The explosion in orchids as houseplants: what does it tell us about how flowers evolve?

Orchids 20180512_112533.jpg

One of the major trends in horticulture over the last 20 years or so has been the rise in popularity of orchids as house plants.  Orchids used to have a reputation as being delicate, choosy, costly things that needed expensive glasshouses, heating, and humidity systems to grow.  Some groups of orchids are certainly like that, but many are not (Orchidaceae is one of the two largest families of plants, after all).  These days it’s impossible to walk into any supermarket or department store and not see orchids for sale at a reasonable price, orchids that are tough and can withstand the relatively dry, centrally heated houses in which most of us in Britain live. 

The majority of these orchids are varieties of Phalaenopsis, the moth orchids.  Intensive hybridisation by commercial growers has meant that there is an almost inexhaustible range of flower colours, shapes, sizes and patterning available.  Take a look at this gallery of images and you’ll see what I mean, or go into a shop that sells such orchids and observe that almost no two are alike.

This is the stuff of natural selection: genetic variation in the phenotype that can be acted upon by a selective agent.  In this case it’s the growers of orchids who choose the most attractive types to sell and discard the others.  If this variation emerged in wild populations most of it would disappear over time, but some, just occasionally, would be selected for by a different group of pollinators and go on to form a new species.  This is much more likely to happen if the individuals with this variation are isolated from the rest of the population in time or space, for example if they flower later or have been dispersed to a distant valley or mountaintop (termed allopatric speciation).  But it can also happen within populations – sympatric speciation.

Back in 1996, near the start of this orchid explosion, one of my earliest papers was a speculative commentary in Journal of Ecology called “Reconciling ecological processes with phylogenetic patterns: the apparent paradox of plant-pollinator systems”.  It generated some interest in the field at the time and has picked up >250 citations over the years, mostly other researchers using it as supporting evidence for the discrepancies we see when trying to understand how flowers evolve within a milieu of lots of different types of potential pollinators selecting for possibly diverse and contradictory aspects of floral form.  In that paper I made a passing comment that I expected the reviewers to criticise, which they did not.  Once it was published I thought that perhaps other researchers in the field would critique it or use it as a jumping off point for further study, which has not really happened either.  This is what I wrote:

         “It appears that pollination systems are labile and may evolve quite rapidly….plant breeders can obtain a fantastic range of horticultural novelties through selective breeding over just a few generations.”

This is horticulture holding up a mirror to the natural world and saying: “This is how we do it in the glasshouse, look at the variety we can produce over a short space of time by selecting for flower forms; can nature do it as quickly, and if so what are the mechanisms?”  

I still believe that pollination ecologists could learn a lot from horticulture and there’s some fruitful (flowerful?) lines of enquiry that could be pursued by creative PhD students or postdocs.  Here’s one suggestion: part of the reason why these Phalaenopsis orchids are so popular as house plants is that they have very long individual flower life times, often many weeks.  Now we suspect that floral longevity is under strong selection; see for example research by Tia-Lynn Ashman and Daniel Schoen in the 1990s.  This showed that there is a negative correlation between rate of pollinator visitation and how long flowers stay open.  Plants with flowers that are not visited very frequently stay open much longer, for example the bird-pollinated flowers of the Canary Islands that may only be visited once or twice a day, and which can remain open for more than 20 days.  Is the floral longevity shown by these orchids (or other groups of plants that have been horticulturally selected) beyond the range found in natural populations?  If so, what are the underlying physiological mechanisms that allow such extreme longevity?  If not, does this mean that there is an upper limit to the lifespan of flowers, and if so, why?  

In the mean time I’m going to enjoy the orchids above that sit on our kitchen windowsill.  They actually belong to my wife Karin who has developed something of an interest in them in recent months.  The big spotty one is a late birthday gift for her that I picked up this morning from a local flower shop, and which stimulated this post as I was walking home.  I’d bet that we never see another one like it!

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15 Comments

Filed under Biodiversity, Biodiversity and culture, Birds, British Ecological Society, Evolution, Gardens, Personal biodiversity, Pollination

15 responses to “The explosion in orchids as houseplants: what does it tell us about how flowers evolve?

  1. I bet the flowers soon drop if you pollinate them with a paintbrush. They’re only going to stay open long enough to serve their purpose, and hybrids probably stay open longer because vital parts of them have been used to make extra petals, etc. and pollination can no longer happen.

