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 Height5-20cm tall (usually less than 10cm tall); robust stem8-25 cm tall; slender stem
Sterile plantsYesYes
Leaves6 – 7 ovate or elliptic-ovate (ie range from oval to egg-shaped) leaves in rosettes on long petioles3 – 8 ovate leaves in small rosettes on long petioles
Leaf edgesSmooth
Flowering PlantsNo rosettes or basal leaves No rosettes or basal leaves
Cauline LeavesAlternating 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 longSlender lanceolate, cauline leaves less than 3cm long
FLOWER
Blooms can last up to 8 weeks in sheltered placesDelicate flowers can soon collapse with strong drying winds
InflorescenceSingular flower Singular flower
ColourBright green & white with deeper green, longitudinal stripesPale-green or white with darker striations
GaleaErect; bulbous near the base Erect; bulbous near the base
Length 25 – 45 mm; diameter more than 20 mm; gradually curved forward at the apexLength 20 – 25 mm long; Diameter less than 18 mm; gradually incurved
Dorsal SepalEnds in a long fine point to 5 mm longApex blunt; ends in a short fine point
PetalsBluntBlunt or acute
Lateral SepalsErect; 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 sideNarrow sinus, with a notch in the middle; not bulging
LabellumMovable claw; nearly straight Movable claw; nearly straight
Dark greenGreenish
Erect potitionRecaches height of the columnSlightly exceeding the height of the column
ColumnColumn erect Column erect
HabitatForms small to extensive colonies Forms small to extensive colonies
in rocky places; forest or scrublandsin rocky or shady locations; forest or forest heathlands
RegionsMt Lofty Ranges Mt Lofty Ranges
Flinders Ranges; Eyre Peninsula; Yorke Pensinsula; Upper South EastKangaroo Island; South East; possibly Eyre Peninsula
Rainfall areaGreater than 250 mmGreater than 600 mm
Flowering TimeMay – SeptemberMay – 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,

Thelymitra Column Features Part Two

This article is a completion of the Thelymitra Column article which appeared in the NOSSA Journal, Volume 42 No 8 September 2018. Click here for Part One.

The first part looked at the features and terms used by botanists to describe various parts of the column, a major identification feature of the sun orchids.

And as previously stated we cannot physically dissect an individual flower, but we can make use of photographs to spot the various features.

The diagram below is that of T. nuda (based on the taxonomy of 1984) column whilst the photographs are that of T. glaucophylla column (as T. glaucophylla is one of the T. nuda complex). The column of these two are similar.

 

April 2018 Winning Photograph

1804 sm JF oligochaetochilus excelsus koongawa 2

Oligochaetochilus excelsus, an impressive name for the winning photo, taken by John Fennell. It was originally formally described and named Pterostylis excelsa by Mark Clement in 1986 from a specimen cultivated from a tuber taken from Eyre Peninsula. This was subsequently published in the fourth edition of Black’s Flora of South Australia. In the early 2000s, the genus Pterostylis was split into several different genera of which Oligochaetochilus was one.

Although not everyone accepted this change, it is helpful for understanding the characteristics of this group. They are found only in Australia and are primarily a semi-arid inland group, sometimes the only orchids to occur in a locality.

Bob Bates has documented some of the drought tolerant and drought avoidance features found in this group as follows.

Drought tolerance:

  • Large moisture-storing tubers, shallowly buried to take advantage of light rain.
  • Waxy leaves pressed flat to the soil thus avoiding water loss.
  • Fast growth, some species are able to flower on just two good rainfalls.
  • Leaves senesce (die off) before or soon after flowering begins; moisture and food from the leaves is then stored in the tuber and scape. Leaves are able to absorb moisture from dew.
  • Leaves also contain an anti-freeze and can tolerate black frosts.
  • Just one month after rain a replacement storage tuber is produced as large as the old.

Drought avoidance:

  • Plants favour damper microhabitats, growing at the base of larger rocks and in seepage zones or on the cooler damper south side of bushes.
  • Tubers of desert species do not usually germinate in drought years.
  • Leaf senesces (dies off) before hot weather meaning plants avoid moisture loss during flowering.
  • Plants cease respiration in long dry periods and resume after rain even up to three months later, staying green even in bone dry soil.
  • Leaves are pressed to the soil.

References:

https://en.wikipedia.org/wiki/Pterostylis accessed 10 May 2018

Jessop, J. P. and Toelken, H. R. (eds) (1986). Flora of South Australia. 4th ed. Adelaide: Government Printers Adelaide.

Bates, R. J., ed. (2011). South Australian Native Orchids. Electronic version. NOSSA