Geranium rubricum Heenan & Courtney, 2017

HEENAN, PETER B & COURTNEY, SHANNEL P, 2017, Geranium rubricum (Geraniaceae), a new species from ultramafic soils in the Red Hills, northern South Island, New Zealand, Phytotaxa 314 (1), pp. 89-95 : 90-93

Geranium rubricum Heenan & Courtney , sp. nov. ( Fig. 1 )

A new species distinguished from Geranium microphyllum by its well-developed rhizomes, short aerial stems and compact growth habit; the leaves being coriaceous, glabrous and 6–10 mm wide; larger sepals with short appressed hairs; larger flowers, 18–25 mm in diameter and petals 10–13 mm long.

Type:— NEW ZEALAND. Nelson. Red Hills above Motueka River, rocky ridge, ultramafic rocks, 1200 m, December 1990, S. Courtney s.n. (holotype CHR 469918!).

Description:— Perennial herb; rhizomes well-developed, up to 1000 mm long, up to 2 mm in diameter, covered in appressed, retrorse, caducous hairs, cortex deep beetroot-red; aerial stems 10–35 mm long, 2.5 mm in diameter. Petioles up to 25 mm long, 0.4–0.5 mm in diameter, sparsely to moderately hairy; hairs appressed, retrorse, 0.3–0.6 mm long, terete, white; stipules basal, 1.2–2.1 mm long, up to 0.5 mm wide at base, narrowly triangular, margin entire, apex acute, base with hyaline margins. Lamina 6–10 mm wide, coriaceous, glabrous, glossy, adaxial surface green to dark green with main veins impressed, abaxial surface red-brown to green, turning bright yellow when senescent, lobe margins red-brown; primary lobes 3–5, deeply incised to base, broadly elliptic or obovate; terminal lobe entire, toothed toward apex or divided up to ¾ of their length into secondary lobes; lateral lobes toothed toward apex or divided up to ¾ of their length into secondary lobes; apices subacute to obtuse; basal secondary lobes erect. Flowers axillary, solitary, nodding in bud, inodorous. Peduncle 18–40 mm long, 0.4–0.6 mm in diameter, erect at anthesis, acutely geniculate to pedicel at bracts during gynoecia development; densely hairy in distal half, sparsely hairy in proximal half, hairs retrorse, appressed, 0.2–0.6 mm long, white; bracts 2, opposite, inserted 1/2 to ¾ of the way along peduncle-pedicel, 2.5–4.5 mm long, 0.6–0.8 mm wide at base, lanceolate to narrowly triangular, sometimes falcate, red-brown, apex acute; pedicel 10–23 mm long, 0.4–0.7 mm in diameter. Sepals 5, quincuncial, 6.8–7.5 mm long, 3.0– 3.4 mm wide, elliptic to ovate, green and flushed red-brown at apex; margin hyaline, cream and flushed red-brown distally; apex with weft of hairs; apiculus subapical, obtuse, 0.3–0.4 mm long; adaxial surface glabrous; abaxial surface sparsely hairy; hairs eglandular antrorse, appressed, 0.1–0.4 mm long; inner sepals slightly narrower than outer sepals, nerves 3–5, mid-nerve and sometimes lateral nerves brownish-red. Corolla 18.0–25.0 mm diameter when expanded, cochleate. Petals 5, 10.0–13.0 mm long, 6.0–10.0 mm wide, white, broadly obovate; margins slightly undulate; apex truncate, praemorse; base cuneate to attenuate; primary nerves 5, translucent, not or hardly reaching petal margins. Stamens 10, 4.8–6.5 mm long, 0.7–0.9 mm wide at base, tapering to 0.1 mm wide at apex, margin ciliate in lower half and glabrous in upper half, white or white-translucent. Anthers 0.5–0.6 mm long, yellow-brown, dehiscing longitudinally, pollen yellow. Gynoecium with 5-loculed ovary, pistil up to 6.5 mm long, carpels densely hairy; hairs 0.1–0.2 mm long, white, appressed; stigma 2.5–2.6 mm long, stigmatic papillae on adaxial surface; abaxial surface glabrous to moderately hairy. Fruit a 5-parted schizocarp, mericarp brown, initially hairy becoming glabrous; hairs appressed, antrorse, caducous; rostrum c. 16 mm long, sparsely pubescent. Seeds not seen.

Other specimen (paratype):— NEW ZEALAND. Nelson. Red Hills, Alpine Creek, 3 January 2007, C. Ashton s.n. (AK 298474!).

Distribution:— New Zealand, endemic. G. rubricum is known from seven sub-populations (see Introduction) scattered across the ultramafic Red Hills, northern South Island, all within a 5km radius of the Motueka River Right Branch headwaters.

Habitats and associated species:— Geranium rubricum typically occurs on open, sparsely vegetated, stable to semi-stable scree, fines and soil derived from harzburgite rock ( Fig. 2 ). Rhizomatous stems typically grow between cobbles and along bedrock interstices where there are friable fines. It occurs over a range of aspects and gradients up to 30 o, above which slopes become too unstable. It occasionally grows amongst open prostrate shrubs and rarely in tussockland or on deflation surfaces.

