Paphiopedilum rothschildianum, Orchid of the Month, July 2017

Paphiopedilum rothschildianum flower, which can be 20 to 30 cm across

Paphiopedilum rothschildianum is a commanding plant with an extraordinary flower and is much beloved of Paphiopedilum growers, but it also has other charms that make for a good story. The plant has long glossy strap-like leaves and a tall multi-flowered spike with one of the most distinctive flowers in the plant world. It is terrestrial and grows in Borneo (more about that later) on steep slopes on rocks or among plant detritus that isn't quite soil, usually above running water, often exposed to unusually sunny conditions for an orchid.

Paph. rothschildianum plants in situ in Borneo

If growing only in Borneo isn't enough to make it feel exotic to you, this plant has been found only on the lower slopes of a single mountain in Borneo, Mt. Kinabalu. Okay, it is a really big wide mountain, but still this is one rare plant in nature. There is presumably something special about this location, because this is not a plant struggling to make it by - it is locally abundant. When it has the right conditions it thrives. It could be the microclimate or the soil/rock type is just right, or it could be that its coevolved syrphid fly pollinator is found only in that area. Tropical climates generally support more biological diversity, in part because species are native to a smaller area, but this example is extreme. This gradient of biological diversity is called, cleverly enough, the latitudinal diversity gradient, and it well worth your time to read about - for one thing nobody is sure exactly why it happens.

Speaking of syrphid flies, also known as hoverflies, these are thought to be the pollinators of Paph. rothschildianum. These flies are familiar to those in temperate climate because many species look rather like a bee, with black and yellow stripes (hoverflies don't sting, and their coloration is a case of Batesian mimicry, but the full story takes us too far afield). The larvae of many syrphid flies eat other insects, and mother fly provides for her young by laying eggs among their preferred dinner. In the case of the fly that pollinates Paph. rothschildianum, dinner is aphids and the staminode of the flower has two parts: one part packed with bristles with a fat white tip that apparently looks like a bad aphid infestation to mother fly, and the other part waxy and presumably slippery to the fly. The fly lands to lay eggs (and often does lay eggs, thus dooming her aphid-eating larvae), slips and falls into the bucket-like lip below, and the rest of the process is the same as for all of the Lady Slipper orchids: the slippery walls, the escape route, the pollinia - described many times all over the web. Apparently the trick of luring unwary syrphid flies by mimicking aphids is shared by some other Paphiopedilum and Phragmipedium species, though I am not sure how many. The staminode bristles don't look quite like aphids to me, but then again I don't know what kind of aphid the fly is looking for, and there may be olfactory and tactile cues as well. As for why the rest of the flower is so large and boldly marked, I confess I have only a poor idea. To me it says "beware syrphid fly, here be fake aphids", but perhaps the fly can't figure this out, but is smart enough to learn that huge aphid colonies (appear to) infest these places. This should be an evolutionarily stable strategy if the frequency of real aphid infestations is much higher than Paph. rothschildianum flowers.

Close up of the staminode (the V-shaped structure near the middle), with the white-tipped aphid mimic bristles covering all but the outer (leftward) face, photo from IOSPE.

And finally, another picture showing the strap leaves and the bold flowers as they might appear to a female syrphid fly looking for a great place to lay eggs. Oh yeah, and they look pretty awesome to us humans too.

Peloric Flowers and Orchid Evolution

If you browse for novel orchid flower types for sale or for fun, you will occasionally run across "peloric" flowers. Peloric in botany means abnormally regular or symmetrical, and that's what these flowers tend toward. To explain how and why, I need to talk about orchid evolution and the genetics of flower parts. Though the genetics of orchid flower parts has not been studied in detail, we can make reasonable inferences from studies of other flowers that have been studied.

Orchids originated from a group with flowers with 3 identical sepals and 3 identical petals. The sepals and petals were 3-fold symmetric and each formed a "whorl" in the developing flower bud, the sepals forming the outer whorl and the petals the inner whorl. (Some plants have additional symmetric inner whorls that form the stamens and styles, which contain the pollen and female receptive organs respectively. In orchids these parts are transformed almost beyond recognition and form the single column.)  One of several evolutionary innovations in the orchids was the breaking of the 3-fold petal symmetry, such that one of the petals became the labellum (lip) of the flower. In many orchids, the 3 sepals remain nearly identical, though this symmetry is also broken in some specific groups. Typically, in currently extant orchids the lip is dramatically changed in shape and color, but usually the lip plus the two petals retain 3-fold positional symmetry.

