Kunzea serotina de Lange et Toelken, 2014

de Lange, Peter J., 2014, A revision of the New Zealand Kunzea ericoides (Myrtaceae) complex, PhytoKeys 40, pp. 1-185 : 27-36

2. Kunzea serotina de Lange et Toelken sp. nov.

A K. ericoide habitu in arboribus juvenalis et juveni-adultis, erecto columnare fastigiato vel pyramidale, transformante in arboribus veterrimis habitu laxe ramoso divergente apice applanata; cortice maturo crisparenti circinanti et decorticanti promte partibus parvis irregularibus chartaceis, habitu fastigiato, pherophyllis spathulatis, hypanthio urceolato vel campanulato, ovariis saepe trilocularibus, glandibus oleosis flavis petalorum differt.

Holotype

(Fig. 8). New Zealand: North Island, 3.5 km north-east of Rangitaiki River, 38°55'26"S, 176°26'1"E, 743 m a.s.l. 'Abundant at interface between frost flat and upland Podocarp forest. Growing in skeletal soil overlying Taupo Pumice (186 A.D. ejecta), in association with dense Dracophyllum subulatum '. P. J. de Lange 6695, 18 Feb 2005, AK 297548! Isotypes: AD! BM! CHR! MEL! WELT!

Etymology.

The specific epithet serotina refers to the later flowering habit of the species (peaking January-February) when compared to Kunzea robusta and Kunzea tenuicaulis , earlier flowering species (peaking October-December) with which Kunzea serotina is sympatric in the North Island.

