Greenhoods are Great!

 

It's spring, and an old (in my case) man's fancy turns to thoughts of orchids. That's a vast topic; there are some 1700 orchid species in Australia alone, and orchids comprise some 8% (one in twelve) of the world's flowering plant species. Accordingly I'm going to limit myself today to just one group, less colourful than some orchids but nonetheless attractive, and indeed fascinating, to many of us. Within the wider orchid family they seem to be an old group with no close relations; indeed they are so specialised that they are not always immediately recognised as orchids. There are some 400 species of greenhoods, most of them Australian and the rest nearby, in New Guinea, New Zealand and New Caledonia. 

Summer Greenhood Diplodium decurvum, Brindabella Ranges, above Canberra.

To understand this curious flower structure, let me remind you of the basic orchid form (on which there are a myriad variations) using a rather more typical orchid flower. (You can skip this if you like, though that might make it harder to understand some of what follows - don't miss the pictures though!)

Purple Donkey Orchid Diuris punctata, Tallong, New South Wales.
Unlike most flowers, orchids (and lilies) have sepals - the outer ring of flower parts - which are as large and colourful as the petals. There is one dorsal sepal at the top of the flower, and two lateral sepals lower down. There are two dorsal petals, with the third petal forming an insect landing platform called the labellum (lip). (In this photo the dorsal sepal looks to be in front of the petals, but if you look at the top flower - you might have to magnify it by clicking on it - you'll see that it really does rise from behind them.) And that'll do for now!

The greenhood in the previous photo looks entirely different, but the basic structure of the flower is exactly the same. However in greenhoods the two dorsal petals and the dorsal sepal strongly overlap to form the hood, or galea; it may look as though it's a single fused structure, but it's not. The inconspicuous labellum of the Summer Greenhood can just be seen protruding under the hood. The two lateral sepals, which droop down in the donkey orchid, stand stiffly up in this greenhood, though this is isn't true of all greenhood species. However the important difference is that they're conspicuously fused at the base, while those of most other orchids are free of each other. Again, that'll do for now!

As I mentioned some greenhoods have the lateral sepals hanging down like the donkey orchid above, and many other orchids. Here's an example.

Tall Greenhood Bunochilus longifolius, Callala, south coast New South Wales.
The conspicuous labellum is very clear here, which brings us to greenhood pollination.

No greenhood provides a nectar reward to hard-working pollinating insects; all of them attract small male flies, mostly fungus gnats (like small non-biting mosquitoes), with a pseudo-pheromone, a chemical that mimics the 'come hither' scent of an interested female gnat. The labellum, which may be out in the open like this Tall Greenhood, or mostly hidden in the flower so it is just visible, like the Summer Greenhood earlier. When the amorously hopeful insect contacts the hinged labellum it snaps back, pinning the insect against the column, which contains both pollen and style. In its struggle to escape the unfortunate gnat either collects the sticky pollen, or delivers a bundle it's already carrying.

Rainforest Greenhood Pterostylis hildae, Katoomba, Blue Mountains, NSW.
Here the flower has been recently 'triggered', so the labellum is tucked away
out of sight inside. It may take 30 minutes for the labellum to reset, and
another 30 to become sensitive again; in part this is likely to be to allow
the last pollinating gnat to get well away so it doesn't return the pollen to its source.

The ovary is below the flower. After pollination the flower begins to shrivel and the ovary to swell; within it the tiny wind-borne dust-like seeds develop - this is characteristic of all orchids.

Nodding Greenhood Pterostylis nutans, Black Mountain, Canberra;
the flower is losing its colour and the ovary is starting to swell.

The process almost completed. Later in the blog is a photo of a healthy unfertilised flower.

 If you're at all familiar with the Australian orchid scene you won't be surprised to read that there is controversy over greenhood taxonomy. Until recently they were lumped into just one unwieldy big genus, Pterostylis, which contained obvious groups of species, each quite different from the others. Then in 2003 two highly respected Canberra-based orchid experts, David Jones and Mark Clerments, divided the genus into 16 genera, based on biochemical work. (The main reference is Jones, D.L. and M.A.Clements (2003b). A New Classification of Pterostylis R.Br. (Orchidaceae). Austral. Orch. Res. 4: 64-124 but it doesn't seem to be readily available on line.) 

