A K. ericoide habitu fruticis decumbentis ad serpentis vel arboris erectae sed patentis multicaulis ad pendentibus, caulibus et ramibus multis tenuibus vel ramulibus numerosis patentibus ad pendentibus tenuissimis, ramulibus juvenibus dense tomentosis pilis multis brevibus patentibus, foliis brevioribus oblanceolatis ad obovatis; hypanthio minore cupuliformi campanulato gracile puberulenti; lobis calicis distincte incrassatis basipetale et sulco ad basim, fructibusque minoribis doliiformibus differt. Chromosomatibus constanter parvis et equatis seriebusque singularibus rDNA ITS et ETS differt.

(Figs 13, 14, 15) (Spread over three sheets). New Zealand: North Island, Central Volcanic Plateau, Paeroa Range, Te Kopia Thermal Area, 38°24'S, 176°13'E, 420m a.s.l. ‘Dominant shrub and small tree on active geothermal field. Abundant around vents. Growing with Leucopogon fasciculatus, Leptospermum scoparium and Dracophyllum subulatum, Seedling to adult collections from same site, over 3 sheets (AK 288088!, AK 288171!, AK 288172!)’. P. J. de Lange 4702A, B, C 16 Nov 2000, AK 288172 (Adult branch in bud, and branch with flowers and buds), AK 288088 (three seedlings), and AK 288171 (One sapling). Isotypi: AD, CHR.

The holotype gathering of Kunzea tenuicaulis comprises six specimens spread over three sheets and lodged at the same herbarium. The two adult specimens mounted on AK 288172, de Lange 4702A, come from the same plant, while the three seedlings (AK 288088, de Lange 4702B) and sapling (AK 288171, de Lange 4702C) were collected from the ground directly beneath that plant.

The manner in which I have collected and designated these sheets as holotype is in accordance with the International Code of Nomenclature (McNeill et al. 2012) Article 8.2 ‘….the holotype may consist of a single plant, parts of one or several plants, or of multiple plants…’ Thus in accordance with Article 8.3, Example 4 of the International Code of Nomenclature (McNeill et al. 2012), my collecting numbers reflects my intended association of these gatherings as type.

Kunzea tenuicaulis most probably equates with Kunzea ericoides var. microflora (G.Simpson) W.Harris which is based on Leptospermum ericoides var. microflorum G.Simpson (Simpson 1945). This variety was described from garden specimens sent to George Simpson by Norman Potts of Opotiki, and which, according to Simpson, came from ‘Rainbow Mountain, Nelson’ where its habitat was said to be the ‘Mineral Belt, Nelson’. As noted by Allan (1961; pp. 322–323), no plants matching Simpson’s description occur in the Nelson area or, indeed, the rest of the South Island. Furthermore, there is no Rainbow Mountain in the South Island. However, plants similar to Simpson’s description have been found in active geothermal areas within the Taupo Volcanic Zone of the North Island from a geothermal site near Lake Rotoiti (Tikitere) in the north west and Kawerau in north east to just south of Tokaanu, near Turangi at the southern end of Lake Taupo. These are the plants referred here to Kunzea tenuicaulis.

Allan (1961; p. 322) had also recognised this, and sought to rectify what he considered to be a genuine geographic mistake in Simpson’s protologue, by his statement that Simpson’s type locality was in fact ‘Rainbow Mountain near Waiotapu’. However, because Allan’s opinion cannot be matched with any supporting statement or evidence from Simpson, we simply cannot be certain where Simpson’s type (based on Norman Pott’s garden specimens) really came from. Further, the only specimen that I can unequivocally say is labelled by Simpson as Leptospermum ericoides var. microflorum is in extremely poor condition (AK 22886; Fig. 16A, B). The all-important diagnostic branchlet hairs are scant, there are only eight flowers left that are so shrivelled and damaged as to make a proper reconstruction impossible, and most of the foliage is missing. While I am convinced that Simpson’s type matches what I have named Kunzea tenuicaulis, I have elected to remove any further ambiguity by redescribing the Kunzea endemic to the geothermal fields of the Taupo Volcanic Zone at the rank of species, with a full and detailed description, and an unambiguous wild type and duplicates gathered from a wild legally protected site where the species is uniform and widespread, and hybridism is not evident.

The specific epithet tenuicaulis refers to the numerous very fine and slender branchlets produced by this species, irrespective of its overall growth habit.

= Leptospermum ericoides var. microflorum G.Simpson in T.R.S.N.Z. 75, (1945), 189.

≡ Kunzea ericoides var. microflora (G.Simpson) W.Harris in N.Z.J.Bot. 25, (1987), 134.

