Tuatara: Volume 7, Issue 2, December 1958
A Key to the Divaricating Shrubs of New Zealand
A Key to the Divaricating Shrubs of New Zealand
The bewildering array of small-leaved tangled shrubs which are so common in the New Zealand bush present a real problem when one comes to identify them. They are botanically diverse yet so strikingly similar in habit that their fine distinctions require very careful study. Most people will come to recognise only two kinds, Coprosmas and the rest.
These ‘wiggy’ bushes or mikimikis are of rare occurrence in overseas floras excepting that of Tasmania, which has some resemblance to New Zealand in coastal and alpine areas. Botanists describe them as divaricating, a term derived from Latin meaning ‘stretched apart’. It refers to the branching, where branchlets diverge at an angle of 90°or more from the main axis. Divaricating shrubs usually form an inseparably interlaced mass of twigs. The leaves are small, and the branches, although always tough, may vary from rigid and spiny with frequent branching to wiry or flexible with occasional branching. The habit is well fitted for survival in exposed situations, and is found most commonly in plants of the sea coast and mountains. Divaricating shrubs are largely responsible for the distinctly weird appearance of some vegetation. They have not yet been found to have economically useful properties, except that they do act as stabilisers on soil exposed to severe erosion.
The divaricating form is not sharply defined but grades into the normally branched small-leaved shrub, so that there are intermediate forms difficult to classify. Manuka is not normally divaricating, but when growing exposed to wind or salt spray which kill back the young shoots it becomes a closely branched wind-shorn mass very similar to the truly divaricating shrubs of the same habitat. At extremes of exposure the ultimate branchlets of Aristotelia fruticosa become spines, but on the other hand the same shrub loses its divaricating nature and spines, and becomes more lax, open and leafy when growing in the protection of the forest. Amongst scrub communities one may come across barbed-wire entanglements of almost leafless stems belonging to species of Rubus, Clematis or Muehlenbeckia, which in sheltered conditions are climbing plants. The hummocks formed by these lianes look like divaricating shrubs. Thus the habit of any species is not necessarily fixed, but often varies according to habitat.
Some shrubs remain divaricating throughout their life, while others are merely the juvenile form of a forest tree, which after a number of years will put out erect branches and pass into the adult. One common type of development in such plants involves three stages of growth, a normal page 49 seedling form, a juvenile divaricating form persistent for a varying length of time (even up to 60 years in Elaeocarpus hookerianus), and an adult tree form. This sequence is found in Sophora microphylla, Pennantia corymbosa and Paratrophis microphylla. Sometimes juvenile-stage reversion shoots appear on the adult form, perhaps as a result of wounding. In some cases the juvenile is capable of flowering before the adult stage is reached, or juvenile branches will flower at the same time as the adult branches above them. Even truly divaricating shrubs may have a non-divaricating seedling form so that their life history corresponds to the first two stages above. This is so with Nothopanax anomalum and Aristotelia fruticosa. It has been suggested that in some plants the production of flowers by the juvenile form has arrested further development, so that an adult form has been lost. The theory accounts very well for the situation in Sophora, where S. prostrata may have arisen as a flowering persistent juvenile form of S. microphylla. This divaricating juvenile is better suited to exposed alpine situations than the adult form. However, although the explanation is plausible in this case, it is unwise to attempt a comprehensive theory when other examples can be quoted in which the juvenile is the more tender, and the adult better fitted to rigorous conditions.
The divaricating form occurs in widely different plant families and is often peculiar to the New Zealand members of a family or genus. Because divaricating shrubs appear to be adapted to conditions of low humidity and extremes of temperature rather than to the present mild New Zealand climate. Cockayne speculated that the habit arose in a former geological age as a response to a dry continental climate, and has persisted through the subsequent climatic change. There is some doubt whether this elaborate explanation is necessary, since the strong winds experienced at the present day in the typical habitat of divaricating shrubs may cause conditions approaching the continental.
