Plasticfruits, part 5: the case of Dioscorea (Dioscoreaceae)

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...continued from https://www.inaturalist.org/journal/milewski/73269-plasticfruits-the-case-of-chenopodium-amaranthaceae#

The herbaceous genus Dioscorea (https://link.springer.com/chapter/10.1007/13836_2021_94 and https://biblio.iita.org/documents/U11InbkBhattacharjeeDioscoreaNothomDev.pdf-61e9e4ea95947bbb95aa36658f29059c.pdf) contains more than 600 spp.

It occurs on all vegetated continents, and many islands (please scroll to map in http://sanjeetbiotech.blogspot.com/2012/11/dioscoreaceae-family-of-flowering.html).

There is significant variation in the vegetative features. For example:

the leaves vary from simple to compound (https://www.jstor.org/stable/4111021),
three clades within the genus, namely subgenus Dioscorea, section Stenophora, and section Pseudostenophora, have rhizomes, in contrast to the usual stem-tubers (https://www.jstor.org/stable/2473209 and https://www.jstage.jst.go.jp/article/apg/71/3/71_202003/_pdf and https://okayama.elsevierpure.com/en/publications/a-revised-infrageneric-classification-of-old-world-species-of-dioand https://www.jstage.jst.go.jp/article/apg/71/3/71_202003/_article/-char/ja/ and https://cir.nii.ac.jp/crid/1391412326424452608 and https://repository.kulib.kyoto-u.ac.jp/dspace/bitstream/2433/253476/2/grigk04620.pdf),
some spp. are succulent caudiciforms, with pachycaul above-ground tubers (https://succulent-plant.com/families/dioscoreaceae.html and https://powo.science.kew.org/taxon/urn:lsid:ipni.org:names:317936-1),
the stem-tubers are annual in section Brachyandra of Madagascar, vs perennial in other sections (e.g. Perennia of South Africa),
axillary, above-ground (aerial) tubers (https://en.wikipedia.org/wiki/Dioscorea_bulbifera and https://strictlymedicinalseeds.com/product/wild-yam-japanese-dioscorea-japonica-packet-of-3-aerial-tubers-organic/) occur in some spp.,
some spp. are non-spinescent, whereas others are spinescent, and
there are at least three types of spines, viz. caular (https://pza.sanbi.org/dioscorea-dregeana and https://www.pestnet.org/crops-roots-tubers-yam-dioscorea-hispida-poisonous-pohnpei-fsm/ and http://www.bihrmann.com/caudiciforms/subs/dio-bas-sub.asp and http://www.cacti.co.nz/library/dioscorea-dumetorum/ and https://www.zambiaflora.com/speciesdata/species-record.php?record_id=53181), stipular (see Fig. 1C in https://naturalhistory.si.edu/sites/default/files/media/file/dioscoreaceae.pdf), and petiolar (https://naturalhistory.si.edu/sites/default/files/media/file/dioscoreaceae.pdf and https://fm-digital-assets.fieldmuseum.org/1508/080/DIOS_dios_per_15045.jpg).

However, the variation in the fruits of Dioscorea is extreme (https://idtools.org/seed_families/index.cfm?packageID=1140&entityID=5525).

Many spp. are 'doubly-adapted for dispersal by wind, by virtue of wings on both the fruits and the seeds; by contrast, a few are so clearly adapted for dispersal in the gastrointestinal tracts of birds that they were formerly assumed to constitute a separate genus (Tamus).

CAPSULES

A clade of spp. in Brazil, in which the plants are short, has round, wingless capsules (https://www.biotaxa.org/Phytotaxa/article/view/phytotaxa.163.4.3 and https://www.scielo.br/j/hoehnea/a/jvRrZ6KKC5rYwx7bXfk96sF/?lang=en&format=html and https://link.springer.com/article/10.1007/s12225-016-9635-8).

Most of the sections and spp. of Dioscorea bear winged, dehiscent capsules, containing seeds that

lack wings (e.g. section Borderea of the Pyrenees, and section Afroborderea of West Africa), or
in at least 15 sections, have wings (e.g. https://inspection.canada.ca/plant-health/seeds/seed-testing-and-grading/seeds-identification/dioscorea-polystachya/eng/1397668090275/1397668126629 and https://www.alamy.com/stock-photo-dioscorea-villosa-wild-yam-yamswurzel-seed-close-up-seed-size-10-12-130345643.html), which - depending on the species - occur at the base (https://www.jstor.org/stable/4111020) or apex of the seed, at both base and apex, or surrounding the whole seed.