(here designated) (Figs 16, 17). “Leptospermum ericoides var. microflorum, [R]ainbow Mt, Potts” AK 22886! (label in George Simpson’s hand, written in pencil on back of piece of printed paper (possibly newspaper) (Fig. 16B)).

Leptospermum ericoides var. microflorum was briefly described by Simpson (1945) and for most of his protologue his intent is clear. Simpson’s type collections were based on a specimen that had been cultivated by Mr N. Potts of Opotiki. Potts’s plant was said to have come from Rainbow Mountain (Simpson 1945). The fact that

Potts, a North Island botanist, wrote to Simpson stating “the plant occupies craters on Rainbow Mountain” strongly suggests that his plant had come from Rainbow (Maungakakaramea) Mountain (38°19'S, 176°23'E), an old volcanic vent and active geothermal field just to the north east of the small settlement of Waiotapu on the western marches of the Kaingaroa State Forest in the North Island.

Despite this, Simpson explicitly states ‘Habitat: Mineral belt, Nelson’ (a South Island location), and further ‘Specimens from a plant in cultivation by Mr N. Potts’ garden at Opotiki, collected at Rainbow Mountain, Nelson’. Subsequently, Allan (1961; p. 322) stated that the variety is ‘known with certainty only from the type locality: Rainbow Mountain near Waiotapu’ and that Simpson has ‘inadvertently given the locality as “Mineral belt, Nelson”’. This, while probably true (see above) is not strictly correct, as Simpson twice cited Nelson as the source of the plants, and as far as I can determine never clarified the apparent ambiguity in subsequent literature or correspondence with Allan or anyone else—though the handwriting on CHR 48079, ‘Note published as Mineral Belt by mistake. cf. Miss L.B.Moore’ suggests that L. B. Moore might have obtained some comment from someone about the original source of Potts’s specimens. Irrespective, based on available evidence we cannot be sure of what Simpson’s statements about the source of his type material really meant.

Simpson (1945) also explicitly states that the ‘specimens’ (my emphasis) on which he based his name were lodged in the ‘Herbarium Plant Research Bureau, Wellington’ then known as BD (Botany Division) and now CHR. Allan (1961; p. 322) lectotypified the name (from a specimen in the former Botany Division Herbarium that he evidently considered was part of the type gathering) in the following manner ‘Type: BD 48079, from a plant cultivated by N. Potts’. That specimen (Fig. 17), now CHR 48079, is clearly labelled ‘TYPE’ in red ink, in what is probably the hand of T. Rawson, then Technician to Allan (P. B. Heenan pers. comm.). However none of the associated handwriting on the label is in Simpson’s hand (see Heenan 1995) and, beyond the filing of the specimen in the ‘Simpson Herbarium’ there is nothing to clearly identify this gathering as one that Simpson had actually handled, let alone anything to show that Potts gathered the specimen. For these reasons I reject Allan’s typification.

In AK I have located a further gathering attributed to Simpson, AK 22886, bearing several labels (Fig. 16A, B). The main label is an official one of the type used at AK between 1929 and about the early 1970s (E. K. Cameron pers. comm.) and is labelled in blue ink ‘Rainbow Mt., Nelson, N. Potts’ and ‘cotype’ in handwriting that is most likely that of the herbarium curator at AK toward the end of the 1940s, B. E. Molesworth. Beneath that label, on the back of a small scrap of what appears to be newspaper, is a pencil annotation in Simpson’s distinctive handwriting (Fig. 16B; see also Heenan 1995), ‘Leptospermum ericoides var. microflorum …[R]ainbow Mt…Potts’. As the official AK label was inadvertently glued over part of Simpson’s handwriting, what I regard as the letter ‘R’ has been partially erased by glue and dirt and is thus no longer fully legible (Fig. 16B). There is no doubt in my mind however, that the locality on the label is Rainbow Mountain.

Although Simpson makes it clear that specimens of his new variety were to be found in what is now the Allan Herbarium (CHR), I cannot now find any specimens there that unequivocally show this, and yet, as Simpson indicates that he had lodged ‘specimens’, I feel it unwise to regard the AK specimen as a holotype because other collections may exist. For this reason I select AK 22886 as lectotype. I consider CHR 48079 as having no nomenclatural status because there is no evidence that Simpson ever handled or in anyway used it to describe his variety.

The varietal epithet ‘microflorum’ was adopted by Simpson (1945) in the mistaken belief that his Leptospermum ericoides var. microflorum had smaller flowers than the type variety.

