Leptinella featherstonii

Chatham oddities – the anomalous Chatham Island button daisy

Leptinella featherstonii in full flower, Kaiangaroa Point, Kaiangaroa.
Leptinella featherstonii in full flower, Kaiangaroa Point, Kaiangaroa. Photo: P. J. de Lange

Leptinella belong to the daisy family (Asteraceae / Compositae). As a rule, they are perennial creeping herbs forming a compact turf. Current estimates suggest there are c.33 species centred on Australasia with outliers in South Africa and South America. New Zealand has c.24 species, most of them endemic. However, the taxonomy of the New Zealand species is well overdue for revision having last been treated in 1972 (Lloyd 1972), with only minor tweaks since then (Heenan 2009), indications are that we probably have a few more species yet to describe, and a few adjustments will also need to be made.

Leptinella are probably better known to people as ‘cotula’, and under that name, they are renowned for the ‘no-mow’ lawns that they can create when planted closely together. Indeed, cotula are (or at least they were before ‘astro-turf’ dulled the imaginative) the preferred turf for New Zealand’s bowling greens.

All of the New Zealand species are creeping or small tufted herbs, that is except one, the Chatham Islands button daisy, Leptinella featherstonii – this one seriously bucks the trend. Instead of forming a turf it is a woody shrub up to 1.2 m tall.

Leptinella featherstonii is named after Dr Issac E. Featherston (1813–1876) who settled in New Zealand in 1841. He resided in Wellington where he was a physician, politician, first Superintendent of Wellington Province, and first Agent-General for New Zealand in London. The species was named for him by the renowned German botanist Ferdinand von Mueller (1825–1896) who was the state botanist of Victoria, Australia. Featherston, along with William T.L. Travers (1819–1903) helped finance the first serious botanical investigation of the Chatham Islands (Mueller 1864; Connor 1998).

Mueller was at first puzzled by the specimens of Chatham Islands button daisy that he received. Their upright woody growth habit he considered sufficiently unusual that he briefly flirted with the idea of naming a new genus, “Traversia” (in honour of his main New Zealand based financial botanical backer for the Chatham’s project W.T.L. Travers) to accommodate it. However, he eventually placed the plant in the genus Leptinella, a decision which prompted Joseph D. Hooker (1817–1911) his arch rival in all things botanical (Connor 1998), to place Mueller’s new species in Cotula. There it stayed until 1987 (123 years later no less!) when the Late David Lloyd and Colin Webb reassigned it Leptinella (Lloyd & Webb 1987).

When I first saw this species in 1996, I could not understand how on earth it was ever placed in Leptinella or Cotula. That was my first jaunt to the Chatham Islands – the most easterly outlier of the New Zealand archipelago, sitting perched on the Chatham Rise c.830 km east of Christchurch. The plants I saw then were located on a small rock stack near the north-eastern settlement of Kaiangaroa, on Rekohu (Chatham Island), the largest of the islands in the group.

At that site the species was all but functionally extinct. It had been discovered that Leptinella featherstonii thrives on a high nutrient overload. Without frequent guano and faecal enrichment, and constant disturbance, plants simply wither away and die. At the time the Department of Conservation elected to fertilize the remnant population with dollops of slow-release fertilizer. This measure has worked exceptionally well, allowing island visitors with an interest in the Chathams biota to see a plant that is otherwise known only from the predator-free, largely inaccessible often privately-owned outer islands, islets and rock stacks (see for example, an account of the Flora of Western Reef by de Lange & Sawyer (2008)). On those pockets of land, the seabird / seal ecosystem (known to ecologists as the ‘ornithocoprophilous’ ecosystem (see Norton et al. 1997)) remains intact, and there Leptinella featherstonii flourishes, on Rekohu (Chatham Island) that ecosystem is effectively extinct; so on that island the Leptinella, is also all but extinct.

Recently (over the last decade), the Taiko Trust (see https://www.taiko.org.nz/) have, in an ambitious restoration programme, started to recreate the ‘ornithocoprophilous’ ecosystem on headlands along the South Chatham coast of Rekohu. As part of that work they have been translocating Chatham Island seabirds and their associated flora to Rekohu. It’s working very well, and it is pleasing to see that new functional Leptinella featherstonii populations are now present within their restored sites, thriving on the ‘mess’ left behind by the albatrosses and petrels they have restored to the headlands.

Taxonomically though, Leptinella featherstonii remains anomalous. No other Leptinella has such a prominent, upright, shrubby habit, or produces wood. Was Mueller right to place this plant in Leptinella, or should it go into another genus after all? The advent of molecular systematics has helped clear up the situation. Leptinella featherstonii it transpires is correctly assigned to Leptinella (Himmelreich et al. 2014). Mueller was indeed right to make that decision. What is even more bizarre is that the sister species to it, is Leptinella pyrethrifolia, a South Island, scree-inhabiting species with the usual scrambling herb habit (de Lange 2018). We now know that the Chatham Islands endemic flora is derived from 29 separate dispersal events from mostly the westerly lying main islands of New Zealand, followed by some 6–2 million years of separate isolation and divergence (Heenan et al.  2010). The ancestral lineage of what of is now Leptinella featherstonii and L. pyrethrifolia split two ways, one branch colonized the Chatham Islands where it developed the unique, woody shrub habit to become L. featherstonii, whilst the other became a scree specialist we know as L. pyrethrifolia today.

References

  • Connor, H.E. 1998: The Vegetation of the Chatham Islands by Ferdinand Mueller (1864): an appreciation. Muelleria 11: 13–25.
  • de Lange, P.J. 2018: Leptinella pyrethrifolia var. pyrethrifolia Fact Sheet (content continuously updated). New Zealand Plant Conservation Network. http://www.nzpcn.org.nz/flora_details.aspx?ID=918 (23 November 2018)
  • de Lange, P.J.; Sawyer, J.W.D. 2008: Flora of Western Reef, Chatham Islands. New Zealand Journal of Botany 46: 425-431
  • Heenan, P. B. 2009: A diminutive new species of Leptinella (Asteraceae) from arid habitats of the South Island, New Zealand. New Zealand Journal of Botany 47: 127–132.
  • Heenan, P.B.; Mitchell, A.D.; de Lange, P.J.; Keeling, J.; Paterson, A.M. 2010: Late Cenozoic origin and diversification of Chatham Islands endemic plant species revealed by analyses of DNA sequence data. New Zealand Journal of Botany 48: 83–136.
  • Himmelreich, S. Breitwieser, I.; Oberprieler, C. 2014: Phylogenetic relationships in the extreme polyploid complex of the New Zealand genus Leptinella (Compositae: Anthemideae) based on AFLP data. Taxon 63: 883–898.
  • Lloyd, D.G. 1972: A revision of the New Zealand, Subantarctic, and South American species of Cotula, section Leptinella. New Zealand Journal of Botany 10: 277-372.
  • Lloyd, D.G.; Webb, C. J. 1987: The reinstatement of Leptinella at generic rank, and the status of the ‘Cotuleae’ (Asteraceae, Anthemideae). New Zealand Journal of Botany 25: 99-105
  • Mueller, F. 1864: The vegetation of the Chatham-Islands – a flora of Chatham Island plants including descriptions of 129 indigenous species. Melbourne, Australia.
  • Norton, D.A.; de Lange, P.J.; Garnock-Jones, P.J.; Given, D.A. 1997: The role of seabirds and seals in the survival of coastal plants: lessons from New Zealand Lepidium (Brassicaceae). Biodiversity and Conservation 6: 765-785