Alien evolution

This is one of my succulents flowering: Orbea lutea, one of the most widespread Stapeliads.

(Thanks to Filipa Domingues of Check my plants for the inspiration of black background shot).

It occurs over huge parts of South Africa, Zimbabwe and Namibia, to the interior. It might not be rare, but damn what is up with these flowers?!

What the heng evolution what are you playing at?! I went looking for answers among the extensive literature available on this group of plant’s pollination ecology. One paper really tackled this weirdo head on:

Suttleworth et al., 2017 (Entering through the narrow gate: A morphological filter explains specialized pollination of a carrion-scented stapeliad).

Stapeliads are a large group of succulents that occur in Africa, Europe and Asia, but the centre of endemism (where the most species occur and seem to have evolved from) is in southern Africa. Stapeliads have amazingly intricate and unique flowers that most often try to mimic rotting flesh. From Suttleworth et al.: “flowers of this group are characterised by reddish or flesh-colouring, foetid odour, contrasting pale and dark patterning, and the presence of vibratile cilia (“flickering bodies”).... It is apparent that pollination systems within the Stapeliads appear to be almost exclusively associated with either larger Saprophilous flies... or Microdiptera such as fungus gnats or drosophilids”.

This Stapeliad, Orbea lutea, is a complete outlier.

The flowers are bright yellow and the “Corolla lobes are bordered by deep purple vibratile clavate cilia (flickering bodies). The flowers are well known for their strong foetid scent, describe by White and Sloane (1937) as “an abominable odour of stale fish””. I can confirm.

So hold on, this Stapeliad is trying to mimic rotting fish, in the interior of Africa, by being yellow and having shocking purple flickering thingmajigs (see flickering in video below)?! WHAT?!

According to Shuttleworth the yellow colour is not completely understood but is probably to contrast with the flickering bodies so they stand out even more. But what is the point of the flickering bodies in the first place?!

Many Stapeliads have them and they are apparently an adaptation that does result in more visitation by their pollinators: flies. It is thought that these flickering bodies fool the flies into thinking the flower really is carrion. What it looks like to me is carrion, covered in ants. The illusion is so complete in the multifaceted eyes of flies, that some even lay their eggs on the flowers (gross). Again, I can confirm.

I wasn’t able to find a satisfactory explanation for the odd colour combination of shocking purple and yellow. Despite my own confusion, Shuttleworth found that the yellow colour was not even very visibly distinct to the composite eyes of flies, and despite this the yellow flowers had similar pollination success to other “normal” Stapeliads, so what do I know about what makes sense?

The successful pollination of this flower is a feat in itself. Shuttleworth found that although many fly species were attracted to the stench of the flowers, only one species could fit it’s head under the ridges shown below in the middle of the flower to get the pollen stuck to its head, and conversely stick that pollen in the right place at the next flowering plant to ensure pollination (my reserves of outraged are done).....That means, through co-evolution, this species has evolved to exclude other fly pollinators from accidentally getting pollen on them, that would not be able to place on the right spot on the next flower to ensure pollination, thereby wasting the pollen the flower had spent energy producing. I love pollination ecology so much.

In this case it seems beauty is in the eye (or nose) of the beholder. And judging by the tons of huge flies we had flying around during the time this beautiful cluster of flowers was omitting the foulest stench, these flowers are a beauty of the ages to this group of discerning pollinators. We thank you for your service, flies.