Phalaenopsis Fantasy Musick, comparing normal flower form (left) with strong petal to lip peloric form (right)

Peloric flowers most often arise when the two petals acquire some or all of the character of the labellum, resulting in a flower that is more symmetric than normal. In extreme cases, the two petals look nearly identical to the lip, giving rise to a true 3-fold radially symmetric flower with respect to both petals and sepals (photo above). More often, the two petals acquire bumps, deformations, or colors that suggest some characters of the labellum, but the transformation is incomplete. Sometimes the "peloric" changes are so slight that it is seems to me to be a guess that they have become lip-like and the flowers certainly are not radially symmetric. In rare cases, the peloric transformation is the reverse - the lip becomes more like the petals (photo below). These are peloric in exactly the sense as the more common type - the flower approaches 3-fold radial symmetry - though the transformation is reversed and the visual effect is very different. All of these changes are probably due to mutations in the genome because they are stable in a given plant, though the best test is to make crosses and flower the progeny and I am not aware of any such data.

Dendrobium Kuranda Classic x Classic Gem individual showing strong lip to petal peloric form

Often flowers in which the petals look odd in any way are called "peloric", but this isn't strictly correct unless some element of additional floral symmetry results. The genetic basis of such changes might be partial petal to lip transformations, or they could simply be changes in genes that control petal form (and have nothing to do with the lip). Nevertheless, a lot of these odd petals do look reminiscent of the lip on the same plant and I think extending the meaning of peloric to these is sensible. Examples of all types are easily observed by a web search for "peloric orchid". 

What does this tell us about orchid flower development? Now I am only guessing, but I think these are educated guesses. First, the genes that determine lip shape have been added on top of an originally three-fold symmetric petal whorl. Second, since the most common peloric type causes petals to look more like lips, the lip-shape genetic program has the potential to be expressed at an early stage in petal development, but it is normally shut off in petals. Mutations that partially or fully prevent this shut off give rise to the common peloric type. Third, it is possible, though rarer, to acquire mutations in the genetic program that specifies the labellum shape, so that the lip becomes more petal like. Why these are rarer I don't know, but it suggests that the number of possible mutations of the latter type is smaller than the former (in genetics jargon, the "target size" is smaller).

I don't find peloric flowers to be particularly attractive, but they are interesting and someday perhaps we will understand in detail which genes are affected and how. The genes involved in controlling flower parts are well understood in model plants such as Arabidopsis thaliana, and the same sorts of genes are probably responsible for flower parts in orchids. Orchids are a poor model system for geneticists because they grow so slowly, but they have one huge advantage - thousands of people all over the world are growing millions of orchids and keeping an eye out for strange flower forms. These might form the basis of effective inference about the nature of these genetic changes at some time in the future, probably through a lot of genome sequencing combined with a few genetic crosses.

Windowsill Orchid Growing Part 1

Orchid magazines and orchid shows in temperate climates are dominated by greenhouse growers. Growing orchids in your home has some obvious disadvantages - relatively hard to control humidity, light, and temperature most obvious among them. You should not try to grow difficult species in the home, unless you invest in or build an orchidarium, which amounts to a miniature indoor greenhouse. However, if you choose plants that don't need crazy humidity and with the appropriate temperature and light needs for your particular windowsill, you have already leveled the field a great deal. Add a humidifier and you are about level. Add personal attention to each plant as an individual and you may have the advantage. Take that rich dead Victorian white guys!

The smaller scale of windowsill growing provides some distinct advantages over any but the most meticulous greenhouser. Many of the pests associated with greenhouses are absent or easy to control at the windowsill, including slugs, snails, and fungus gnats. Furthermore, the attention given to each plant as an individual is very difficult to achieve in greenhouse growing, where the emphasis tips toward scale. As one of many examples,  a lot of the watering in a greenhouse is done by automated misters and drippers or at best by walking around with a hose wand. At the windowsill you know every plant or you stick your finger in the medium and water when needed, and your watering (with a little knowledge and skill) is always near perfect.

I have grown at the windowsill for many years and here I will share some of the knowledge I have gained that isn't always clear when reading literature written by and for greenhouse growers ("position the plant near the wet wall and use 70% shade cloth" ... gee thanks, great advice!). There are other windowsill methods out there that I am sure can work just as well - I am just telling you what I do and why. 