The following show the winged, dehiscent capsules in various spp. in Australia, Asia, and North America:

Dioscorea transversa, in which the seeds themselves are also winged (https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Dioscorea~transversa and https://www.flickr.com/photos/blackdiamondimages/4206246322/ and http://lepidoptera.butterflyhouse.com.au/plants/dios/dioscorea-transversa.html),
Dioscorea hispida (https://www.dreamstime.com/royalty-free-stock-photos-dioscorea-hispida-dennst-winged-seed-blowing-wind-image32000058 and https://www.inaturalist.org/observations/166208505), and
Dioscorea villosa (https://pixels.com/featured/wild-yam-seeds-deb-fedeler.html and https://www.inaturalist.org/observations?verifiable=true&taxon_id=129324&locale=en-US).

Also please see http://www.namethatplant.net/picpage.shtml?path=/Images/ImagesFire/s0/s071011_ab2.jpg&plant=476&photo=8077 and http://www.namethatplant.net/plantdetail.shtml?plant=476.

SAMARAS

One section (Rajania, restricted to the Caribbean islands) has samaras (https://www.biorxiv.org/content/10.1101/224790v1.full and https://en.wikipedia.org/wiki/Samara_(fruit) and https://www.plant-ecology.com/EN/10.17521/cjpe.2018.0053 and https://www.inaturalist.org/taxa/914933-Dioscorea-cordata) instead of capsules (https://plants.jstor.org/stable/10.5555/al.ap.specimen.k000099322 and https://plants.jstor.org/stable/10.5555/al.ap.specimen.k000099330).

BERRIES

Most relevant for this Post, one 'infragenus', namely Tamus, has succulent, bright-hued fruits (https://www.inaturalist.org/observations/168975065), and several other clades within Dioscorea also have fleshy fruits, or fruits intermediate between dehiscent capsules and fleshy fruits (e.g. Dioscorea ovinala and Dioscorea anataly of Madagascar, https://www.ingentaconnect.com/content/aspt/sb/2005/00000030/00000004/art00005 and https://www.researchgate.net/publication/250054391_A_Plastid_Gene_Phylogeny_Of_the_Yam_Genus_Dioscorea_Roots_Fruits_and_Madagascar).

The best-known examples are Dioscorea communis (https://www.inaturalist.org/taxa/82691-Dioscorea-communis) and Dioscorea orientalis (https://www.inaturalist.org/taxa/496089-Dioscorea-orientalis), which occur in the Canary Islands and Madeira (https://en.wikipedia.org/wiki/Macaronesia), Europe, the Maghreb, the Caucasus, and the Levant.

It is remarkable enough that a single genus stretches from samaras (with specialised dispersal of the diaspore by wind) to fleshy fruits (with specialised dispersal and sowing by birds).

However, what is particularly remarkable is that the variation in fruit-form cuts across the clades within the genus. This suggests that variation in fruit-form has arisen independently, in the evolutionary process, repeatedly within Dioscorea.

Dioscorea communis and D. orientalis, bearing red berries attractive to seed-dispersing birds, are most closely related to section Borderea, in which the fruits are capsules, containing seeds that lack wings (https://academic.oup.com/aob/article-abstract/131/4/635/6995440?redirectedFrom=fulltext&login=false and see Fig. 2a, on page 190, in https://www.jstage.jst.go.jp/article/apg/71/3/71_202003/_pdf).

CONCLUSIONS

In summary, fleshy fruits within Dioscorea are clearly-defined morphologically and adaptively, but poorly-defined phylogenetically. This further exemplifies the evolutionary plasticity of fruits within genera worldwide - which is the focus of this series of Posts.

ILLUSTRATIONS OF FLESHY FRUITS (succulent berries) IN DIOSCOREA:

Dioscorea communis:

https://www.inaturalist.org/observations/134028799
https://www.inaturalist.org/observations/171461763
https://www.inaturalist.org/observations/167520182
https://www.inaturalist.org/observations/146785572
https://www.inaturalist.org/observations/143725011
https://www.inaturalist.org/observations/141252088
https://www.alamy.com/stock-photo-young-blackcap-sylvia-atricapilla-and-black-bryony-tamus-communis-28187925.html?imageid=3B3FC1F6-6E4C-4CEA-96A6-19903E9F6CC3&p=70471&pn=1&searchId=258e88c085469378f74257459438288a&searchtype=0
https://www.alamy.com/kingfisher-alcedo-atthis-female-kingfisher-perched-amongst-black-bryony-tamus-communis-england-autumn-image184124218.html?imageid=BE5DAA3B-5601-412D-A7EB-E40E89F291C9&p=703368&pn=1&searchId=258e88c085469378f74257459438288a&searchtype=0
https://www.alamy.com/stock-image-scarlet-berries-of-black-bryony-tamus-communis-hanging-from-a-tree-163016632.html?imageid=40F845D2-723A-4639-B446-F98671953773&p=75359&pn=1&searchId=258e88c085469378f74257459438288a&searchtype=0