(Figs 18, 19, 20). Growth habit decumbent, trailing subshrubs, shrubs or small trees 0.1–6.0(–8.0) × 2.0–6.0(–8.0) m. For specimens with a tree habit, crown widely spreading, often arching to somewhat pendulous. For specimens found around active fumaroles or on open, geothermally heated ground, growth habit varying from completely decumbent and densely branched, with stems sprawling across ground, to semi-erect, densely branched, widely spreading, often pendulous. Trunk in tree forms (1–)4–6 arising from base, 0.1–0.6 m d.b.h., these branching from close to base, with branches thinning in close canopies only; in decumbent plants trunk virtually indistinguishable, 0.01–0.10 m diam., trailing to semi-erect, curved and somewhat sinuous, in erect plants at first erect, soon widely spreading and curving to somewhat sinuous. Bark early bark greyish brown to brown, initially firm, somewhat sinuous-fluted, elongate, over time cracking transversely (especially on branch flanges and decurrent leaf bases), and with margins gradually detaching and rolling-in to present as easily detached, papery, narrowly short to long, somewhat irregular-margined flakes; old bark grey-brown to grey, chartaceous to mildly corky, flaking readily in short to long, usually narrow and slightly sinuous to irregular, tabular shards, these usually remaining attached in several places with the spaces between detached, cracked and more or less raised, upper bark surface often with much secondary peeling and transverse cracking, crumbling in hand easily. Branches numerous, rather narrow and long, often weakly flexuose, in decumbent plants prostrate, trailing, otherwise initially ascending, soon suberect to widely spreading, and arching, often pendulous; branchlets numerous, very leafy, rather slender, quadrangular, sericeous, with dense, silky indumentum; hairs persistent, divergent, weakly flexuose, 0.03–0.06(–0.08) mm, hyaline to translucent (appearing white when young maturing grey), hair apices more or less straight. Vegetative buds inconspicuous, usually obscured by surrounding foliage; at resting stage 0.5–1.0(–1.6) mm diam.; scales scarious, deciduous, (0.3–)0.8(–1.3) mm long, red-brown to dark brown, initially broadly ovate grading through to broadly lanceolate; midrib prominent, strongly keeled, prolonged to cuspidate tip, with 1–2 lateral veins either side, and two prominent rows of 3–8 oil glands straddling midrib, margins and keel apex ciliate. Leaves heterophyllous, seedling and subadult leaves flat or involute, ± spreading to recurved; 0.9–3.0(–4.5) × 0.2–0.4(–0.6) mm, red-green or pale green suffused with red, rarely bright green; lamina finely linear-lanceolate, long persistent in stressed habitats (in damaged plants reversion shoots bearing juvenile foliage frequent); adult leaves ± spreading to patent; lamina (1.1–)4.0(–10.0) × (0.8–)1.3(–2.8) mm, dark glossy green, red-green, to bronze-green, narrowly oblanceolate, oblanceolate, obovate to obovate-rostrate; usually recurved from about half of total length, apex usually obtuse, rounded, rarely subacute, cuspidate; base attenuate; adaxial surface convex, finely glandular punctate; oil glands up to 590, more evident when dry, midrib slightly raised to depressed near base, otherwise depressed for entire length, glabrous, very rarely with fine antrorse hairs near base; abaxial surface slightly concave, finely glandular punctate, oil glands less obvious, up to 280, these more evident when dry; midrib depressed, finely and sparsely covered with sericeous, deciduous, antrorse-appressed hairs, these increasing in density toward base; lamina margin sparsely to densely, finely sericeous, hairy; hairs weakly flexuose, appressed to weakly spreading, antrorse to subantrorse, up to 0.1 mm, hyaline to translucent, appearing as white to naked eye, aligned in 1 row not quite meeting at cuspidate leaf apex. Perules scarious, basal ones usually persistent, these 0.4–1.0 mm long, pale brown to brown, broadly oblong to oblong-lanceolate, margins involute especially in upper third, midrib strongly keeled, prolonged as a cuspidate apex, with one row of 4–8 oil glands on each side of midrib, glabrous except for finely ciliate margin and apex; remaining perules deciduous, chartaceous, (0.6–)0.8(–1.4) mm long, pink to pinkish-white when fresh, drying apricot to apricot-brown, ovate to broadly oval, apex obtuse often appearing acute due to apical infolding, ± cuspidate, glabrous except for sparsely ciliate margin, strongly keeled, keel ± prolonged. Inflorescence usually a compact, (1–)6(–10)-flowered corymbiform botryum up to 25 mm long, borne on alternate brachyblasts up to 15 mm long, with those near branchlet apex usually subopposite; inflorescences at the ultimate branchlet tips rarely elongated, in which case these are invariably surmounted with terminal vegetative growth. Inflorescence axis densely invested with divergent hairs. Pherophylls deciduous (falling very early), tightly clasping pedicels to ± spreading, 0.5–1.0 mm long, initially foliose soon squamiform; foliose pherophylls pale green, oblong, oblong-obovate to oblanceolate, margins and apex finely ciliate; squamiform pherophylls brown or pink, drying apricot-brown or amber, broadly deltoid to oblong-ovate, margins involute especially in upper one-third, midrib strongly keeled, prolonged as cuspidate apex, with one row of 4–8 oil glands on each side; glabrous except for the finely ciliate margin and apex; similar to perules in size and shape at apex. Pedicels (1.0–)2.1(–2.4) mm long at anthesis, elongating slightly after anthesis, terete, copiously invested in slightly flexuose, antrorse to subantrorse sericeous hairs. Flower buds clavate to pyriform, apex distinctly domed (due to thickened calyx lobes) prior to bud burst with calyx valves ± meeting. Fresh flowers when fully expanded (3.3–)5.5(–9.0) mm diam. Hypanthium (1.8–)2.5(–3.3) × (1.7–)2.4(–3.1) mm, with free portion 0.3–0.8(–1.0) mm long, dark green often basally mottled or flushed with red when fresh, drying brown to grey; narrowly cupular to campanulate terminating in a slightly thicker rim bearing five persistent calyx lobes; surface smooth, finely gland-dotted, and puberulent, with weakly defined ridges leading up to calyx lobes (these becoming more distinct upon drying); hairs shortly subantrorse to antrorse. Calyx lobes 5, upright (not spreading), firmly fleshy, 0.4(–0.8) × 0.4(–1.0) mm, persistent, oblong, oblong-ovate to broadly triangular, in longitudinal-section distinctly thicker at base, ± subtended by a faint to prominent groove at the external junction with the hypanthium, otherwise tapering to apex, scarcely keeled (the keel if evident recognisable as a darker green or pink, thicker central prolongation of the hypanthium ridges), margins cream to pale pink, gland-dotted, oil glands usually colourless sometimes pink; otherwise glabrate except for ciliate margins; cilia widely spreading. Receptacle green or pale pink at anthesis, darkening to crimson-red or magenta after fertilisation. Petals 5(–6), 1.4–1.6(–2.0) × 1.4–1.6(–2.0) mm, white or pinkish white, usually basally flushed pink, very rarely completely pink, orbicular, sometimes cuneate, apex obtuse to rotund, margins plane or finely crimped 3–12 times, oil glands not evident when fresh, drying colourless. Stamens 10–24(–32) in 1(–2) weakly defined whorls, arising from receptacular rim, filaments white often tinged rose-pink toward base. Antipetalous stamens 2(–3), antisepalous 1(–4). Outermost antipetalous stamens usually weakly to strongly incurved, on filaments 0.9–2.2 mm long; inner stamen, if present, 0.6–0.8 mm, strongly incurved; very rarely a further 1–2 strongly incurved stamens, 0.4–0.7 mm long, may be present at the base of the outermost antipetalous pair. Antisepalous stamens much shorter than outermost antipetalous stamens, 0.3–0.8 mm, incurved, rarely outcurved or in mixtures of both. Anthers dorsifixed, 0.04–0.08 × 0.02–0.04 mm, testiculate, latrorse. Pollen white (12.8–)14.7(–16.6) μm. Anther connective gland prominent, orange when fresh, drying pale brown, spheroidal, distinctly papillate. Ovary (3–)4(–5) locular, each with 15–18(–22) ovules in two rows on each placental lobe. Style 2.0–2.6(–3.6) mm long at anthesis, often elongating slightly after anthesis, white basally flushed with pink; stigma capitate, scarcely wider than style, domed along margins with a central depression, pale cream to pink, surface papillate to distinctly rugulose. Fruits ± persistent, (1.0–)2.3(–3.3) × (1.6–)2.2(–3.2) mm, light brown to grey, usually barrel-shaped, rarely cupular, splits concealed by dried, suberect to erect, free portion of hypanthium. Seeds 0.80–1.00 × 0.45–0.50 mm, narrowly oblong, oblong, oblong-obovate to falcate-oblong, curved near apex, laterally compressed, 2–3-angled with convex to flattened faces, apex rounded, base cuneate to oblique, ± flattened; testa semi-glossy, orange-brown, surface coarsely reticulate. FL: (Aug–)Sep–Oct(–Mar) FT: Jan–May(–Nov). Chromosome Number n = 11_II, 2n = 22 (de Lange and Murray 2004).