Water quality. First, get a total dissolved solids (TDS) meter. They are cheap and if you grow sensitive plants and follow my plan, you get one for 'free' (it comes with the deionizing system). Unless you grow sensitive orchid types, mostly Pleurothallids such as the genus Masdevallia, if your tap water has less than 100 TDS you should be fine using tap water for everything. I am fortunate that my tap water has about 30 TDS and I use it for the large majority of my watering. Ignore occasionally stated fears about chlorination - it might be a minor issue but trust me, you can grow fabulous orchids with chlorinated water. If you do grow sensitive plants or your water has very high TDS, just get a ZeroWater pitcher or the equivalent. This is a simple and *very* effective system for removing impurities in water, consisting of activated charcoal and an ion exchange resin. The charcoal will get rid of most organic molecules and chlorine, but the ion exchange resin is much more important for your orchids because it gets rid of the salts. My water goes from 30 TDS to 0 TDS with one pass through the ZeroWater cartridge (and the pitcher comes with a perfectly good TDS meter - I was cynical and got another meter and it gives identical values), and it is extremely easy to use. The flow rate through a ZeroWater is not very high, so I just make collecting the modest amount I need an occasional chore as I pass through my kitchen - pitcher full? decant into plastic jug, top off pitcher, time 20 seconds. I change the cartridge when the outflow goes above a few TDS. Buy the cartridges in bulk direct from ZeroWater (or equivalent) and the cost is very modest - for me it is perhaps $3 per month. Cost could become an issue if you use a lot of water and you have very salty tap water because that will exhaust the ion exchange resin faster. In this case you can purchase a reverse osmosis system or collect rainwater, but I don't recommend that unless you need a lot of water - they are a pain in the neck and have their own costs. There are also simple deionizing columns available from marine aquarium vendors; these may be more cost effective than ZeroWater. Another advantage of having deionized water is that you can water your small plants by spraying the medium at the windowsill, which is easier and works especially well for plants in all spaghnum, such as Neofinetia falcata potted in the traditional Japanese fashion. Still flush at the sink once in a while, as discussed below. [A side note on TDS: the usual method used to measure TDS is imperfect - you are really measuring the electrical conductivity of water, which is dominated by dissolved ions like sodium, potassium, chloride, and magnesium. If you dump pure sugar into your water you will find that it barely registers on a TDS meter even though sugar is definitely a dissolved solid. Fortunately the dissolved solids in ground water are dominated by dissolved ions and all the ions have about the same effect on conductivity, so the TDS meter is effective.]

Watering. Here you have the advantage over greenhouse growers, at least if you are reasonably conscientious. Every plant gets individually watered when it needs to be. Simple. Well, mostly simple. If you are like me when I started growing orchids you wonder: what does it mean to water "just when the medium gets dry"? Dry on top? Dry in the middle? Bone dry? Or how about "keep evenly moist". Huh? Honestly, I don't think anyone knows quite what they mean when they make such statements, but they do give you a relative guide - obviously the latter is wetter than the former. My method (profoundly original) is to stick my finger down an inch or two into the medium. In good open orchid medium it will never feel sopping wet (if it does, repot), but if it feels damp you are fine for another day. Of course you have to adjust this depending on how wet the plant likes to be, and perhaps seasonally. Until you get the hang of it, be very consistent about checking each pot each day - it is amazing how much plants will vary from each other and from season to season. Media vary in how much water they hold, pot size matters (surface to volume ratio), temperature and humidity have a big effect, and less obviously, if you have a plant with a lot of leaf area and a pot packed with roots, it is amazing how much water the plant itself will suck out and transpire - in warm weather, daily watering may not be enough (see repotting in a future blog post to see how to deal with this). So just ignore all these variables and use the finger test every day for a while. Eventually you will get the feel for when you need to check a plant.