Plants are recognised and classified most surely by their reproductive structures. This is particularly true of divaricating shrubs since examples from different families come to resemble one another so closely when not in flower or fruit that they are difficult to distinguish. However, in order to be more generally useful, the accompanying key to divaricating shrubs makes use of vegetative characters for identification at least to the generic level, though within the genera Olearia and Pittosporum it has not been possible to avoid using some flower and fruit characters.
The shrubs in the key fall into two main groups, those with alternate leaves forming section A, and those with opposite paired leaves section B. Where leaves arise in clusters these fascicles are themselves correspondingly alternate or opposite. The leaf arrangement of Aristotelia fruticosa may present some difficulty as occasional branches bear a few leaves not arising exactly opposite one another, although the majority will be strictly paired.
Specimens for identification should be as fresh as possible, and not too small. It is best to collect specimens from two or three different parts of the plant to be sure of obtaining the range of leaf variation in the species. page 50 Variability not caused by differences in age or degree of exposure, will be in the nature of the species itself. The illustrations show a representative selection of leaf forms which can be used for comparison. Some species occur more than once in the key because they vary in appearance or structure, and have several possible pathways to their identification.
The genera Plagianthus and Nothofagus produce hybrid forms intermediate between the species listed in the key. Olearias vary even more widely, and because the key to this genus contains only a selection of well-marked species, plants which cannot be diagnosed will be either uncommon and not listed, hybrids, or horticultural varieties.
In deciding whether stipules are present or absent it must be borne in mind that they may be very small, or early deciduous. It will be necessary to examine the bases of developing or newly expanded leaves at the tips of the branches, preferably with a pocket magnifier. Withered specimens may be impossible to investigate for stipules. In such cases it is best to follow out the key for both possibilities and then decide from the final descriptions which of the two answers is correct. For full details of any species, always consult a standard flora. The importance of minute observation with a lens cannot be too strongly emphasised. It is only to the casual observer that divaricating shrubs present a baffling uniformity.
|1||Leaves alternate or in alternate clusters.||SECTION A||2|
|Leaves opposite or in opposite clusters.||SECTION B||43|
|2||Leaf bearing white tomentum on under surface.||—||3|
|Leaf without white tomentum on under surface.||—||7|
|3||Leaf base sheathing and clasping the stem. Flowers in globular heads.|
|Seeds with a parachute of hairs.||HELICHRYSUM||4|
|Leaf base not sheathing.||—||5|
|4||Leaf rounded, upper surface with minute raised pattern. (Fig. 8.)||* Helichrysum glomeratum|
|Leaf narrow.||* Helichrysum lanceolatum|
|5||Leaf spathulate, tomentum dull, cottony. Flowers starry, yellow. Fruit globular, red or yellow. (Fig. 3.)||† Corokia cotoneaster|
|Leaf not spathulate, tomentum shiny, silky. Seeds dry, each with a parachute of hairs.||OLEARIA||6|
|6||Leaves 6-12 mm. long. Flowers in open corymbs.||Olearia capillaris|
|Leaves 18-36 mm. long. Flowers in dense globose sessile heads, scented. (Fig. 28.)||Olearia fragrantissima|
|7||Leaf jointed between blade and petiole (leaf occasionally 3-5 foliolate).page 51|
|Branchlets rough like sandpaper. Flowers small, greenish, in clusters. Fruit flattened, crowned with 2 stigmas, white with violet markings. (Figs. 23, 24.)||Nothopanax anomalum|
|Leaf not jointed.||—||8|
|8||Leaf compound, pinnate.||—||9|
|9||Branchlets flattened, greenish, with strong longitudinal ridges. Flowers purplish, pea-shaped. Fruit a beaked pod. (Fig. 6.)||*†Carmichaelia grandiflora var. divaricata|
|Branchlets not flattened, brownish or yellow.||SOPHORA||10|
|10||Leaves usually not more than 13 mm. long, 1-4 prs. leaflets. Branchlets stout, wiry, polished, orange-yellow. Flowers yellow, pea-shaped. Short hanging pod with a few reddish seeds. (Fig. 42.)||† Sophora prostrata|