(80 sheets seen). New Zealand (North Island). Kawerau, Ruruanga Stream (Parimahana Geothermal Field), P. J. de Lange 4628, 7 Nov 2000, (K 288085); Tikitere (Hell’s Gate) Geothermal Field, Upper Waiohewa Stream, P. J. de Lange 4628, 7 Nov 2000, (AK 288086); Rotorua, Kuirau Park, P. J. de Lange 4627, 7 Nov 2000, (AK 286156); Whakarewarewa Park, L. Cockayne s.n., 29 Dec 1905, (WELT SP029450); Waimangu Thermal Area, near Lake Rotomahana, R. J. Chinnock s.n., 17 Oct 1967, (WELTU 9731); Maungakakaramea (Rainbow Mountain), P. J. de Lange 4223, 26 Jan 2000, (AK 286186); Te Kopia Geothermal Area, P. J. de Lange 4700, 16 Nov 2000, (AK 288099, Duplicates: AD, MEL, MO); Paeroa Range, Waikite Geothermal Reserve, P. J. de Lange 4713 & R. O. Gardner, 19 Nov 2000, (AK 286168, Duplicates: AD, WELT); Te Kopia – Waihunuhunu Road, Waihunuhunu Stream, P. J. de Lange 4699, 16 Nov 2000, (AK 288087, Duplicates: AD, FI, HO, MSC, P); Waikato River, Lake Ohakuri, Orakeikorako, P. J. de Lange 4693, 16 Nov 2000, (AK 286170); Waikato River, Wairakei, P. J. de Lange 4683, 10 Nov 2000, (AK 288084, Duplicate: AD); Wairakei Geothermal Field, Karapiti, Craters of the Moon, P. J. de Lange 5765, 10 Nov 2003, (AK 286152, Duplicates: CANB, CANU, MSC, NSW, Z); Lake Taupo, The Spa, D. Petrie s.n., Dec 1895, (WELT SP029561); Tokaanu, Tokaanu Geothermal Reserve, P. J. de Lange 4582, 19 Oct 2000, (AK 288103, Duplicates: AD, HO, MEL, WELT).

