The predominance of white and cream flowers within the New Zealand flora is often commented upon. However, there exists a wide array of plants that are adorned by flowers of other colours; such as the yellow of kowhai, the red of pohutukawa, the purple of poroporo, and the orange of waiu-atua. Although relatively small, the flowers of waiu-atua (Rhadothamnus solandri) are a conspicuous feature of the dark interior of many of our northern forests. In addition to their normal orange colouration, they are made doubly striking by the blood-red stripes that bedeck their tubes.
Rhabdothamnus is a genus of just one species, which is confined to New Zealand; and it is the only member of its family (the Gesneriaceae) to occur on our shores. Its name is derived from the Greek words rhabdos (rod) and thamnos (shrub), and translates as “twiggy shrub”1 – an obvious reference to its growth habit.
As is my wont, I shall diverge for a moment to explain a term that one sometimes meets in descriptions of plants. “Rupestral” is a commonly-encountered word in botanical literature. It simply means “rock-dwelling”, and can refer to plants that either grow on cliffs or bluffs, or those that grow on rocky ground or atop boulders.
Although Rhabdothamnus solandri also grows with its feet firmly on the forest floor (usually in sloping situations), it is especially associated with rocky sites, such as cliff faces – and is therefore an example of a species that is frequently rupestral. The photograph above illustrates a typical habitat for R. solandri; in this case, within an opening in the limestone cliffs on the southern side of Kawhia Harbour. Its range extends from the tip of the North Island (on the toxic cliffs of North Cape) down to the vicinity of Wellington, although it is uncommon in the south of its natural range.
Waiu-atua exhibits a characteristic that is common amongst several northern natives – in that forms from offshore islands bear larger leaves than their mainland counterparts. These larger-leaved forms (of which the Maunganui Bluff form is pictured below) make attractive garden specimens, and are occasionally available via specialist growers. Variation also occurs within the flower colour, with plants ranging from a dull red to orange (the most common colour) to yellow.
The pollination of Rhabdothamnus solandri is a surprising affair, considering the delicate, flexuous nature of its stems – for it is bird-pollinated. Our native honeyeaters (tui, bellbirds and stitchbirds) derive the nectar that is their stock-in-trade from the flowers of waiu-atua, although quite how these birds balance upon the thin, arching stems is beyond me. This process would be particularly fascinating to observe when effected by the largest of our honeyeaters, the tui.
Waiu-atua was discovered to science on Cook’s first voyage to New Zealand in 1769, by Joseph Banks and Daniel Solander (who collected it at Mercury Bay). However, as Banks and Solander’s manuscript was not published within their lifetimes, the authority for naming the species was assumed by Allan Cunningham, who collected it in 1826. Although the plant does not bear the name that Banks and Solander applied to it (Columnea scabrosa), Cunningham honoured Solander in waiu-atua’s specific epithet, ‘solandri‘.