Description

(Figs 9, 10, 11). Growth habit erect, initially columnar to tightly pyramidal, fastigiate, densely branched shrubs or trees 3-20 × 2-4 m developing with time into less densely branched, open pyramidal crowns; in very stable conditions growth habit changing in aged specimens to a more openly branched, flat-topped, divergent crown, with branches restricted to upper half to third of trunk. Trunk usually single, very rarely 2-3 arising from base, 0.10-0.45(-0.86) m d.b.h., often basally buttressed, with basal portion of trunk covered in numerous, curled, chartaceous bark remnants. Bark early bark chartaceous, greyish-white to pinkish-white, ± elongate, initially with few transverse cracks but soon becoming heavily cracked (especially on branch flanges and decurrent leaf bases), often crumpled, soon detaching as in-rolled, curled, sinuous, irregular pieces, with ± frayed margins, detached pieces often congregating in branch forks and forming deep drifts at trunk base; old bark similar though more distinctly chartaceous-corky, upper surface with much secondary peeling, transverse cracking and crumpling; detaching readily, with flakes often hanging in loose curled masses beneath main branch forks and along trunk, margins rather irregular, sinuous, very rarely somewhat tabular; early and old bark flakes crumbling readily in hand. Branches numerous, usually arising at or near trunk base; short and stout, obliquely ascending, fastigiate; branchlets numerous, very leafy with many brachyblasts, quadrangular, indumentum copious, sericeous; persistent, divergent 0.05-0.06(-0.08) μm, hyaline to translucent (appearing white when young maturing grey) apices curved or slightly curled. Vegetative buds usually inconspicuous and obscured by surrounding foliage; at resting stage 0.2-0.5(-1.3) mm diam.; scales scarious, deciduous, (0.3-)0.8(-1.3) mm long, yellow-brown to red-brown, ovate, ovate-deltoid to broadly deltoid-rostrate; midrib prominent, strongly keeled in upper half, prolonged to long cuspidate tip, lateral veins absent, oil glands usually absent, upper half of scale margins, keel, and keel apex ciliate. Leaves heterophyllous; seedling, subadult leaves and those of reversion shoots, spreading to patent; lamina (0.8-)5.2(-7.8) × (0.6-)0.8(-1.2) mm, red-green or pale green suffused with red, rarely bright green, linear-lanceolate to lanceolate; flat or involute, apex acute to obtuse, finely cuspidate; adult leaves usually densely aggregated along brachyblasts of branchlets, initially obliquely ascending to suberect, spreading; lamina (2.0-)3.7(-6.3) × (0.8-)1.1(-1.8) mm, dark glossy green or bronze-green, margins and base often flushed red, linear-oblanceolate, oblanceolate to obovate; strongly recurved from about half of total length, apex initially acute to subacute, maturing obtuse to rounded, often cuspidate; base attenuate; adaxial surface concave or flat, glandular punctate; oil glands up to 780, more evident when dry, midrib slightly raised near base, otherwise not evident for rest of length, glabrous, very rarely with fine antrorse hairs near base; abaxial surface convex, glandular punctate, oil glands up to 180, more evident when dry; midrib flush with surface or depressed, glabrous, very rarely with a fine covering of silky, antrorse-appressed, antrorse to patent hairs near base; lamina margin sparsely hairy, hairs finely silky, flexuose, appressed to spreading, antrorse to subantrorse up to 0.08 mm long, hyaline to translucent, appearing as white to naked eye, aligned in one usually interrupted row failing well short of cuspidate leaf apex. Perules scarious, persistent, (0.3-)0.6(-1.0) mm; basal ones amber-brown to dark brown, broadly ovate, ovate-oblong, ± rostrate, apex acute, margins flat to involute especially in upper third, midrib weakly keeled, usually prolonged as a very short, deciduous, cuspidate apex, with one row of 4-12 oil glands on each side of midrib, glabrous except for finely ciliate margin and apex; intermediate perules deciduous, chartaceous, (0.2-)0.6(-0.8) mm long, initially pale brown to orange, upper perules usually pinkish-white when fresh, drying amber-brown to amber-orange, ovate to ovate-oblong, apex obtuse often appearing acute due to apical infolding, ± cuspidate, glabrous except for sparsely ciliate margin, weakly keeled, keel ± prolonged. Inflorescence a compact (1-)8(-12)-flowered corymbiform botryum up to 25 mm long, mostly