Botanic Gardens Trust, Sydney, Australia


Amazing Double Discovery in Australia

Overlooked, kept in the dark, and fed on mushrooms: the peculiar lifestyle of Danhatchia australis and its amazing double discovery in Australia.

Peter Weston, Senior Principal Research Scientist    

Imagine a creature that burrows through the soil of its rainforest home, its elongated, pale flesh-coloured body lying just a few centimetres below the leaf litter, slowly consuming its favorite fungus as it goes, emerging above ground for only a couple of months a year to engage in an orgy of sexual reproduction with itself.

The ‘creature’ I have in mind is not a worm, nor any other kind of animal, but an orchid, Danhatchia australis. The most surprising thing about this plant is not the bizarre life style that I have just described, which is actually not all that unusual for an orchid, but the fact that it has turned up twice at widely separated sites in eastern Australia in the past two years, having been known for almost half a century only from New Zealand.

The only known species of Danhatchia was first described by its namesake, Edwin Daniel Hatch, from specimens collected on the North Island of New Zealand and named by him in 1963 as Yoania australis. Pigeon-holing this species into Yoania, the other four species of which are known only from southern and eastern Asia, was not a great idea. It turned out that Danhatchia is only distantly related to Yoania - they are both orchids but they belong to different subfamilies, the most basic subdivisions of the Orchidaceae - and their close resemblance is largely superficial. Other botanists transferred Yoania australis to the new genus, Danhatchia, in 1995.

Danhatchia was first discovered in Australia in December 2010, by a botanical enthusiast, John Stockard, in a rainforest nature reserve on the mid north coast of New South Wales, when he found a small clump of pale, flesh-coloured, leafless stems bearing closed flower buds on the trackside. Although he did not recognise the plant, he thought it looked like an orchid, so he emailed a photograph of it to the  National Herbarium of New South Wales for identification. Trust Technical Officer Wayne Cherry and I made a quick dash up the Pacific Highway to observe it and collect specimens and we were able to confirm its identity as Danhatchia australis. Amazingly, another group of botanists, led by Greg Steenebeke, discovered a second population in a national park on the Central Tablelands in January 2012. One is led to wonder how rare this species really is and how many other populations of this elusive orchid have gone undetected. We plan to conduct more targeted searches for it in coming summers but Danhatchia australis will almost certainly remain a rare plant. We are fortunate that both of the sites at which it has been found in Australia are protected areas.

Danhatchia is what botanists call ‘mycoheterotrophic’, which literally means ‘feeding on fungi’. For most of the year it grows only as a network of subterranean stems and roots but for a couple of months in summer, leafless aerial stems emerge, bearing self-pollinating flowers that rarely open, and which quickly develop into capsules containing thousands of microscopic seeds. In New Zealand, this species parasitizes the common puffball fungus, Lycoperdon perlatum, which has an association with the roots of a native laurel tree, the taraire, Beilschmiedia tarairi. Danhatchia is usually found growing with tarairi in the wild. We know nothing yet of the intimate associates of Danhatchia in Australia but as the common puffball is a cosmopolitan species that is associated with the roots of a wide range of different trees, Danhatchia probably relies on the same fungus here. This kind of parasitic relationship is not unusual in orchids, in fact all species of orchids are thought to be parasitic on their mycorrhizal fungi, at least to germinate from their minute seeds into tiny seedlings. Danhatchia and other mycoheterotrophs have evolved to an extreme state of specialization where they rely completely on their fungus for their whole lives, dispensing with leaves, chlorophyll and photosynthesis altogether. This gives the plants their surreal, carnal appearance, rather like a collection of randomly reconnected body parts.

Other mycoheterotrophic orchids that botanically interested people are likely to recognize include the potato orchids (Gastrodia), hyacinth orchids (Dipodium) and underground orchids (Rhizanthella). But Danhatchia is unusual in being the only species in the group to which it belongs, the jewel orchids, that has evolved down the leafless path. Most other species of jewel orchids are tropical rainforest plants that have retained beautifully veined or variegated leaves, hence their collective nick-name. Like many other leafless orchids, Danhatchia lives in colder environments than its close leafy relatives and it could be that losing leaves has released these plants from a constraint that has restricted many leafy orchids to warmer climates.

A fascinating feature of all orchids, including Danhatchia, is the way they parasitise their mycorrizal fungi. This process might be better described as ‘consumption’ than ‘parasitism’. The fungal threads invade the outer cell layers of the roots and/or stems and actually penetrate the ‘digestive cells’. This is where they come in for a shock. The fungal hyphae are induced by the plant to form into clumps or ‘peletons’, which are then digested by the orchid cells, appropriating all of the hyphal nutrients. Since many of the species of fungi that are exploited by orchids are plant pathogens, it is tempting to see this predatory behavior as a way for plants to get one back on their fungal enemies.