(Fig. 7). Endemic, New Zealand, North Island, Bay of Plenty to the Central North Island (40–580 m a.s.l.). Confined to active geothermal fields (i.e. those with surface expression) of the Taupo Volcanic Zone (for geology see Healy 1992; Houghton et al. 1995; Wilson et al. 1995; Neall 2001) from the vicinity of Kawerau (Parimahana Geothermal Field) and Lake Rotoiti (Tikitere) south to Tokaanu and the hills above Waaihi, Lake Taupo (Figs 20A–C, 21).

Kunzea tenuicaulis is recognised by a combination of growth habit, branchlet hair and floral characters (Figs 19, 20; see also Table 1) supplemented by cytological and molecular differences. The ITS and ETS sequence data (Table 2) show that Kunzea tenuicaulis is the most diverged of the New Zealand members of Kunzea ericoides complex (de Lange 2007; de Lange et al. 2010). Uniquely within the Kunzea ericoides complex, the ITS sequence of Kunzea tenuicaulis possesses two adenine nucleotides rather than the guanine common to all other members of the complex at ITS-1 alignment position 639, and at ITS-2 alignment position 994 (Table 2; see also de Lange 2007). Otherwise it shares a guanine/thiamine mix with Kunzea salterae (de Lange 2007). The ETS sequence (Table 2) showed two further unique characters; a thiamine at alignment position 18 (whereas all other members of the complex possess a cytosine), and a cytosine at alignment position 202 (whereas all other members of the complex possess an adenine) (de Lange 2007). Otherwise the aligned ETS sequence of Kunzea tenuicaulis has an adenine at position 269 in common with the other ‘small-leaved’ New Zealand Kunzea, Kunzea salterae, Kunzea serotina and Kunzea toelkenii (de Lange 2007). In view of the geologically recent (estimated to be a maximum of 2 million years old (Neall 2001; Briggs et al. 2005)) habitats this species occupies, this molecular divergence from all other members of the Kunzea ericoides complex is considered remarkable (de Lange 2007; de Lange et al. 2010).