borne on alternate, distinctly spiralled, basally densely leafy brachyblasts up to 15 mm long, each often bearing a terminal tuft of pherophylls and emergent leaves at anthesis; brachyblasts near branchlet apex usually subopposite; inflorescences at the ultimate branchlet terminus, uncommon, if present then often rather elongated and bearing well developed terminal vegetative growth. Inflorescence axis densely invested with divergent hairs. Pherophylls deciduous (falling very early), mostly foliose (rarely squamiform), 0.9-2.5 mm long, green to bronze-green, spathulate, spathulate-orbicular, rarely pandurate or lanceolate, margins and apex finely ciliate, grading into leaves at inflorescence axis apex. Pedicels (3.0-)3.5(-4.8) mm long at anthesis, usually elongating slightly after anthesis, terete, copiously invested in short, divergent to subantrorse, silky hairs. Flower buds clavate to pyriform, apex flat to weakly domed prior to bud burst with calyx valves not or scarcely meeting. Fresh flowers when fully expanded (2.8-)5.2(-8.8) mm diam. Hypanthium (1.6-)2.0(-3.4) × (1.5-)1.9(-3.8) mm, with free portion 0.4-0.8 mm long, dark green or red-green, if green then basally flushed with red when fresh, drying brown-green to red-brown; urceolate to campanulate terminating in a distinctly thicker rim bearing five persistent calyx lobes; surface smooth, copiously dotted with red oil glands, finely puberulent to ± glabrescent, with weakly defined ridges leading up to calyx lobes (these becoming more distinct upon drying); hairs if present, very short, divergent. Calyx lobes 5, upright (not spreading), firmly fleshy, (0.8-)1.0(-1.2) × (0.7-)1.0(-1.2) mm, persistent, ovate to broadly ovate, weakly keeled (keel evident only in dried specimens, where it is seen as a slightly thicker, often pale yellow, green or pink, central ridge), central portion of lobe pale green or yellow-green, with margins usually cream to pale pink, surface glandular punctate, oil glands usually pink in exposed situations otherwise ± colourless, glabrous except for distinctly spreading, ciliate margins. Receptacle usually pink at anthesis, consistently darkening to dark crimson magenta after fertilisation. Petals 5(-6), 1.4-1.6(-2.0) × 1.2-1.6(-2.0) mm, white, sometimes basally flushed pink, narrowly orbicular to broadly ovate or cuneate, apex obtuse to rounded, margins ± frayed to finely and irregularly toothed, oil glands yellow when fresh, when dried very pale yellow to colourless. Stamens 20-26(-38) in 1(-2) weakly defined whorls, arising from the receptacle rim, filaments white occasionally tinged rose-pink toward base. Antipetalous stamens (2-)3(-4), antisepalous stamens (1-)3(-6). Outermost antipetalous stamens usually weakly incurved, on filaments 0.7-1.9 mm long, inner stamen if present, 0.3-0.8 mm, strongly or weakly incurved, sometimes strongly outcurved, very rarely a further 1-2 strongly incurved stamens, 0.3-0.6 mm long, may be present at the base of the outermost antipetalous pair. Antisepalous stamens much shorter than outermost antipetalous stamens, 0.2-0.6 mm, usually incurved, rarely outcurved or in mixtures of both. Anthers dorsifixed, 0.04-0.06 × 0.02-0.04 mm, testiculate to ellipsoid, latrorse. Pollen white (11.1-)12.4(-13.7) μm. Anther connective gland prominent, orange often flushed with rose when fresh, drying dark orange-brown or purple, spheroidal, distinctly papillate. Ovary 3-4(-5) locular, each with 10-18(-23) ovules in two rows on each placental lobe. Style 0.6-0.8(-1.2) mm long at anthesis, often elongating slightly after anthesis, white; stigma capitate, scarcely wider than style, usually flat to very weakly domed along margins with a basal central depression, greenish-white, cream or pale pink, surface finely papillate. Fruits rarely persistent (1.2-)2.1(-3.0) × (1.2-)2.1(-3.4) mm, light brown to grey, finely hairy, urceolate to shortly-campanulate, rarely cupular, splits concealed by dried, suberect to erect, free portion of hypanthium and incurved calyx lobes. Seeds 0.60-0.90(-1.00) × 0.48-0.50(-0.60) mm, narrowly oblong, oblong, oblong-obovate, curved near apex, laterally compressed, 2-3-angled with convex to flattened faces, apex rounded to subacute; base cuneate to oblique, ± flattened; testa semi-glossy, orange-brown to dark brown, surface coarsely reticulate. FL: (Nov-)Jan-Feb(-May) FT: Jan-Dec. Chromosome Number n = 11II, 2 n = 22 (see de Lange and Murray 2004).

