It has been quiet for a while here, but that doesn’t mean nothing has happened. On the contrary, I am happy to report that a project proposal on mycoheterotrophy was funded by the European Research Council. In the project, named MIXOTROPH, I will test the hypothesis that many green plants can take up carbon from mycorrhizal fungi, just like the fully mycoheterotrophic plants featured on this site. Exciting times ahead!
More info about the project here:
The genus Burmannia (Burmanniaceae) is one of the few genera of flowering plants that contain both green species and non-green fully mycoheterotrophic species. Therefore, it is an excellent model to study the change in fungal partners that accompanies the evolution of mycoheterotrophy.
Zhongtao Zhao and a team of coauthors investigated the fungal communities in the roots of different species of Burmannia from Asia – both green and non-green – using DNA sequencing methods. Here you see the how each of the analysed specimens interact with arbuscular mycorrhizal fungi:
Although many fungal species were shared by different Burmannia species, fully mycoheterotrophic species typically host more narrow fungal assemblages, suggesting that they have a preference for the selected fungi. These fungi are a subset of the partners found in the green species, suggesting that the specialisation results from a loss in fungal partners.
Full paper:
Mycoheterotrophs never fail to fascinate. With their rarity and weird shapes they really are the aliens of the plants world. Some species, like the mythical Thismia americana, almost reach a ‘Loch Ness monster’ status: seen a few times, a long time ago, and never again. Yet maybe, somewhere, it is still out there…
In 2013 I wrote:
“Since many mycoheterotrophic species, particularly those occurring in tropical rainforests, grow in inaccessible areas and are extremely difficult to spot, it is impossible to declare any mycoheterotrophic species as extinct with confidence. Even when the type locality is destroyed and a species has not been seen for many decades, it is still possible that other populations escaped discovery. Sometimes species have been rediscovered after a notably long hiatus. Haplothismia exannulata (Thismiaceae) was rediscovered at its type locality in India in 2000, 49 years after its discovery and only a few years after being declared “extinct” (Sasidharan and Sujanapal 2000). The second collection of Thismia clavigera (Thismiaceae) was made 115 years after the first and over 1,000 km from the type locality (Stone 1980)”
And this is exactly what happened with Thismia neptunis. Discovered in Borneo by Italian botanist Odoardo Beccari in 1866, and beautifully illustrated by him:
Thismia neptunis (from Beccari 1878)
This marvelous species was recently rediscovered by Czech botanist Michal Sochor and colleagues, in Sarawak, Borneo, probably near or at the same locality as it was seen for the first time, 151 years ago. These rediscoveries are always great news, and fuel hopes that other assumed-extinct species are still waiting to be found again.
Thismia neptunis (from Sochor et al. 2018)
The paper Sochor et al. Phytotaxa (2018) can be found here.
EDIT: The original collection year was wrongly stated as 1876. Thanks @AdrienCoffinet for spotting this.
A while ago, Wetenschap.nu made these really nice vlogs about our field trip in Colombia. The videos didn’t pick up a lot of attention, but nevertheless I am happy that they are out. Now everyone who is interested can see and experience what is like to go on a field trip. Moreover, I hope the videos give an idea about why we go to these remote places, and how we search and sample mycoheterotrophic plants.
In the first video I try to explain our goals, and show the places we will visit in Colombia.
In the second video, it is time to enter the rain forest. We travel to the beautiful coastal forests of Chucheros, and almost immediately find what we are looking for: mycoheterotrophic plants!
In the third video you see how we sample the plants and we show that the work does not stop after returning to basecamp. Cleaning and sorting the samples may not be very adventurous, it is an essential step in the whole process.
After sampling in Chucheros, on the Pacific coast of Colombia, we travel to Letitia, along the Amazon river, and then to Capurgana, on the Caribbean coast. You get a flavour of these adventures in the fourth video.
Obviously, the sampling is just the very beginning of the project. After out return to the Netherlands we process the sampled in the lab. How is that done? Discover it in the fifth and last video!
At the time of writing the material and data collected during this trip is still being analysed, but if everything is going well we should get the first results out soon!
This blog has been quiet for a while due to a recurring health issue. Last December my left lung spontaneously collapsed again (5th time). So unfortunately, the two surgeries I received earlier had failed. Just before Christmas I underwent another surgery and I am currently recovering at home. I expect to make a full recovery.
I hope 2018 will be a year without hospital visits, and with some long-overdue papers finally being submitted and published. I also plan to update and strengthen this website, so that it will become a real hub of mycoheterotrophic plant knowledge. Stay tuned!
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 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 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
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).
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:
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
If you have ever searched for mycoheterotrophic plants in rain forest, you may be familiar with this phenomenon:
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.
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
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.
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.
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)
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
mycoheterotrophy 