Multitudinous biota associate with Lophomyrtus plants

Bryophyte and Lichen growth on the lower trunk and branches of ramarama (Lophomyrtus bullata), Awaroa Scenic Reserve, Kawhia. Image by P.J. de Lange.

Lophomyrtus is a genus endemic to Aotearoa New Zealand. There are two species within the genus, ramarama (L. bullata) and rōhutu (L. obcordata), as well as their naturally occurring hybrids where the two species occur together. 

These two species are far from rare.

“Because they are so common, no one had studied them,” says Peter de Lange, corresponding author on a paper on Lophomyrtus associates, which has recently been published in Perspectives in Biosecurity.

Both species are now experiencing a rapid trajectory of decline due to their extreme susceptibility to myrtle rust. Ramarama is in decline throughout its range, with local extinctions noted in Tairawhiti / East Cape and the western Waikato. Rōhutu may be less threatened, since some of its range does not currently overlap with the current environmental range of the disease. However, the species is declining in part of its northern range where it co-occurs with the disease.

Local loss of these plants will impact the biotic communities they support, like lichens, fungi, and even bacteria. And because Lophomyrtus is an understudied genus, the associated species at risk have yet to be comprehensively identified.

Peter and colleagues set out to describe some of this community. Their study looked at bryophytes and lichens, as well as ferns and flowering plants. They found 221 taxa associated with Lophomyrtus from sampling just eight Lophomyrtus populations. Taxa found on ramarama included bryophytes (one hornwort and several liverworts and mosses), pteridophytes, spermatophytes and lichenized mycobiota. Taxa found on rōhutu included many of the above as well as one cyanobacterium and one alga.

Some of these species may be new to science.

“Some of the lichens we found are the only known examples,” says Peter.

Peter would like to see studies like this expanded to include more locations and more taxa – the study was largely limited to bryophytes and lichens. Additional microbiota, such as fungi and bacteria, would give a more complete picture of the community hosted by Lophomyrtus.

“We needed to look at what lives naturally on these trees or shrubs to see if anything interacts with myrtle rust in a positive way (enhancing its ability to infect the plant) or a negative way (helping the plant withstand or combat infection).”

Are any of the species found in this study expected to interact with myrtle rust? Peter says it’s unlikely. But the sheer volume of taxa found highlights how much more there could be to discover.

“There’s quite a lot of diversity that lives on these plants that we didn’t know about,” says Peter.