either through conservation legislation or Heritage Agreements. Habitat loss can also occur indirectly and that is through Phytophthora being introduced into the sites. Although the direct effect of Phytophtora on the orchid is unknown, it is known that it can affect the plants that grow in association with this orchid. This threat can be reduced by all of us implementing good hygiene practices.

These were some of the threats noted in the Recovery Plan. This plan was not just defensive, ie attempt to halt and minimalize the damage; but it was also proactive with measures outlined to increase the population. These included seed and fungi collection eventually resulting in germination and cultivation with a view to re-introduction.

It is good to see that there is a plan and active steps are being taken to bring this orchid back from threat of extinction.

June 2015 other entrants — Photographers from L to R: Claire Chesson, Rosalie Lawrence, Lorraine Badger, Robert Lawrence

References

Websites accessed 1 July 2015

White Beauty Spider Orchid (Caladenia argocalla) Recovery Plan
http://www.environment.gov.au/archive/biodiversity/threatened/publications/recovery/c-argocalla/index.html
Caladenia argocalla – White-beauty spider-orchid, biodiversity species Profile and Threats Database
http://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=54991
Recovery Plan For twelve threatened Orchids in the Lofty Block Region of South Australia
http://www.environment.gov.au/system/files/resources/e362cfd2-a37b-443a-b007-db3a2b7b64dd/files/lofty-block-orchids-recovery-plan.pdf

Bates R J, South Australia’s Native Orchids 2011 DVD

The Great Orchid Pretender

Actually there is more than one.

Frequently NOSSA receives a request to identify an orchid in someone’s garden. Often, instead of an orchid (but occasionally there are orchids), it is the Ariasrum vulgare (common name Friar’s Cowl Lily or Cobra Lily).

Native to Asia and Europe, notably the Mediterranean and introduced to Australia, it is often mistaken for one of the flowers of the Pterostylis (Greenhood Orchids) or Diplodium (Shell Orchids). Some have called it a Blackhood orchid others Snake Orchid. It’s resemblance to the Greenhoods and Shell Orchids is superficial as they have none of the orchid features. The dark purple hooded part is not the flower; it is a spathe (bract). The flowers are minute hidden on deep down on the “tongue”.

The hood of the orchids is the combination of a deeply concave dorsal sepal interlocking with the lateral petals; and the fusing of the two lateral sepals. Tucked away within the hood is the labellum (a modified petal) and the column (the reproductive organs of the flower). The leaves of Ariasrum are quite large and distinctly different from any of the Greenhood orchids.

The following article has been adapted from the 2019 July Winning Photograph

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