    The flowers on my Jade plants stay open and producing sticky nectar for months, until they dry out and fall off still open.

    Liked by 2 people

    • Yes, it’s possible that they would drop after pollination, but this varies a lot between different species. Another purpose of flowers, beyond their immediate reproductive role, is to act en masse as a long-distance attractant. So some plants hang on to their old flowers for this reason, and in some cases change colour to signal that they do not contain nectar.

      Liked by 1 person

      • If you like making home brew wine, you can use the pollination trick to harvest just the corollas from umbels of elderflowers, leaving the berries to develop, and so getting two different crops, whilst also avoiding the cat pee smell of the green parts.

        When you get your eye used to the change, you can see fertilised umbels from the orange, rather than yellow, colour of the anthers. Once the anthers have emptied, you can put a paper bag over the umbel, and twirl it around inside, and all the corollas drop into the bag. (There’ll also be lots of earwigs and fluorescent green spiders, so you have to let them get away when you spread out the corollas to dry on newspaper.).

        Elderflowers are great to dry and keep for flavouring drinks–though you may have an annual battle with the local ants for the sap of the bush, that they harvest from sleeves of aphids on every new umbel stalk! 🙂

        Liked by 1 person

      • Incidentally: how come we in the UK, have so few red/scarlet flowers? I can only think of poppies and Scarlet Pimpernel, that are native. Others tend to the wine red end of purple, pink, and blue, but pure scarlet/crimson seems to be mainly on garden imports. Why’s that?

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      • In fact there are even fewer than you think: poppies are from the Mediterranean originally, introduced by the Romans. It’s a good question; one answer may be that there are no native bird-pollinated plants which are often associated with red. That can’t be the sole reason though as the poppies are beetle and bee pollinated in their native range, and red flowers can be butterfly pollinated in South Africa.

        Liked by 1 person

  2. P A Azeez

    That is interesting; thanks for that insightful write-up

    Liked by 1 person

  3. Thanks for posting this. It maybe explains a lot about garden centre plants and why so many of them do not appear to be attractive to bees. They have been selected for long flowering characteristics and that means there is probably something about them that is unattractive. Would I be correct in thinking that from the plants point of view as soon as pollination is achieved there is no longer any evolutionary advantage in keeping the flower open?

    Liked by 2 people

    • See my comment above which I’ll copy here: Another purpose of flowers, beyond their immediate reproductive role, is to act en masse as a long-distance attractant. So some plants hang on to their old flowers for this reason, and in some cases change colour to signal that they do not contain nectar.

      Liked by 1 person

  4. Frank Jordan

    I’m trying a pair of Paw Paw trees ( asimina triloba) in my back garden – while it will be a couple of years before they flower it will be interesting to see how pollination works as they rely on flies and beetles rather than bees and butterflies – I suspect I will be doing a fair bit of hand pollination- fascinating trees that I remember from my youth in Appalachia

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    • Oh it will be really interesting to see how you get on! They are great plants that belong to a very ancient group. Will they be hardy in your garden? Where did you source them from?

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      • Frank Jordan

        I sourced them from a German nursery- the native range is the Bible Belt all the way up to Canada and apparently they are very well suited to this climate- the weather in the mountainous area of the Southern US is not dissimilar – if a bit hotter in the summer – I have chosen two varieties native to Pennsylvania ( you need two genetically distinct cultivars for fruit)- so particularly suited to cooler weather

        Liked by 1 person

      • OK, I didn’t realise they got so far north. Good luck with them!

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      • Frank Jordan

        The nursery is Lubera- they have a few great videos on YouTube about their Paw Paw selection – also highly recommend “Paw Paw: in search of America’s Forgotten Fruit” by Andrew Moore

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      • A long time ago, I discovered the species tips sheets made by the California Rare Fruit Growers, when I was looking up whether I might be able to coax various fruit seeds into life at home in the UK. It’s developed into a good all round unusual fruit tips site. Here’s the sheet on PawPaw (the US calls what we call pawpaw, ‘papaya’:

        https://crfg.org/wiki/fruit/pawpaw/

        For an even wider range of fruits, some that most people don’t realise are edible, ‘Plants For a Future’ has a similar, but bigger, database.

        Liked by 1 person

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