 

No-one seemed to disagree that these were valid sub-groupings but the main botanical 'establishment' preferred to leave things as they were and just regard them as sub-genera. Subsequent further work using new tools by Clements combined some of those genera again, leaving eleven greenhood genera. Now things have settled down somewhat there seems to be a fairly healthy 'live and let live' approach taken. Take for instance two recent field guides relevant to my part of the world. The Field Guide to the Orchids of the Southern Tablelands of NSW including the ACT (Jean Egan et al, 2020) uses the 'new' genera. The Guide to Native Orchids of NSW and ACT (Copeland and Backhouse 2022) calls them all Pterostylis but finishes each entry with 'also called .....', acknowledging that those genus names are also in wide usage. 

Without claiming any expertise it seems to me that the more nuanced approach of Jones and Clements is more informative in recognising clearly separate greenhood groups. Jones' vast (800 pages) and hugely influential recent work, his 2021 full revision of Complete Guide to Native Orchids of Australia, obviously uses his own names. For these reasons I have chosen to also use them here; just bear in mind that some books will call them all Pterostylis.

And with that I'll just get on with introducing you to representatives of nine of those eleven genera, and hoping you enjoy meeting them as much as I do. (The other two contain just one species each, but I've not yet had the pleasure of meeting them.) As mentioned earlier, two basic groups of greenhoods are recognised. The larger group in terms of species, though only containing three genera, is characterised by having upswept lateral sepals like the summer greenhood above. Here are some more of this grouping, starting with a few from the big genus Diplodium, containing some 80 species, all but four of them being from Australia.

Scarlet Greenhood Diplodium coccinum, near Monga, inland south-east NSW.
This is an unusually colourful greenhood, a truly beautiful one that I've not often seen.

Common Autumn Greenhood D. reflexum, Black Mountain, Canberra.
Quite a few greenhoods, in this part of the world at least, flower in autumn.
(And Black Mountain, in the heart of the national capital, is an orchid nirvana,
with 51 species recorded there!)

Common Autumn Greenhoods often grow in large colonies;
this is also on Black Mountain.

Large Autumn Greenhood D. ampliatum, Chiltern Forest, central Victoria.
(This was until recently called D. revolutum, but inland plants are now
recognised as a separate species.)

Little Dumpies (or more formally Brittle Greenhood, though I don't know why)
D. truncatum, Black Mountain. I love the spontaneously arising folk names though.

Hairy-stemmed Snail Orchid D. setulosum, southern Flinders Ranges, South Australia.
There are over 30 species of the little snail orchids, mostly in Western Australia; until recently
they were given their own genus (Linguella) but Clements and Jones, after further work,
moved them into Diplodium.

Trim Greenhood D. concinnum, Callala, south coast New South Wales.
Again the labellum is obvious, protruding through the join of the two lateral sepals;
this angle is the sinus, and is used for identification of greenhoods. This species too
was once assigned to a separate species (Taurantha) which has since been withdrawn.

About 26 species remained in the old genus Pterostylis, along with some still to be named, and some 15 in other parts of Australasia. They include two of the commonest greenhoods in this part of the world and throughout much of eastern Australia. Both can form very big colonies.

 

Nodding Greenhood Pterostylis nutans, Micalong Falls, New South Wales.
Not dozing, they always look like this!

 

Maroonhood P. pedunculata, Woods Reserve, ACT.
This little one in particular can occur in hundreds.

The third genus in this group comprises very small-flowered orchids, often referred to as tiny orchids. There are 23 species of Speculantha, all confined to eastern Australia. They are distinctively dumpy little characters with short 'horns' ie lateral sepals and often a rusty tinge. Here are a couple of them.

 

Red-tipped or Blushing Tiny Greenhood, S. rubescens, Black Mountain, Canberra.
This one is widespread across the southern inland slopes and plains of NSW,
whereas most tiny greenhoods are coastal.

Squat or Swarthy Tiny Greenhood S. furva, Mongarlowe, south-eastern NSW.

