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.
(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|
|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|
|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|
|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|
|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!
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,