Cosmos ‘Cupcakes’ – a botanical conundrum

A few years ago when I first heard about cosmos ‘Cupcakes’ I was excited. Cosmos are simply lovely annuals.

But first, a few general points. Most cosmos are derived from Cosmos bipinnatus, the name referring to the twice-pinnate (divided) leaves, distinguishing it from the simpler lobed leaves of the yellow and red flowered species. This feathery foliage is almost reason enough to grow cosmos, but the masses of daisy-shaped flowers, that continue right to the frost, make this a great border filler. Cosmos bipinnatus is a short day plant, not flowering until the days are shorter than the nights. I have had many emails in the past few weeks about lack of flowers on cosmos. The tall plants of ‘Sensation’ can reach 1.5m high and do not flower as early as the newer, dwarf kinds such as ‘Sonata’ but you should expect flowers by August. However, the strain has been allowed to deteriorate. I remember growing them 30 years ago when there were always a few plants, usually whites, that refused to bloom until the plants had reached at least 2m high with stems like tree trunks. It seems that things have not improved and a batch grown this year have about 10% of the plants with no sign of flowers yet and I know that I am not alone. So why not just grow the dwarf kinds? Well, I like the taller kinds and the dwarf ones do run out of steam rather early – the present ones here look pretty ropey at present, daring me to pull them up. A better bet is to sow the named, single colours such as the gorgeous ‘Rubenza’ which are more reliable.

But back to ‘Cupcakes’. This strain is derived from a plant found by Diane Engdahl in her garden in Santa Rosa, California in 2007. This plant had, instead of the usual flowers, cup-shaped blooms. She took up the offer given by seed company Thompson & Morgan to develop any unusual plants gardeners find, and sent the seeds to them and they spent many years stabilising the strange flower shape before introducing it. So far all good. The flowers have a cup shape with some thinner ‘petals’ in the centre of the flower in some cases. As far as I know, so far, the colour range is pinks and white though the whites often have a very pastel pink blush.

So why am I puzzled by this? Every description I see of this plant states that the petals are fuse to form a cup. Nothing weird about this really because petals get fused together in many flowers, quite naturally, or we wouldn’t have tubular foxgloves.

Now, ‘petals fused together’ is not new in cosmos, the problem is that cosmos is a member of that great plant family Asteraceae (formerly Compositae), the main characteristic is which is that the ‘flowers’ are not flowers at all but a head of flowers. Each petal of the ‘flower’ is actually an individual flower. Look carefully at a cosmos ‘petal’ and it will have five notches at the ends – the five true petals are fused but split along one side to open as a flat ‘petal’. There are usually eight ‘petals’, the same as in single dahlias (they are closely related) – see below. In the ‘Seashells’ and ‘Pied Piper’ cosmos these five true petals are fused along the length and not split so the ‘petals’ appear to be tubular. You can see something similar in some gaillardias and coreopsis.

So, in order for ‘Cupcakes’ to form these cupped ‘flowers’ it means that the whole outer row of true flowers has had to fuse, in a ring, around the flower head. How on earth can this be so? It seems too much to expect. It just doesn’t make sense to me. Petals fusing is one thing but for eight individual flowers to fuse together in such as way seems impossible to me.

The mystery does not spoil my enjoyment of the plant – almost the reverse – but I am old fashioned enough to like to know how things happen, despite living with technology that is basically magic and with Trump as President of the USA. Wonders never cease.

And now – Sunday Puzzler: September 17

Hopefully you took the letters from the photos:
















And this gave you E E C M L S E A

And if you rearrange these you get McAleese – Mary McAleese, who was president of Ireland from 1997- 2011.




7 Comments on “Cosmos ‘Cupcakes’ – a botanical conundrum”

  1. derrickjknight
    September 18, 2017 at 11:42 am #

    I think this must be what our raggedy ones are. Thanks

  2. digwithdorris
    September 19, 2017 at 6:15 pm #

    Interesting info thanks.
    Your quiz is too hard for me though

    • thebikinggardener
      September 20, 2017 at 7:50 pm #

      I try to vary the quiz so please don’t give up on me quite yet 🙂

  3. Meriel
    September 20, 2017 at 4:11 pm #

    Rather belatedly, welcome back to the sunny South East. Hopefully I may run into you at some stage. As usual I can’t keep up with your blogs – just now & again.
    Your depth of knowledge never ceases to amaze me. I saw these Cosmos last month on a visit to Charleville House, Enniskerry, grown in large pots. I thought they were lovely and reminded me of an upside down crinoline. It is a wonderful house/garden to visit, rarely open and one has to book. I believe Tom Stuart Smith has had a hand in it and visits regularly.

    • thebikinggardener
      September 20, 2017 at 7:51 pm #

      Good to have you back. I am sure we will meet up again. I am glad you saw the cosmos – it sounds as though they looked lovely.

  4. FlowerWarrior
    March 26, 2018 at 9:25 pm #

    You show the flower pure love.


  1. Cosmos old and new | The Biking Gardener - July 20, 2021

    […] of recent years has been the ‘Cupcakes’ strain and I have written about them before. About twenty years ago the ‘Double Click’ cosmos had us all aghast and now there are […]

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