Mutant Orchids Have a lot to Teach Us About Parasitic Plants

A) Albino and (B) green individual of  Goodyera velutina .

A) Albino and (B) green individual of Goodyera velutina.

The botanical world is synonymous with the idea of photosynthesis. Plants take in carbon dioxide and water and utilize light to make their own food. However, not all plants make a living this way. There are many different species of plants that have evolved a parasitic lifestyle to one degree or another. Some of my favorites are those that parasitize mycorrhizal fungi. We call these plants “mycoheterotrophs” and they are fascinating to say the least. Orchids are especially prone to this strategy, with over 1% of all known species having completely lost the ability to photosynthesize.

Our knowledge of the mycoheterotrophic strategy is fragmentary at best. We still don’t fully understand things like how the plants obtain what they need from the fungus nor how they are able to maintain their parasitic lifestyle without the fungus catching on and rejecting the one-sided partnership. This is not to say we know nothing. In fact, as technologies advance, we are unlocking at least some of the mysteries of mycoheterotrophic plants. Some of the best advances come from studying mutant, albino orchids. To understand how, we have to take a closer look at the “average” orchid lifestyle.

Orchids in general make great candidates for understanding the evolution of mycoheterotrophy because all of them start their lives as parasites. Orchids produce some of the smallest seeds in the plant kingdom and without the help of mycorrhizal fungi, they would never be able to germinate. For much of their early life, orchids rely on fungi to provide them with both their mineral and carbohydrate needs. Only after the orchids are large enough to grow leaves will most of them start to give back to their fungal partners in the form of carbohydrates generated from photosynthesis.

Still, many orchids never fully let go of this parasitic lifestyle. This is especially true for orchids living under dense forest canopies. With light in limited supply, many orchids adopt a mixotrophic lifestyle. Essentially this means that although they actively photosynthesize, they nonetheless rely on fungi to provide them with both carbohydrates and minerals. Mixotrphy is likely the most wide-spread orchid strategy and it has been hypothesized that it is also the first step along the path to becoming fully parasitic. This is where the mutant orchids enter the equation.

(A) Albino and (B) green individuals of  Epipactis helleborine

(A) Albino and (B) green individuals of Epipactis helleborine

Every once in a while, some orchids will germinate and grow into albino versions of their species. Without the ability to produce chlorophyll, these mutants should be destined for a quick death. Such is not the case for many of these orchids. Albino orchids often go on to live full lives, growing and flowering just like their photosynthetic progenitors. Although they do exhibit signs of reduced fitness, the fact that they are able to live at all brings up a lot of questions ready for science to tackle.

Recent investigations into the lives of these albino mutants has revealed some interesting insights into how mycoheterotrophy may have evolved in the first place. By studying the fungal partners of both healthy plants and the albinos, researchers have been able to demonstrate that albinos are doing things a bit differently than their photosynthetic parents. Using isotopes of carbon and nitrogen, scientists are discovering that the albinos have switched their interaction with the fungi in such a way that they more resemble fully mycoheterotrophic orchid species. This is done despite the fact that both albinos and their fully functional parents associate with the same guild of mycorrhizal fungi.

Another interesting difference between albinos and their photosynthetic parents is the fact that the genes involved both antioxidant metabolism and metabolite transfer (mainly carbon in this case) were more active in the albinos than they were in functioning plants. The uptick in gene functioning related to antioxidant metabolism suggests that the mutant plants are undergoing greater oxidative stress than their functional parents. This may have something to do with how the albinos are able to obtain nutrients from their fungal partners. It is thought that mycoheterotrophs actively digest parts of the fungi, which allows them to access the carbon and minerals they need to survive. This process exposes their cells to reactive oxygen compounds that can be very damaging. Antioxidants would help to reduce such damage.

The uptick in genes associated with metabolite transfer was more surprising because it suggests that despite being parasites, the plants are actively transferring substances back to the fungi. It has long been assumed that mycoheterotrophy was a one way street, with fungi transferring nutrients to plants only. These genes now suggest that, at least in some species, such transfer is a two-way street. The exact nature of this two-way transfer remains a mystery and certainly brings up many more questions that must be asked before we can better understand this relationship.

All of this is not to say that such albino mutants are fruitful “next steps” in the evolution of these species. Far from it, in fact. Two things that most albino orchid variants have in common is the fact that they are rare and, of those that have been studied, produce far fewer seeds. There are a lot of anatomical and physiological differences between true mycoheterotrophic species and albino variants and it appears that without those anatomical adaptations, the albinos are a lot less fit than their photosynthetic parents. As authors Selosse and Roy put it:

“non-chlorophyllous variants are likely to represent unique snapshots of failed transitions from mixotrophy to mycoheterotrophy. They are ecological equivalents to mutants in genetics, that is, their dysfunctions might suggest what makes mycoheterotrophy successful. Although their determinism remains unknown, they offer fascinating models for comparing the physiology of mixo- and mycoheterotrophs within similar genetic backgrounds.”

Mutants are strange indeed but with the right kinds of questions and approaches, they have a lot to teach us about ecology, evolution, and life at large.

Photo Credits: [1] [2]

Further Reading: [1] [2] [3]

Are Algae Plants?


I was nibbling on some nori the other day when a thought suddenly hit me. I don't know squat about algae. I know it comes in many shapes, sizes, and colors. I know it is that stuff that we used to throw at each other on the beach. I know that it photosynthesizes. That's about it. What are algae? Are they even plants?

The shortest answer I can give you is "it depends." The term algae is a bit nebulous in and of itself. In Latin, the word "alga" simply means "seaweed." Algae are paraphyletic, meaning they do not share a recent common ancestor with one another. In fact, without specification, algae may refer to entirely different kingdoms of life including Plantae (which is often divided in the broad sense, Archaeplastida and the narrow sense, Viridiplantae), Chromista, Protista, or Bacteria.

