Taxonomy, ecology, and conservation of Olearia adenocarpa (Asteraceae), a new species from braided riverbeds in Canterbury, New Zealand

A new species of small‐leaved shrubby Olearia is described from lowland parts of the Rakaia and Waimakariri river systems in Canterbury, New Zealand. Olearia adenocarpa belongs in Olearia sect. Divaricaster and is placed with five other species in an informal group with terete and two‐ridged stems. It differs from other species of this group in its low‐growing and open habit, slender branches that often originate from below ground, lanceolate involucral bracts with appressed simple eglandular hairs, and an ovary and achene that have a sparse to moderate covering of glandular hairs. Olearia adenocarpa is a coloniser of abandoned river channels composed of stony sandy sediments which are well drained and drought prone but relatively fertile. It originally shared this habitat with a small group of other indigenous shrubs, herbs, and cosmopolitan mosses, but is now surrounded by cultural grasslands dominated by Australian and Eurasian grasses and annual herbs. About 650 plants of O. adenocarpa divided unequally between two subpopulations are known. Of these only 11 mature plants are considered capable of sexual reproduction. The remaining plants are moderately to severely browsed by animals and reproductively suppressed. Currently, there is no recruitment of young plants of O. adenocarpa. We recommend that the species be ranked as Nationally Critical.