Hebe

At the outset of this profile, it is important to note a significant change that has affected how this genus is known. After a period of considerable debate, Hebe has been transferred into Veronica (along with its related genera) – the genus in which it was originally described. Regardless of the current stance on this matter, I personally favour continuing usage of the name Hebe herein, for the same reasons as the authors of the most comprehensive monograph on the genus¹. Within that work, M. Bayly and A. Kellow contended that lumping all species back into a very large, wide-ranging genus, Veronica, would “create a classification that is information-poor, obscuring obvious diversity and some clear relationships.”

More important than my personal preference on this matter (which is obviously not better-informed than the eminent botanists who made the change) is the simple fact that it continues to be referred to almost universally within horticulture as Hebe (as well as within practically all literature about the genus).

When one considers the plethora of information that has been produced about this popular genus of shrubs, it is hard to see what more needs to be written. However, in my opinion, there is still much to be said regarding Hebe‘s place in gardens. As with several other native genera (of which Pittosporum is perhaps the best example), a great deal of interest has been expressed in artificial hybrids and a limited range of species; yet many beautiful species are ignored by gardeners and landscapers.

It also seems to me that there is a lack of knowledge regarding the limitations of many species/varieties in certain climates; especially the warm, humid north, where inappropriate varieties are commonly peddled by garden centres and nurseries.

In his fine book on the cultivation of hebes², Lawrie Metcalf gives a very good explanation of the reasons that we can misinterpret the environments that plants occupy within nature. For example, he recounts that although a plant may inhabit a moist climate, the effects of wind and topography create an entirely different set of conditions than one may surmise (on the basis of straight geography).

This is a particularly salient point for northern species of Hebe, many of which grow in exposed situations on sloping ground (like cliffs and outcrops) – conditions that are not particularly analagous with many positions in the garden. Accordingly, plants like Hebe bishopiana and H. obtusata (which grow in Auckland’s Waitakere Ranges) generally require careful placement within gardens just 10 or 20km away from their natural homes – due largely to humidity and a lack of air movement.

So, as Lawrie Metcalf has pointed out, the cultivation of this beautiful genus of shrubs is best accompanied with some knowledge of the kinds of places that they are adapted to. In my opinion, the key to growing many hebes successfully is providing some level of resistance. Wind is a major editing factor in many of the habitats in which Hebe has evolved, as is the influence of salt. Likewise, cold weather is a necessary limitation for a significant number of (mostly southern) Hebe spp.

The observations that are noted above are obviously not applicable to all members of Hebe, as there is a great range of species – including a few that grow in reasonably sheltered forest conditions. However, I wish to make the point that a significant proportion of hebes have evolved towards open, exposed habitats – and gardeners should position plants with this knowledge in mind, to achieve the best results in the long term.

Of the many species that we have trialled in Auckland, we have been most impressed by Hebe parviflora, H. stenophylla var. oliveri, H. diosmifolia, H. pubescens ssp. sejuncta and H. treadwellii. One of our main criteria for assessing their merit is the ability of these species to retain a dense habit in our mild climate – especially where grown in close proximity to other plants.

Hebes put on some of the most spectacular flowering displays in the New Zealand flora. These are epicentres of insect activity, and constitute an important source of nectar and pollen for many of our native insect species (particularly native bees and flies – such as the small bee pictured below, on Hebe parviflora, which I suspect is a member of the genus, Lasioglossum). This ecological service is a worthwhile incentive for cultivating our hebes, and should be borne in mind by anyone wishing to encourage wildlife in their gardens.

Hebe‘s name befits the beauty of so many of its species; as it is named after the Greek goddess of youth, Hebe, who was a daughter of Zeus. As noted above, the title of the genus has been a subject of taxonomic debate, as several eminent botanists have successfully argued to return all of our species into the widespread genus, Veronica, to which they were originally assigned.

Context counts for a great deal within horticulture; not just for understanding plants’ growing requirements, but also for developing a more nuanced stance on aesthetics. I am often conscious of this when I consider the place of certain bold-leaved species in gardens, such as Astelia grandis or Ligularia reniformis (whose correct name is now Cremanthodium reniforme), for plants such as these tend not to occur within a clash of neatly-defined, bold forms in the manner that one often sees deployed within gardens.

To the contrary, in naturally-occurring plant communities, their bold forms read more often as points within a sea of fine, shifting textures that offer a subtle counterpoint to their more readily digestible forms. It is for this reason that I am not fond of the kinds of rampant displays of obvious contrast that some landscape designers employ – a technique that can result in an imbalanced visual cacophony in which the eye is neither allowed to rest nor linger.

For me, this sentiment extends to certain plants with particularly neat, contained growth forms, like Hebe diosmifolia. Having seen them utilised too often like stiff, prim participants in the horticultural equivalent of a dictator’s military parade, viewing how H. diosmifolia sits within wild habitats is both refreshing and informative.

