Range extensions of Thismia and Geosiris

Despite being often locally rare, mycoheterotrophic plants can have large distribution ranges, spanning many countries and even multiple continents. Likewise, many genera of mycoheterotrophic plants have broad distribution ranges. For example, Monotropa (Ericaceae) occurs throughout all temperate regions in the northern hemisphere, and even reaches tropical latitudes (on mountains). Sciaphila (Triuridaceae) can be found in nearly all tropical forests in the world.

Our knowledge of plant distribution ranges is based on plant collections. Once in a while, a new discovery significantly extends the known distribution range of a species, genus, or family. In the last few months, two new discoveries have been published that requires us to update the known distribution ranges of Thismia (Thismiaceae) and Geosiris (Iridaceae).

The genus Thismia is know from tropical rain forests in South America and Asia, and its distribution extends into subtropical and temperate areas in Japan, Australia, and New Zealand (and strangely enough also Chicago, USA). However, the genus is absent in the Pacific islands, Africa, Madagascar, and India. The latter can now be included in the list, since Indian researchers found a new species of Thismia in the Western Ghats. The new species, Thismia sahyadrica, is the first record of the genus from the Western Ghats, a tiny strip of rain forest in western India with biogeographical links to both Madagascar and Asia. The family Thismiaceae was already known to occur here (the enigmatic Haplothismia exannulata is endemic to the Western Ghats), but Thismia had so far only be found on Sri Lanka and not on the Indian main land.

Thismia sahyadrica

Thismia sahyadrica from the Western Ghats (India) – Sujanapal et al. (2017)

A much larger expansion of distribution range is caused by the discovery of a new species of Geosiris in tropical Australia. Geosiris was know to occur only in eastern Madagascar (G. aphylla) and on the Comoros (G. albiflora). Recently, pictures emerged of a specimen of Geosiris from Mindanao, an island of the Philippines (see here), suggesting that the genus might have a much wider distribution than previously assumed. And indeed, the discovery of Geosiris australiensis, in a rain forest in Australia, a whopping 5,400 km from Madagascar, has now confirmed this.

Geosiris australiensis

Geosiris australiensis from Daintree National Park (Australia) – Grey & Low (2017)

These remarkable discoveries, once again, show us how much there is still to discover about these intriguing plants. And how important it is to keep looking. Expect the unexpected!

Sources:

Sujanapal et al. (2017) Thismia (Thismiaceae): the first record of the mycoheterotrophic genus to the Flora of India with a new species revealing the phytogeographical significance of Western Ghats. Blumea

Grey & Low (2017) First record of Geosiris (Iridaceae: Geosiridoideae) from Australasia : a new record and a new species from the Wet Tropics of Queensland, Australia. Candollea

 

The biogeographic history of below-ground interactions: Thismia in Australia and New Zealand

Species of Thismia may are in my biased opinion the most remarkable and mysterious plants on this planet. But studying them is complicated, as most species are known from only very few collections made in remote rain forest areas. Luckily, there are exceptions. In Australia and New Zealand there are a few species of Thismia, and in recent years more and more localities have been discovered. Nevertheless, even down under Thismia has a very patchy distribution and is considered to be a very rare plant.

Since these plants rely entirely on their mycorrhizal fungi for survival, they are excellent examples to study potential limitations in their distribution due to their interactions. In other words: if their preferred fungus is absent in a region, do they fail to colonize this region, or can they adapt and start exploiting another fungus? That is exactly what I wanted to address in the project ‘Does specialization lead to rarity?’ funded by the Netherlands Organization for Scientific Research (NWO).

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Thismia clavarioides (Thismiaceae) – Morton National Park, Australia

First of all, we needed samples. With the help of several local experts we collected specimens of Thismia from as many populations as possible in Australia and New Zealand. This was an unforgettable experience!

We managed to sample many more populations than expected, and during the field work we discovered several new localities and even a putative new species. The DNA of all plant specimens was analyzed to reconstruct their evolutionary relationships. At the same time, we identified the mycorrhizal fungi in the roots of each plants by DNA barcoding. The results look like this:

Figure2

Almost all sampled specimens of Thismia grown with the same fungus (or very narrow lineage of fungi – we don’t really know). Only one species was found growing with an different lineage of fungi. Evolutionary reconstructions indicate that this specificity was already present in the common ancestor of these species, and apparently it did not limit the recent radiation and dispersal (from Australia to Tasmania and New Zealand) of the plants. The fungus these plants use is probably quite widespread, and does not seem to limit the distribution of the plants. Therefore, specialization is not necessarily an evolutionary disadvantage (as it is sometime seen), particularly if your host is successful and widespread.

The full paper published in Journal of Biogeography can be found here (open access): http://onlinelibrary.wiley.com/doi/10.1111/jbi.12994/full

Coexistence of mycoheterotrophic plants may be mediated by their fungal interactions

If you have ever searched for mycoheterotrophic plants in rain forest, you may be familiar with this phenomenon:

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Voyria truncata (blue) and Voyria aurantiaca (yellow) co-occurring in a rain forest in Colombia.