Caulerpa racemosa , a beautiful green algae.

Caulerpa racemosa, a beautiful green algae.

Taxonomy being what it is, these groupings may differ depending on who you ask. The point I am trying to make here is that algae are quite diverse from an evolutionary standpoint. Even calling them seaweed is a bit misleading as many different species of algae can be found in fresh water as well as growing on land.

Cyanobacteria are photosynthetic bacteria, not plants.

Cyanobacteria are photosynthetic bacteria, not plants.

Take for instance what is referred to as cyanobacteria. Known commonly as blue-green algae, colonies of these photosynthetic bacteria represent some of the earliest evidence of life in the fossil record. Remains of colonial blue-green algae have been found in rocks dating back more than 4 billion years. As a whole, these types of fossils represent nearly 7/8th of the history of life on this planet! However, they are considered bacteria, not plants.

Diatoms (Chromista)

Diatoms (Chromista)

Diatoms (Chromista) are another enormously important group. The single celled, photosynthetic organisms are encased in beautiful glass shells that make up entire layers of geologic strata. They comprise a majority of the phytoplankton in the world's oceans and are important indicators of climate. However, they belong to their own kingdom of life - Chromista or the brown algae.

To bring it back to what constitutes true plants, there is one group of algae that really started it all. It is widely believed that land plants share a close evolutionary history with a branch of green algae known as the stoneworts (order Charales). These aquatic, multicellular algae superficially resemble plants with their stalked appearance and radial leaflets.

A nice example of a stonewort ( Chara braunii ).

A nice example of a stonewort (Chara braunii).

It is likely that land plants evolved from a Chara-like ancestor that may have resembling modern day hornworts that lived in shallow freshwater inlets. Estimates of when this happen go back as far as 500 million years before present. Unfortunately, fossil evidence is sparse for this sort of thing and mostly comes in the form of fossilized spores and molecular clock calculations.

Porphyra umbilicalis   - One of the many species of red algae frequently referred to as nori.

Porphyra umbilicalis  - One of the many species of red algae frequently referred to as nori.

Now, to bring it back to what started me down this road in the first place. Nori is made from algae in the genus Porphyra, which is a type of Rhodophyta or red algae. Together with Chlorophyta (the green algae), they make up some of the most familiar groups of algae. They have also been the source of a lot of taxonomic debate. Recent phylogenetic analyses place the red algae as a sister group to all other plants starting with green algae. However, some authors prefer to take a broader look at the tree and thus lump red algae in a member of the plant kingdom. So, depending on the particular paper I am reading, the nori I am currently digesting may or may not be considered a plant in the strictest sense of the word. That being said, the lines are a bit blurry and frankly I don't really care as long as it tastes good.

Photo Credits: [1] [2] [3] [4] [5] [6]

Further Reading: [1] [2] [3] [4]


The Curly-Whirly Plants of South Africa

Gethyllis villosa

Gethyllis villosa

In a region of South Africa traditionally referred to as Namaqualand there exists a guild of plants that exhibit a strange pattern in their growth habits. These plants hail from at least eight different monocot families as well as the family Oxalidaceae. They are all geophytes, meaning they live out the driest months of the year as dormant, bulb-like structure underground. However, this is not the only feature that unites them.

A walk through this region during the growing season would reveal that members of this guild all produce leaves that at least one author has described as "curly-whirly." To the casual observer it would seem that they had left the natural expanse of the desert flora and entered into the garden of someone with very particular tastes.

Albuca  sp.

Albuca sp.

What these plants have managed to do is to converge on a morphological strategy that allows them to take full advantage of their unique geographical location. The region along the coastal belt of Namibia is famous for being a "fog desert." Despite receiving very little rain, humid air blowing in from the southwestern Atlantic runs into colder air blowing down from the north and condenses, carrying fog inland. This produces copious amounts of dew.

Normally dew would be unavailable to most plants. It simply doesn't penetrate the soil enough to be useful for roots. This is where those curly-whirly leaves come in. Researchers have discovered that this leaf anatomy is specifically adapted for capturing and concentrating fog and dew. This has the effect of significantly improving their water budget in this otherwise arid region. What's more, the advantages are additive.

The most obvious advantage has to do with surface area. Curled leaves increase the amount of edge a leaf has. This provides ample area for capturing fog and dew. Also, by curling up, the leaves are able to reduce the overall size of the leaf exposed to the air, which reduces the amount of transpiration stress these plants encounter in their hot desert environment. Another advantage is direct absorption. Although no specific organs exist for absorbing water, the leaves of most of these species are nonetheless capable of absorbing considerable amounts.

Dipcadi crispum

Dipcadi crispum

Albuca  sp.

Albuca sp.

Finally, each curled leaf acts like a mini gutter, channeling water to the base of the plant. Many of these plants have surprisingly shallow root zones. The lack of a deep taproot may seem odd until one considers the fact that dew dripping down from the leaves above doesn't penetrate too deeply into the soil. These roots are sometimes referred to as "dew roots."

I don't know about you but this may be one of the coolest plant guilds I have ever heard about. This is such a wonderfully clear example of just how strong of a selective pressure the combination of geography and climate can be. What's more, this is not the only region in the world where drought-tolerant plants have converged on this curly strategy. Similar guilds exist in other arid regions of Africa, as well as in Turkey, Australia, and Asia.

Albuca spiralis

Albuca spiralis

Photo Credits: Cape Town Botanist (,, roncorylus (, and Wolf G. (

Further Reading: [1]