Friday Fellow: Fungus Root

by Piter Kehoma Boll

Plants are the standard organism when one thinks of photosynthesis, but several species have actually lost the ability to synthesize their own food using light and have become completely heterotrophic. As a result, such plants survive by parasitizing other plants and feeding on their sap. Probably the most famous species of heterotrophic plant is Rafflesia arnoldii, the corpse flower, which has the largest flowers of any plant and was one one our first Friday Fellows almost 10 years ago. But today I will introduce you another, completely unrelated heterotrophic plant, Balanophora fungosa, commonly known as the fungus root.

This species occurs across southeast Asia and Australia, where it lives on the soil and parasitizes the roots of several different plants. As with most heterotrophic plants, the fungus root spends most of its life underground as nothing but a system of roots and rhizomes attached to the host plant. It is only visible on the surface when it produces its flowers, which, like the giant flower of the corpse flower, are also very unusual.

A group of inflorescences coming out of the ground in New Caledonia. We can see the pale bracts and the velvet-like club of female flowers surrounded by the larger male flowers at the base. Photo by iNaturalist user juju98.*

The flowers occur in inflorescences that are actually kind of cute. The overall color varies from pale cream, almost white, to pink. The base of the inflorescence has several bracts (modified, flower-associated leaves) that have the same pale cream to pink color, without any sign of green. The upper part has a club-shaped structure with a velvet-like surface formed by hundreds of tiny female flowers. Surrounding the base of the club are a few male flowers, which are much larger than the female flower, but still very small. The inflorescence as a whole looks similar to some mushrooms, such as puffballs, which is probably the reason for its common name fungus root.

A closeup of an inflorescence in Australia where we can see the male and female flowers in more details. Photo by Aaron Bean.*

I couldn’t find many details about the life cycle of this cute parasite, but it seems to be pollinated by an enormous range of animals, including several types of insects, arachnids and even small vertebrates, which may be attracted to feed on the pollen and nectar or perhaps tricked by the unusual smell that the flowers produce. The smell is unlike the sweet fragrance of most flowers but is also not an unpleasant smell of carrion like that of the corpse flower, the titan arum and so many other plants. Actually, it is said that the flowers smell like a mouse. Perhaps it tricks small mammals to think it is a reproductive member of their species just like some orchids do by mimicking the shape and smell of female bees? This is a possibility, but actually most of the small mammals and birds that visit the flowers are actually nectarivores and are probably only looking for the delicious nectar.

Anyway, there is a lot we still don’t know about this unusual but adorable fungus-like plant.

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References:

Hsiao, S. C., Huang, W. T., & Lin, M. S. (2010). Genetic diversity of Balanophora fungosa and its conservation in Taiwan. Botanical studies, 51(2). https://ejournal.sinica.edu.tw/bbas/content/2010/2/Bot512-10.pdf

Pierce, R., & Ogle, C. (2017). Musky Rat Kangaroos and other vertebrates feeding from the flowers of the root parasite’Balanophora fungosa’. North Queensland Naturalist, 47, 14-20. https://search.informit.org/doi/pdf/10.3316/informit.461078578600745

Wikipedia. Balanophora fungosa. Available at < https://en.wikipedia.org/wiki/Balanophora_fungosa >. Access on 8 July 2022.

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* This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.