Representative specimens

(155 sheets seen): New Zealand (North Island). Waikato River, Lake Waipapa, P. J. de Lange 1197, 6 Jan 1992, (AK 207188, Duplicates AD, CHR); Lake Rerewhakaaitu, W. D. Burke s.n., Jan 1960, (WELTU 3052); Te Kuiti, D. A. Franklin s.n., 1953, (WELTU 3053); Paeroa Range, Te Kopia Road, P. J. de Lange 4701, 16 Nov 2000, (AK 288232, Duplicate: AD); Pureora Forest, Link Road, Mihanga Stream headwaters, P. J. de Lange 4608 & R. O. Gardner, 18 Oct 2000, (AK 288230, Duplicate: AD); Waione Frost Flats, Waione Stream, P. J. de Lange 6440 & P. B. Cashmore, 12 Apr 2005, (AK 289785); Hauhangaroa Range, Waituhi Saddle, P. J. de Lange 4271 & P. de Lange, 31 Jan 2000, (AK 288110, Duplicate: AD); Rangitaiki, Otamatea Plains, A. J. Healy s.n., 19 Feb 1948, (CHR 62349); Puketitiri, Balls Clearing, A. P. Druce s.n., Mar 1973, (CHR 208702); Kaweka Ranges, south-west of Tutaekuri River Gorge, L. R. Perrie 3016, L. Shepherd & M. Shepherd, 14 Dec 2003, (AK 289511); Te Porere Redoubt Historic Reserve, above Waewaeru Stream, P. J. de Lange 4244 & N. J. D. Singers, 27 Jan 2000, (AK 288140, Duplicate: AD, CHR, NSW); Mt Ruapehu, Tukino, upper Mangatoetoenui Stream, P. J. de Lange 5142, 25 Jan 2001, (AK 288142); Kaimanawa Range, Waipahihi Road, P. J. de Lange 5981, 25 Jan 2001, (AK 286070, Duplicate: AD); Rangipo, Waikato Stream, P. J. de Lange 4247 & N. J. D. Singers, 27 Jan 2000, (AK 288133, Duplicates: AD, P); Moawhango - Napier Road, upper Makahikatoa Stream, P. J. de Lange 4382, 10 Aug 2000, (AK 286077, Duplicate: AD); North-West Ruahine Range, Pokopoko Stream, W. D. Burke s.n., 13 Dec 1966, (WELTU 3049); Near Rangiwahia, C. I. Pemberton Memorial Reserve, P. J. de Lange 4376, 10 Aug 2000, (AK 288234, Duplicate: AD); Puketoi Range, near Makuri, P. J. de Lange 6506, 28 May 2001, (AK 289945). New Zealand (South Island). Wangapeka Valley, R. Mason s.n., 22 Dec 1946, (CHR 58114); Hope River, Sandy Creek, P. J. de Lange 5086, 21 Jan 2001, (AK 287549); Lake Rotoiti, West Bay, W. Harris s.n., 30 Jan 1987, (CHR 437953); St Arnaud Range, Nocatchem Stream, P. J. de Lange 5129, 23 Jan 2001, (AK 286973, Duplicate: AD); Wairau Valley, between Coldwater and Judges Creeks, A. P. Druce APD1263, Jan 1991, (CHR 471855); Upper Buller River, Dellows Bluff, P. J. de Lange 4792 & P. I. Knightbridge, 7 Dec 2000, (AK 288290, Duplicate: AD); Maruia Springs, Calf Paddock, P. J. de Lange 6509 & P. I. Knightbridge, 7 Dec 2000, (AK 289968, Duplicate: AD); Red Hills, Maitland Creek, P. J. de Lange 5135, 23 Jan 2001, (AK 288548, Duplicate: AD); Awatere River, between the Hodder and Limestone Rivers, L. B. Moore s.n., 16 Feb 1962, (CHR 129190); Lewis Pass, St James Walkway Shelter, P. J. de Lange 5095, 21 Jan 2001, (AK 286185, Duplicate: AD); Hanmer Forest Park, Waterfall Trail, P. J. de Lange 4285 & B. P. J. Molloy, 8 Feb 2000, (AK 286136, Duplicates: AD, CHR); Culverden, Lowry Peaks Road, Culverden Scientific Reserve, P. J. de Lange 4284 & B. P. J. Molloy, 8 Feb 2000, (AK 2888540, Duplicates: AD, NSW, WAIK); Eyrewell Scientific Reserve, B. P. J. Molloy s.n., 30 Jan 1970, (CHR 201642). OTAGO: The Neck, between Lakes Hawea and Wanaka, B. P. J. Molloy s.n., 13 Apr 2006, (AK 296424); Dunstan Range, near Crippletown, Rocky Point (Tarras -Cromwell Road), Bendigo Reserve, B. P. J. Molloy s.n., 15 Mar 2001, (AK 289978, Duplicate: AD); Lake Roxburgh Bluffs, Clutha Valley, K. J. M. Dickinson s.n. & B. D. Rance, 24 Mar 1986, (OTA 43677); McCraes, Nenthorn Region, Manuka Creek, J. P. Burrell s.n., 18 Jan 1962, (OTA 7352).

Distribution

(Fig. 12). Endemic, New Zealand, North and South Islands (30-2000 m a.s.l.). In the North Island present from about Te Kuiti, the Paeroa Range, Mt Tarawera and Kaingaroa Plain south through the Central Volcanic Plateau to the northern Aorangi Range. Absent from the high country west of Tongariro Forest, including Mt Taranaki/Egmont. In the South Island, present in the east from the upper Wairau River, and west from Karamea and the Wangapeka Valley inland along the upper Buller River and Nelson Lakes area, south through the main axial ranges to Sumner and the upper Hurunui catchment. Extending east into North Canterbury, particularly in the inland Hanmer, Emu and Amuri plains, thence present as isolated remnant stands on the Canterbury Plains. Otherwise apparently absent until Lakes Hawea and Wanaka from where it is locally present through portions of eastern Central Otago to about Roxburgh on the Clutha River and Nenthorn.

Recognition.

Kunzea serotina is recognised by a combination of characters including growth habit, bark type, branchlet hair, leaf, floral and fruit characters. No other member of the Kunzea ericoides complex has the same distinctive narrowly columnar to pyramidal growth habit, with obliquely ascending, fastigiate branches (Fig. 11A-D, G, H), a multitude of such densely leafy brachyblasts, spathulate pherophylls (Figs 9A, J-O, 11G, H), and petals copiously spotted with yellow oil glands (Fig. 9Q-R). The species also generally flowers later than most other species, with flowering tending to peak in January-February, and continuing as late as May.

