Geranium socolateum Heenan & Molloy

Perennial herb, growth habit robust, usually forming a low-growing mat, with a thick, usually branched taproot; aerial stems 10–50 mm long, up to 8.0 mm in diam., woody, caulorrhiza covered with persistent stipules and petioles. Petioles up to 150 mm long, up to 1.5 mm in diameter, sparsely to moderately hairy; hairs appressed, retrorse, 0.3–1.06 mm long, white; stipules 3.0–3.5 mm long, 1.0–1.6 mm wide at base, narrowly triangular, margin entire, hyaline and fimbriate, apex acute to acicular. Lamina 10–35 mm wide, semi-coriaceous, sparsely to moderately covered with appressed and retrorse hairs, matt; adaxial surface usually grey-green to light grey, occasionally green, with main veins immersed; abaxial surface light grey-green with main veins raised; margin with a prominent brown band 1.0–3.0 mm wide; primary lobes 3–5(–6), incised up to halfway, broadly elliptic or broadly obovate, toothed at apex or divided up to ⅓ of their length into secondary lobes, apices subacute to obtuse. Inflorescence with single peduncle-pedicel up to 40 mm long or sometimes a monochasial scorpioid cyme up to 90 cm long, 0.3–1.2 mm in diameter, upright or spreading at anthesis, sparsely to densely hairy; hairs retrorse, appressed, 0.2–0.6 mm long, white; bracts 2, opposite, inserted ½ to ¾ of the way along peduncle-pedicel, 3.9–5.0 mm long, 2.0–2.3 mm wide, lanceolate, strongly keeled, apex acuminate; flowers axillary, solitary, inodorous. Sepals 5, 6.8–7.0 mm long, 3.8–4.0 mm wide, inner sepals slightly narrower than outer sepals, elliptic-ovate to ovate, green and flushed red-brown, nerves 3–5, mid-nerve and sometimes lateral nerves brownish-red; margin hyaline, red-brown; adaxial surface glabrous, reddishbrown; abaxial surface with short appressed antrorse hairs or longer spreading patent hairs; apiculus subapical, 1.3–1.9 mm long, sparsely hairy. Corolla 18.0–22.0 mm diameter when expanded. Petals 5, 9.5–11.5 mm long, 5.5–6.0 mm wide, white, obovate to broadly obovate, sparse hairs at base; apex obtuse; base cuneate to attenuate; primary nerves 5, translucent, not or hardly reaching petal margins. Nectary glands 0.5 mm tall, green. Stamens 10, 4.0–4.8 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 1.0–1.2 mm long, yellow, dehiscing longitudinally, pollen yellow. Gynoecium with 5-loculed ovary, pistil 3.0–3.6 mm long, carpels densely hairy; hairs 0.2–0.5 mm long, white, appressed; stigma 1.7–2.0 mm long, arms recurved, stigmatic papillae on adaxial surface. Fruit a 5-parted schizocarp; mericarp 2.4–2.6 mm long, 1.4–1.5 mm wide, brown, sparsely to moderately hairy, hairs antrorse, appressed to spreading; rostrum 8.5–10.0 mm long, moderately to densely hairy, hairs antrorse. Seeds 1.8–1.9 mm long, 1.1–1.2 mm wide, elliptic-oblong, apex and base obtuse; testa dull, dark-brown to black-brown, glabrous, reticulation scarcely visible (with steromicroscope).

© Magnolia Press. Reproduced from Heenan & Molloy 2019  (Phytotaxa 415 (1): pages 40–41) with permission from Magnolia Press.

Occasionally, some forms of Geranium microphyllum Hook.f. (1844: 8, t. 5) and G. brevicaule can have brown leaf margins, but these two species can be reliably distinguished from G. socolateum. Geranium microphyllum sens. lat. (including plants from Subantarctic Islands, South Island and North Island) differs from G. socolateum by its longer, slender, trailing stems (up to 40 cm long) and an open, loose, straggly growth habit and the lack of short and compact stems, leaves usually being broader than long, thinner and distantly placed on trailing stems, basal leaves not persistent, infloresences with several flowers, and the smaller diameter flower (8–10 mm across) with smaller petals (6.0–9.0 mm long). Geranium brevicaule differs from G. socolateum by its more compact growth habit, leaves being smaller (usually up to 20 mm diameter), polymorphic leaf colour (green, bronze, purple) but not grey-green to light grey in colour, and its smaller sepals (4.0–7.0 mm long) and petals (5.0–7.0 mm long). Geranium sessiliflorum var. arenarium Simpson & Thomson (1943: 158) is a taxon from coastal sites in southern South Island that is very similar to G. brevicaule, mainly differing from that species in its very densely hairy leaves giving them a distinct greyish colour (Allan 1961; Webb et al. 1988). Its characters are otherwise similar to G. brevicaule and therefore it can be readily distinguished from G. socolateum. The single flowered peduncle-pedicel inflorescence is the most common inflorescence type and occurs on compact plants grown in sunny, open situations. The monochasial scorpioid cyme inflorescence, which is when the lateral pedicels develop on alternate sides of the usually elongate inflorescence, usually occurs on well-grown and/or shaded, slightly etiolated plants.

© Magnolia Press.  Reproduced from Heenan & Molloy 2019  (Phytotaxa 415 (1): page 41) with permission from Magnolia Press.

An obligate calcicole. Geranium socolateum typically occurs on open, sparsely vegetated, stable to semi-stable rocky limestone outcrops and associated colluvium, in a range of aspects, including open and sunny or sheltered and shaded. It also grows amongst open prostrate shrubs and rarely tussock-grasses (Heenan & Molloy 2019).