Cardamine panatohea Heenan et de Lange, 2018

Heenan, Peter B. & De Lange, Peter J., 2018, Cardamine panatohea (Brassicaceae), a new, threatened, alpine species from New Zealand, Phytotaxa 379 (3), pp. 255-260 : 256-259

Cardamine panatohea Heenan et de Lange , sp. nov. ( Fig. 1 )

Cardamine panatohea is distinguished from all other New Zealand indigenous Cardamine species by its sprawling, usually prostrate or decumbent inflorescences that have well-developed leafy rosettes in the axils of the lateral branches, and from C. corymbosa by its thicker leaves with the adaxial surface moderately hairy and racemose inflorescences.

Type: — NEW ZEALAND. Wellington Land District, Mt Ruapehu, tributary of Mangaturuturu Stream, permanently wet seepage below waterfall, 1650 m, 12 March 2015, P. B. Heenan s.n. (holotype CHR 640349!).

Perennial herb, single or several rosettes, with 1–10 short lateral branches, stems and branches 0.5–1.5 mm diam. Leaves up to 45 mm long, pinnatisect; lamina 3.3–15.0 × 3.5–13.0 mm, green, semi-coriaceous, sparsely to moderately hairy or glabrate on adaxial surface, margin and petiole, glabrous or sparsely hairy on abaxial surface; terminal pinna 3.3–12.0 × 3.5–13.0 mm, simple, orbicular-reniform to reniform, apex obtuse with an inconspicuous hydathode, base usually cordate, sometimes obtuse or truncate. Lateral pinnae 0–4, 2.0–4.0 × 1.5–2.5 mm, orbicular to orbicularrhomboid, petiolule absent or up to 1.2 mm long; petiole up to 30 mm long; hairs 0.1–0.2 mm long, spreading to patent. Cauline leaves similar to rosette leaves but distally smaller, narrower, with fewer lateral pinnae. Inflorescence with 1–4 racemes, each raceme 4–12-flowered, terminal flowers often in a cyme-like cluster; peduncle up to 140 mm long, 0.5–1.5 mm diam. at base, prostrate, decumbent to seldom upright, glabrous. Pedicels 1.5–8.0 mm long, 0.2–0.8 mm diam., glabrous or rarely hairy, spreading. Sepals 1.8–2.2 × 0.5–1.1 mm, elliptic-oblong to narrowly elliptic-oblong, ± saccate, green, glabrous; margin with a thin membranous white edge, apex obtuse; base truncate. Petals 4; 3.8–5.0 × 1.2–1.5 mm, white, limb obovate to broadly elliptic-obovate; apex obtuse; base cuneate, tapering to a c. 1 mm long claw. Stamens 6; median filaments 4, 2.4–2.7 mm long; lateral filaments 2, 2.1–2.2 mm long; anthers 0.3–0.4 mm long, cream to pale yellow, when dehiscent held at a similar height to or slightly below the stigma. Ovary 2.2–2.4 mm long, 0.3–0.4 mm diam., ± terete, green, glabrous; ovules 18–24; style 0.1–0.2 mm long, ± terete; stigma 0.3–0.4 mm diam. Siliques 12.0–23.0 × 1.3–1.8 mm, glabrous, style 1.0– 1.5 mm long; valves green at maturity and when dehiscent, replum 0.3–0.4 mm wide. Seeds 1.1–1.4 mm long, 0.9–1.0 mm wide, 0.4–0.5 mm thick, orbicular-oblong to broadly oblong, light green to brown-green; wing absent.

Phenology:—Flowering: November–March; Fruiting: December–April.

Recognition:— Cardamine panatohea is readily distinguished from all other indigenous and naturalised species in New Zealand by it decumbent, sprawling racemose inflorescences that have leafy rosettes in the axils of the lateral branches. It differs from C. corymbosa in its thicker leaves and moderate covering of scattered hairs on the adaxial surface.

Distribution and habitat:— Cardamine panatohea is so far known only from two tributary streams in the upper Mangaturuturu Stream headwaters, Mt Ruapehu, Tongariro National Park, Central North Island, New Zealand. Plants have been recorded from 1600‒1700 m elevation, in two closely located but separate seepages and associated alpine flush vegetation. The two habitats occupied are water-saturated, with plants growing threaded through thick, floating bryophyte-dominated mats composed of mostly Breutelia pendula ( Smith 1804: 262) Mitten (1859: 82) and Riccardia furtiva Brown & Braggins (1989: 35) in sites that are partially sheltered by the grasses Hierochloe redolens ( Vahl 1791: 102) Roemer & Schultes (1817: 514‒515) and Chionochloa pallens Zotov (1963: 99) subsp. pallens .

