BOOK REVIEWS

An Illustrated Guide to New Zealand Hebes

By Michael Bayly and Alison Kellow, published by Te Papa Press, PO Box 467, Wellington, New Zealand, 2006, 388 pages, 28.5 × 20.5 cm, ISBN-13: 978-0-909010-12-6, ISBN-10: 0-909010-12-9.

Review by Tony Hayter (aj.me.hayter@boltblue.com)
The Hebe Society (UK)
Reproduced with his permission from
The New Zealand Garden Journal (Journal of the Royal New Zealand Institute of Horticulture), Vol. 9, No. 2, December 2006, p. 27-29.

The September 2002 issue of Hebe News carried an article by Mike Bayly describing current research into the genus Hebe. This research aimed to deliver a range of scientific papers, an interactive computer-based key for the identification of species, and an illustrated guide.

The guide covers the identification, classification and biology of Hebe and the closely related genus Leonohebe. It describes 88 species of naturally occurring Hebe and five of Leonohebe (L. cheesemanii, L. ciliolata, L. cupressoides, L. tetrasticha and L. tumida), but no horticultural forms. Each plant is illustrated with between six and 13 colour photographs; these show the whole plant, branchlet, leaf bud, leaf, inflorescence, flower and capsule. The authors describe each plant in detail including: habit, branches, leaf bud, leaves, inflorescences, bracts, flowers, pedicels, calyx, stamens, ovaries, capsules and seeds. The distribution and habitat are then given, followed by notes on its relationship with other hebes. Finally the etymology (origin of the name) is described.

The book is in three parts: A - general chapters, B - identification, description and nomenclature of each plant, and C - appendices, glossary, references and an index.

In the Introduction the authors point out that Hebe is New Zealand's largest genus, and is particularly conspicuous in the subalpine and alpine regions. Hebes occupy a wide range of habitats, from the coasts to the mountaintops, and have a wide range of forms, from whipcords with tiny leaves to large-leaved shrubs. Many of the species are similar in appearance, and can be variable in form, which has given hebes a reputation as a difficult group to study. It was thought that hybridisation between species is common, but the authors point out that this has been exaggerated, so that with care, and the use of a hand lens, most plants can be identified.

The last complete survey of Hebe was in the Flora of New Zealand, Volume 1, 1961. Research since that time has described further species, revealed possible new taxa, and raised questions about the limits of known species. The research project was planned to try to resolve these questions, to undertake a biosystematic revision of the genus, and to look at the evolution of the species. However in 1993 the paniculate group (Hebe hulkeana, H. lavaudiana, and H. raoulii) was given generic status as Heliohebe and is not included in the book, which is a shortcoming. Eleven species have been described since publication of the Flora, eight species are reinstated (they were not regarded as such in the Flora), and five hebes previously classified as species have been discarded.

The second chapter covers the classification and evolution of Hebe and Leonohebe. Previously Hebe had been placed in Scrophulariaceae, the antirrhinum family; but recently the Angiosperm Phylogeny Group regard it as a member of the Plantaginaceae, the plantain family. The history of the discovery, description and classification of Hebe species is given. From 1984 various authors have classified Hebe based on evolution, at first using the form of each species and latterly DNA derived data. This supports the idea that Hebe is derived from Veronica; relationships within Parahebe and Chionohebe are complex, with most hebes descending from a common ancestor, although Hebe macrantha is less closely related. The supposedly close relationship of Hebe odora and the whipcord hebes is not supported, and the whipcords fall into several groupings. The classification and naming of species included in Veronica and Hebe is in a state of flux, so further research is needed to resolve these problems. The classification of species within Hebe is based on the Flora, although a number of changes have been made based on recent but incomplete research.

The third chapter describes distribution, habitats and biogeographic history of Hebe, which occurs throughout New Zealand and its outlying islands. It is found in most habitats (coastal, near-coast forests, lowland wetland, riverside, cloud forest, beech forest, lakeshores, subalpine scrub, grassland and rocky areas in subalpine to alpine regions), although it is thinly distributed in forests. The number of species in each area varies widely throughout New Zealand, with the maximum number of species (25) in mountains at the borders of Nelson, Marlborough and Canterbury. Here there is a wide range of habitats. Research shows that Hebe arrived in New Zealand 1.5-5.5 million years ago, probably in an alpine region; it formed new species in this region and this was followed by a spread to lowland areas. Hebes are able to colonise over long distances, and one species (Hebe elliptica) extends to the Falkland Islands. The limited changes in DNA confirm the recent origin of Hebe, but more research is needed to pin down exact relationships within Hebe.

Phil Garnock-Jones has contributed the fourth chapter, which examines the structure of Hebe species. Hebes form an extensive system of fibrous roots, which might explain why they rapidly exhaust the compost in pots. Many hebes have a bushy habit, due to branching of the stems. These often have noticeable nodes, i.e., where leaves have been attached. Leaves have a decussate configuration; where opposite pairs of leaves are at right angles to their neighbours. A large leaf bud is a common feature. The leaf sinus, the gap between the bases of the terminal pair of leaves, can be useful in identification, although it can be present or absent within one species, e.g., Hebe pinguifolia. Flowers are usually found as a simple lateral raceme. Other features he discusses are: hairs, calices, corollas, androecium, pollen, gynoecium, seeds, seedlings, juvenile forms, and flower development.

Ken Markham has written the fifth chapter on flavonoids (leaf pigments) in Hebe. Over 80 flavonoids have been found in Hebe, and each species has its own (occasionally well-defined) flavonoid profile, giving it the characteristics of a fingerprint. The profile varies within each species, but this is much less than that displayed between species. This analytical method has been used to explore the relationships between species, and can be used to define hybrids and their parentage.