Kunzea tenuicaulis seems to be most closely allied to Kunzea salterae and Kunzea serotina, and, based on the results obtained from experimental hybridisations (de Lange et al. 2005), Kunzea tenuicaulis may have had a role in the evolution of Kunzea salterae and Kunzea toelkenii through hybridisation with Kunzea linearis and Kunzea robusta. With the exception of Kunzea salterae which has linear-lanceolate leaves, Kunzea serotina, Kunzea tenuicaulis and Kunzea toelkenii all possess small oblanceolate to obovate leaves. Branchlet hairs in all four species tend to be copious, short (up to 0.08 mm), divergent, and persistent (Table 1). Further, as reported by de Lange and Murray (2004) and de Lange et al. (2005) Kunzea tenuicaulis shares with Kunzea serotina and Kunzea toelkenii uniformly small chromosomes (0.9–1.0 μm). Kunzea salterae, has a similar chromosome complement, though this was not reported previously because that species had not yet been recognised when those papers were published. Despite this Genomic In Situ Hybridisation experiments determined that, alone of those taxa analysed, Kunzea tenuicaulis has the most diverged genome (de Lange et al. 2005).

As circumscribed here, Kunzea tenuicaulis includes a range of prostrate to erect plants found in close proximity to active geothermal vents and fields (Fig. 20D–G, J). Although in the past, (probably because of the past poor circumscription of this plant) field workers had formed the impression that Kunzea ericoides var. microflorum applied only to the flat, prostrate to small decumbent shrubs found near active geothermal vents (e.g., Harris et al. 1992; Harris 1996; Smale 1994). There seems little point in trying to separate these prostrate plants from the erect plants they resemble in all respects except stature. Indeed, stature itself often presents as a gradient from thermally heated to thermally quiescent ground. Cultivation experiments showed that while some seedlings raised from seed sampled from prostrate/decumbent plants retained that growth habit, the majority grew into multi-trunked erect small trees with flat topped, spreading to pendulous crowns typical of Kunzea tenuicaulis as defined here. Irrespective of growth habit, all forms of Kunzea tenuicaulis are consistently unified by their many, fine, slender branchlets; copious, short, divergent branchlet hairs (Fig. 19A–F); small oblanceolate to obovate leaves (Fig. 18C–G); small cupular to campanulate, finely puberulent hypanthium (Fig. 18K–L); by the calyx lobes which are thickened toward the base and there subtended by a faint to prominent groove along the external junction with the hypanthium; and by the smaller, barrel-shaped fruit (Fig. 18O). Furthermore the ITS and ETS sequence data obtained from multiple samples spanning the range and variation of this species were consistent, and readily distinguished Kunzea tenuicaulis from the rest of the Kunzea ericoides complex (de Lange 2007; de Lange et al. 2005).

Provided that care is taken to note the growth habit, collect old bark, new season’s growth, and emergent flowers Kunzea tenuicaulis is easily separated from the other New Zealand Kunzea. This is important for although Kunzea tenuicaulis is distinguished ecologically because it is endemic to active geothermal fields (Figs 20A–C, 21), within these habitats it may be found sympatric (or even syntopic) on associated ‘cool’ sites with Kunzea serotina and Kunzea robusta.

Kunzea tenuicaulis can be distinguished from Kunzea serotina by its growth habit, which is either prostrate/decumbent or multi-trunked, with widely spreading pendulous, mostly flat-topped, branches, producing numerous spreading, slender, long branchlets (Fig. 20D–G, J; Table 1). This contrasts with the strictly upright columnar to pyramidal growth habit, with short, obliquely ascending, fastigiate branches of Kunzea serotina. The bark of both species is also diagnostic. The old bark of Kunzea tenuicaulis is grey-brown to brown, readily detached, somewhat corky-chartaceous, flaking in narrow, short to long, slightly sinuous to irregular, tabular shards (Fig. 20H–I; Table 1). The old bark of Kunzea serotina is greyish-white to pinkish-white, and presents as inrolled and curled ‘wood shavings’, these having little if any discernible shape, with highly irregular, sinuous, often frayed margins. Although both species have similar leaves, in Kunzea serotina the leaves are less widely spaced, and tend to be densely clustered around the branchlets. Branchlet hairs however are not overly diagnostic as both species have similarly sized divergent hairs. In general though, those of Kunzea serotina tend to have more curly apices and Kunzea tenuicaulis less so (Fig. 19C–F). The pherophylls, if present, serve to separate both species: those of Kunzea tenuicaulis are mostly foliose oblong, oblong-obovate to oblanceolate while those of Kunzea serotina are characteristically spathulate to spathulate-orbicular. The calyx lobes of Kunzea tenuicaulis are especially diagnostic when fresh because they are distinctly thickened toward the base below which is a faint to prominent groove at the external junction with the hypanthium. Those of Kunzea serotina are slightly keeled and flush with the rest of hypanthium. The petals of Kunzea tenuicaulis are broadly orbicular and have colourless oil glands (often not evident until the petals have dried) while those of Kunzea serotina are narrowly orbicular to broadly ovate and typically have pale yellow oil glands. The mature fruits of Kunzea tenuicaulis tend to be barrel-shaped to cupular, those of Kunzea serotina urceolate to campanulate or, rarely, cupular (Table 1).

