Readers’ wildlife photos

August 19, 2022 • 8:00 am

Much of Darwin’s work and thought was on plants, and today’s submission, by Philip Griffiths, has a Darwinian theme. His notes are indented, and you can enlarge the photos by clicking on them.

I enclose some pictures of Purple loosestrife, Lythrum salicaria, which is plentiful in my local park in central Newcastle upon Tyne (UK) at this time of year. Not only is it a beautiful flower with rumpled purple purple petals that look as though somebody forget to iron them, but it should be significant to readers of Why Evolution is True.

Charles Darwin wrote to Asa Gray  I am stark staring mad over over Lythrum. For the love of heaven have a look at some of your species and if you can get me some seed, do!  He wrote this after voyages to the Galápagos Islands and after his major work on orchids, so it must have been something that really caught his attention. Also, Purple loosestrife is pretty ubiquitous now, so I wonder if that was not the case in Darwin’s day.

What caught Darwin’s attention was the presence of three morphs, with each flower having one:

1) A short styled morph that has medium length stamens with yellow anthers and long stamens with greenish anthers. [Stamens are the pollen-produce male parts of a flower.]
2) A medium styled morph which has short stamens with yellow anthers and long stamens with greenish anthers.
3) A long styled morph with short and medium stamens.

The short-styled morph:

Medium-styled morph:

Long-styled morph:

To sum up, there are three different lengths of style [the female organ that receives the pollen for ferilization], and each is accompanied by two sets of five stamens that are of different length, so you never see a flower whose style and stamens are of the same length.

Darwin realised that this was a mechanism to encourage outcrossing. Each style is preferentially fertilised by stamens of the same length as itself and they are not to be found in the same plant. Thus a seed must be produced by pollen from a different flower.

Perhaps the three morphs (rather than two as in Primroses) increase the probability of successful outcrossing because two out of three morphs can pollinate a given flower rather than simply one out of two.

I am conscious I am ‘teaching my my grandmother to suck eggs’ here and I know the story is more complicated than I have outlined. Anyway, the flowers are beautiful this time of year and it is worth looking closely with magnification.

7 thoughts on “Readers’ wildlife photos

  1. Interesting stuff! Somewhat ironically, not only is purple loosestrife abundant over here in the colonies, it is in many places an invasive species and has been declared a noxious weed in my beloved Commonwealth of Pennsylvania.

    1. Evidence for continent-wide convergent evolution and stasis throughout 150 y of a biological invasion | Proceedings of the National Academy of Sciences

      I am pretty sure as time goes on more natives of fungal & insect tribes, will start to exploit these plants, & possibly eventually it will achieve a new lower level if population & just be part of the general botanical ecology in invaded areas.

  2. It is also declared a noxious weed in
    Illinois (and in 29 states, it seems).
    The Illinois Exotic Weed Act prohibits
    buying, selling, and planting purple
    loosestrife without a permit from the
    Department of Natural Resources.

  3. What an interesting plant/flower, not to mention pretty. But boy is it not welcome where I live. Here’s what the Washington State Agriculture Department has to say:

    Purple loosestrife is also a quarantine species. According to the Lythrum quarantine (WAC 16.752.400-415), it is illegal to transport, buy, sell, offer to sell or to distribute plants, plant parts or seeds of purple loosestrife into or within the state of Washington. The Lythrum quarantine applies to all Lythrum species, including any hybrid cross and all named cultivars.WSDA and the county noxious weed control programs do realize this semi-aquatic weed is found in almost every county in Washington State. It flourishes in some areas, making control difficult if not impossible. In these sites, a long term control plan is the goal. WSDA follows the principles outlined in Integrated Pest Management (IPM), and guidelines for purple loosestrife control are found in the State IPM Plan on the Department of Ecology web site.Washington State has a long history of working together with county, state and federal weed control programs to control this invasive non-native weed – and this work continues.

    1. Was Asa guilty of spreading it, or was he looking for natives in the same genus for Charles?

      I just read yet another book on invasive species finished yesterday. I think you have to accept you cannot possibly eliminate this plant. It seeds so profusely, & possibly has hybrid vigour. Ww have Canadian goldenrod in tge wild, but it does not seem to take over. Himalayan balsam on the other hand, grows bigger than in India & Pakistan where it originated, or rather they, for some control rusts introduced would not affect it all, then it was discovered to have very specific rusts even for varieties, & they were genetically different enough that the rust for one from India would not attack the one from Pakistan.

      One of the commonest weeds in fields here in the British Isles is pineapple mayweed, Matricaria discoidea, which came from the north Pacific. It is harmless though, & apparently edible! As is the invasive Japanese knotweed, supposedly a bit like asparagus.

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