PlantLife SA, Volume 49.5, July 2020. Scadoxus multiflorus and its butterfly pollinators

 Scadoxus multiflorus and its butterfly pollinators

by Hannah C. Butler

As you may have noticed from the cover of December 2019 cover page for PlantLife SA (volume 48.1), Scadoxus multiflorus subspecies katharinae is an absolute joy to behold. When I decided to work on this species, I had in fact never laid eyes on the real thing! But the pictures alone intrigued me - why were the flowers arranged in a ball like that? Why was each flower so open, displaying such bright red petals? And because I am a pollination biologist, I wanted to know what animal would visit these flowers?

I had my theories and had done my research but of course the only thing to do was to find some plants and watch them to see what would happen. It took quite literally a couple of months wandering around Vernon Crookes Nature Reserve where they were rumoured to hang out, before finally bundu bashing through prickly trees and a steep slope with no path and stumbling into what can only be described as an excessively muddy swamp. And there they were!! Dotted along a small stream trickling through the mud, each plant was about a metre in height and many were topped by this incredible display of “fireball” flowers. Now, one might assume at this point that my excitement level had reached its limit but not so, for maybe ten minutes after standing in the mud in awe, there came along a butterfly. A beautiful swallowtail drifted through the dappled sunlight, alighting or passing near almost open flowers. It was, for me, love at first sight.

Image 1. Scadoxus multiflorus subspecies katharinae visited by a male mocker swallowtail. Photo: SD Johnson.

Image 2. Scadoxus multiflorus subspecies katharinae visited by a male mocker swallowtail. Photo: SD Johnson.

But now I wanted to tell the whole world about it! And so the scientific mind comes in. Perhaps watching butterflies visiting these plants for hours sounds tedious to some but this was heaven to me. I recorded every butterfly that visited as well as every butterfly that I observed to be present in my little forest swamp. It turned out that male mocker swallowtails were the primary visitors, despite the area being rich in all kinds of butterflies. I took photos and caught some butterflies and on close examination found that the pollen from the flowers was deposited on the wings of the butterfly. What a satisfying discovery! I even did an experiment where I placed an inflorescence that hadn’t been visited before amongst my population and then counted the pollen deposited on the flowers after watching two butterflies visiting. Finding pollen there meant that indeed, these butterflies were doing a good job of transferring pollen between plants.

Image 3. Pollen of Scadoxus multiflorus subspecies katharinae (in yellow) on the wing of a butterfly under electron microscopy.

Next on the list was some research into a related taxon, Scadoxus multiflorus subspecies multiflorus. These plants have very similar, although slightly smaller, flowers that are also arranged in a ball-shape. However, they flower at a completely different time of the year and in a completely different habitat. Hmm, what to do? Well, the only thing possible – get up at 5 am, drive for 4 hours to a dusty road in a rural community and sit in the sun in over 30°C heat and wait - well, I say wait but really we arrived and watched butterfly after butterfly visit the plants, occasionally catching, occasionally photographing and always recording. What was interesting was the range of butterflies that visited, especially in comparison to the other subspecies. The slightly smaller flowers allowed for smaller butterflies (mostly pierids, but also some swallowtails) to feed on the nectar as well as contact the reproductive parts of the flower, allowing for effective pollination. 

Image 4. Scadoxus multiflorus subspecies multiflorus visited by a citrus swallowtail. Photo: HC Butler.

 

Image 5. Scadoxus multiflorus subspecies multiflorus visited by an African veined white. Photo: HC Butler.

Butterfly wing pollination has been documented by numerous authors for many plant species belonging to a range of plant families. And yet, many of these authors assumed that this mode of pollination was rare. But was this really the case? Just a few days spent watching Scadoxus multiflorus showed this behaviour of butterflies toward flowers of this species to be common, so the butterflies certainly knew what they were doing. Indeed, research by a fellow lab member, Dr Ian Kiepiel, showed that Clivia miniata was pollinated by the same method. Trawling through photos and illustrations of South African Amaryllidaceae, the plant family to which Scadoxus belongs, it struck me that many other species were similar in floral shape to either Scadoxus multiflorus or Clivia miniata. They were characterised by having red to orange flowers with small amounts of nectar in a small tube placed well behind the brush-like reproductive parts. After some digging around in the literature, it transpired that all these species (eight others in total) had been seen to be or had been hypothesised to be visited by butterflies.

Image 6. Flowers of South African Amaryllidaceae suspected or confirmed to be pollinated via butterfly wings. A, Scadoxus multiflorus subspecies katherinae; B, Nerine sarniensis; C, Brunsvigia marginata; D, Clivia miniata; E, Cyrtanthus elatus; F, Cyrtanthus flamossus; G, Cyrtanthus guthrieae; H, Cyrtanthus montanus; I, Cyrtanthus taitii. Illustrations: HC Butler.

So, in conclusion, what does this all mean? Well, now we know that two subspecies of Scadoxus multiflorus are pollinated by butterflies. Not only this but  the flowers appear to have evolved to fit the butterflies in such a way that pollen is transferred on their wings. Because we now know more about the pollination system for this species, we can also hypothesise about the pollination systems of several other species within the South African Amaryllidaceae. This opens up the floor for further studies into Amaryllidaceae as well as other plant families in terms of butterfly wing pollination. Perhaps it is not as rare as previously thought? 

Acknowledgements: The financial assistance of the National Research Foundation (NRF) towards this research is hereby acknowledged. I thank Steve Johnson for his supervision; Ruth Cozien for her comments and statistical input; Ian Kiepiel for his research into and many of his own photos of Clivia miniata as well as for his comments; and Ethan Newman for his help in collecting data for subspecies multiflorus in 2018 as well as his general enthusiasm for this project. Thanks also to my parents and all those in the pollination lab at UKZN over the past few years for their knowledge, support and endless driving.

Further reading: Hannah C Butler, Steven D Johnson, Butterfly-wing pollination in Scadoxus and other South African Amaryllidaceae, Botanical Journal of the Linnean Society, Volume 193, Issue 3, July 2020, Pages 363–374, https://doi.org/10.1093/botlinnean/boaa016

About the author: Hannah C. Butler is currently studying their PhD in Botany, of which this research forms a part, under the supervision of Prof Steven D. Johnson at the University of Kwa-Zulu Natal, Pietermaritzburg campus. Their interest in Amaryllidaceae has led to research into the breeding systems of Cyrtanthus and continued work on Scadoxus and its sister genus, Haemanthus. This article is derived from an initial publication which can be found at
https://academic.oup.com/botlinnean/article-abstract/193/3/363/5803307?redirectedFrom=fulltext