In this sense, it reminds me of comments made by Rob Champion in an inhouse talk (for O2 Landscapes) about a trip that he made through the Pyrenees, wherein Rob waxed lyrical about the beauty of Buxus sempervirens in its natural habitat. In the understorey of Spanish woodlands near the margins of streambeds subjected to volatile seasonal flooding, shrubs of boxwood take on lively forms that are reminiscent of the manner in which the esteemed Belgian landscape architect, Jacques Wirtz, formalised their natural growth forms in many projects.

Similar to boxwood within European woodlands, Hebe diosmifolia‘s orderly growth habit registers well in association with plants that possess differing qualities, such as the dynamic trunks of kanuka or Leucopogon fasciculatus‘ billowing clouds of pale green foliage in the habitat pictured above (in dune forest at Pouto Peninsula). The Pouto population demonstrates the upright, tall habit that this variable species assumes within several wooded areas such as at Pouto and Ahipara.

At Cape Reinga, where very compact bushes of H. diosmifolia are a conspicuous feature of windbeaten shrubland (shown below), low mounds of manuka and Coprosma neglecta offer a similarly contrasting, muted tone amidst scattered specimens of flax and the sinuous orange strands of the peculiar parasitic plant, Cassytha paniculata. There is a marked difference between the flowering time of plants from northern populations (which generally flower in mid-summer) and those from southern populations, which mostly flower in spring.

As with other Hebe species, the abundantly-produced flowers (which appear in shades of pale mauve/blue to white) are visited by legions of bees, butterflies and other invertebrates. In the wild, Hebe diosmifolia is found in New Zealand’s northernmost parts, from Woodhill Forest (to the northwest of Auckland) northwards to Cape Reinga.

Most forms that have traditionally been cultivated are compact wild selections from open habitats. Their ability to withstand the wind and fury of two ocean expanses meeting at Cape Reinga is certainly enough to endorse them for service within exposed conditions. However, the capacity of some populations (such as those at Pouto) to accommodate a position in open shade is of even more consequence, as comparatively few species of Hebe tolerate shade to any significant extent. Interestingly, the closely affiliated Hebe divaricata (from northern parts of the South Island) is also well adapted to shaded situations.

Whilst variable, the foliage on some forms of Hebe diosmifolia foliage develops a particularly attractive pale green hue, which constitutes a distinctive (and useful) point within the spectrum of greens with which we determine planting compositions. As a final note on this species, the neatly arranged, narrow foliage also possesses the benefit of being unaffected by the fungus, Septoria, that disfigures the leaves and stems of many Hebe species in the north of the country – an attribute that should come as little surprise when one considers the range of habitats in which H. diosmifolia grows in the warm, humid north.

We don’t readily think of Māori having actively cultivated plants for their ornamental value in pre-European times. Indeed, I would contend that Eurocentric cultures like ours don’t tend to associate amenity gardening with indigenous societies in general³. However, there is strong evidence that some plants were grown (and moved around the country) on account of their beauty. Of these, kakabeak (Clianthus spp.) is the most high-profile example, whilst the subject of this profile, Hebe speciosa, is another interesting case in point.

Recent genetic studies have indicated that it is probable that the few isolated occurrences of H. speciosa from south of Auckland are derived from translocation of material from the population on the south side of Hokianga Harbour⁴ (where these images were taken).

Hebe speciosa continues to be shifted around, on a more accelerated level, as it has gained popularity as a garden plant over the last forty years – although, as with other plants, many specimens that are sold as this species are in fact hybrids. The latter point is unsurprising, for H. speciosa has been utilised extensively in the breeding of new cultivars of Hebe⁵.

Titirangi is a prime example of a hebe that is frequently misunderstood, with respect to its cultivation requirements. Coming from predominantly open habitats on the west coast of the North Island, H. speciosa is a product of its maritime environment, where it is subjected to almost continual air movement, often savage winds, and a heavy dosage of salt. When grown in sheltered inland conditions, the leaves frequently exhibit spotting and plants assume an ungainly growth form.

In my opinion, titirangi is best suited to gardens near the coast, where similar conditions prevail to those encountered in its natural habitats (and frosts are not an issue). In such situations, it is a fine garden plant, that produces impressive magenta flowerheads above its thick, glossy foliage.

When observing wild populations of this species at South Head, Hokianga, I was interested to see it growing in thick association with oioi (Apodasmia similis) and coastal flax (Phormium cookianum), whereas further down the coastline (at Maunganui Bluff) it also grew on the forest fringe and bare rocky slopes.

Titirangi is an endangered species, with a threat ranking of ‘Nationally Vulnerable’. It has a sporadic distribution, occurring at a small number of sites on the North Island’s west coast (from the Hokianga Harbour to Mokau), and one outlier population in the Marlborough Sounds – although, as mentioned above, the populations south of Auckland are not considered natural. It was discovered to Western Science in the 1830s by the early botanist, Richard Cunningham, who encountered it on the southern side of the Hokianga Harbour.