white foxglove, Digitalis purpurea

Foxglove Falsehood

I know I read somewhere that the flower colour of a foxglove (Digitalis purpurea) plant can be predicted by the colour of the leaf stems (petioles). Foxgloves are biennials; they flower in their second year of life, and then they die. Their normal flower colour is a reddish purple. It’s fairly attractive, but not nearly as elegant as the white form. Fussy gardeners who prefer the white form would therefore want to know which of a batch of seedlings would be likely to produce white flowers the following year.

If the leaf stem shows purple, I understood, the flowers will be purple. Plants with pale green leaf stems are more likely to produce white flowers. Going by this, I picked out a number of seedlings several years ago and planted them around the place. A few of them did turn out to have white flowers, but not all. Some produced blooms of a pale, washed-out pink with nothing to recommend it, and some were just the ordinary purple shade.

After this experience, I didn’t bother with systematic seedling selection. I simply let a few plants produce seed, and left a few of the resulting seedlings where they came up, in spots where a foxglove would be an asset to the scene.

Right now, I have two foxgloves with white flowers. The biggest and most impressive one has dark purple leaf stems. So does the smaller one.


Clearly, the idea that leaf stem colour predicts flower colour is dead wrong.


Just for fun, I checked the leaf stems of a rather impressive purple foxglove also in bloom now.


Its leaf stems have only a slight tinge of purple. If I had looked at them before the plant bloomed, I would very likely have predicted pale or maybe even white flowers.

So much for that notion. Consulting that fount of info, Wikipedia, I find this in the article on Digitalis purpurea:

The colours of the petals of the Digitalis purpurea are known to be determined by at least three genes that interact with each other.[6]

The M gene determined the production of a purple pigment, a type of antocianin. The m gene does not produce this pigment. The D gene is an enhances of the M gene, and leads it to produce a big amount of the pigment. The d gene does not enhance the M gene, and only a small amount of pigment is produced. Lastly, the W gene makes the pigment be deposited only in some spots, while the w gene allows the pigment to be spread all over the flower.

This combination leads to four phenotypes:

  • M/_; W/_; _/_ = a white flower with purple spots;
  • m/m; _/_; _/_ = an albino flower with yellow spots;
  • M/_; w/w; d/d = a light purple flower;
  • M/_; w/w; D/_ = a dark purple flower.

If I could understand the above and make practical use of it, I might be able to predict flower colour in foxglove seedlings. I’d probably get more white flowered plants from my self-sown foxgloves if I pulled up any purple types before they reached full bloom, so as to keep their pollen out of circulation. But I am constitutionally incapable of pulling up (i.e., killing) any plant that is vigorously growing and about to bloom. I even have trouble dispatching certain weeds. So I’m not likely to go around “roguing out” any purple flowered plants if they look good.

In the meantime, I’ll enjoy the blooms I have, and let the white one (which, according to the above, is the white with purple spots phenotype) produce seed. Foxgloves seed like crazy. I’ll harvest a small quantity of seed and sprinkle it around the garden, and in 2019 I’ll see the results.

Update: another, rather small, foxglove plant has since bloomed with white flowers. These are pure white, and without spots of any kind. And the leaf stems are very pale green, without a trace of purple. So now I’m wondering if the leaf stem colour is somehow linked to the colour of the spots within the flower. Observing stuff like this makes gardening — even with common plants — interesting.



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