THE PUZZLE
Dodonaea viscosa (https://www.inaturalist.org/taxa/122711-Dodonaea-viscosa and https://prota.prota4u.org/protav8.asp?g=pe&p=Dodonaea+viscosa and https://www.anbg.gov.au/gnp/interns-2007/dodonaea-viscosa.html and https://anpsa.org.au/APOL27/sep02-1.html) is biologically puzzling in at least six ways.
Firstly, it is uniquely cosmopolitan for a woody plant (https://www.mq.edu.au/__data/assets/pdf_file/0005/1275341/Plant-of-the-week-Dodonaea-viscosa-Hop-Bush-ed-2.pdf). Long before human influence, it spread naturally across several oceans and then far inland on several continents.
Secondly, this wide natural distribution was achieved despite the fact that 60 other members of the same genus remain restricted to the same continent - and in many cases the same landscapes - from which D. viscosa originated.
Thirdly, its original occurrence was on a landmass, namely the 'island continent' of Australia/Sahul (https://en.wikipedia.org/wiki/Sahul), that has never been connected to any continent by a land-bridge.
Fourthly, its diaspores seem not to be particularly adapted for long-distance dispersal.
It is true that the seed-capsules have papery wings, suggesting anemochory (https://www.dictionary.com/browse/anemochory), and the seeds survive immersion in sea water (West, 1984, https://www.publish.csiro.au/sb/BRU9840001).
However,
Fifthly, D. viscosa is 'polymorphic', in a way incongruent with subspeciation/raciality/ecotypy (https://en.wikipedia.org/wiki/Ecotype and https://digital.library.adelaide.edu.au/dspace/handle/2440/119801 and https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2699.2009.02176.x).
In a given population, the leaves may take a distinctive form (e.g. https://wtlandcare.org/details/dodonaea-viscosa-subsp-cuneata/) without any geographical isolation from other forms (see 'key to the subspecies' in https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Dodonaea~viscosa).
By the same token, the leaves may remain true to form despite having been subjected to environmental pressures and 'genetic drift' on a completely different continent for hundreds of thousands of years.
Sixthly, D. viscosa has remarkably dense wood (https://www.inaturalist.org/journal/milewski/100396-a-plant-that-seems-to-defy-biogeographical-and-evolutionary-rules-dodonaea-viscosa-sapindaceae-part-2-wood-density#).
DISCUSSION
The literature lacks any satisfactory hypothesis on how D. viscosa achieved its unique spread, either ecologically or mechanistically.
The following review of fruit-form and seed-dispersal in the family Sapindaceae, more generally, highlights the puzzle.
No sapindaceous plant seems to be adapted for long-distance dispersal.
This is because
In Dodonaea, the aril is an outgrowth of the funicle (West, page 33). It is
Two relevant mysteries are
Please also see https://www.inaturalist.org/journal/milewski/100103-a-comparison-of-sapindaceae-in-the-mediterranean-and-adjacent-arid-climates-of-australia-and-southern-africa#.
to be continued in https://www.inaturalist.org/journal/milewski/100396-a-plant-that-seems-to-defy-biogeographical-and-evolutionary-rules-dodonaea-viscosa-sapindaceae-part-2-wood-density#...
