Orchid species (Orchidaceae) have colonized every part of the world, as humans have. Though, humans are one species and orchid species number in the tens of thousands. And of course, describing a group of plants with global reach and varied life strategies is an impossible task, like capturing all of humanity in one image.
Collectively, like humans, orchids are exquisite specialists. They have adapted to specific pollinators that fascinated Charles Darwin who wrote a book about orchids and their pollinators. Darwin even predicted a pollinator that must exist for an orchid with a long nectar spur only to have it discovered decades after his lifetime.
Like all plants (all multi-celled life?), orchids associate with fungi. However, orchids may require fungi more than most plants do. Noël Bernard, a French scientist in the late 19th century trained a bit in both microbiology and plant science, found evidence that orchid seed germination was enhanced by mycorrhizae, fungi primarily living in soil. Humans did eventually figure out how to germinate and preserve orchid seeds in entirely artificial medium (it’s how orchid competitions exist), an important aspect in their conservation.
Orchid seeds are small, lack a nutritive endosperm, and are quite whispy. They’ve taken a strategy of producing thousands of seeds and dispersing them all over by wind, hoping a few land in a place suitable to germinate and importantly find a fungus to help fuel their growth.
Finding a partner
How hard is it for orchid + fungus to find one another?
Perhaps not as hard as one might think, however, still a challenge. Fungi are everywhere – potentially millions of species (they are hard to study). They’re among the earliest colonizers of land (only beaten by bacteria). They associate with plants and animals and are just another part of the natural living medium we all exist in and depend upon, but rarely fully acknowledge.
Now it might seem likely that an orchid that is terrestrial, that is, lives on the ground would be more likely to find a proper fungal partner because of how much fungi is present in soil. One study studied a single genus of many Australian orchid species that associate mainly with a single genus of fungi. So given land area and wind dispersal, at least a few orchid seeds are likely to find a fungal garden to associate with (a question I don’t know: there may be ways orchid seeds can actively attract fungi. Their flowers are master attractors, so perhaps their seeds could be as well).
A lot of orchid species, however, are epiphytes. Especially in tropical regions. They are plants that live on plants. That would seem to make finding the right fungi parter even harder in a forest. Epiphytic fungi do exist and associate with orchids, as this study from Madagascar examined. And yet it’s a more fragmentary habitat.
The fact that orchids pull this off is another case of the seemingly improbable success of flowering plants. Attracting a pollinator twice (once to pick up pollen, the second time to deposit it in another flower of the same species) is the least of it. Orchids have specialized in tricking their pollinators to visit them through both visual and chemical mimicry. Having two orchids flowering at the same time in the same area would seem improbable. On top of this, the orchid seeds have to find fungi, germinate, and grow before flowering.
As stated above, any old fungus won’t do either. Most orchids require specific species or genera of fungi. As microbes, fungi are messy and it can be hard to define a “species”. However, with DNA sequencing, mycologists can define Operational Taxonomical Units (OTUs) that are at least all close relatives. Orchids vary a bit in their host fungi needs (some a bit wider range than others).
Happy Valentarwin Week
This week is Valentine’s Day and Darwin Day. It’s a good week to think about an ancient partnership, that is likely sometimes parasitic (in either direction), sometimes symbiotic, but no less remarkable that such plants exist with near invisible seeds and largely out of sight fungi that eventually produce strikingly beautiful flowers, often designed to outright trick a pollinator. Whatever kind of relationship you might have or enjoy, there is likely an orchid that has a similar story.
The remarkableness of orchids is in no small part down to the ubiquity of fungi. While not every seed or fungal spore will land in a suitable spot, enough do to form a partnership that has conquered the globe and won our hearts and minds. Purely speculative, but orchids may have been at the fore of Darwin’s mind when he wrote his final iconic lines in On the Origin of the Species:
“There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”
*The name and inspiration of this post was inspired by a recent episode of the podcast I cohost, Recovering Academic.
The Quiet Branches 