As illustrated earlier, in the other greenhood sub-group the lateral sepals point downwards (ie they are deflexed if you're feeling erudite. There are eight genera of these, and I'm happy to be able to offer you examples of six of them. In addition there are two genera each with just one species - Daintree's Greenhood Pharochilus daintreanum from southern Queensland and northern NSW, and the Frog Greenhood Ranorchis sargentii from the south-west of the continent.

 

The leafy greenhoods, genus Bunochilus, are good examples of this group. There are 15 recognised species down the east coast of Australia, including the Tall Leafy Greenhood above and these two.

Brown-lipped, or Broad-sepaled, Leafy Greenhood B. umbrinus,
Tidbinbilla NR, ACT lower mountains; it is limited to the
NSW southern tablelands. In this plant the labellum has been triggered
so is pressed back into the flower; behind it the fungus gnat
is struggling to get out, carrying its pollen load. Otherwise the labellum
looks like that of the Tall Leafy Greenhood near the start of this blog post.

Montane Leafy Greenhood B. montanus, Black Mountain, Canberra.
Sorry about the poor lighting. This was described by David Jones in 2006,
but one recent publication prefers B. jonesii, doubtless a tribute to David Jones.
However that was published in 2007, so I can't shed any light on that story.

Hymenochilus is a genus of 24 very small-flowered greenhoods (called midget greenhoods, appropriately). Two of them are from New Zealand, the rest are Australian. Any they really are tiny - you can't properly see them unless you get right down to their level.

Black-tipped Greenhood H. bicolor, Black Mountain, Canberra.
The distinctive black appendage at the base of the labellum is only seen
when the labellum has not been triggered.

Alpine Swan Greenhood H. crassicaulis, high Brindabellas, Namadgi NP, ACT.
Named by Jones in 2008, it grows in high grassy areas of the Brindabellas and the
Snowy Mountains. This stem is coming to the end of its flowering,
with only the top flowers still fresh.

Midget Greenhoods H. muticus, Nangar NP, central western slopes, NSW.
This is mostly an inland species, found from Queensland to Victoria.

The rustyhoods, Oligochaetochilus, include some of the most striking greenhoods to my eye. There are some 80 species of them, up to 15 of which are still awaiting description. Many are reddish, as the group name reflects, many have long pointed lateral sepals, and many have hairs around the fringe of the labellum. Many also grow much further inland, and in drier areas, than most orchids.

Boorman's Rustyhood or Baggy Britches (!) or even Sikh's Whiskers, though that is
understandably falling from favour these days, Oligochaetochilus boormanii,
Weddin Mtns NP, south-western slopes New South Wales.

Slender Rustyhood O. aciculiformis, Mount Tennent, south of Canberra.
This species and the next were flowering together in a very nice site in dry
casuarina woodland.

Southern Hooked or Scaly Rustyhood O. hamatus (see previous caption).
This is an especially distinctive species with those long curving sepals.

The bearded greenhoods are, if anything, even more striking with their nodding labellum fringed with long thick yellow hairs. Plumatichilos contains some 25 species, nearly all of which are endemic to Australia and most to WA. I haven't had much luck with them over there, but here's a nice one from my home state of South Australia.

Leafy Bearded Greenhood Plumatichilos foliaceus, Alligator Gorge,
southern Flinders Ranges. Unfortunately the characteristic dark red knob on the tip
of the labellum is largely hidden in front of the shadow.

There are seven species of the pretty banded greenhoods Urochilus spp., five of them limited to WA.

 

Banded Greenhood U. vittatus, Shannon NP, south-west WA.
This one is fairly common across the sandy south-west.

Red-banded Greenhood U. sanguinea Kings Park, Perth. This one has a remarkably wide range across southern Australia from Tasmania to Perth and north to Kalbarri.

My last offering is a pretty weirdly and unmistakably striking single-species genus from WA.

Jug Orchid Stamnorchis recurva, Twin Creek NR, Western Australia.

So, the greenhoods, subtle beauties. I hope my enthusiasm hasn't led to you feeling buried in too much information and that you've been able to enjoy them as much as I do. Look for them in damp shady places (especially in the east) and in autumn and even winter when most other orchids are waiting their turn. You may well end up entranced.

NEXT POSTING THURSDAY 27 OCTOBER

 

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