Comentarios
https://keys.lucidcentral.org/keys/v3/eafrinet/weeds/key/weeds/Media/Html/Dodonaea_viscosa_(Sand_Olive).htm
https://onlinelibrary.wiley.com/doi/10.1111/j.1365-2699.2009.02176.x
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6007226/
https://www.florabank.org.au/static/34de8e9cf148e1ad3883d6a8c378a317/f9412fca697f7dd0b9c87c6def4556ef.pdf
https://qldnativeseeds.com.au/plant-profiles/dodonaea-viscosa-subsp-cuneata
https://profiles.ala.org.au/opus/foa/profile/Dodonaea%20viscosa
https://waterwisegardenplanner.org/plants/dodonaea-viscosa-purpurea/
https://prota.prota4u.org/protav8.asp?g=pe&p=Dodonaea+viscosa
https://onlinelibrary.wiley.com/doi/10.1111/j.1442-9993.1995.tb00573.x
https://www.publish.csiro.au/sb/BRU9840001
https://www.inaturalist.org/taxa/367314-Dodonaea-madagascariensis
https://academic.oup.com/aob/article/101/9/1349/132874
https://www.researchgate.net/profile/Ganesh-Jaganathan/publication/268431247_Role_of_seed_sowing_time_and_microclimate_on_germination_and_seedling_establishment_of_Dodonaea_viscosa_Sapindaceae_in_a_seasonal_dry_tropical_environment_-_an_insight_into_restoration_efforts/links/54aa86d20cf25c4c472f2fa1/Role-of-seed-sowing-time-and-microclimate-on-germination-and-seedling-establishment-of-Dodonaea-viscosa-Sapindaceae-in-a-seasonal-dry-tropical-environment-an-insight-into-restoration-efforts.pdf
https://www.sciencedirect.com/science/article/pii/S1319562X20302163
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC7451594/
https://lkcnhm.nus.edu.sg/wp-content/uploads/sites/10/2021/05/NIS-2021-0039.pdf
https://florabase.dbca.wa.gov.au/browse/profile/4782
https://anpsa.org.au/APOL27/sep02-1.html
In North America, there are two 'subspecies' of Dodonaea viscosa that occur nowhere else, viz. elaeagnoides (https://repository.naturalis.nl/pub/524969/) and arizonica.
The following illustrates the narrow leaves of arizonica:
https://www.inaturalist.org/observations/210564468
For comparison, the following illustrates angustifolia, in the same species, in South Africa:
https://www.inaturalist.org/observations/240383919.
What is the difference?
In southern Africa, there are two 'subspecies', viz. viscosa and angustifolia (https://treesa.org/dodonaea-viscosa/).
https://en.wikipedia.org/wiki/Atalaya_(plant)
https://www.perplexity.ai/search/in-which-genera-of-sapindaceae-WEyA7VFYSvayb3_UnE7xsA
Page 73 in West (1984):
Dodonaea rigida (https://www.inaturalist.org/observations?taxon_id=1413116) seems foliar-spinescent.
https://onlinelibrary.wiley.com/doi/abs/10.2307/1220777
https://academic.oup.com/aob/article/104/5/833/138202?login=false
https://openjournals.library.sydney.edu.au/TEL/article/view/14438
https://www.environment.nsw.gov.au/topics/animals-and-plants/threatened-species/nsw-threatened-species-scientific-committee/determinations/final-determinations/2008-2010/dodonaea-stenozyga-critically-endangered-species-listing
https://toowoombaplants2008.blogspot.com/2013/10/
https://pza.sanbi.org/erythrophysa-alata
@iancastle @lloyd_esler @alan_dandie @tonyrebelo @arthur_chapman
The interpretation of variation within D. viscosa in the literature seems garbled and nonsensical. I suspect that this is mainly because the whole concept of subspeciation (https://en.wikipedia.org/wiki/Subspecies) does not apply to this species in the first place.
Various 'subspecies' of Dodonaea viscosa are described in https://anpsa.org.au/plant_profiles/dodonaea-viscosa/, where the spelling 'spathulata' is used.
Further information is presented in https://www.anbg.gov.au/gnp/interns-2007/dodonaea-viscosa.html and https://www.florabank.org.au/static/34de8e9cf148e1ad3883d6a8c378a317/f9412fca697f7dd0b9c87c6def4556ef.pdf.
As an example of the incoherence of the literature, w.r.t. the so-called 'subspecies' of Dodonaea viscosa, please consider 'spatulata'.
This 'subspecies' a) is reported right across Australia, from Perth to Sydney, yet b) remains sympatric with several other 'subspecies'.
In Perth, Powell (1990, https://catalogue.nla.gov.au/catalog/362451), on pages 90-91, describes 'spatulata' as the only form present. This classification is inconsistent with the accompanying illustrations, which do not show the leaf-shape claimed.
In and near Sydney, 'subsp. spatulata' is again reported, with the claim of synonymy with 'var. arborescens', and the caveat that it 'shows a great amount of leaf morphological variation, with leaf characters intergrading with those of subsp. angustissima, subs. cuneata and subs. mucronata' (https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?lvl=in&name=Dodonaea~viscosa+subsp.~spatulata&page=nswfl).