Kunzea serotina was first recognised as distinct by W. Colenso who collected specimens in 1849 from the headwaters of the Makaroro River, eastern Ruahine Range (Colenso 1618, K, WELT SP022869-both mixed sheets, with the gatherings cited here being those labelled ‘A’) and who sent these to J.D. Hooker at Kew recommending their formal recognition with the suggested manuscript name "Leptospermum pulchrum". Kunzea serotina was also recognised by Allan (1961) who described it briefly as a 'thicket-forming variant’ confined to Marlborough, and it was mentioned by Harris (1996) who described it as 'a small-leaved variant possibly worthy of taxonomic segregation’, and 'occupying stations south of about Latitude 38° S’. As is often the case for New Zealand vascular plants (see Heenan 1998; Heenan et al. 2001; Heenan and de Lange 2004; Heenan and de Lange 2006) this species’ distinctiveness, so long overlooked by biosystematists, has long been appreciated by horticulturists who, in the North Island especially, have grown it widely, usually under the informal horticultural name Kunzea 'Central North Island’ (R. Mains pers. comm.).

Throughout its range Kunzea serotina is sympatric with Kunzea ericoides , Kunzea robusta , and, in some thermal areas (notably around Lake Taupo), with Kunzea tenuicaulis . In these areas despite the widespread sympatry, Kunzea serotina mostly forms pure populations with little evidence of hybridism (see below).

Kunzea serotina is distinguished from Kunzea robusta , by its columnar, pyramidal growth habit and singular bark-type (Fig. 11A-H). However, in very old specimens of Kunzea serotina the columnar, pyramidal growth habit tends to be less marked or lost altogether because the lower branches thin with age, leaving trees with usually flat-topped branches crowded toward the top. In these situations, the bark-type will distinguish both species when it is not possible to observe foliage or flowers. Kunzea serotina , uniquely of the New Zealand species, has bark that is very easily detached, chartaceous, greyish-white to pinkish-white in colour, with highly irregular and sinuous margins (Fig. 11E-F). The bark is often found hanging partially detached as inrolled or curled up lengths within the branch forks, or it forms piles of curled up 'wood shavings’ around the trunk base. In contrast, the bark of Kunzea robusta has a distinctly coriaceous texture which detaches basally first then peels up the trunk forming long (up to 4 m) broad to narrowly tabular strips with ± smooth, ± entire margins.

The branchlet hairs of Kunzea serotina consistently differ from those of most Kunzea robusta populations by their smaller (up to 0.08 mm) divergent, apically curved or curled (Fig. 10B, C-E) rather than longer (up to 0.38 mm), weakly flexuose, antrorse-appressed hairs. However, in some parts of the eastern Central Volcanic Plateau the length of the branchlet hairs of Kunzea robusta falls within the range cited for Kunzea serotina , although in these situations the hairs are still antrorse rather than divergent. In the upper Rangitikei, distinction of seedlings and saplings of Kunzea robusta from Kunzea serotina can be difficult because in that area young plants of Kunzea robusta usually have short divergent hairs of the same size range and form as Kunzea serotina . However, adult trees of Kunzea robusta from the same area (and those raised from these sites in cultivation) possess the more usual antrorse hairs. In these areas the growth habit of both species immediately distinguishes them. Floral and fruit characters also separate both species. In particular the spathulate to spathulate-orbicular pherophylls of Kunzea serotina (Fig. 9L-O) are unique among the New Zealand species and are a marked contrast to the narrowly deltoid, lanceolate, elliptic, oblanceolate to broadly oblanceolate, squamiform and/or foliose pherophylls typical of Kunzea robusta . Further, the petals of Kunzea serotina are uniquely dotted with yellow rather than the colourless or rose-pink oil-glands typical of other New Zealand species. Although the distributions of both species frequently overlap, Kunzea serotina is ecologically distinctive, being a species of inland basins, upland river flats, frost flats, tussock grassland, ridge crests of mountain ranges, and subalpine scrub, favouring sites prone to extremes of climate and often with recent or skeletal soils. Kunzea robusta is much more generalist in its habitat preferences but as a rule it is more of a coastal, lowland to montane species favouring better developed soils, less extreme climates, and conditions that tend to suit the development of mixed lowland forest types. While Kunzea serotina has been found at an upper altitudinal limit of 2000 m a.s.l. on Mt Ruapehu, Kunzea robusta is rarely seen above 800 m a.s.l. Thus, the main areas of sympatry are generally places where Kunzea serotina has colonised suitable lowland habitats abutting those dominated by Kunzea robusta , e.g., the pseudo-karst ignimbrite country around and north of Lake Taupo toward Te Kuiti and Tokoroa, or the steep-sided river valleys of the Kaimanawa and Kaweka Ranges.