The surveys for this species between 2012 and 2018 in flush and wetland habitats on Mt Ruapehu have been sufficient to conclude that C. panatohea has probably always been an uncommon plant of the alpine flushes and seepages of the Central Volcanic Plateau. The habitat C. panatohea occupies is unusual for its dominance of Breutelia pendula and, notably, it also occurs in a part of the mountain range that would have been sheltered from the numerous volcanic blasts, tephra and ignimbrite deposits of the nearby Taupo Volcano eruption in c. 200 AD ( Barker et al. 2014, Wilson 1993). This part of the mountain contains several species not otherwise known from the Central Volcanic Peaks and associated ranges; plants that are otherwise only known in the North Island from Mt Taranaki, 150 km to the west, e.g, Polystichum cystostegium ( Hooker 1862: 26) Armstrong (1881: 364) , or from the South Island, e.g., Cardamine mutabilis Heenan (2017: 114‒116) . These occurrences suggest that C. panatohea may be a narrow-range and habitatspecific endemic, perhaps a remnant of a formerly large wider-ranging population that was possibly destroyed by volcanic ejecta during the Taupo Volcano eruption. Alternatively, it may have as yet unrecognised occurrences beyond the Central North Island volcanoes.

Representative specimens:— NEW ZEALAND. Mt Ruapehu , Mangaturuturu Headwaters, 9 February 2012, P. J. de Lange 10852 & N. J. Singers ( AK 331072 !) ; Mt Ruapehu , Mangaturuturu Headwaters, 12 March 2015, P. J. de Lange 12563 & P. B. Heenan ( AK 356828 !) ; Mt Ruapehu , 12 March 2015, P. B. Heenan s.n. ( CHR 688807 !) ; Mangaturuturu Stream , Mt Ruapehu, 12 March 2015, P. B. Heenan s.n. ( CHR 640344 !, CHR 640346 – CHR 640348 !) ; Mt Ruapehu , Mangaturuturu Headwaters, 25 April 2018, P. J. de Lange 14176 ( AK 370824 !) ; cultivated. ex Turoa Alpine Village , near waterfall, collected P. J. de Lange, cultivated experimental nursery, Landcare Research, 6 March 2014, P. B. Heenan s.n. ( CHR 636106 !) .

Conservation status:—The water-saturated alpine flush habitat of C. panatohea is sensitive to trampling damage from being traversed by animals and people. At the time of the species’ discovery in 2012, the main habitat was relatively free of damage from the most commonly encountered browsing animal pests on Mt Ruapehu, red deer ( Cervus elaphus Linnaeus (1758: 67)) and hare ( Lepus europaeus Pallas (1778: 30)) . At that time a population estimate of about 80 individual plants was made. By March 2015 the Cardamine habitat had deteriorated markedly, due to red deer trampling and pugging the bryophyte turf of the alpine flush habitat whilst browsing Chionochloa pallens subsp. pallens and Hierochloe redolens . Observations at this time suggested that red deer and hares were also browsing plants of C. panatohea . Only those plants found in the less accessible parts of the alpine flush were still flourishing: the species had vanished from the main habitat in which it had been found in 2012 and 2013. During April 2018 a careful survey of the two known populations of C. panatohea noted 30‒38 plants. Although those plants seemed healthy there has been no recolonization into the habitat occupied in 2012 and 2013. While it is possible that the initial population estimates of 2012 were too high, animal browse and the trampling damage to the fragile alpine flush habitat of C. panatohea are serious threats to this species and will remain so unless the red deer and hare are controlled.

In summary, C. panatohea remains an enigmatic, extreme narrow-range Central Volcanic Plateau endemic. The two known occurrences, in different tributary streams of the Mangaturuturu Stream headwaters collectively occupy an area of <1 ha. The main population of 30‒38 plants is threatened by animal browse and loss of habitat through trampling. The second site, comprising a single patch (possibly only a single plant) growing within the spray zone of a waterfall, is extremely vulnerable to a stochastic event such as flooding, but is less likely to be threatened by animal browse and trampling. Following the criteria of Townsend et al. (2008), namely the area of occupancy (<1 ha) and total population size of ≤ 31‒39 individuals, the species has been assessed using the tag name Cardamine (p) (CHR 640349; Turoa) as ‘Threatened – Nationally Critical’ qualified ‘DP’ [Data Poor] by the New Zealand Indigenous Vascular Plant Threat Listing Panel ( de Lange et al. 2018). The qualifier ‘DP’ reflects that further data is needed on species population trends. We see no reason to adjust this threat assessment.

Species epithet:—The Te Reo Māori epithet ‘ panatohea ’ gifted by Ngāti Rangi who hold Mana Whenua over the portion of Ruapehu where this species grows originates from the names ‘panapana’, a common name for this type of cress, and ‘tītōhea’ which is the description of the land above the bush line on Mt Ruapehu. The term ‘tîtôhea’ is usually translated to mean ‘barren’, but for Whanganui tribes it means a sacred area, usually desert or mountainous, where special species live. In giving this name for this specific Mt Ruapehu centred species, Ngāti Rangi wish to acknowledge the need for people of all nations and cultures to treat C. panatohea and Ruapehu with special care. The species epithet is therefore not only a name for a species but also serves as an encouragement to remember that Ruapehu is sacred to all Whanganui tribes and has notable cultural and natural heritage status.

Figures

FIGURE 1. Cardamine panatohea. A. Mature plant with prostrate inflorescences. B. Plant with rosette leaves. C. Rosette leaves. D. Hairs on leaf adaxial surface. E. Flowers top view. F. Flowers side view. G. Inflorescence with axillary rosettes. H. Inflorescence with siliques. Scale bars: C, G = 10 mm; D = 5 mm.