|Leaves up to 30 mm. long, up to 6 prs. leaflets. Branchlets slender, green or brown, velvety when young. No flowers at this stage. (Fig. 41.)||† juv. Sophora microphylla|
|11||Some leaves fiddle-shaped.||—||12|
|Leaves never fiddle-shaped.||—||13|
|12||Conspicuous sheathing stipules present, leaf margin smooth or lobed. (Fig. 17.)||*†Muehlenbeckia complexa (see 27)|
|Stipules early deciduous, not present with mature leaves, leaf margin toothed. Stems have raised lenticels and milky sap. Plant sometimes flowers at this stage, flowers minute, green. (Fig. 25.)||juv. Paratrophis microphylla|
|13||Mature leaves variable, some toothed or lobed, others with smooth margins.||—||14|
|Mature leaves uniform.||—||25|
|15||Stipules present with mature leaves, and may be represented by light-coloured swellings flanking the petiole.||HYMENANTHERA||16|
|Stipules minute, pointed, early deciduous, not present with mature leaves. They are easily overlooked. (Fig. 7.)||Elaeocarpus hookerianus (see 17)|
|16||Leaf narrow, thick, 4-8 mm. long, branchlets spiny. Lenticels conspicuous. (Fig. 10.)||†Hymenanthera alpina (see 30)|
|Leaf narrow, thick or thin, shade leaves up to 25 mm. long. Lenticels conspicuous pale dots on rough bark. Stems not very rigid. Flowers greenish. Berry 2-seeded, purplish. (Figs. 11, 13.)||†Hymenanthera angustifolia (see 30)|
|17||Leaf leathery, veins inconspicuous, young branchlets usually hairy. Young leaves may be covered with tomentum before they expand.||PITTOSPORUM||18|
|Leaf not leathery, vein network clearly visible on under surface, branchlets hairless. Leaves extremely variable, sometimes reddish blotched, never pointed at the tip. Distinguished from Pittosporum by minute stipules and pointed projections at the tips of leaf lobes. (Fig. 7.)||Elaeocarpus hookerianus (see 15)page 52|
|18||Capsules split to show a papery covering over the dry seeds. Some leaves linear and saw-toothed. Plant red-brown in winter. Flower yellow. Fruit a narrow or oval beaked capsule. (Fig. 30.)||† Pittosporum anomalum|
|No papery covering, seeds sticky.||—||19|
|19||Entire type of leaf shows a few pairs of secondary veins below.||—||20|
|Entire type of leaf shows midrib only.||—||22|
|20||Leaves show rounded apex and lobing.||—||21|
|Leaves show obtuse or just pointed apex and toothed irregularities. Tomentum rusty or grey. Flower large, purple-black. Capsule round, hairy, with 3-7 dark seeds. (Fig. 34.)||*Pittosporum rigidum (see 22)|
|21||Leaf orbicular, often spathulate, may be reddish margined. Branchlets silky. Flower mauve, yellow or whitish. Capsule oval, woody, slightly beaked, with 4-7 dark seeds. (Fig. 39.)||Pittosporum obcordatum|
|Leaf not orbicular, broader at the tip than the base. Plants seems to be restricted to the Volcanic Plateau, in swamps. (Fig. 35.)||juv. Pittosporum turneri|
|22||Mature capsule up to 10 mm. across with up to 12 seeds. (Fig. 34.)||*Pittosporum rigidum (see 20)|
|Mature capsule with 2-5 seeds.||—||23|
|23||Capsule warty. Tomentum white. Flower purple. (Fig. 33.)||Pittosporum crassicaule|
|Capsule not warty.||—||24|
|24||Leaves narrow linear up to 15 mm. long, lobed leaves rare. Branchlets slender, black, with a few white hairs. Flower purple. Distinguished from Plagianthus divaricatus by lack of stipules. (Fig. 32.) Pittosporum lineare Leaves variable in width, lobed leaves common. Branchlets thick. Flower purple. Capsule rounded. (Fig. 31.)||Pittosporum divaricatum|
|26||Stipules large, papery, sheathing stem. Flowers clustered, greenish white. Fruit a 3-angled black nut in a white fleshy cup.||MUEHLENBECKIA||27|
|Stipules small, winglike, on either side of leaf base.||—||28|
|27||Leaves heart-shaped, notched at the apex, usually borne in clusters. Plant seems to be restricted to two localities on opposite shores of Cook Strait. (Fig. 14.)||† Muehlenbeckia astoni|
|Leaves not heart-shaped, often multiform, borne singly. (Fig. 17.)||*†Muehlenbeckia complexa (see 12)|
|28||Ultimate branchlets thick, narrowing abruptly, bearing prominent lenticels.||HYMENANTHERA||29|
|Ultimate branchlets slender, tapering gradually, no prominent lenticels.||31|
1 a-c, Aristotelia fruticosa seedling; 2 a-j, A. fruticosa adult; 3 a-f, Corokia cotoneaster; 4, Carpodetus serratus juvenile; 5 a-c, Discaria toumatou; 6 a-b, Carmichaelia grandiflora var. divaricata; 7 a-m, Elaeocarpus hookerianus juvenile. All figures 1 ½ times natural size.