The growth habit of Kunzea serotina (Fig. 11A-D) readily distinguishes it from the prostrate/decumbent shrub or multi-trunked widely spreading, flat-topped tree habit of Kunzea tenuicaulis . In addition, both species can be distinguished by their branching pattern with the obliquely ascending, shortly fastigiate branches of Kunzea serotina a marked contrast to the slender, widely spreading to pendulous branches of Kunzea tenuicaulis . The pherophylls are also distinctive; those of Kunzea tenuicaulis are mostly oblong, oblong-obovate to oblanceolate while those of Kunzea serotina are characteristically spathulate. The calyx lobes of Kunzea serotina are weakly keeled and flush with the rest of the hypanthium whereas in Kunzea tenuicaulis they are distinctly thickened toward the base, and the external junction with the hypanthium is marked by a faint to prominent groove. The flower petals of Kunzea serotina readily distinguish the species due to their being uniquely furnished with yellow rather than colourless oil glands. The fruit of both species is also diagnostic, with those of Kunzea serotina mostly urceolate to campanulate (rarely cupular) (Fig. 9V), while the fruits of Kunzea tenuicaulis tend to be barrel-shaped to cupular. Kunzea serotina and Kunzea tenuicaulis are generally separated by their ecology, with the latter endemic to geothermal habitats. Sympatry occurs mostly in the vicinity of LakeTaupo where the ranges of both species overlap, and where on occasion Kunzea serotina will colonise the more quiescent ground or cold ‘inliers’ of geothermal fields. Induced sympatry also occurs along the urbanised northern shoreline of Lake Taupo and at Wairakei, Karapiti and Tokaanu, where modification of the geothermal field for tourism has allowed Kunzea serotina (and Kunzea robusta ) to more freely colonise habitats more usually occupied by Kunzea tenuicaulis .

The columnar to pyramidal growth habit of Kunzea serotina readily separates it from Kunzea ericoides . Sometimes, as in shaded, damp or upland areas, the old bark of Kunzea ericoides may have secondary peeling, some of which curls in a manner reminiscent of Kunzea serotina . In these situations the foliage separates the species from each other. The leaves of Kunzea ericoides are much longer (up to 25 mm long), mostly bright green and mostly linear, whereas Kunzea serotina has distinctly shorter (up to 6.3 mm long), bronze-green to dark green, oblanceolate to obovate leaves. Both species have divergent branchlet hairs, but in Kunzea ericoides they are sparse, shed early in branchlet maturation, smaller (up to 0.05 mm long) and have straight apices; in Kunzea serotina , they are copious, persistent, longer (up to 0.08 mm long), with curved or curled apices. The flowers and fruits also differ. The petals of Kunzea ericoides are usually sparsely dotted with ± colourless oil glands, and the fruits are slightly larger (up to 3.4 × 3.9 mm), mostly glabrous, typically 5-locular, and mostly cupular, barrel-shaped, shortly cylindrical or hemispherical. The petals of Kunzea serotina are copiously dotted with yellow oil glands and the fruits are smaller (up to 3.0 × 3.4 mm), finely hairy, 3-4 locular, and urceolate to shortly-campanulate (Fig. 9V).

Although the other ‘small-leaved’ Kunzea species, Kunzea salterae and Kunzea toelkenii , are allopatric from Kunzea serotina , they could be confused in the herbarium. Kunzea serotina leaves (up to 6.3 × 1.8 mm) are smaller than the leaves of Kunzea salterae (up to 18 × 2 mm), and in Kunzea serotina they are oblanceolate to obovate rather than linear-lanceolate to narrowly oblanceolate. Kunzea serotina has spathulate pherophylls, and urceolate to campanulate, very rarely cupular, rather than cupular to sub-campanulate fruits. Herbarium material of Kunzea serotina differs from Kunzea toelkenii by its consistently divergent branchlet hairs rather than admixed large, antrorse-appressed, weakly flexuose, and small, divergent, curled hairs. Kunzea serotina also has smaller leaves (up to 6.3 × 1.8 mm) than Kunzea toelkenii (up to 8.5 × 2.5 mm) and Kunzea serotina lacks functionally male late season flowers. Other differences are summarised by Table 1 .

