Is Drosera meristocaulis the carnivorous plant that walked?

In the classic novel The Day of the Triffids carnivorous plants hunted a blinded human population. Drosera meristocaulis cannot walk, but that makes it even more peculiar because its not found where you’d expect to find it.

Drosera meristocaulis looks and act like a pygmy sundew, a carnivorous plant that catches insects in its sticky leaves. If you want to find a pygmy sundew the best place to go is the southwestern part of Australia. Nearly all the pygmy sundews in the world live there. There’s one other species, but even that only lives in Australia and New Zealand. Nature’s messy and things might be in unexpected place, but if you didn’t know better you’d expect to find D. meristocaulis somewhere in Oceania. And you’d be wrong because it lives a long way from the other pygmy sundews. It’s endemic to a region called the Neblina massif. This is a highland area of the Amazon rainforest on the border between Brazil and Venezuela.

It’s the fact it’s endemic that’s important. Endemic isn’t the same as indigenous. Indigenous means that the species is naturally found there. Endemic means that it’s found in one place and nowhere else. The Neblina massif has a large number of endemic species. Islands are a good place to find endemic species because they’re hemmed in by the sea. In contrast the Neblina massif has no hard boundary, so what keeps its species bounded? Does the elevation of the massif keep the ecosystem effectively isolated or are there routes for colonisation? A closer look at D. meristocaulis suggests something very odd has happened.

Rivadavia et al. (2012) included Drosera meristocaulis with other Droseraceae and some other plants like Dionaea. Why ot just compare with the pygmy sundews? Why do you need so many others? The connection with the other pygmy sundews is what you want proven or disproved. Common descent means that there are going to be plenty of similarities, but will there be more similarities with an obscure branch of sundews? You won’t know until you test them.

What the team found is that Drosera meristocaulis best fits with an Australian clade of sundews. Though the exact relationship isn’t yet certain, all methods agree it is related to the Australian pygmy sundews. Further, other methods such as morphological analysis support the relationship. While this seems like an established fact, it’s a weird fact when you look at how far apart they are.

How did D. meristocaulis cross the Pacific Ocean? The answer would be simplest if it didn’t have to. Over geological time continents shuffle about, collide and part. Australia and South America were connected as part of Gondwana. However, Rivadavia et al. point out that pygmy sundews started to diversify around 13–12 Mya. The continents had broken up long before then. This means the plant cannot be palaeoendemic. It’s not something everywhere between Australia and South America that’s retreated to a last stronghold. If that’s not the case Rivadavia et al. say there must have been a long distance dispersal, but they’re puzzled as to how that happened.

Birds carry seeds, but birds don’t fly between Australia and South America, so bird-transport seems about as likely as a swallow carrying a coconut. Rivadavia et al. say that leaves the wind. It seems astonishingly unlikely, but if the evidence says that the divergence is only twelve million years, then other explanations seem even stranger.

“Despite the lack of information on a dispersal route from Australia to northern South America, the evidence that this did in fact occur cannot be rejected.”
Rivadavia et al. 2012

They also note there are a few other species and that the assumption is that the species are of Gondawanan origin. But could a freak event strong enough to carry the ancestors of Drosera meristocaulis have carried other Miocene plants too? In this case the Neblina Massif seems to have provided a home to an exotic arrival, but one that has kept the visitor isolated for millions of years.

Reference

Rivadavia F., de Miranda V.F.O., Hoogenstrijd G., Pinheiro F., Heubl G. & Fleischmann A. (2012). Is Drosera meristocaulis a pygmy sundew? Evidence of a long-distance dispersal between Western Australia and northern South America, Annals of Botany, 110 (1) 11-21. DOI: 10.1093/aob/mcs096