|29||Leaves broadly obovate to oblong, thick, sometimes notched at the tip. Flower yellowish green, hidden on under side of branches. Berry 2-seeded, white or purplish. (Fig. 12.)||Hymenanthera crassifolia|
|Leaves narrow, sometimes very few, margin may be irregularly toothed.||30|
|30||Leaf thick, 4-8 mm. long, branchlets like spines. (Fig. 10.)||†Hymenanthera alpina (see 16)|
|Leaf thick or thin, up to 25 mm. long. (Figs. 11, 13.)||†Hymenanthera angustifolia (see 16)|
|31||Leaf narrow, much longer than broad. Flower minute, yellowish white. Capsule rounded or beaked, with 1 or 2 dark seeds. Distinguished from Pittosporum lineare by presence of stipules and netted inner bark. (Fig. 38.)||Plagianthus divaricatus|
|Leaf nearly as broad as long.||32|
|32||Both sides of leaf bearing star-shaped hairs, inner bark netted.||—||33|
|Leaf not hairy, no netted bark.||—||34|
|33||Leaf blade sloping gradually into petiole, often 3-5 toothed at tip. In some varieties the star-shaped hairs are sparse. (Fig. 9.)||† juv. Hoheria angustifolia 1|
|Leaf blade abruptly contracted into petiole, leaf variously lobed, sometimes kidney-shaped. Distinguished from Pennantia by the stipules and netted bark. (Fig. 40.)||*† juv. Plagianthus betulinus1|
|34||Stipules and branchlets pale. Leaf may have paler marking at the base, vein network very distinct. Flowers small, greenish yellow. Berry dark violet. (Fig. 16.)||Melicytus micranthus|
|Stipules and branchlets brown or dark. Leaves may be reddish blotched.||NOTHOFAGUS||35|
|35||Leaf margin entire or wavy. Leaf may have whitish bloom on under surface. (Fig. 20.)||* juv. Nothofagus solandri|
|Leaf margin toothed.||—||36|
8 a-b, Helichrysum glomeratum; 9 a-d, Hoheria angustifolia juvenile, Egmont Ranges; 9e, H. angustifolia semi-juvenile, Egmont Ranges; 9 f-g, H. angustifolia juvenile, Wairoa; 9h, H. angustifolia juvenile, Christchurch; 10 a-d, Hymenanthera alpina; 11 a-e, H. angustifolia thin-leaved form; 12 a-c, H. crassifolia; 13 a-d, H. angustifolia thick-leaved form; 14 a-b, Muehlenbeckia astoni; 15 a-b, Melicope simplex, adult; 15 c-d, M. simplex seedling; 16 a-c, Melicytus micranthus; 17 a-f, Muehlenbeckia complexa. All figures 1½ times natural size.