 

Once you find a species, more species can often be found in the direct surroundings. Many botanists who studied mycoheterotrophic plants noticed this. In his treatment of the Burmanniaceae Frederik Jonker (1938) wrote:

“It is striking that at a certain habitat often a number of species grow together, often too in company with Triuridaceae and saprophytic Gentianaceae or Polygalaceae, so that one sometimes meets in a herbarium with several saprophytic species under the same collector’s number”

“In the literature several cases of saprophytes growing together are described, see van der Pijl (1934). van der Pijl presumes that this is produced by the presence of a fungus. However it is not yet known if the endophyte of all these saprophytes is identical, it is quite likely that it is in every case a Phycomycete, probably belonging to the Peronosporaceae”

We now know that the plants Jonker mentions target Glomeromycotina (not ‘Glomeromycota’ anymore, see here). Also, research has suggested that co-existing mycoheterotrophs do not necessarily grow on the same fungus. And indeed, if the fungi are ‘food’ for the mycoheterotrophs, then having a diverse diet may help to avoid competition with other mycoheterotrophs, and promore co-existence. But if the diets of two plants are completely different, then it becomes unlikely that they co-occur. To test this hypothesis, PhD student Sofia Gomes and myself teamed with MIT professor Serguei Saavedra. Together, we explored the fungal interaction patterns of mycoheterotrophs from several sites in French Guiana and Brazil.

 

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Our hypothesis on how plant co-existence may be influenced by mycorrhizal interactions.

 

And indeed, the results show that in communities of co-occurring mycoheterotrophic plant species, the diversity of their fungal ‘diet’ appears to increase proportionally to their overlap in fungal ‘diet’. These results indicate that fungus-plant interactions can be better explained by understanding plant–plant interactions generated by sharing resources or fungal hosts.

It remains to be tested whether this symmetry between diversity and overlap in fungal diet may respond to an ecological mechanism driven by maximizing co-occurrence and avoiding competitive exclusion among mycoheterotrophic plants. However, the results show that plant coexistence cannot be fully understood without attention to their underground interactions.

The paper can be found here (open access): http://onlinelibrary.wiley.com/doi/10.1002/ece3.2974/full

Field work in Colombia 2016

We just finished an exciting and adventurous collection trip in Colombia. We collected mycoheterotrophic plants in three different areas in Colombia (see map below). Reaching these places was often a challenge, but always rewarding! We found and collected a lot of mycoheterotrophs, including many species we have never been able to sample before. The list of observed species is presented at the end of this post.

map_colombia-001

Areas in Colombia where we sampled.

It was a privilege to explore the remote rain forest of the Choco and Amazonas area – and see the mighty Amazon river in person! The purpose of this trip was not only to collect mycoheterotrophic plants, but also to obtain data for a study on the ecological drivers of mycoheterotrophy.

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Rain forest in the Amazon region of Colombia

Apart from taking pictures, we recorded a lot of video during our trip. These videos will be used to produce a short documentary of the collection trip and the science behind it.

 

Chucheros

Soridium sp. (Triuridaceae)
Sciaphila purpurea (Triuridaceae)
Sciaphila aff. polygyna (Triuridaceae)
Voyria tenella (Gentianaceae)
Voyria aphylla (Gentianaceae)
Apteria aphylla (Burmanniaceae)
Gymnosiphon divaricatus (Burmanniaceae)
Gymnosiphon panamensis (Burmanniaceae)
Gymnosiphon brachycephalus (Burmanniaceae)

Amazonas

Voyria tenella (Gentianaceae)
Voyria chionea (Gentianaceae)
Voyria pittieri (Gentianaceae)
Gymnosiphon divaricatus (Burmanniaceae)

Capurgana

Sciaphila albescens (Triuridaceae)
Voyria aurantiaca (Gentianaceae)
Voyria flavescens (Gentianaceae)
Voyria corymbosa (Gentianaceae)
Voyria aff. truncata (Gentianaceae)
Voyria pittieri (Gentianaceae)
Apteria aphylla (Burmanniaceae)
Gymnosiphon sp. (Burmanniaceae)

The diet of mycoheterotrophic plants

Since the hallmark papers of Ken Cullings et al. (1996) and Martin Bidartondo et al. (2002) – both in Nature – many studies have reported on the high mycorrhizal specificity of mycoheterotrophic plants. But specificity is a relative thing, and may differ over the geographic distribution of a species. Therefore Sofia Gomes compared the mycorrhizal specificity of several Thismia species in Australia and New Zealand with that of surrounding plants. She found that mycoheterotrophs always chose for a very specific lineage of fungi, unlike green plants for which mycorrhizal interactions are much less specific. The results were recently published in the journal New Phytologist.

http://onlinelibrary.wiley.com/doi/10.1111/nph.14249/full

thismia-026

Website launched!

I own this domain for several years, but never found the time to develop my plans: built an attractive website that sheds light on some of the most intriguing plants on our planet: mycoheterotrophs.

Thanks to (?) some serious health issues that have grounded me this summer (and the previous one) I was finally able to develop this site. The website, which will be forever ‘under construction’, provides an overview of the enigmatic plants, some information about their taxonomy and ecology, and – most importantly – shows a lot of pictures. Because the plants deserve to be seen!

With this blog I plan to highlight news on mycoheterotrophs. New species, publications, amazing pictures,… it all deserves to be here.

Enjoy!

Group portret

The author looking at Epirixanthes cylindrica in a rain forest in Borneo