A Moraea and its scent

The South African irid Moraea ochroleuca is in flower here at the moment, with its characteristic buttercup-yellow bowl-shaped flowers. The shiny brown veins that radiate from the base of the perianth secrete nectar, and each flower lasts for just two days.

Goldblatt et al. (2005) described its smell as putrid and the pollination syndrome as sapromyophily by carrion flies in the families Calliphoridae, Muscidae, and Sarcophagidae. However, the M. ochroleuca in my garden has a faint smell of yeast, just like the medium used to culture Drosophila in genetics labs. And, sure enough, a species of Drosophila is attracted to these flowers where it remains for long periods apparently feeding on the nectar. I doubt that Drosophila could pollinate this flower, since it stays on the nectaries and would only contact the stigmas, which are held far above the nectaries, by accident. In any case, my M. ochroleuca have never set seed in 12 years despite an attempt at hand pollination, and this is probably due to self-incompatibility as they are all one clone.

Maybe this clone is atypical in its scent. Or maybe we’re describing the same scent in different ways; it’s probably a subjective judgement whether a smell should be called putrid. Humans don’t perceive smells the same way that insects do, and there is lot of variation among humans in judging a perfume. The scent of another sapromyophilous irid, Ferraria crispa, has sometimes been compared to carrion. But to me, it has more of a pungent chemical smell reminiscent of iodine; and my wife says it’s like very stale spices. Neither the Moraea or the Ferraria has the pervasive rotting-corpse stench of Stapelia (Apocynaceae) or Dracunculus (Araceae); it’s necessary to get up close to detect their scent at all.

The presence of nectar is unusual in a sapromyophilous flower; it may be that, having only recently evolved this pollination strategy, Moraea ochroleuca still needs to provide a food reward to the pollinator. Goldblatt et al. also recorded a range of other Diptera including syrphids (hoverflies) as well as honeybees as occasional visitors.

The history of Moraea ochroleuca in Australian gardens is obscure. Unlike many other showy South African irids, the species formerly placed in Homeria were not promoted in 20th century gardening literature or advertised by retail nurseries. However, a few of them were early introductions into botanic gardens, and there may even be some truth in the anecdotes about Boer war veterans bringing back “Cape tulips” as souvenirs. The plant growing at the Adelaide Botanic Garden in 1859 under the name of ‘Moraea grandiflora’ may have been M. ochroleuca. The flower pictured above is heritage garden stock from the Adelaide area, and is a close match to a feral specimen collected by Ray Alcock at Yallunda Flat, AD96452089, that Peter Goldblatt determined as M. ochroleuca.

References

Francis, G.W. (1859) Catalogue of the Plants under Cultivation in the Government Botanic Gardens, Adelaide South Australia.

Goldblatt, P., Bernhardt, P. & Manning, J.C. (2005) Pollination mechanisms in the African genus Moraea (Iridaceae, Iridoideae): floral divergence and adaptation for pollinators. Adansonia 27: 21-46.

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