A few days ago the journal Lankestariana published the description of a new species of orchid I discovered thirteen years ago in what is now our Rio Zunac Reserve in central Ecuador. My friend Sebastian Vieira independently discovered another population of the same species near Sibundoy in southern Colombia, and we wrote the article together. This orchid, which we named Neooreophilus chaoae, is a tiny but beautiful orchid with a very unusual growth habit. A nearly universal rule about plants is that they grow toward the light. For reasons unknown, the genus Neooreophilus defies this rule: its growing tip points downward, toward the ground, so that the newest leaves are lower than the older leaves. The chains of tiny roundish leaves usually hang from a branch or trunk. The chain of leaves looks a lot like some of the small pendant fern fronds that grow in the same habitat. The fern rhizome grows towards the light, like most self-respecting plants, so that each new frond is higher than the last, but each individual frond unfolds downward on a weak stem, just like the orchid.
The resemblance between the orchid and the fern may not be an accident. If there are herbivorous insects that eat orchids and that use their eyes to spot potential hosts, they may have a hard time finding these orchids amid the much more common ferns. The presence of such herbivores would drive the evolution of orchids that mimic other more common plants. In our area there are other orchids that do this, such as certain Elleanthus species that mimic bamboo. (I think plant mimicry of other plants is more common than people realize, and I’ll devote a later post to this topic, complete with local examples.)
Maybe the resemblance to these common ferns also fools field botanists. Members of this very rich genus are rarely noticed or collected by non-specialist botanists, so they are poorly represented in the world’s herbaria. It doesn’t help that they are often partly covered by moss. They are also very fussy about where they grow. They need wet but bright and airy cloud forests, and even within such forests their distributions are patchy, occupying only a small percentage of the seemingly-suitable habitat. The patch size is often just a few meters, but curiously there are often many different species of Neooreophilus in a given patch. Many orchid biologists suspect that this genus-level patchiness is probably due to the presence of a particular fungus in the patch. Orchid seeds need to form relationships with specific fungi in order to germinate, and if the right fungus for Neooreophilus is present in an area, seeds of all the species in the region will eventually fall there and germinate.
Sebastian’s discovery of a second population of this species in Colombia, more than 250 km to the north of the population I found, was very surprising. He was on a conservation trip with directors of the Orchid Conservation Alliance (US); the trip led the Alliance to fund the establishment of a new reserve in that area. Sebastian’s discovery was especially interesting because there is another rare and local orchid species shared between Sibundoy and our Rio Zunac Reserve, Dracula exasperata. Neither of these two species are known from any other places in between these two reserves. In the case of N. chaoae, the forms appear to be absolutely identical in the two locations, suggesting that there may be connecting populations somewhere in the poorly-known mountains between the reserves. The Dracula populations, on the other hand, show quite significant differences between the two reserves, and several of my Dracula specialist friends think that the Zunac population should be described as a new species. I’ll write more about this later.
The story of N. chaoae’s twin discoveries highlights our poor level of knowledge about east Andean orchid distributions. Orchid specialists had visited both the Sibundoy and Zunac populations multiple times over the past thirty years, as indicated by the early discoveries of Dracula exasperata in Sibundoy, and Dracula fuligifera, Lepanthes zunagensis, and many others in the Rio Zunac area. Yet none of these specialists noticed N. chaoe. After the first population of N. chaoae was finally found, it took another ten years to find a second population. It is one of many cryptic, often-undetected species in these mountains. A similar story surrounds the discovery of another member of the genus, Neooreophilus (ex Lepanthes) exiguus. Stig Dalstrom and I discovered this species at a remote site in extreme southern Ecuador. Many years later my student Stella Copeland and I found a second population 150 km away in our Rio Zunac Reserve (the same area where I had found N. chaoae). The existence of so many species known from only a few widely separated sites suggests that many new species remain to be discovered in the eastern Andes of Ecuador and Colombia.
My colleague Anne Chao is famous for showing that this relation between the number of rare species and the number of still-undetected species can actually be made precise. She proved that when individuals are randomly sampled, the number of undetected species in the population is expected to be greater than
where is the number of species represented by only a single individual in the sample, and is the number of species represented by exactly two individuals in the sample. Her formula is widely used in biology and is known as the Chao estimator. Thus it is particularly appropriate that Sebastian and I named our cryptic, often-undetected new species in honor of Anne.
The genus Neooreophilus is very diverse and deserves more attention from botanists. Since I’ve started paying attention to them I’ve been able to discover several new species besides N. chaoae: N. exigua, N. viebrockiana, N. ariasii, and several others that I have not yet published. I am sure there are many more waiting to be discovered!
Incidentally, my earlier Neooreophilus discoveries were published under the genus Lepanthes, subgenus Brachycladium, where they had originally been placed (Reichenbach 1856, Luer 1996). The flower structure and the characteristics of the sheaths around the leaves and stems suggested this placement. However, recent DNA analyses by Mark Wilson, Alec Pridgeon, and coauthors have clearly shown that these plants are not particularly closely related to Lepanthes, and belong in a completely different branch of the orchid family tree. [Note added Nov 17 2015: The flowers look like Lepanthes flowers because they use the same pollination method: pseudocopulation. The distinctive sheaths apparently evolved independently in the two groups as good solutions to some unknown environmental challenge in wet cloud forests.] Scientists recently proposed the replacement names Brachycladium and Oreophilus for this group, but both these names violate the careful rules of botanical nomenclature, and are hence illegitimate; they were replaced by the new name Neooreophilus which follows the rules and is legitimate. In a few days Mark, Alec, Sebastian, Frank Graham, and I will submit an extensive article about the correct phylogenetic placement of these orchids and their relatives. I’ll post a link here after acceptance.