Of all the roughly 2360 vascular plant species that are native to New Zealand, few command the attention of New Zealanders as much as the pohutukawa. The genus to which pohutukawa belongs, Metrosideros, also contains 11 other beautiful species that are native to this country, most of which are not embedded in the public consciousness as emphatically as pohutukawa. The next best known members of the genus are the two tree rātā species; northern rātā (Metrosideros robusta) and southern rātā (Metrosideros umbellata). The former is one of the most impressive of our forest giants, whilst the latter is a notable component of forests in southern parts of New Zealand, stretching down towards the country's southernmost limits in the subantarctic Auckland Islands.

Sometimes, a bit of detailed botanical information can be very useful in understanding garden plants better. Bearing this in mind, it is worth pointing out here that the genus, Metrosideros, is divided into three groups (called subgenera), of which two are represented in New Zealand. Put simply, this means that New Zealand species of Metrosideros fall within one of these two groups; one of which is confusingly also called Metrosideros (i.e., genus Metrosideros, subgenus Metrosideros), whilst the other subgenus is called Mearnsia. Generally speaking, the large tree species (like pohutukawa and the tree rātā) fall within subgenus, Metrosideros, and the climbing/shrubby species are part of the Mearnsia subgenus. This distinction helps one understand the relationship between an imposing tree like pohutukawa and a compact climbing shrub like Metrosideros colensoi.

The primary reason that pohutukawa and rātā are so beloved within New Zealand is the summer appearance of their brilliant red flowers. These are loaded with nectar, and consequently attract large numbers of birds and insects (from whom the plant receives the benefit of pollination). Previously, before their populations were seriously affected by the impact of humans, native bats and lizards also played a role in the pollination of the flowers. The brilliant floral displays are mainly created by large clusters of the male part of the flower, which are called stamens. This is different from the way in which many garden flowers (such as a daffodil) announce their presence, which is through coloured petals (and other similar structures). The nectar that is so attractive to certain animals sits at the base of the flower (beneath the riotous display of stamens), in a cup-like part called a hypanthium.

All New Zealand Metrosideros species bear this same basic floral form, although they also appear in a variety of sizes and colours, including white, light pink, orange-red, and even yellow (in certain natural variants, such as one form of pohutukawa). The name, Metrosideros, is derived from the Greek terms, metra and sideron, which mean 'core/heartwood' and 'iron' respectively. This refers to the extremely hard heartwood of many members of the genus. The genus is part of the widespread myrtle family, named for the common myrtle (Myrtus communis) which is of such cultural significance to Mediterranean cultures. Other members of the family include feijoa, guava and Eucalyptus.

For in-depth information on the genus (including its cultural and mythological significance), an excellent book was published in 2005 by Te Papa Press. Entitled 'Pohutukawa & Rata : New Zealand's Iron-hearted Trees', the author Philip Simpson presented an exhaustive and fascinating resource on the main tree species, as he did in his previous work on cabbage trees.

Metrosideros perforata
Small white rātā; akatea; akatorotoro

Plants can go through many botanical names throughout history. These names are often quite interesting, as they not only give information about the characteristics of a plant, but also of people's impressions of a plant. With regards to this, it is worth noting that one name formerly applied to this species (by the botanist, Allan Cunningham) is Metrosideros buxifolia. That is interesting because Cunningham made a comparison between this plant and the common box (Buxus spp.), which is ubiquitous as a hedging plant within New Zealand and abroad.

New Zealand has many species that should be turned towards common uses, such as hedging, for which we consistently utilise exotic species based on the tired (and often inappropriate) answers handed down by our European forebears, or from overseas trends. The photograph above shows a specimen of this plant (which is normally a root climber), growing in pasture as a compact shrub. If we take nature as our teacher, it is obvious that this is a plant that can be turned towards use as a compact hedge - in my opinion, best applied as a slightly informal hedge, so that one can enjoy the flowers.

As mentioned above, Metrosideros perforata usually grows as a climbing shrub (like other members of the subgenus, Mearnsia). Within the normal course of events, the species has two growth forms; the smaller-leaved juvenile state, which clings to tree trunks or other supports by specialised roots, and the adult state, which is exhibited in the plant shown above. In the absence of something to climb on, the plant assumes the adult growth form, and grows as a relatively compact shrub. This tendency is also aided by the propagation of plants from cuttings taken off adult plants.

Although it can grow to in excess of 1.5m as a ground shrub, M. perforata is very amenable to being trimmed to as low as 40cm high. Its bright, dark green foliage is highly attractive, and is arranged in a very ordered manner along the stems. In summer, it produces large quantities of pure white flowers, which are a favourite of bees. Whilst it is able to grow within the damp interior of northern forests (albeit in juvenile form), M. perforata is also capable of growing in difficult, exposed situations, such as dry hillsides. It is predominantly a species of warmer areas, occurring in lowland forest as far south as the northern tip of Fiordland. Consequently, it is intolerant of heavy frosts.

Due to the beauty of its foliage, flowers and growth habit, and to the wide range of conditions in which it will thrive, Metrosideros perforata is a species that should be used much more extensively than it is, especially for the purpose of providing structure within plantings.

Metrosideros colensoi

This climbing rātā is an elegant and distinctive plant, which forms curtains of hanging branches upon tree trunks or rock faces. It is especially associated with limestone areas, but is found in other habitats. The weeping habit is the most remarkable feature of this species; a characteristic that, furthermore, is unusual to find in any species (from New Zealand or otherwise).

This species has vibrant green foliage, like M. perforata, although with more pointed leaves. The new season's foliage comes out in a comparatively lighter shade of green, which contrasts with the darker colour of the existing foliage. The delicate, pinkish-white flowers appear in early summer, towards the end of the branches.

Within the garden, M. colensoi can be used to similar effect as its natural growth form (for climbing up trees or walls), or as a low shrub. If it is to be used for the latter application, it should be planted in a slightly raised position, so that its pendent habit can be best appreciated. Due in part to the comparatively small size of the flowers, M. colensoi has consistently been undervalued as a garden plant, in favour of its relatives that exhibit more spectacular flowering (it doesn't feature, or barely receives mention, within most books on native trees and shrubs for gardens). However, it is in several ways superior to more commonly grown species, such as Metrosideros carminea, on account of the ordered appearance of its growth form, and the 'movement' conveyed by its downward arching branches.

The specific name commemorates William Colenso, an early missionary who was one of the great characters of New Zealand botany. On his travels through New Zealand (many conducted by foot), Colenso developed a familiarity with the New Zealand flora that few could emulate. Metrosideros colensoi grows within lowland forest as far south as Greymouth and Kaikoura.