Theobroma cacao flower

Here are some close-ups of Theobroma cacao flowers at Longwood Gardens in Kennett Square. The plant is economically important (because chocolate) so people fuss over pollination a lot, but its bizarre floral anatomy is noteworthy regardless of the species value. The catchiest structures are the pointy red staminodes, stamens that became neutered over evolutionary time, which probably have roles in visual attraction of pollinators (ceratopogonid midges) and in preventing self pollination. The real stamens are enclosed in translucent petal pouches, though I chose to photograph this flower because one of the anthers has popped out.

Colin Purrington Photography: Plants &emdash; Theobroma cacao flower

According to one scenario I read, the flies first land on the exterior of the pouch, then crawl inside to lap up nectar from minute glands on the adaxial surface near the anthers. During their foraging they get coated with pollen, and some of the pollen gets deposited on the style (small white structure encircled by the staminodes) when they exit the pouch. Here’s a close-up that shows the translucent pouches:

Theobroma cacao anther sacs

Presumably some of transferred pollen is from previous visits at different trees (because most types are self-incompatible). These flies do such a terrible job pollinating that farmers often just do it themselves with paintbrushes and forceps. There’s even speculation that the domestication of T. cacao some 1500 years ago slowly changed the plant enough that the original pollinator(s) (bees?) were lost, with the midges being the only insects still interested in the meager nectar rewards.

The photograph below shows the cauliflory habit of the flowers, and the “parallel staminodes” variant of the flower.

Colin Purrington Photography: Plants &emdash; Theobroma cacao flower

About Colin Purrington

PhD in evolutionary biology • twitterinstagram
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2 Responses to Theobroma cacao flower

  1. Gary Stenzel says:

    Very nice pictures! Thank you for all of the info too! My Theobroma just flowered for the first time and I was wondering about self pollination. I was going to try to pollinate them myself but it looks like that probably wont work. I’ll just have to buy a few more trees so I can pollinate them! My Vanilla Orchid is making a few flowers so I thought my “Chocolate Factory” was almost ready. Haha! Do you think I should grow some Sugar Cane also? You have a great day, and thanks again!

    • You should definitely try pollinating. One trick that can work for other species is to heat the stigma or put a few droplets of salt water on it. That reduces the functioning of the self-incompatibility mechanisms that might be at play. It’s worth a shot even if odds are remote. Or, as you say, buy some more plants!! Good luck.

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