Sophora

The genus Sophora is a member of the distinctive ‘pea’ family (Fabaceae), a group of plants that provides us with some of our most attractive garden subjects. It consists of more than 50 species, which are found in subtropical and temperate regions of the world. The name Sophora is derived from the Arabic word (Sophero) to describe a tree bearing the distinctive flowers that are characteristic of the ‘pea’ family.

New Zealand has eight species of Sophora, collectively referred to by their Maori name, kowhai. Prior to 2001, just three species of kowhai were recognised, one of which (Sophora microphylla) was somewhat of a catch-all for a number of obviously distinct forms (which were subsequently described as new species). Interestingly, some of these species are associated with particular geologies, such as northwest Nelson’s Sophora longicarinata (which occurs over limestone and marble), Sophora godleyi (which is primarily found over sandstone and mudstone) and Sophora fulvida (a species with an affiliation for volcanic basalt and andesite).

The scientific name of this impressive species of kowhai is a potential misnomer that carries an interesting tale with it; a tale that is tinged with sadness and brutality. However, that story is not the starting point for a description of this tree. First and foremost, it should be appreciated as a beautiful and ecologically significant member of our northern coastal forests – such as at Wenderholm, where these photographs were taken.

The spring-flowering of Sophora chathamica is one of the great displays of our native flora. Its intended audience (primarily our native birds) attends this show with enthusiasm, for the tangible reward of nectar (which is borne in abundance within the flowers).

S. chathamica is a relatively recently described species which used to be considered part of the formerly variable S. microphylla complex of species. Its foliage is larger and more densely packed than most other forms of kowhai (approaching S. tetraptera in size), and it also differs from S. microphylla by not passing through a tangled, divaricating, juvenile phase.

Significantly, this species generally flowers earlier in its life than S. microphylla (and S. fulvida) – an attribute that weighs heavily in its favour for cultivation in the north of New Zealand.

Returning to the story of S. chathamica‘s misleading name, it was initially proposed as a distinct species by Leonard Cockayne, who visited the Chatham Islands in 1901, and recorded S. chathamica‘s abundance in limestone forest on the Chathams.

In his account, Cockayne referred to the earlier account of Henry Travers, who visited the Chathams in 1867. Contrary to Cockayne’s experience, Travers only saw three trees. All of them were a similar age, growing in the same location, and approximately 5m tall. Further back from this point in time, we must rely on supposition to surmise the remaining details of the story.

The indigenous people of the Chatham Islands, the Moriori¹, are relatively well-known, particularly due to the unusually peaceful nature of their society (compared to mainland Māori tribes of the time). In the 1830s, two North Island tribes occupied the islands, where they were transported aboard a European ship. Although one must always consider historical events with some idea of beliefs and context of the time, the sad manner in which these tribes displaced and killed Moriori can only be described as brutal.

The theory that has held most credence with botanists is that some of these North Island Māori (Ngati Mutunga and Ngati Tama) may have taken material of Sophora chathamica to Wellington (where they resided for a period) and consequently to the Chatham Islands as a valued plant. The original rohe of these tribes was on the border of northern Taranaki and the King Country, at the southern limit of S. chathamica‘s supposed natural distribution.

The timing of the Māori occupation of the Chathams (the mid-1830s) fits well with the size of the specimens that Travers recorded in 1867, to indicate that S. chathamica could well have been brought to these islands by these North Island tribes. Therefore, this species’ intriguing disjunct distribution may track the path of an interesting chapter of our social history.

To others, taxonomists can appear a fickle bunch; shifting plants around, creating new species, and sometimes deciding that old species should never have been recognised in the first instance. Although consensus is often not universal, this mostly takes place for good reason – so that we can develop a sound understanding of what our plants are, which plants are special to particular areas, and which plants are in need of protection².