My watering method is simplicity itself and is reasonably fast: I carry the plants to my kitchen sink and run a heavy stream of tap water directed at the medium (not the plant) of each until it runs FREELY out of the bottom and then a couple seconds more ("flush" the medium every time you water). I let them sit a few minutes so I don't drip all over my wood floors and carry them back. Some plants might appreciate a light misting on their leaves as well, but if you do this use deionized water, otherwise you will build up those ugly white stains on the leaves. Even with a sizable collection on a typical day there is less than one sink full of plants; quite efficient. If you grow other houseplants and are new to orchids, notice that this is nothing like the watering you are used to. Let it flow, let it flow! Pretend you are mother nature dumping a tropical rain onto an epiphyte: the roots are soaked in the first minute and then the rest just runs off. Orchids hate salt on their roots, and if you don't flush your pots when you water, it will build up by evaporation. You will quickly see how to adapt this method a bit to various media, such as small pots or pure spaghnum or very fine bark (lower the flow rate but still flush). You can't overdo the flushing. More won't hurt; this is not over watering - that means watering too often so the roots don't get enough air - this is making sure the medium is evenly wet and salts don't accumulate. The medium won't be any wetter when you finish, but it will be clean clean clean. When medium such as fir bark is brand new you can let the pot soak in a bucket for a few minutes, because new bark doesn't soak up water very well, but I doubt it matters much and this method is much more time consuming and it risks transmitting disease unless you do one at a time and clean the bucket every time. I just soak new bark repots once and then water a bit more often for a month or two.

For mounted plants, which are not common at the windowsill because they are a pain, just use the same method. You can also water by misting mounted plants (or smaller pots), but if you do this be sure to use deionized water or flush the plant at the sink often!! Salt can build up on mounted plants very fast when you are reluctant to let your sprayed mounts drip all over your carpet or wood floors.

Water this way conscientiously and you have solved 90% of the problems people have growing orchids at the window sill. Well okay, 80%.

Fertilizing. This part is easy. First, follow the mantra "fertilize weakly weekly" (or less), weakly meaning at no more than half the label-recommended strength. Second, when you fertilize, water first as described above and then pour on some fertilizer water until it just starts flowing out the bottom (I am not sure the issue is real when dealing with dilute liquid fertilizer, but this is supposed to avoid "fertilizer burn"). Third, purchase an epiphyte-specific fertilizer with all the micronutrients (calcium, magnesium, boron, cobalt, copper, iron, manganese, molybdenum, and zinc, in addition to the big three, nitrogen, phosphorous, and potassium). Plants also need sodium, chlorine (chloride), and sulfur, but those come as the counterions for the other nutrients, and for some reason aren't listed as nutrients in fertilizer I use. (They also need lots of carbon and oxygen but those they get from the air.) If you use only tap water with moderate TDS, you don't have to bother with all the micronutrients because they are already in your water. 

If you poke around enough you will find people who never use any fertilizer, but that is not a good idea. Apparently they manage, but the nutrients have to come from somewhere, probably the potting media and tap water. Plants are amazing, but they are not alchemists. If you own parrots you could try leaving them loose in your home - that might work but it would get a bit messy unless you can train them. It would be very natural.

That's it. Ignore all the rest of the hoopla. I use Dyna-Gro Orchid-Pro, but I don't specifically endorse it - there are several other brands out there that are equivalent. Just read the fine print on the label and ignore the rest. I am not sure why there is so much hoopla out there about fertilizers, most from the companies of course, but a surprising amount from growers. There are studies on urea as a source of nitrogen (under normal conditions it is fine, because bacterial rapidly convert it to plant-usable nitrogen), but as far as I can tell all the rest of the endless discussion is marketing, placebo effect, or minutiae. 

Foliar fertilizing, blossom booster, vitamins, hormones, magic additives, annoying names, it is all bunk. Gack! Boycott more hype! My favorite bunk - the SUPERthrive label is like a caricature of snake oil sales pitches. And the fine print is even weirder: 

“SUPERthrive saves plants from waiting to make many life-process complexes, carbon-hydrogen-oxygen groups. Bankruptcy protection. Turgidity maintenance. Displaced groves salvage. Marginal methods, times, places and plants. For immediate use by your plants.”

Sounds mentally ill to me, or at best very confused. Go ahead, be one of those suckers born every minute. But first watch the YouTube video on a reasonably controlled experimental test by BrightGreenThumb (conclusion - it has no discernible effect, though the experiment is on common garden plants not orchids). 

My favorite empty hype - pure snake oil. The label is an impressive mishmash of hot button words. There is no evidence I am aware of that the product does anything useful. It does contain low concentrations of auxin (a plant hormone) and B-vitamins, which plants make for themselves. And it also contains "over 50 secret proprietary ingredients that we do not disclose", always a comforting claim. In case you missed the point, these ingredients are private, confidential, under wraps, classified, and concealed (as well as secret, proprietary, and not disclosed). So who knows, maybe it will "super extra life champion miracle hormone science vitamin millions revive world proof thrive" your plants! 

More to follow in Part 2, complete with occasional rants...