Non-convergence among orchids in mediterranean-type climates in Australia and California, in the evolution of geophytes
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Geophytes are defined as perennial, deciduous, herbaceous plants which die down to ground level after each growing season, regenerating vegetatively, year after year.
This regeneration is by means of underground storage organs (https://en.wikipedia.org/wiki/Storage_organ), i.e. tubers, derived from either stems or roots.
According to the Raunkiaer classication, geophytes are terrestrial cryptophytes (https://www.pacificbulbsociety.org/pbswiki/index.php/Geophyte).
In southern and southwestern Australia,
- most of the many genera and spp. of orchids are geophytic (https://www.researchgate.net/publication/268037630_Identification_and_Ecology_of_Southwest_Australian_Orchids),
- these possess (small) root-tubers, not corms or bulbs, and
- root-tuberous orchids are by far the most speciose category of geophytes in the floras.
See https://www.publish.csiro.au/BT/BT98056 and https://www.inaturalist.org/journal/milewski/72929-geophytes-by-habitat-in-fitzgerald-river-national-park-western-australia# and https://www.publish.csiro.au/bt/BT02067 and https://www.inaturalist.org/journal/milewski/73016-geophytic-flora-of-wongan-hills-nature-reserve-southwestern-western-australia#.
The floristic richness of orchids in Australia, under mediterranean-type climates, is remarkable: hundreds of spp. in more than a dozen genera (https://www.inaturalist.org/observations?place_id=6827&taxon_id=47217&view=species).
Based on the above, it seems reasonable to assume that the geophytic growth-form reflects the seasonality of mediterranean-type climates, viz. those with warm dry summers and cool wet winters.
Hence, it would also seem reasonable to predict that the incidence of geophytic orchids would be similar in California, most of which has a mediterranean-type climate.
However, orchids are not mentioned in the abstract of https://www.jstor.org/stable/41425147. There are many geophytes in California, but do these include orchids?
With this question in mind, I have attempted to assess the incidence of underground storage organs in orchids in California (https://www.inaturalist.org/observations?place_id=14&taxon_id=47217&view=species).
The following is a full list of the genera of orchids in California, according to iNaturalist.
Goodyera oblongifolia
https://www.inaturalist.org/taxa/50719-Goodyera-oblongifolia
https://www.pacificbulbsociety.org/pbswiki/index.php/Goodyera
(habitat: coniferous forests at high altitudes)
fleshy creeping rhizome
hemicryptophytic but not not geophytic
Cypripedium
https://www.inaturalist.org/observations?place_id=14&taxon_id=47589&view=species
fibrous roots
(habitat: forests and dry, open hillsides)
not geophytic
Calypso bulbosa
https://en.wikipedia.org/wiki/Calypso_bulbosa
https://www.inaturalist.org/taxa/47215-Calypso-bulbosa
bulb-like corm
geophytic
Platanthera
https://en.wikipedia.org/wiki/Platanthera
https://www.inaturalist.org/observations?place_id=14&taxon_id=48031&view=species
'bulbous caudex' (e.g. https://www.inaturalist.org/taxa/840640-Platanthera-leptopetala and https://www.inaturalist.org/taxa/840644-Platanthera-cooperi); ?root-tubers in some spp. (descriptions unclear/contradictory)
some possibly geophytic (e.g. https://www.inaturalist.org/taxa/500491-Platanthera-yadonii and https://goorchids.northamericanorchidcenter.org/species/platanthera/yadonii/), but descriptions ambivalent
Spiranthes
https://www.inaturalist.org/observations?place_id=14&taxon_id=50741&view=species
root-tubers
rhizomes absent
(habitat: marshy meadows, including at high altitudes)
Are any species geophytic in California?