In https://profiles.ala.org.au/opus/foa/profile/Dodonaea%20viscosa%20subsp.%20spatulata, 'subsp. spatulata' is described as occurring over most of Australia, including Tasmania.
In Victoria (https://vicflora.rbg.vic.gov.au/flora/taxon/9fe71aed-2b5c-46df-b229-a52c25b23518), 'subsp. spatulata' is confusingly described as showing certain variations within the subspecies (e.g. between the Grampians and Warrandyte), yet somehow elsewhere also intergrading with subspp. cuneata and angustissima.
Overall, the current treatment seems to confuse adjective with taxonomy, not so?
Parasitisation by Viscum capense:
https://pza.sanbi.org/dodonaea-viscosa-var-angustifolia
Also see https://www.inaturalist.org/journal/milewski/80176-thought-provoking-observations-from-a-brief-visit-to-the-karoo-desert-national-botanical-garden-and-paarl-mountain-botanic-garden-october-2001.
A POSSIBLY NEW CONCEPTUAL FRAMEWORK FOR SO-CALLED SUBSPECIFIC VARIATION IN DODONAEA
In Dodonaea, there is a pattern of remarkable inconsistency in the form of the leaves. This applies both within Dodonaea viscosa, and interspecifically.
Interspecifically, I refer mainly to the distinction between simple and complex (pinnate) leaves.
Among the nearly 70 spp. of Dodonaea, many have complex leaves (https://bie.ala.org.au/species/https://id.biodiversity.org.au/node/apni/2905673), categorically different in form from simple leaves. Certain spp. have 'lobed' leaves of a shape intermediate between simple and complex (https://www.inaturalist.org/taxa/353810-Dodonaea-lobulata).
Is it possible that the variation is largely phenotypic, not genotypic? In other words, is it possible that Dodonaea is heterophyllic/heteroblastic at a generic level, as opposed to merely intraspecifically or within a given individual?
Heterophylly/heteroblasty are, by definition, phenotypic, not genotypic, phenomena, in which the variation in the form of the leaves reflects the switching on/off of certain genes.
As far as I know, no species of Dodonaea shows heteroblasty in the sense of 'juvenile' foliage.
However, even in D. viscosa, there are traces of complexity in the leaves, which are occasionally 3-toothed or minutely dentate (https://vicflora.rbg.vic.gov.au/flora/taxon/26a2dd86-3afa-43cf-8f95-83d8cf125ec2).
https://edis.ifas.ufl.edu/publication/FP181
OCHLOSPECIES
http://cronklab.wikidot.com/taxonomic-problems:the-ochlospecies-concept
https://scholar.sun.ac.za/items/ead2d8c8-3a2f-4e14-9171-47d7abe2acd0
https://profiles.ala.org.au/opus/foa/profile/Dodonaea
https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=gn&name=Dodonaea
https://florabase.dbca.wa.gov.au/browse/profile/21726
https://onlinelibrary.wiley.com/doi/am-pdf/10.1111/aec.12474
https://www.sciencedirect.com/science/article/pii/S1319562X20302163
Reference: Harrington and Driver (1995, https://onlinelibrary.wiley.com/doi/abs/10.1111/j.1442-9993.1995.tb00573.x).
Location: http://bonzle.com/c/a?a=p&p=240847&cmd=sp and https://en.wikipedia.org/wiki/Bourke,_New_South_Wales
Seed-harvesting ants (Pheidole spp., https://www.inaturalist.org/observations?place_id=6825&subview=map&taxon_id=47343) are important in regulating the abundance of seeds of Dodonaea viscosa.
The ants are initially attracted to fallen seeds by virtue of the elaiosomes. They remove the small food-body, and then discard the seeds in middens outside the entrance of the nest. The ants later take the seeds back into the nest during the cool season, storing them in chambers 2-30 cm deep.
Germination of D. viscosa is plentiful at the study site, both after fire (which breaks the dormancy of those seeds that remain on the surface, having escaped initial collection by the ants), and after unusual rains (which percolate deep enough to reach the seeds stored deep in the nests of Pheidole).
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