Plant profiles > Sophora

Family: Fabaceae

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. New Zealand has eight species of Sophora, collectively referred to by their Maori name, kowhai. Interestingly, 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.

Sophora fulvida
Waitakere kowhai

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. However, it must be remembered that this mostly takes place for good reason - so that we can have a good understanding of what our plants are, what plants are special to particular areas, and what plants are in need of protection¹.

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 height², 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'³, 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 Anawhata⁴, in the Waitakeres. It is a suitable epithet, as similar hairs give the flowers' calyces⁵ 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.

Sophora prostrata
Prostrate kowhai

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.  

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).

Footnotes

1. Other reasons also exist, such as the value in gaining a wider understanding of the way in which different plant groups are related, and by association a more thorough knowledge of the natural world (including evolution).
2. Sophora fulvida can reach significantly taller than 4m, but the size range indicated is more usual, in both natural and garden conditions.
3. As stated within 'Meanings and origins of botanical names of New Zealand plants' (Taylor, M. 2002. Auckland Botanical Society Bulletin 26.).
4. This information, on the etymology of 'fulvida' was provided within the major revision of 2001, by Heenan, De Lange and Wilton - Sophora (Fabaceae) in New Zealand : taxonomy, distribution and biogeography. New Zealand Journal of Botany, 2001, Vol. 39 : 17 - 53.
5. The outer parts of the flower, that form what looks like a cup, within which the petals sit.