Ranunculus callianthus Molloy & Heenan

Rosettes single or forming compact patches comprising several tightly placed rosettes, appressed to the ground in exposed sites but taller in the shelter of rocks and other vegetation. Lamina 10–28 × 8–26 mm, broadrhomboid, rhomboid or orbicular-deltoid, glossy, coriaceous, stiff, dark green, black-brown on proximal veins and at sinus lobe; 3(–5)-lobed, often to about halfway across lamina, adaxial and abaxial surfaces sparsely to moderately hairy with shaggy, loosely appressed white hairs, hairs up to 1.8 mm long; base cuneate to obtuse; margin crenate or serrate, sparsely to moderately hairy; apex of main and lateral lobes subacute, with white hydathode an abaxial surface. Petioles 10–70 mm long, green, dark-mottled hairs patent and sparse to dense; basal sheath broad, membranous, glabrous to sparsely hairy, entire, margin sometimes sparsely hairy. Peduncle 15–140 mm long, up to 3 mm diam., spreading to ascending, strongly recurved in fruit; dark green and dark-mottled throughout, hairs moderate to dense, patent, white; bracts usually absent, sometimes or 1–2 simple narrow bracts. Flowers 1(–2), 21–30 mm diam. Sepals 5, 5.5–10.0 × 2.5–4.0 mm, yellow-green, caducous, abaxial surface sparsely to moderately hairy, adaxial surface glabrous, margin translucent, apex obtuse. Petals 5, 11.0–15.0 × 5.0–7.5 mm, obovate-oblong, glossy, yellow with yellow-brown basal blotch above, pale yellow below. Nectary c. 1.0 mm from base of petal; scale c. 1.0 mm long, oblong or broad-oblong, apex bifid. Stamens 28–38; filaments 2.0–4.0 mm long, white; anthers 1.3–1.8 mm long, yellow; receptacle sparsely to moderately hairy; carpels 11–20, 3.0–4.0 mm long. Achenes 11–20, yellow-brown with red to red-black blotches, 4.5–6.5 mm long, ellipsoid, lateral faces compressed; body 3.0–3.5 × 2.0–2.7 mm; beak strongly curved, 1.6–3.0 mm long. Chromosome number 2n = 48 (de Lange et al. 2004).

© Magnolia Press. Reproduced from Heenan & Molloy 2019 (Phytotaxa 415 (1): pages 43–44) with permission from Magnolia Press.

Ranunculus callianthus is placed in Ranunculus section Ranunculus (Garnock-Jones, in Webb et al. 1988, p. 1014). In this section it belongs in the following species group: (1) tufted; (ii) nectary at base of limb; (a) stem 1–3(–10)-flowered, with 1 or more bracts. Other New Zealand species in this group are R. foliosus Kirk (1899: 14), R. kirkii Petrie (1887: 323), R. mirus Garnock-Jones (in Connor & Edgar 1987: 126), R. stylosus, and R. subscaposus Hooker (1844–1845: 5). Of these species, R. callianthus is most similar to R. stylosus as described by Wilson  Garnock-Jones (1983). Ranunculus callianthus differs from R. stylosus by its more robust growth habit, larger leaves, petiole and peduncle with patent and white hairs, larger flower and petals, abaxial surface of the sepals and petals pale yellow, more stamens and carpels/achenes per flower, nectary scale with bifid apex, and the achene with a strongly curved beak. A further difference is provided by chromosome number, as R. callianthus has 2n = 48 and R. stylosus has 2n = 32 (de Lange et al. 2004). R. callianthus is also similar to some forms of R. foliosus, but that species usually has duller and often membranous leaves, fulvous hairs, one or several flowers per stem, flowers sometimes apetalous (South Island alpine forms), and 30–60 achenes per head. Garnock-Jones (in Webb et al. 1988, p. 1029) commented that on limestone in parts of Nelson and Canterbury, the leaves of R. foliosus may be distinctly 3-foliolate, a feature that does not occur in R. callianthus.

© Magnolia Press. Reproduced from Heenan & Molloy 2019 (Phytotaxa 415 (1): page 44) with permission from Magnolia Press.

An obligate calcicole. R. callianthus grows in pasture among exotic grasses at the crest of the limestone scarp and the dip-slope, often on ledges and in crevices. Common species competing with R. callianthus include Pilosella officinarum Vaillant (1754: 703) and Sedum acre Linnaeus (1753: 432), (Heenan & Molloy 2019).