Epipactis
https://www.inaturalist.org/observations?place_id=14&taxon_id=50716&view=species
creeping, fleshy rhizomes with offshoots
(habitat: streambanks)
not geophytic
Neottia
https://www.inaturalist.org/observations?place_id=14&taxon_id=1190532&view=species
fibrous creeping roots and/or rhizomes
(habitat: moist, shady places in forests)
not geophytic
Malaxis brachypoda
https://www.inaturalist.org/taxa/165091-Malaxis-brachypoda
solid bulb ('pseudobulbous')
(habitat: moist, high altitudes)
?geophytic
Cephalanthera austiniae
https://en.wikipedia.org/wiki/Cephalanthera_austiniae
https://www.inaturalist.org/taxa/50706-Cephalanthera-austiniae
https://ucjeps.berkeley.edu/eflora/eflora_display.php?tid=18611
rhizomes, not tubers
(habitat: dense forests at high altitudes)
non-green, myco-heterotrophic (https://en.wikipedia.org/wiki/Myco-heterotrophy)
not geophytic
Corallorrhiza
https://www.inaturalist.org/observations?place_id=14&taxon_id=49445&view=species
coral-shaped rhizomes
myco-heterotrophic, most spp. leafless and rootless
not geophytic
DISCUSSION
What emerges is that the flora of geophytic orchids in California, even under the mediterranean-type climate, is negligible.
Calypso bulbosa and Platanthera yadonii do seem to qualify, but their categorisation as geophytes might not even occur to anyone, were it not for the search-image arising in the flora of Australia (and, to a lesser degree, southern Africa).
Furthermore, the few geophytic orchids in California - if any - that might correspond to the Australian category, in having root-tubers, are one or more species of Platanthera (https://www.pacificbulbsociety.org/pbswiki/index.php/Platanthera). Even in this case, it remains unclear that any tubers are actually derived from roots, and that both the foliage and the inflorescence/infructescence die back during the summer.
What emerges is one of the most categorical ecological/evolutionary differences yet found among the various regions of mediterranean-type climate on Earth: a 'world-class' proliferation of geophytic, root-tuberous orchids in the case of Australia, compared with the virtual absence of such plants in the case of North America.
FOOTNOTE:
The genus Spiranthes is shared between California and Australia. It is geophytic in Australia, and at least one species may be geophytic in California. However, note that the genus has hardly penetrated the mediterranean-type climate in Australia.
Comments
https://www.jstor.org/stable/20063929
https://www.floridamuseum.ufl.edu/science/five-facts-geophytes/
https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:651833-1
https://anpsa.org.au/APOL19/sep00-1.html
https://link.springer.com/article/10.1007/s11258-011-9987-y
@arethusa @catullus
Please could you help with the growth-form classification of Spiranthes in California? Is any species a geophyte?
In order for the species to qualify as a geophyte, the above-ground parts must die down to ground level each summer.
And, for any Californian orchid to conform to the hundreds of geophytic orchids under a similar climate in Australia, the tubers would have to be derived from roots, as opposed to being rhizomatous (https://en.wikipedia.org/wiki/Rhizome), cormous (https://en.wikipedia.org/wiki/Corm), or bulbous (https://en.wikipedia.org/wiki/Bulb).
Your thoughts?
In April 1982, curious about the incidence of orchids in what is now the Cape Point section of Table Mountain National Park (https://en.wikipedia.org/wiki/Table_Mountain_National_Park), I wrote to C Howard Langley.
He replied:
"The number of orchid species coexisting in a given area is difficult to give, as numbers present differ widely from one locality to another (in what was then Cape of Good Hope Nature Reserve). Furthermore, although a number of species may be present in a given area, they may only appear above ground or flower at differing times of the year. However in one exceptional locality, a peaty marsh near the coast that had been burnt about four months previously, a total of seven species were found growing together, although not all were in flower. At Cape Point, it would appear that damp peaty soils have the greatest diversity of orchid species, while dry sandy soils on slopes have the fewest. To my knowledge, no species occur on the stabilised beach dunes immediately on the shore, although a number of species do occur on the coastal flats within 500 m of the shore, these areas being old beaches on which coastal scrub has become established."
@ludwig_muller
Could you please tell me, how many of the spp. of orchids at Cape Point are cryptophytes, defined as being perennial but dying down to ground level each year?
(Cryptophyte corresponds more or less to geophyte, except that plants growing on permanently waterlogged soils are disqualified.)