Molecular evidence (rDNA ITS) grouped Kunzea serotina with Kunzea ericoides , Kunzea linearis , Kunzea triregensis , Kunzea robusta , Kunzea sinclairii and Kunzea tenuicaulis (Table 2 ; see also de Lange 2007; de Lange et al. 2010) while the rDNA ETS sequence of Kunzea serotina shares a guanine/cytosine mix with Kunzea ericoides , Kunzea linearis , Kunzea robusta (Mt Egmont samples only), Kunzea salterae and Kunzea toelkenii , and an adenine with Kunzea salterae , Kunzea tenuicaulis and Kunzea toelkenii (Table 2 ; see also de Lange 2007; de Lange et al. 2010). Although there are no unique characters present in either of these marker regions, the inferred relationship of Kunzea serotina with Kunzea salterae , Kunzea tenuicaulis and Kunzea toelkenii , was already noted karyologically by de Lange and Murray (2004). Those data, coupled with the morphology of these ‘small-leaved’ species suggests that they are probably related and may form a natural group.

Ecology.

Kunzea serotina is an important component of the vegetation of the central North Island ranges. In the South Island Kunzea serotina attains local prominence in the montane vegetation of the Marlborough, the northern Southern Alps, and the dry intermontane basins of north Canterbury and eastern Central Otago.

Kunzea serotina has the highest altitudinal limit of all the New Zealand Kunzea , frequently growing above 1000 m a.s.l., and reaching its maximum recorded elevation as stunted shrubs at 2000 m a.s.l. on steep, sparsely vegetated slopes growing amongst other alpine herbs and grasses in the upper Mangatoetoenui Stream, on the eastern flanks of Mt Ruapehu. This habitat is, however, rather unusual. More typically, in the North Island Kunzea serotina grows along the ecotone between tall forest and tussock grassland, wetlands, frost flats or within grey scrub. In some places, most notably within the ignimbritic pseudo-karst of the north and eastern Volcanic Plateau, Kunzea serotina forms a distinct, often ecotonal forest along the boundaries of the frost flats formed by numerous low aspect ratio ignimbritic eruptions, mostly sourced from the Taupo Volcanic Centre, ( Houghton et al. 1995; Wilson et al. 1995). The South Island equivalent of this habitat seems to be the dry intermontane basins east of the main divide, especially those of north Canterbury, where remnant stands of Kunzea serotina are still locally common. In these montane and inland basin habitats, Kunzea serotina appears to have a long-term presence, and, if left undisturbed by fire, it probably would form the natural climax woody vegetation, particularly in areas prone to summer drought and extreme frosts and snow falls during winter.

Hybridism.

Although Kunzea serotina is sympatric with Kunzea ericoides , Kunzea robusta and Kunzea tenuicaulis . It appears to hybridise most frequently with Kunzea robusta .

Hybrids with Kunzea ericoides are easily recognised in the field and in herbaria because of the obvious differences in branching pattern, leaf colour, size and shape. This hybrid is probably uncommon because the distributions of Kunzea ericoides and Kunzea serotina rarely overlap. Putative Kunzea ericoides × Kunzea serotina has been been sparingly collected from Mt Dun, the Barnicoat Range and Hackett areas of eastern Nelson, and from the upper Buller and Sabine Rivers in southern Nelson are recognised. These are all areas where for various reasons the normally more montane and cold tolerant Kunzea serotina extends outside its usual range.

Kunzea ericoides × Kunzea serotina is easily recognised by the erect, somewhat open, sub-pyramidal growth habit, short, weakly fastigiate branchlets, and bright yellow-green, red-tinged leaves which are broadly lanceolate to linear-lanceolate. In most cases the branchlets tend to be distinctly hairy, though they can also be glabrescent. The inflorescences vary from corymbiform to widely spaced, elongate botrya. The pherophylls are deciduous and mostly pandurate to elliptic, and usually intermediate in length between either of the parents.

