Toropapa - The Fragrant Delight Hidden in the Forest
LARA SHEPHERD (Museum of New Zealand Te Papa Tongarewa)
The stunning flowers of Alseuosmia macrophylla. They not only look beautiful but are also very fragrant (Photo: Jaqui Geux)
Have you ever been walking through the forest and been delighted by a strong floral perfume? You may have walked near a flowering toropapa bush. Toropapa is a genus of small shrubs found in New Zealand. Their flowers are among the most fragrant of any New Zealand plant and their scientific name (Alseuosmia) means ‘perfumed grove’, which is very apt! Unfortunately, they are very difficult to cultivate; otherwise, I’m sure they would be a popular plant for the home garden.
Typical Alseuosmia quercifolia. The red leaf stems and white central vein of the leaf is distinctive for this species (Photo: Lara Shepherd)
Five species of toropapa are currently recognised(1). However, several of the species have extremely variable leaves. This has made it difficult to determine both the number of species and the boundaries between them, and is currently being researched by botanists at Te Papa.
This form of Alseuosmia banksii resembles ramarama (Lophomyrtus bullata) (Photo: Lara Shepherd)
Perhaps, the most interesting feature of toropapa is that the leaves of some forms appear to mimic unrelated plant species, such as horopito, ramarama and red matipo(2). The leaves of toropapa are palatable to browsers but some of the species they appear to mimic produce anti-browse chemicals. By resembling plants that taste awful, did toropapa gain protection from browsing by animals like moa, tricking them into thinking they were inedible?
This form of Alseuosmia banksii resembles red matipo (Myrsine australis) (Photo: Peter de Lange)
Mimicry has been demonstrated in many animals but appears to be rare in plants. An elegant study by a student from Victoria University of Wellington(3),(4) recently provided the first direct evidence of this type of mimicry (defensive mimicry) in plants – using the toropapa species Alseuosmia pusilla and horopito, which it closely resembles. The student set up browsing experiments that showed farmed deer would quite happily eat toropapa if it was the only species present. But once the deer had eaten horopito, with its peppery taste, they were less likely to eat toropapa.
Three species of toropapa occur on Aotea: Alseuosmia macrophylla, A. quercifolia and A. banksii. Toropapa prefers to grow under a forest canopy in shady, moist habitats so keep an eye out for them on your next bush walk (or follow your nose during late winter and spring, when they are flowering).
References:
This form of Alseuosmia banksii resembles tawheowheo (Quintina serrata) (Photo: Lara Shepherd)
Shepherd LD, de Lange PJ, Townsend A, Perrie LR. 2020. A biological and ecological review of the endemic New Zea-land genus Alseuosmia (toropapa; Alseuosmiaceae). New Zealand Journal of Botany 58: 2-18. https://doi.org/10.1080/0028825X.2019.1659376
Shepherd LD. 2018. How many species of the confusing shrub toropapa are disguised in the bush? How many species of the confusing shrub toropapa are disguised in the bush? | Te Papa’s Blog
Yager KG. 2018. Batesian mimicry in plants: the significance of shared leaf shape between Alseuosmia pusilla and Pseudowintera colorata. PhD thesis. Victoria University of Wellington, Wellington. http://hdl.handle.net/10063/7662
Canadian Science Publishing. 2016. New research uses novel approach to study plant mimicry: Research provides first detailed evidence of leaf shape being matched between an undefended, protected plant species. www.sciencedaily.com/releases/2016/06/160613130703.htm