When taxonomists re-assess a genus, it is called a revision. These usually happen when it is suspected that current knowledge (and decisions that have been made previously) are not as complete or accurate as they should be. This was the case several years ago, when a major revision of the kowhai genus, Sophora, was undertaken. One of the outcomes was the decision that this small tree, Sophora fulvida, is indeed a distinct species.

Sophora fulvida is a naturally uncommon coastal species, which mostly occurs on the west coast of the upper North Island from near Raglan to Maunganui Bluff in Northland (as well as on the east coast near Whangarei). Its most substantial populations are in the Waitakere Ranges, and as such it should become a plant that Aucklanders embrace as a special feature of the area. It is most commonly found on or near volcanic cliffs and rocky ground; repeating the preference of several kowhai species for open or disturbed ground. In the vicinity of Auckland, good places to view it in flower are in coastal forest near Karekare, and on the cliffs adjacent to the Waitakere Dam.

The flowers of S. fulvida are amongst the largest of our kowhai, and are profusely borne in good years. They appear in late spring/early summer, slightly later than the more common Sophora microphylla and S. chathamica (both species that occur in northern areas where S. fulvida grows). One of the most distinguishing features of S. fulvida as a garden plant is its compact size and somewhat stiff, spreading form. It normally forms densely-branched trees, to 3 or 4m in height³, but it can also grow as a shrub within nature, where harsh conditions often dictate plants’ growth patterns. The leaves have an attractive matte, greyish-green colour, that recedes in comparison with darker or glossier foliage.

The species name, ‘fulvida‘⁴, means golden-brown or tawny, and this refers to hairs on the leaves of the original plants that were collected (by the botanist H.H. Allan) at Anawhata⁵, in the Waitakeres. It is a suitable epithet, as similar hairs give the flowers’ calyces⁶ a beautiful golden-brown hue, whilst the combination of the matte leaves and fawn midribs also contribute towards lending the overall tree an attractive brownish tinge.

Considering that S. fulvida grows on naturally fertile sites within nature, it is a good idea to provide plants with high fertility in the garden (particularly as this will result in rapid growth and reasonably early flowering). Another piece of advice for growing all kowhai (with the exception of S. prostrata) in gardens is to avoid pruning in the months between November and February, as that is when borer are on the wing. Borer can be a damaging pest to kowhai, although it should also be stated that borer needs to be understood as a naturally-occurring pest – one that many kowhai can live with for an extremely long time.

Therefore, although borer should be avoided where possible (by treating trees early on in an infestation), they do not necessarily spell a death sentence for established trees. It is worth noting here that the ability of plants to withstand (or even avoid) the influence of other organisms (such as borer) is greatly assisted by planting diverse environments.

This small-growing species is distinct amongst the New Zealand members of Sophora, in that it maintains the divaricate growth form throughout its entire life. It has not traditionally been as popular for garden use as other kowhai species, due to its unusual growth form and comparatively small flowers.

However, it has become increasingly appreciated in recent years for its resilience, sculptural form and attractive colouration (especially on its orangish branches). The stiff habit of this shrub lends it well to either establishing structure within plantings (whether assuming its natural form or used as informal hedging), or even for use as a bonsai specimen. It is one of the finest native plants for long-term cultivation in pots, as it will tolerate severe root restriction, drought and exposure to sun and wind.

Sophora prostrata is native to the dry eastern side of the Southern Alps, from Marlborough to southern Canterbury. Accordingly, it is well adapted to many of the conditions that are prevalent within urban environments; such as high winds, extreme light levels and frequent drought.

The form of individual plants is determined by the degree of exposure to the elements and soil environment, demonstrating a wide range of sizes and forms (from low hummocks to large shrubs). Despite its exclusively southern distribution, S. prostrata is amenable to cultivation in most parts of the country (even in the humid north), and is a versatile landscape plant.

The flowers of S. prostrata are unusual in both colour (often attaining quite orange hues, in contrast to the more typical yellows of other kowhai species) and in the manner in which flowers are borne upon the plants (they are often held in an ‘upside-down’ position, when compared with other kowhai species).