Kunzea tenuicaulis is distinguished from Kunzea robusta by its smaller size (up to 8 m cf. up to 30 m in Kunzea robusta) and growth habit (see Table 1). Kunzea robusta is mostly an arborescent species, and so usually forms a single-trunked tall tree, with a broad trunk, stout, ascending to spreading branches, and a very wide, spreading, multi-tiered canopy. However, occasionally Kunzea robusta can be a low (up to 2 m tall) shrub with prostrate to pendulous branches, or be a tree with entirely pendulous branches, in which case leaf size, shape and branchlet hair type serve to distinguish it from Kunzea tenuicaulis. The bark of Kunzea robusta is particularly distinctive, being very coriaceous, long persistent, typically detaching with age as long (up to 4 m), broad to narrowly tabular strips, with ± smooth, ± entire margins, which when deliberately bent and snapped have ± entire or weakly frayed broken surfaces. In contrast, the bark of Kunzea tenuicaulis is not long persistent, readily detaches, and is distinctly corky-chartaceous, flaking as rather narrow, much shorter (up to 100 mm long) tabular shards with slightly sinuous to irregular margins. The oblanceolate to lanceolate leaves of Kunzea robusta, up to 20.1 × 3.0 mm, are usually much larger and broader than the leaves of Kunzea tenuicaulis which grow to 4.5 × 0.6 mm. A key difference between these species is the branchlet hairs. In Kunzea robusta populations that occur within the range of Kunzea tenuicaulis, branchlet hairs are mostly antrorse-appressed, larger (up to 0.38 mm) and straight to weakly flexuose. Kunzea robusta also has larger inflorescences containing more flowers (up to 30, more usually 12) than Kunzea tenuicaulis. The inflorescences of Kunzea robusta typically progress from a compact corymbiform botryum at the onset of flowering to an elongated botryum as the flowering season progresses due to activation of the apical vegetative bud. In Kunzea tenuicaulis this very rarely happens, and then only to the terminal inflorescence, those of the brachyblasts tending to remain as compact corymbiform botrya bearing far fewer (up to 10, more usually six) flowers (Figs 18A, 20K). The flowers of Kunzea robusta tend to have a greater overall diameter (up to 12.0 mm, more usually 7.7 mm cf. up to 9.9 mm, more usually 5.5 mm) and in the field more stamens (up to 60 cf. up to 32 in Kunzea tenuicaulis) (see Table 1). The fruits of both species are also rather different, those of Kunzea tenuicaulis tending to be smaller (up to 3.3 × 3.2 mm )and barrel-shaped to cupular (Fig. 18B, O), while those of Kunzea robusta are much larger (up to 4.6 × 5.3 mm), and mostly obconic, broadly obconic to ± turbinate (see Table 1).

Although Kunzea salterae and Kunzea toelkenii are allopatric from Kunzea tenuicaulis, they could be confused in the herbarium. The oblanceolate to obovate leaves of Kunzea tenuicaulis, which grow up to 4.5 × 0.6 mm, are smaller than the 18 × 2 mm, linear-lanceolate to narrowly oblanceolate leaves of Kunzea salterae. Furthermore, the fruits of Kunzea tenuicaulis are barrel-shaped to cupular rather than cupular to subcampanulate (see Table 1). The consistently divergent branchlet hairs of Kunzea tenuicaulis are distinct from the admixed large, antrorse-appressed, weakly flexuose, and small, divergent, curled hairs of Kunzea toelkenii. The leaves of Kunzea tenuicaulis are also smaller than those of Kunzea toelkenii, which grow to 8.5 × 2.5 mm, and Kunzea tenuicaulis lacks functionally male late season flowers, unlike Kunzea toelkenii (see Table 1).