|36||Leaf with 1-3 domatia, thin texture, margin deeply cut with sharp teeth. (Fig. 21.)||* juv. Nothofagus fusca|
|Leaf without domatia, thick, margin bears blunt shallow teeth. (Fig. 22.)||* juv. Nothofagus truncata|
|37||Leaf narrow, linear.||—||38|
|Leaf not linear.||—||40|
|38||Leaf with midrib produced as a point.||PODOCARPUS||39|
|Leaf with midrib not produced, occasional leaves lobed. (Fig. 32.)||Pittosporum lineare (see 24)|
|39||Leaves double-curved and crowded along stem in 2 ranks. Branchlets appear feathery. Trunk straight and vertical, with main branches horizontal. (Fig. 44.)||* juv. Podocarpus dacrydioides|
|Leaves straight or single-curved, scattered, or crowded and 2 ranked only at tips of occasional branchlets, whitish below. Branches weeping and tangled, wiry, greenish or orange brown. (Fig. 36.)||† juv. Podocarpus spicatus|
|40||Leaf margin entire.||—||41|
|Leaf margin toothed.||—||42|
|41||Leaf dotted with orange coloured glands. Leaf may have dark marking at the base. Branchlet tips recurved. Flowers clustered, greenish. Berry bright blue-violet. (Fig. 45.)||Suttonia divaricata|
|Leaf not gland dotted. Leaf variation is not obvious, but the plants belong to a typically variable genus.||Pittosporum lineare, P. rigidum or adult P. obcordatum (see 19)|
|42||Upper surface of leaf of ‘marbled’ appearance owing to darker colour along veins. Leaf may be purplish below. Stems often bear galls or swellings caused by small insects. (Fig. 4.)||juv. Carpodetus serratus|
|Upper surface of leaf not ‘marbled’. Leaves, especially young ones, thin and softly hairy on both surfaces. Tips of branchlets soft and weak, bark light coloured. Distinguished from Plagianthus and Hoheria by absence of netted bark and stipules. (Fig. 37.)||juv. Pennantia corymbosa|
|43||Plant with 2 or 4 rows of conspicuous spines. Leaves sometimes very few, clustered below the spines. Flowers minute, greenish, without petals. Capsule 3-lobed. (Fig. 5.)||Discaria toumatou|
|Plant without spines.||—||44|
|44||Leaf with tomentum on under surface. Flowers small, white, in clusters. Seeds with a parachute of hairs.||OLEARIA||45|
18 a-b, Myrtus pedunculata; 19 a-c, M. obcordata; 20 a-b, Nothofagus solandri juvenile; 21 a-b, N. fusca juvenile; 22 a-b, N. truncata juvenile; 23 a-c, Nothopanax anomalum seedling; 24 a-d, N. anomalum adult; 25 a-d, Paratrophis microphylla juvenile; 26 a-b, Olearia lineata; 27 a-c, O. odorata; 28 a-b, O. fragrantissima; 29 a-b, O. virgata. All figures 1½ times natural size.
|Leaf without tomentum.||—||49|
|45||Tomentum on branchlets coloured.||—||46|
|46||Tomentum on leaves, branchlets and flower heads rust coloured.||Olearia divaricata|
|Tomentum on branchlets and flower heads yellow, sticky; on leaves, white. Foliage scented.||* Olearia solandri|
|47||Bracts of flower head sticky, glandular. Branchlets stout. (Fig. 27.)||Olearia odorata|
|Bracts of flower head neither sticky nor glandular.||—||48|
|48||Leaf 6-12 mm. long, linear, or broader at the tip to almost spathulate. Branchlets faintly 4-angled. (Fig. 29.)||Olearia virgata|
|Leaf 12-50 mm. long, linear, margins rolled under. Leaf clusters in distant pairs. Branchlets slender, weeping. (Fig. 26.)||* Olearia lineata|
|49||Leaf gland dotted.||—||50|
|Leaf not gland dotted.||—||52|
|50||Leaf jointed between blade and petiole (leaf occasionally 2-3 foliolate). Petiole flattened. Flower greenish yellow, scented. Capsule 4-lobed with 4 shiny black seeds. (Fig. 15.)||Melicope simplex|
|Leaf not jointed. Flower white, with conspicuous stamens.||MYRTUS||51|
|51||Leaf heart-shaped, notched at apex. Branchlets rounded. Berry dark red. (Fig. 19.)||* Myrtus obcordata|
|Leaf not heart-shaped, apex rounded or pointed. Branchlets 4-angled. Berry yellow or bright red on a long stalk. (Fig. 18.)||* Myrtus pedunculata|
|52||Branchlets 4-angled. Flower small, white. Fruit 4-lobed in a leafy cup. (Fig. 46.)||* Teucridium parvifolium|
|53||Stipules present, clasping stem between leaf bases. Leaves may bear domatia.||COPROSMA 2|
|54||Leaves rough with hairs. Flower bell-shaped, striped, orange-red. Capsule many-seeded. (Fig. 43.)||* Rhabdothamnus solandri|
|Leaves smooth, multiform, not always strictly opposite. Branchlets often spiny, bark reddish. Flower dark red. Berry coloured wine purple. (Figs. 1, 2.)||† Aristotelia fruticosa|
- Bract: A leaf-like organ associated with groups of flowers.