The following shows all the spp. of orchids recorded in iNaturalist from the area in question:
https://www.inaturalist.org/observations?nelat=-34.12910799726047&nelng=18.49836184038502&place_id=any&subview=table&swlat=-34.35980591789258&swlng=18.31910297805594&taxon_id=47217&view=species
It is difficult to interpret the intercontinental difference, described in this Post, without explaining the occurrence of many spp. of orchids in Israel (https://www.inaturalist.org/observations?place_id=6815&subview=table&taxon_id=47217&view=species). How many of these are geophytes?
@milewski
I have had little experience with orchids outside the Southern Cape and none whatsoever with orchids at Cape Point. But I believe that the great majority are cryptophytes.
@milewski sorry for the late reply! I believe that Calypso bulbosa produces corms, and members of genus Platanthera section Piperia (including P. yadonii, P. elegans, etc.) are also tuberous.
I think you're making a very interesting comparison, but there could be a few flaws. For one, many Californian orchids don't inhabit areas with seasonally dry soils (eg. Platanthera sect. Limnorchis, Neottia, etc.), so there's no need to evolve geophytic adaptations. Our largest group of orchids that is known to be specially adapted to chaparral, section Piperia, does produce tubers and has radiated rather extensively. Other groups, such as Corallorhiza, have fleshy rhizomes, which seem to perform the same function as tubers/corms/bulbs. For another, much of California is not chaparral (even areas receiving a relatively Mediterranean climate). 25% of the state is desert, and vast swaths of it are coniferous forest or other dense woodlands in which geophytes might not radiate as extensively. I get the impression that the many of Australia's tuberous orchids inhabit open shrubland/chaparral-type environments.
(Also, just a quick side-note, Zeuxine is not native to North America and was anthropogenically introduced).
That being said, I've also wondered why the terrestrial orchid flora of South Africa and Australia are so much more diverse than what we see in California. I'm sure there are valid factors, some of which might just be more speculation. Maybe it has to do with the conditions at the last glacial maxima and what ancestral plants occurred in those areas/what adaptations those ancestral plants had.
@arethusa @afid do you have any thoughts?
@catullus
Many thanks for your welcome comments.
I have removed Zeuxine accordingly.
Do you think that any species of Platanthera section Piperia qualifies as geophytic?
I would not necessarily agree that the woodland/shrubland distinction explains much of the anomaly between California and Australia.
In Western Australia under the mediterranean-type climate, there are extensive open-forests, originally up to 40 m high, dominated mainly by Eucalyptus marginata (https://upload.wikimedia.org/wikipedia/commons/7/7b/The_Looming_Relic.jpg and https://en.wikipedia.org/wiki/Eucalyptus_marginata).
Geophytic orchids occur in these, in the form of many genera and 300 spp. (https://www.wilderness.org.au/iconic-places/wa-jarrah-forests and https://www.researchgate.net/publication/240509476_Orchid_species_succession_in_rehabilitated_bauxite_mines_in_Western_Australia and https://www.publish.csiro.au/BT/BT06170 and https://www.dcceew.gov.au/sites/default/files/env/pages/cde27319-968a-472e-a952-ee2483e7589d/files/caladenia-arrecta.pdf and https://www.bibbulmuntrack.org.au/the-track/flora-fauna/).
What seems to emerge here is a profound difference between the two regions, that - as far as I know - has not been adequately pointed out in the literature.
My impression is that the main reason for the proliferation of geophytic orchids under the mediterranean-type climate in Australia and South Africa is nutrient-poverty.
The soils in forest or woodland of E. marginata are extremely poor in phosphorus, zinc, and other elements, although rich in iron and aluminium (http://www.bgff.org.au/diversity.htm and https://www.researchgate.net/publication/230145998_Nutrients_in_the_litter_in_Jarrah_forest_soils and https://onlinelibrary.wiley.com/doi/10.1111/avsc.12046).
The adaptations usually associated with nutrient-poverty are e.g. sclerophylly and pollination by vertebrates. However, geophytic orchids seem to be part of the same adaptive syndrome. This idea could perhaps be tested by examining the geophytic orchid floras of Florida and/or temperate Europe, where the range of substrates includes nutrient-poor sands.
https://botanicalgarden.berkeley.edu/wp-content/uploads/2016/05/Newsletter-1993-2.pdf
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