Kunzea tenuicaulis is the dominant woody plant on the active geothermal fields within the Taupo Volcanic Zone (Fig. 20A–C) where it colonises not only heated ground but quiescent and/or ‘cool’ ground associated with each geothermal field. In these ‘cool’ peripheral situations it may be dominant, though it usually associates with Leptospermum scoparium, Weinmannia racemosa L.f., Knightia excelsa R.Br. and Kunzea robusta. The understorey of this peripheral vegetation is usually dominated by shrubs and ferns such as Leptecophylla juniperina (J.R.Forst. et G.Forst.) C.M.Weiller, Leucopogon fasciculatus (G.Forst.) A.Rich., Dracophyllum subulatum Hook.f., Pteridium esculentum (G.Forst.) Cockayne, Histiopteris incisa (Thunb.) J.Sm., and Lycopodiella cernua (L.) Pic.Serm. Toward the active geothermal vents, where surface temperatures can abruptly rise to as much as 90 °C (Burns 1997) and most woody vegetation becomes scarce, Kunzea tenuicaulis is the dominant macro-vegetation. In these habitats, which may include extensive areas of steam field, heated mud pools and hot springs, active and quiescent hydrothermal explosion craters, and fumaroles, the low shrub or prostrate trailing form of Kunzea tenuicaulis is best developed (Fig. 20A, C, J). It is this form which may be found flowering at less than 40 mm tall and which is the plant referred to in past literature as Kunzea ericoides var. microflora (see Given 1980a; Harris et al. 1992; Smale 1994; Harris 1996; Burns 1997). However, in many geothermal areas (e.g., Tikitere, Kuiarau Park andTokaanu) this decumbent form of Kunzea tenuicaulis is mostly replaced by multi-trunked, erect to suberect trees of Kunzea tenuicaulis (see Fig. 20D–G) identical to those seen growing in peripheral ‘cold’ and/or thermally quiescent areas in more active fields. Further study is needed to determine why the low shrub form of Kunzea tenuicaulis seems to be favoured in the more unstable geothermal systems, though physiological stress and aluminium toxicity has been suggested as a partial explanation (Burns 1997). Irrespective, in these geothermally more active habitats Kunzea tenuicaulis frequently associates with the ferns Dicranopteris linearis (Burm.f.) Underw., Nephrolepis flexuosa Colenso, Cheilanthes distans (R.Br.) Mett. and Cheilanthes sieberi Kunze subsp. sieberi, sparse, stunted Leucopogon fasciculatus and Dracophyllum subulatum shrubs, the lilies Dianella nigra Colenso, Dianella haematica Heenan et de Lange and the exotic love grass Eragrostis brownii (Kunth) Wight. Underneath Kunzea tenuicaulis shrubs a ground cover of liverworts and mosses dominated by Chiloscyphus semiteres (Lehm.) Lehm. and Campylopus pyriformis (Schultz) Brid. is usually present. In these habitats and also in the peripheral cool soils, ectomycorrhizal fungi of the genus Pisolithus Alb. et Schwein. (see Burns 1997; Moyersoen and Beever 2004) have been found in exclusive association with Kunzea tenuicaulis (McKenzie et al. 2006 as Kunzea ericoides var. microflora). Kunzea tenuicaulis is also occasionally, and at times rather heavily, parasitised by the dwarf mistletoe Korthalsella salicornioides.

The putative hybrids Kunzea robusta × Kunzea tenuicaulis and Kunzea serotina × Kunzea tenuicaulis have been collected throughout the range of Kunzea tenuicaulis. However, of these hybrids, only Kunzea robusta × Kunzea tenuicaulis is commonly encountered, because Kunzea robusta is more frequently sympatric with Kunzea tenuicaulis along the margins of that species’ geothermal habitats, and in the plantation forests abutting many of the geothermal fields within the Rotorua Volcanic Centre (for geology see Briggs et al. 2005; Neall 2001). Putative gatherings of Kunzea serotina × Kunzea tenuicaulis are less common because the ranges of those species rarely overlap (except around Karapiti and Tokaanu). These hybrids are discussed in detail under Kunzea serotina.

Hybrids involving Kunzea robusta are best recognised by the presence of mixtures of long, appressed, weakly flexuose and shortly divergent branchlet hairs. However, in the field they can be distinguished by their general tendency to form single trunked, weakly spreading trees, with fewer branches and branchlets that are often somewhat slender and semi-pendulous to pendulous. Kunzea robusta × Kunzea tenuicaulis is usually present as introgressive hybrid swarms because most of the geothermal habitats are now extensively modified.

Artificial hybrids involving Kunzea tenuicaulis 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 serotina, which were sterile (de Lange and Murray 2004; de Lange et al. 2005).

No specific Maori name for this species seems to have been recorded.

Currently, as Kunzea ericoides var. microflora, Kunzea tenuicaulis is appropriately listed as ‘At Risk/Naturally Uncommon’ qualified ‘RR’ [Range Restricted] by de Lange et al. (2013b).