The reflective qualities of white flowers make them particularly noticeable in low light – such as within heavily shaded sites or under the faint nighttime glow of the moon. It is therefore unsurprising that this colouration is common in plants that are pollinated by nocturnal insects (such as night-flying moths).
In the case of Ourisia, this fact is a bit of a red herring, as pollination is actually mostly carried out by native bees1 and hoverflies (both of which are chiefly active in the day). However, the reason that I mention it is to convey one of my most vivid impressions of this beautiful genus of herbs – namely, the way in which their white flowers light up the shaded spots in which they often thrive. Few flowers illuminate a dark space with quite the same brilliance as our larger species of Ourisia.
We have c. 13 native species of Ourisia, which vary considerably in size – from smaller, creeping species like O. caespitosa and O. vulcanica, to the statuesque O. macrophylla and O. macrocarpa (both of which can reach half a metre in height). The primary flower colour of our New Zealand species is white, and most of them are further embellished by a splash of yellow in the throat of their flowers. The South American species display a greater variety of flower colour, with species exhibiting a range of hues from white to pale lilac, vibrant pink and red.
Ourisia has an interesting distribution, as it is only found in New Zealand and South America (bar one outlier species in Tasmania)2. Other native genera that strongly demonstrate the links between our flora and South America include Nothofagus, Jovellana and Fuchsia.
One floral character that is exhibited well in the flowers of New Zealand’s Ourisia spp. is bilateral symmetry (or zygomorphy, as it is otherwise known). Despite sounding technical, this is a very simple affair. It means that a flower is arranged like a human face – in that it is only symmetrical along one axis (which in our case, is the line that runs down the centre of our noses)3.
Bilateral symmetry (or zygomorphy as it is otherwise known) is an advanced state in floral evolution, that is associated with specialisation towards certain pollinators. However, it also delivers an added level of satisfaction in our appreciation of flowers, for we read them as we might read a face.
With its well presented spires of pure white flowers and rosettes of deep green foliage, Ourisia macrophylla ranks amongst the most gardenworthy of all our native herbs. This North Island species of mountain ‘foxglove’ is the sole species of Ourisia that I have looked to cultivate in our northern climate – as I learned about it via Terry and Lindsey Hatch, who grow it very successfully in Pukekohe.
The key to cultivating many plants is growing the right form; and in the case of Ourisia macrophylla, Terry and Lindsey grow a form that has been planted at New Plymouth’s Pukekura Park for many years. It has performed exceptionally well in the fern growing area of Terry and Lindsey’s nursery, to the extent that it has freely seeded through many of the other bags or tubes in the shadehouse (an appealing bonus for discerning gardeners). It has also performed very well on a damp, south-facing slope, where seepage provides a fairly consistent supply of moisture.
Planting Ourisia macrophylla on a bank provides it with two factors that aid in cultivating it in a northern climate; air movement (to mitigate the effect of our humid summers) and drainage (so that it is not sitting in boggy ground). Another situation that is useful for growing plants like O. macrophylla is to plant them at the base of boulders – as water tends to be available underneath stones, and a boulder can provide shade for the roots of the mountain foxglove. Both of these niches (damp banks and boulders) are the kinds of habitats in which Ourisia macrophylla thrives in the wild.
The species is divided into two subspecies; O. macrophylla ssp. macrophylla, which is found in the North Island, from Mt Pirongia in the north to the Tararua Ranges in the south, and O. macrophylla ssp. lactea, which is found throughout much of the South Island. There is a degree of variation within the subspecies, O. macrophylla ssp. macrophylla; to the extent that plants that occur on Mt Taranaki were previously considered to be taxonomically distinct from other North Island plants4.