Senecio Sterquilinus On the Chatham Islands
Senecio sterquilinus is an annual to short-lived perennial daisy with rather fleshy leaves and bright yellow flowers. It is part of the so called “lautusoid” group (sensu Belcher), and was formally segregated from the closely related S. lautus by Dr Bob Ornduff in the late 1950s. The original gathering and type specimen was made by William Colenso in the 1840s from an Island in the Ahuriri Lagoon, near Napier (now low lying land and salt marsh following the 1931 Napier Earthquake). However when Ornduff recognised this species he knew it in the fresh state only from the Brothers, a series of small islands and rock stacks at the eastern entrance of the Cook Strait. Various botanists have since recognised S. sterquilinus from Stephens Island. However major changes to its distribution were made, first in 1988 when Colin Webb recognised the species as a local component of coastal vegetation from about Cape Foulwind (near Westport) south to Point Elizabeth on the north-western side of the South Island, and then in 1992 when it was discovered in the Wellington Harbour on Maitu (Somes) and Makaro (Ward) Islands. Later in 1994 S. sterquilinus was also collected from Stack “H”, one of a series of informally named islets and rock stacks located within the outer Hauraki Gulf around the main northern Mokohinau Island group.The Mokohinau discovery is rather unusual and the specimens are perhaps the largest in terms of leaf size and shape seen in this species. Only a small number of plants were found in a small area at the entrance of Diving Petrel burrows. Some botanists have speculated that the plant had to have been accidentally introduced there from the Cook Strait region by ornithologists or herpetologists.
On the 14 January 2006 botanists visiting the remote Western Reef, at the north western extremity of the main Chatham Island discovered S. sterquilinus as a local component of the sparsely vegetated central platform of the reef. The low lying reef may be completely submerged in moderate to heavy swells, so it is truly amazing that any terrestrial vascular plants grow there at all. Western Reef has a vascular plant flora of 11 species, the dominant of which is Chatham Button Daisy (Leptinella featherstonii). Senecio sterquilinus was found mainly in deep crevices and flags within the heavily eroded Chatham schist that forms the reef. On the reef it grew with another Chatham endemic groundsel, Senecio radiolatus subsp. radiolatus. A subsequent search of the Auckland Museum Herbarium (AK) located specimens of S. sterquilinus that had been incorrectly referred to S. radiolatus from two other northern Chatham Island groups, the Sisters and the Forty Fours.
Of interest is that the morphology of the Western Reef plants is a very close match to the specimens from Stack “H” in the Mokohinau Island group.
Collectively these disjunctions are more probably remnant populations rather than real disjunctions. Senecio sterquilinus is one of a group of species Ornduff recognised as part of what he called the Ornithocophrophilous Ecosystem (work that out!). Botanists now speculate that many of these peculiar disjunctions actually represent fragments of a formerly widespread and interconnected sea bird driven ecosystem. With the loss of sea birds from large parts of New Zealand, many of the plants dependent on their guano deposition, frequent disturbance, and subsequent rejuvenation of stale soils and habitat have died out. What we are now seeing is perhaps small relicts of that vegetation type, persisting in places where the ornithocoprophilous ecosystem is still more or less intact and functioning.
Posted: 24/01/2006