Geranium rubricum is most often associated with Aristotelia fruticosa Hooker (1853: 34) , Carex breviculmis Brown (1810: 242) , Dracophyllum pronum Oliver (1928: 686) , Notothlaspi australe Hooker (1864: 15) , Pimelea suteri Kirk 1894: 259 ), and Rytidosperma setifolium ( Hooker 1853: 304) Connor and Edgar (1979: 316) along with the Nelson mineral belt endemics Carex devia Cheeseman (1883: 301) , Festuca ultramafica Connor (1998: 363) , Leptinella pyrethrifolia var. linearifolia ( Cheeseman 1883: 299) Lloyd & Webb (1987: 103) , Montia racemosa ( Buchanan 1871: 210) Heenan (2007: 438) , Poa acicularifolia ssp. ophitalis Edgar (1986: 444) , and Wahlenbergia ablomarginata subsp. olivina Petterson (1997: 36) .

Recognition:— Geranium rubricum is related to G. microphyllum and G. potentilloides , two species whose acceptance in the New Zealand flora has been the subject of much consternation. Bentham & Mueller (1863) treated Australian and New Zealand plants as G. dissectum var. australe Bentham & Mueller (1863: 296) (= G. solanderi Carolin (1965: 350)) , considered G. potentilloides to be a synonym, and did not mention G. microphyllum . However, Hooker (1864), Kirk (1899) and Cheeseman (1906, 1925) all accepted G. microphyllum and treated G. potentilloides as a synonym, but they also accepted as indigenous G. dissectum ; Hooker (1864) accepted G. dissectum var. carolinianum ( Linnaeus 1753: 682) Hooker (1864: 36) , and Kirk (1899) and Cheeseman (1906, 1925) accepted G. dissectum var. australe . Allan (1961) also accepted G. microphyllum and treated G. potentilloides as a synonym, accepted G. microphyllum var. obtusatum Simpson & Thomson (1943: 156) and G. microphyllum var. discolor Simpson & Thomson (1943: 156) , and noted that G. microphyllum was a polymorphic species. Allan (1961) only treated indigenous species, but Allan (1940) regarded G. dissectum as naturalised as did Webb et al. (1988). Carolin (1965) recognised that G. potentilloides was the earlier name based on a New Zealand type specimen, and treated G. microphyllum (also based on a New Zealand type specimen) and G. dissectum var. australe as synonyms.

The most recent Flora of New Zealand treatment accepted G. microphyllum and G. potentilloides of the basis of growth habit, leaf, floral and seed characters ( Webb et al. 1988; see Table 1), a decision based on examination of extensive New Zealand herbaria collections and considerable local field knowledge.Further details of the seed characters were elaborated by Webb & Simpson (2001), and G. microphyllum and G. potentilloides were also distinguished in the nr DNA ETS and ITS phylogenetic study of Mitchell et al. (2009). In a world checklist of Geranium, Aedo et al. (1998) accepted G. potentilloides but did not accept G. microphyllum , choosing not to follow the most recent regional New Zealand flora treatment of Webb et al. (1988). As noted in the Introduction, G. rubricum is related to G. microphyllum and G. potentilloides as these species share one flowered cymules and have leaves usually less than 30 mm diameter. Table 1 provides a summary of the morphological characters that distinguish G. microphyllum , G. potentilloides and G. rubricum , with the data being taken from Webb et al. (1988) and herbarium specimens in CHR examined for this study. G. rubricum is distinguished from G. microphyllum and G. potentilloides by a suite of growth habit, leaf and floral characters ( Table 1). Notable among these characters are a low growing compact growth habit with short aerial stems only 10–35 mm long, well-developed rhizomatous stems up to 1000 mm long, and the rhizomes with a deep beetroot-red cortex; the leaves are coriaceous, glabrous, glossy and 6–10 mm diameter; large sepals (6.8–7.5 mm long) with uniformly short appressed hairs on the midrib, margins and lamina; and larger flowers 18–25 mm in diameter and petals 10–13 mm long.

Etymology:—The specific epithet rubricum refers to the red ochre colour of the ultramafic rocks and soils where this species occurs ( Whitaker 2007), and also to the red colouration of the lamina margins and deep red colour of the stolon cortices.

Conservation status:—Limited browsing of G. rubricum has been observed despite its palatable appearance. Browse is largely restricted to the removal of inflorescences by hares, thereby limiting seed production. The impacts of this are unknown, although seedling recruitment has been observed. Goats are also implicated in rare observations of foliar browse. In the medium to long term, the spread of wilding pines ( Pinus species) onto the Red Hills from surrounding plantations threatens to over-run the open habitats of G. rubricum unless their ongoing control is maintained.

The total population estimate of G. rubricum is between 500 and 1000 individuals. Empirical population trend data is lacking and so the stability or otherwise of the total population cannot be accurately determined. Given the relatively small population size and at least one potentially serious threat (wilding pines) we therefore precautiously assess G. rubricum as having a conservation status of Threatened, Nationally Endangered, with the criteria A(1/1), a total population size of 250–1000 mature individuals and a predicted decline of>10% due to existing threats, along with the qualifiers “conservation dependent” and “range-restricted” ( Townsend et al. 2008; de Lange et al. 2013).

Figures

FIGURE 1. Geranium rubricum. A. Compact growth habit. B. Rhizomatous growth habit. C. Coriaceous leaves with deeply incised lobes. D. Bracts inserted at peduncle-pedicel junction (scale bar 2 mm).E. Flower with dehiscent anthers (scale bar 7 mm).F. Sepals (scale bar 2 mm). G. Mericarp (scale bar 5 mm).

FIGURE 2. Eroding rockland at type locality producing semi-stable scree with cobbles and fines occupied by Geranium rubricum.