Chromosomes are the topic covered by the authors in the sixth chapter, where there is a comprehensive compendium of chromosome numbers for Hebe. The variation of these throughout the genus is examined, and work to unravel the ancestry of hebes is mentioned.

In the seventh chapter Phil Garnock-Jones considers the reproductive biology of Hebe. Some aspects have been studied, e.g., maintenance of gynodioecy (some flowers having male and female reproductive organs, while others have just female organs), breeding systems for Hebe stricta, H. subalpina and H. strictissima, and seed shape. However we have little knowledge of the breeding systems of most species, their pollinators and development of flowers. Hebe flowers are structurally similar, although there is a great diversity in size and detail, but all lack the nectar guides of Parahebe. The dominant flower colour is white, although some species have strong colours, e.g., magenta in Hebe speciosa. Most hebes flower in spring or early summer, with individual flowers lasting from 2-5 weeks in Hebe strictissima and 2-3 days in H. pinguifolia. Pollinators are a wide range of insects, although H. speciosa is visited by birds.

In the eighth chapter Peter de Lange describes the conservation status of Hebe. Peter and co-workers have developed a system to classify the conservation status of New Zealand native plants; this distinguishes between plants that are under threat from human activities, and those that are local or uncommon. Hebe is the largest genus in New Zealand, but few are greatly at risk. 'Acutely Threatened' is the highest risk category and this contains nine species of Hebe and one of Leonohebe. Plants in this category are considered management priorities. This category is further divided into three, with the highest risk being 'Nationally Critical', in which are included Hebe breviracemosa and H. societatis. The former is an island endemic and the latter has apparently very local distribution in penalpine (between alpine and subalpine) grassland. Peter then outlines the risks facing hebes, many of which are of very limited distribution.

The final chapter in Part A is on cultivation. There is a summary of cultivation requirements, a list of books on hebes, a mention of the Hebe Society and a photograph of hebes for sale at a New Zealand garden centre.

Part B, the largest section of the book, starts with a chapter on Material and Methods. Plants were studied in the field, and as herbarium specimens and cultivated plants (of known origin). The authors have arranged the species into groups similar to those in the Flora, although with significant differences. Within each group similar species are placed together. Next there is a list of the characteristics. These are used to describe each species and are: habit and form, branches, leaves, juvenile leaves, inflorescences, flowers, pedicels, corolla, stamens, nectarial disc, ovary and style, capsules and seeds.

Taxonomic Treatment gives a synopsis of the eleven groups (nine for Hebe, two for Leonohebe) used for identification. Each group is colour coded, and the distinguishing features listed. In describing these groups I have given some of the more well known examples in each.

The first group described are the 'flagriformes' (whipcords). There is a key to the hebes in this group, and then each plant is portrayed with a page of text and a page of illustrations. There are nine species including Hebe armstrongii, H. hectorii and H. ochracea.

The second group is the 'Connatae' (pairs of leaves are connate, joined at base). This group has seven species including Hebe epacridea and H. haastii.

The third group is the 'Subcarnosae' (somewhat fleshy), which has dull, grey-green, waxy, often fleshy leaves and usually no sinus. This group has seven species including Hebe buchananii, H. gibbsii and H. pimeleoides.

The fourth group is the 'Occlusae' (closed, i.e., no sinus), which has glossy or dull, but not usually glaucous, leaves (except in Hebe albicans, H. glaucophylla and H. topiaria). There are 31 species, and these include Hebe albicans, H. macrocarpa and H. stricta. Here Hebe recurva has been included with H. albicans, as recent research has shown that the latter is very variable and no clear grounds could be found to separate them.

The fifth group is the 'Buxifoliatae' (box-leaved, a former name for Hebe odora). The leaf sinus is shield shaped, each flower is directly attached, i.e., no flower stalk). There are four species, and these include Hebe odora and H. pauciramosa.

The sixth group is the 'Small-leaved Apertae' (conspicuous leaf sinus). The sinus is narrow; the leaves are less than 4 cm long. There are 20 species and these include Hebe diosmifolia, H. elliptica and H. venustula.

The seventh group is the 'Large-leaved Apertae' (conspicuous leaf sinus). The sinus is narrow; the leaves are greater than 4 cm long. There are eight species and these include Hebe salicifolia and H. speciosa.

The eighth group is the 'Grandiflorae' (large flowers). The leaves have noticeable teeth. There is one species, Hebe macrantha.

The ninth group is the 'Pauciflorae' (few flowers). This is a low-growing subshrub with leaves narrowing to a conspicuous leaf stalk (petiole). There is one species, Hebe pauciflora.

The tenth group is Leonohebe section Leonohebe (semi-whipcords). The plants are low-growing subshrubs, with leaves overlapping the stems. There are four species and these include Leonohebe cheesemanii and L. tetrasticha. These were formerly included in Hebe.

A chapter on nomenclature follows. It considers the naming at all levels, from the genera Hebe and Leonohebe, through species to possible wild hybrids to horticultural forms. Finally there is a list of common and Maori names.

Part C, Indices, has an appendix which lists informal hebe names used by Audrey Eagle in her books, and by A. P. Druce in two checklists. The second and third appendices describe the variation in some characteristics of Hebe hectorii and H. lycopodioides. The fourth appendix illustrates the considerable variation in the size and shape of the leaf outlines of 40 Hebe species. The fifth appendix lists the sources of the plant specimens used in the photographs of hebes and leonohebes. The book ends with a list of references, a glossary and an index.

This is an excellent book. The authors have succeeded in presenting a huge quantity of data which shows the current understanding of Hebe and Leonohebe. The language used is of necessity technical, but the glossary helps the attempts of an amateur botanist like me to understand it. The quality of the text, layout and photographs throughout is very high.

A version of this review is also published in Hebe News, 2006, Vol. 21, No. 4.

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