The plant family Burmanniaceae is a long-standing botanical heartthrob (#Botanicalheartthrob) of mine. Ghost-like obligate parasites, bound by their evolutionary heritage to a strange existence amongst the fallen debris that litters a forest floor, the Burmaniaceae feed on fungus.
The condition of this odd plant variety is called mycoheterotrophism. It’s a parasitic relationship between certain plants and fungi, where the plant derives some, if not all, of it’s food by parasitising the fungus.
That’s right. Instead of feeding on sunlight like good old regular plants, mycoheterotrophs feed on fungus. Cheaters.
Amazingly, many of the Burmanniaceae have completely lost their ability to photosynthesise. They are achlorophyllous (pronounced ‘ay-cloro-fi-lus’), meaning they have no chlorophyll. In other words,none of the cellular centres for converting harvested sunlight into sugars that feed the plant.
No chlorophyll at all folks. That’s like being an animal without a stomach.
The habit of plants deriving at least some nutrition from fungus has evolved several times independently, including in both monocots and eudicots, and is most prolifically represented among the Orchidaceae (orchids) and Ericaceae (e.g. Epacris impressa, the stunning floral emblem of Victoria). Similarly, it is likely that the extreme, obligate fungus-sucking habit necessitated by a complete evolutionary loss of chlorophyll has arisen several times independently within the Burmanniaceae family alone (Merckx et al. 2008). Their abhorrent behaviour is considered an adaptation to deal with the dank, dark, low light conditions that persist on the forest floor (Bidartondo et al. 2004).
As the first fungus-sucking plants I had knowingly encountered, Burmaniaceae instantly captured my imagination. Too many zombie films, perhaps, but also a novel insight into the oddities of natural selection.
There is considerable conflicting information available on the number of genera and species within the family Burmanniaceae. Listings range from between seven and seventeen genera, and 95 to 159 species (see also Merckx et al. 2006). It is unclear whether this issue is due to conflicting opinions on synonymous species (where some botanists believe two differently named species constitute one and the same), synonymy of the families Burmanniaceae and Thismiaceae, or outdated information on a number of online databases and in the literature.
“…eking out what appears a rather diminished and utterly fragile existence for a traditionally photosynethic organism…”
According to the APG IV system (Angiosperm Phylogeny Group: APG IV 2016), a modern, mostly molecular-based system of classifying flowering plants, there are eight genera in the Burmanniaceae family, comprising some 96 species of fungus-sucking plants.
The biggest of these genera, Burmannia, includes roughly two thirds of these species, and is spread across tropical and subtropical parts of Africa, Oceania and the Western Hemisphere. The next largest genus is Gymnosiphon, comprising 24 species across the Old and New World tropics, but the remaining genera are far less speciated; Apteria (3 species, tropical and subtropical America), Dictyostega (1 species, Mexico and Brazil), Marthella (1 species, Trinidad), and four genera native to tropical S. America, including Campylosiphon (1 species), Cymbocarpa (2 species), Hexapterella (2 species) and Miersiella (1 species).
In Australia, Burmanniaceae is represented by just two native species; Burmannia juncea (above left), native to Northern Australia (swampy areas, streamsides and wetlands), and Burmannia disticha, native to the east coast of NSW and QLD (swamps and wetlands in coastal regions). According to the Atlas of Living Australia, a community science database on the continent’s flora and fauna, the southeast Asian B. coelestis (Zhang & Saunders 2000) also occurs across far northern Australia. But these particular species are not obligate mycoheterotrophs.
Despite eking out what appears a rather diminished and utterly fragile existence for a traditionally photosynethic organism, these little creeps, at least in Australia, are considered not threatened and of least conservation concern.
Good job zombie herbs. Keep on keeping on.
Online references are linked to via in-text hyperlinks.
APG IV (2016) An update of the Angiosperm Phylogeny Group classification for the orders and families of flowering plants: APG IV. Botanical Journal of the Linnean Society 181 (1): 1–20. doi:10.1111/boj.12385.
Bidartondo M. I., Burghardt B., Gebauer G., Bruns T. D. & Read D. J. (2004) Changing partners in the dark: isotopic and molecular evidence of ectomycorrhizal liaisons between forest orchids and trees. Proceedings of the Royal Society of London B 271: 1799–1806.
Merckx V., Chatrou L., Lemaire B., Sainge M., Huysmans S. & Smets E. (2008) Diversification of myco-heterotrophic angio- sperms: evidence from Burmanniaceae. BMC Evolutionary Biology 8: 178.
Merckx V., Schols P., Kamer H. M.-V. D., Maas P., Huysmans S. & Smets E. (2006) Phylogeny and evolution of Burmanniaceae (Dioscoreales) based on nuclear and mitochondrial data. American Journal of Botany 93: 1684–1698.
Morton, J.B., Walker, C. (1984) Glomus diaphanum: A new species in the Endogonaceae common in West Virginia. Mycotaxon 21: 431-440.Zhang D. & Saunders R. M. K. (2000) Systematics of the Burmannia coelestis complex (Burmanniaceae). Nordic Journal of Botany 20: 385–394.
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