- Corymb: A branched flower head with a flat top.
- Domatium: A pit, sometimes hair-fringed, found on the lower surface of a leaf at the junction of the midrib and secondary veins.
- Fascicle: A cluster or bunch.
- Lenticel: An area of powdery bark through which air penetrates into the underlying tissues.
- Linear: Very narrow with parallel margins.
- Obovate: Egg-shaped, with the narrower end towards the petiole.
- Orbicular: With a circular outline.
- Petiole: Leaf stalk.
- Pinnate: With a row of leaflets on either side of the midrib.
- Sessile: Without a stalk.
- Spathulate: Spoon-shaped; a leaf blade narrowing into a parallel winged petiole.
- Stipule: A lateral outgrowth from the base of a petiole.
- Tomentum: A thick felted covering of hairs.
ALLAN, H. H. (1928)— New Zealand Trees and Shrubs.
CHEESEMAN, T. F. (1925)— Manual of the New Zealand Flora.
COCKAYNE, L. (1899)— Seedling forms of New Zealand Phanerogams I. T.N.Z.I. 31: 354-398.
COCKAYNE, L. (1900)— Seedling forms of N.Z. Phanerogams IV. T.N.Z.I. 33: 265-298.
COCKAYNE, L. (1911)— Ecological Studies in Evolution. T.N.Z.I. 44: 1-50.
COCKAYNE, L. (1919)— New Zealand Plants and their Story.
COCKAYNE, L. (1928)— The Vegetation of New Zealand. 2nd ed.
COOPER, R. C. (1956)— The Australian and N.Z. Species of Pittosporum. Ann. Miss. Bot. Garden 43: 87-188.
DAVIES, W. C. (1956)— N.Z. Native Plant Studies.
KIRK, T. (1999)— The Forest Flora of N.Z.
LAING, R. M., and GOURLAY, H. W. (1935)— The small-leaved species of Pittosporum. T.N.Z.I. 65: 44-62.
MARTIN, W.— The Flora of New Zealand.
SAINSBURY, G. O. K. (1923)— Notes on Pittosporum obcordatum. T.N.Z.I. 54: 572.page break
36, Podocarpus spicatus juvenile; 37 a-d, Pennantia corymbosa juvenile; 38 a-d, Plagianthus divaricatus; 39 a-f, Pittosporum obcordatum; 40 a-g, Plagianthus betulinus juvenile; 41, Sophora microphylla juvenile; 42 a-b, S. prostrata; 43 a-b, Rhabdothamnus solandri; 44, Podocarpus dacrydioides juvenile; 45 a-d, Suttonia divaricata; 46 a-b, Teucridium parvifolium. All figures 1½ times natural size.
1 Plagianthus betulinus and Hoheria angustifolia are difficult to separate in the juvenile stage. Broken twigs of both plants have a characteristic smell like cucumber or melon. The leaf base character is variable in P. betulinus but at least some of the leaves should show it. Observe the adult trees in the neighbourhood for possible parents. Adult H. angustifolia has narrow leaves toothed like holly, and white starry flowers. Adult P. betulinus has thin, almost triangular leaves, with the broad base attached to the petiole, and the margin irregularly cut. The flowers are greenish.
2 Small leaved species of Coprosma will be the subject of a later key.