Recognition of the hybrid Kunzea serotina × Kunzea tenuicaulis is difficult, and examples of this hybrid have probably gone undetected during this study in herbaria (see Kunzea tenuicaulis ). The difficulty arises not so much in the field where the intermediate growth habit assists with hybrid recognition, but rather with herbarium material, from which hybridism can be difficult to infer if the accompanying notes are scant. Irrespective, it does seem that this hybrid is genuinely scarce, probably in part because it is only in the southern two-thirds of the Taupo Volcanic Centre that the ranges of either parent species overlap, and then mostly because human disturbance has induced novel habitats that both species (and the ubiquitous Kunzea robusta ) have utilised. Nevertheless, putative hybrids are represented by three herbarium specimens, from Karapiti (Craters of the Moon), Taupo on the shores of Lake Taupo, and at Tokaanu. Constant human activity at these places has allowed the ranges of these species to overlap and this disturbance has maintained the conditions for them. Beyond these modified habitats, Kunzea serotina though frequently found near sites of geothermal activity appears to avoid colonising them. Even in modified geothermal habitats, Kunzea serotina remains scarce, favouring local cold spots often on higher ground, well away from the main areas of thermal activity. However, because Kunzea tenuicaulis frequently colonises cold spots within thermal areas, it is not unusual to find isolated shrubs or trees of Kunzea serotina surrounded by and often partially smothered by Kunzea tenuicaulis growth. Under such conditions it is surprising that hybridism between these two species seems to be so uncommon, especially as the flowering times of both species overlap. The scarcity of hybrids possibly reflects something deeper. In the experimental cross Kunzea serotina ♀ × Kunzea tenuicaulis ♂, and its reciprocal, the progeny all had 2 n = 23 chromosomes ( de Lange and Murray 2004; de Lange et al. 2005). Few of these plants flowered. Pollen stainability from these plants was markedly reduced (12-23%). These results suggest that there might be some reproductive barrier in place which could explain the scarcity of this hybrid in the wild. Further investigation into this is needed.

The most commonly encountered hybrid is Kunzea robusta × Kunzea serotina because the ranges of both species frequently overlap. This is particularly the case in the North Island, around the northern Central Volcanic Plateau, southern Kaweka Ranges, and upper Rangitikei catchment. Hybrid swarms are common in these places, especially in grossly disturbed habitats such as reverting farmland or roadsides. Field recognition of hybrids is aided by the effect of the distinctive growth habit of Kunzea serotina , which results in somewhat openly branched, sub-pyramidal to widely spreading, sparingly branched, small spindly trees. The branchlets may be fastigiate or spreading but are usually shorter than in Kunzea robusta . The distinctive bark of Kunzea serotina is often present to some degree, though it tends to peel off in long tabular strips like Kunzea robusta but with much secondary peeling. It is the secondary peels that tend to curl up as Kunzea serotina bark normally does. Branchlet hairs are particularly diagnostic because Kunzea robusta has antrorse-appressed and Kunzea serotina has divergent hairs, with hybrids showing obvious mixtures of both. The pherophylls of Kunzea robusta , though very variable in shape and length, are mostly deltoid to lanceolate, and are usually present in mixtures of foliose and squamiform types. In Kunzea serotina the pherophylls are usually foliose and spathulate, spathulate-orbicular, only rarely pandurate or lanceolate. Thus, hybrids tend to show mixtures of sparse deciduous, pandurate, and lanceolate foliose and frequent squamiform pherophylls.

Artificial hybrids involving Kunzea serotina as staminate or pistillate parent and other New Zealand members of the Kunzea ericoides complex were easily produced and showed no obvious reduction in fertility except for crosses involving Kunzea tenuicaulis , which were effectively sterile (see de Lange and Murray 2004; de Lange et al. 2005).

Vernacular.

Kunzea serotina is (or was) locally known to Maori inhabiting the Central North Island as ‘makahikatoa’. Makahikatoa is said to mean 'white kahikatoa’ referring to the wood colour, and is a name intended to distinguish white-wooded Kunzea serotina from the red-wooded ‘warrior-wood’ of kahikatoa ( Leptospermum scoparium ) (W. Kawhaki pers. comm.). A few herbarium gatherings made during the 1800s also refer to this species as ‘manuka’.

Conservation status.

Kunzea serotina is an abundant and widespread species which should not be regarded as threatened or at risk (a more detailed account of its conservation status, using the criteria of Townsend et al. (2008) at both national and regional levels is provided by de Lange (2007).